Decision

GDA Step 2 of the Holtec SMR-300 design: Fundamental Assessment report

Published 31 March 2026

Applies to England and Wales

1. Introduction

This report sets out our findings following Step 2 of a generic design assessment (GDA) of the SMR-300 Small Modular Reactor (SMR) nuclear reactor design.

Holtec International is the Requesting Party (RP) for the GDA. It is also the design authority. The design being assessed is the SMR-300. The GDA is being managed by Holtec Britain Limited, a wholly owned UK subsidiary of Holtec International.

Holtec International applied to the Department for Energy Security and Net Zero (DESNZ) for its Holtec SMR-160 design to enter the GDA process and the application was successful. The regulators (the Environment Agency, the Office for Nuclear Regulation (ONR), and Natural Resources Wales (NRW)) were asked by the Minister to begin a GDA for this design. Step 1 (Initiation) of the GDA formally began on 18 October 2023. Following a design change, the reactor was renamed the Holtec SMR-300 in January 2024.

The RP proposed a 2-step GDA taking 24 months. Step 1 started in October 2023 and finished in August 2024, taking 10 months (Step 1: statement of findings). Step 2 started in August 2024 and finished in March 2026, taking 19 months. The objective for the RP is to meet the requirements needed to receive a Step 2 statement from the Environment Agency, NRW and the ONR, setting out our regulatory position at this point and our findings from the fundamental assessment. There are currently no plans to continue to Step 3 of a GDA.

1.1 Step 2 objectives

The top-level objectives for Step 2 are for the:

• Environment Agency to carry out an assessment to identify any fundamental environmental protection shortfalls in the design
• RP to complete the submissions needed for Step 2 (and in preparation for Step 3, if required) and to publish the submissions on its website
• RP to launch and publicise its public comments process

We will assess the design against regulatory requirements and expectations. This includes identifying any fundamental environmental protection shortfalls that could prevent the design from being potentially acceptable for deployment on sites in England or in Wales, where NRW is the environmental regulator.

In this report, we:    

• present the work we have done and the conclusions we have reached so far
• outline any fundamental environmental protection shortfalls, benchmarked against the level of detail we would expect to allow us to issue a Statement of Design Acceptability (SoDA) if the RP was to progress to GDA Step 3
• state whether we consider changes to the design might be needed

We have considered relevant comments received from the public or interested organisations through the RP’s comments process and the responses made to those comments.

We have worked with NRW to carry out our assessment of fundamental environmental protection shortfalls during Step 2.

2. Holtec International’s SMR-300 Small Modular Reactor

This section outlines the SMR-300 reactor design and details the mechanisms by which radioactive waste will be created, processed, managed and ultimately disposed of. Further information on the reactor design can be found on the Holtec Britain website, with GDA specific documents available on the Documents section of Holtec Britain’s website.

2.1 Outline of the design

The SMR-300 is a pressurised water reactor (PWR), with a single steam generator including an integrated pressuriser. The design utilises 2 cold legs, each with a vertically mounted reactor coolant pump (RCP), providing forced circulation in normal operation (HOLTEC BRITAIN, 2025o). Water is heated under high pressure and carried through the coolant loops to the steam generator. Once inside the steam generator, the heat boils the water in a secondary loop, creating steam. This steam is used to run the turbine, powering the generator to generate electricity. The steam enters the condenser, where it undergoes condensation and transforms back into water. This resulting water is pumped out of the condenser and returns to the steam generator to be heated again.

Figure 1: Simple schematic of Holtec SMR-300

Copyright Holtec Britain.

PWRs are the dominant nuclear reactor technology worldwide and have been in commercial operation for over 60 years. The SMR-300 is a Gen III+ PWR design. The RP’s original design concept was for a 160 megawatt electrical (MWe) SMR. However, in September 2023, the SMR-160 design was upgraded from approximately 160 MWe to 320 MWe and introduced 2 reactor coolant pumps (RCPs) to provide forced flow in the reactor coolant system (RCS) during normal operation. Following this modification, the reactor design was rebranded from SMR-160 to SMR-300 in January 2024.

The SMR-300 is based on well-established PWR technology. The target electrical power output of each SMR-300 unit is approximately 320 MWe (from a thermal power of 1,050 megawatt thermal – MWth). The SMR-300 design is a twin-unit design comprising 2 SMR-300 reactors in separate containment buildings, with a common control room and associated plant. The plant is designed for 80 years of operation, with a nominal 18-month refuelling cycle. Reactivity control uses a boron chemical shim and rod cluster control assemblies.

The SMR-300 incorporates an annular reservoir which is contained in the annulus between the containment structure (CS) and the containment enclosure structure (CES). The annular reservoir contains a large body of water, whose primary function is to provide a heat sink in the event of an accident. This is a novel concept to PWR safety systems in the UK. The reactor pressure vessel (RPV) is housed within the CS, which is a cylindrical steel containment vessel with a domed upper head and steel-lined reinforced concrete base which is partially embedded below grade. This partial below-ground deployment of the reactor and reactor containment is novel to the UK. This may present a risk to the environment associated with managing and monitoring the groundwater throughout the lifetime of the plant, as well as additional challenges during the construction and decommissioning of the facility.

The SMR-300 reactor incorporates the Framatome GAIA fuel assembly. This fuel assembly is new to the UK but has extensive operating experience (OPEX) from operating nuclear power stations in the USA. The SMR-300 reactor core comprises 69 fuel assemblies, each consisting of 264 fuel rods in a 17 x 17 array, with 24 guide tubes and a single central instrumentation tube. Each of the fuel rods consists of a metallic zirconium alloy cladding housing the nuclear fuel, which is in the form of small ceramic pellets that contain up to 5% enriched uranium dioxide fuel (HOLTEC BRITAIN, 2025u).

Holtec International has started a programme to deploy a twin-unit design comprising 2 SMR-300 reactors at the Palisades Nuclear Generating Station site in Covert, Michigan, USA. The US Reference SMR-300 Plant is the GDA Input Reference Design.

More information on the design of the SMR-300 can be found in Preliminary Safety Report (PSR) Part A Chapter 2 (HOLTEC BRITAIN, 2025p).

2.2 Sources, processing and disposal of radioactive waste

Radioactive waste in the form of solids, liquids and gases will arise from activities associated directly or indirectly with operating and maintaining the reactor, and ultimately, from decommissioning the plant. The SMR-300 radioactive waste systems are not novel compared to other PWR designs. Like other operating PWR fleets, it is expected that radioactive waste arisings from the lifecycle of the SMR-300 will be generated through operation and decommissioning.

2.2.1 Liquid radioactive wastes

The liquid radioactive waste management strategy for the SMR-300 is to separately collect and process liquid effluents to enable recycling where practicable and, where unavoidable, discharging to the environment. The generic SMR-300 liquid radioactive effluents are segregated at source into:

• borated, reactor quality effluent
• liquid radioactive wastes from radioactive drains system
• steam generator blowdown effluent

Borated, reactor quality effluent is expected to make up the largest quantity of the effluent generated during normal operations of the generic SMR-300. Letdown of primary reactor coolant is treated using filtration and ion-exchange to enable it to be reused as makeup water in the primary circuit. Based on typical PWR operation, effluent that is unsuitable for reuse is typically generated towards the end of the fuel cycle and is treated as liquid radioactive waste (HOLTEC BRITAIN, 2025i).

Radioactive liquid effluents are segregated at source, collected, processed by the abatement systems (including ion exchangers, pre-filters and after filters) before being sampled and monitored prior to discharge. Four holdup tanks are available, which provide the capability to temporarily store and segregate wastes of different characteristics if required. Effluent is sampled upstream of abatement systems in the holdup tanks to characterise tank contents. Effluent is also sampled downstream of abatement systems to measure performance of components. Treated effluent is then collected in monitoring tanks for sampling prior to discharge. Depending on the sampling results, the tank contents may either be discharged to the site outfall or returned to the holdup tanks for reprocessing.

Other sources of radioactive aqueous effluent may include:

• residual water transferred from spent resins
• floor drains within the radiologically controlled area (RCA)
• chemical drains within the reactor auxiliary building (RAB)
• other miscellaneous drains, which typically consist of effluent generated through maintenance operations

In normal operation, blowdown from the steam generator is processed and then reused as condensate in the secondary circuit. In the event of any abnormal conditions, contaminated blowdown can be processed via mobile demineralisation equipment prior to discharge to the environment (HOLTEC BRITAIN, 2025i).

Sampling and monitoring arrangements for liquid radioactive waste include both in-process and final sampling and monitoring.

2.2.2 Gaseous radioactive wastes

In the generic SMR-300, gaseous radioactive effluent is segregated into:

• primary gaseous effluent from the chemical and volume control system (CVC) holdup tanks and volume control tanks (VCT)
• gaseous effluent from heating, ventilation and air conditioning (HVAC) in the RCA
• secondary gaseous effluent from the steam generator

During plant operation, radioactive gases are generated within the RCS and transported with the reactor coolant, which is collected in tanks. Prior to plant shutdown and refuelling, gaseous effluent is flushed from the tanks by nitrogen to the gaseous radwaste system (GRW). This is designed to collect, process, decay store and discharge gaseous radioactive waste generated from plant operations. Once the effluent enters the GRW, it undergoes compression for storage and moisture removal. The compressed gas is then collected in the decay tanks for holdup until short-lived radionuclides like xenon and krypton have decayed to suitable levels. Once representative sampling confirms compliance with the permitted discharge limits, the processed gaseous effluent is transferred to the HVAC system where it passes through HEPA filtration, and (if required) iodine adsorption, before being monitored and released via the main stack (HOLTEC BRITAIN, 2025i).

The main process buildings are serviced by the HVAC systems. Air from the RCA and containment and any secondary gaseous effluent from the steam generator is extracted by the HVAC systems. The gaseous effluent is passed through filtration units, such as high efficiency particulate air (HEPA) filters, to remove radioactive particulates. The resulting gaseous effluent is monitored and discharged to the environment via the main stack.

2.2.3 Solid radioactive wastes and spent fuel

Solid radioactive wastes expected to be generated through normal operations of the generic SMR-300 include: 

• wet solid wastes, which consist of spent resin, spent filter cartridges and filter bed media from radioactively contaminated systems
• dry solid wastes, which include HVAC filters, personal protective equipment (PPE), paper, cloth, wood, plastic, rubber, glass and metal components that are potentially contaminated
• mixed wastes defined as being both radioactive and hazardous (for example, oily wastes generated from maintenance or decontamination of equipment and chemical wastes)
• non-fuel waste (NFW), for example, redundant activated items associated with fuel assemblies and other in-core components

The RP has produced an integrated waste strategy (IWS) (HOLTEC BRITAIN, 2025aa), which describes the overarching baseline strategies of waste management and spent fuel management for the SMR-300, in line with UK legislation, policies and strategies. Waste management arrangements for the SMR-300 are to control and segregate waste generation at source to enable the most effective means of pre-treatment, treatment, conditioning, storage and disposal. Facilities include:

• spent resin storage tanks for short-term decay
• treatment and packaging facilities
• interim storage facilities for packaged low-level waste (LLW) and intermediate-level waste (ILW), prior to dispatch to an off-site disposal facility

Dry solid wastes are characterised as metallic waste, combustible waste or non-combustible and compactable waste. Dry solid wastes are generated as a result of operational and maintenance activities performed within the RCA and consist of any solid, dry material that becomes contaminated with radioactive material and is discarded as waste.

Miscellaneous solid wastes consist of mixed wastes that are defined as being both radioactive and hazardous (for example, radioactive oily wastes that could be generated from maintenance or decontamination of equipment, and chemical wastes). Miscellaneous wastes generated from the generic SMR-300 are expected to be LLW and be managed via an appropriate LLW management route. The RP has identified off-site incineration as the most practicable option for the disposal of miscellaneous solid radioactive wastes (HOLTEC BRITAIN, 2025aa).

Radioactive waste arisings may contain non-radioactive materials that may influence its management and environmental impact. The management of non-radioactive solid wastes are outside the scope of GDA and will be assessed at an appropriate time in the future.

All radioactive plant components, including structural and non-fuel core components that have become activated over their lifetime will become waste when the plant is decommissioned. NFW will be stored in spent fuel storage racks (SFSRs) within the spent fuel pool (SFP) prior to dry interim storage in an appropriate ILW storage facility. Decommissioning LLW and very low-level waste (VLLW) will be sorted and segregated further into different types of waste, such as metal, combustible, non-combustible and compactable, and non-combustible and non-compactable waste. Once conditioned and packaged, wastes will be sent off-site for disposal or treatment based on their characteristics.

The RP’s baseline strategy is that spent fuel will be cooled in the SFP before being processed, dried and packaged for long-term dry storage in a passively safe form within the onsite dry storage facility, in readiness for disposal in a future geological disposal facility (GDF). This is on the assumption that a suitable GDF or disposal facility will be available.

2.3 Non-radioactive waste

Non-radioactive waste is produced from all lifecycle phases of a nuclear power station. When operating and maintaining the ‘conventional’ side of a PWR power station, this will include:

• combustion gases discharged to air from the diesel generators and auxiliary boiler
• water containing water treatment chemicals from the turbine-condenser cooling system and other non-active cooling systems, which can be discharged to the sea, lakes or other water bodies in accordance with a regulated environmental permit
• oils and any other non-aqueous wastes or sludges
• worn-out plant and components
• general waste materials

3. Scope of GDA and design developments

3.1 Requirements for the scope of GDA

Requirements for the scope of GDA are defined in the Environment Agency’s guidance for Requesting Parties (2023). We expect the RP to provide a scope of GDA with enough information and sufficient functional specifications for the design so that we can carry out a meaningful GDA.

A meaningful scope means that the combined scope and the information provided by the RP should cover the full breadth and depth necessary for ONR, the Environment Agency and NRW to carry out their assessments.

The scope should include all relevant topics and sufficient details about the nuclear power plant design. Regulators require that the scope should state which structures, systems and components (SSCs) and regulatory assessment topics are considered, and for the RP to declare at which step the GDA is proposed to conclude.

The design of the SSCs that support the environmental protection functions (EPFs) (relevant to waste and environmental assessment) need to be mature enough to enable meaningful assessment.

The scope of the GDA should include a statement indicating whether the RP is seeking a 2 or 3-step assessment, or a 3-step assessment targeting the issue of a SoDA from the Environment Agency and NRW and a Design Acceptance Certificate (DAC) from ONR. The RP has requested a 2-step GDA, therefore the output from this GDA will be a Step 2 statement.

3.2 Declared scope of GDA

The scope of the SMR-300 GDA is defined across the following 3 documents:

• the SMR-300 UK Generic Design Assessment Scope (HOLTEC BRITAIN, 2024g)
• GDA Design Reference Point (DRP) (HOLTEC BRITAIN, 2025b) see section 3.4.1 for more detail
• the SMR-300 GDA Master Document Submission List (MDSL) for GDA, which is a live document detailing the latest version of each submission which, at the end of GDA, form the submissions assessed under the scope of this GDA – at the close of this GDA, the final MDSL was revision 17 (HOLTEC BRITAIN, 2025ac)

The GDA scope refers to the boundaries of the GDA and what it includes and excludes. The RP has documented the agreed GDA scope in PSR Part A Chapter 1 (HOLTEC BRITAIN, 2025o) and Part A Chapter 2 (HOLTEC BRITAIN, 2025p). This includes:

• SSCs of the reactor design which are applicable to safety, environmental protection or security
• the level of design maturity, including design evolution of the SMR-300
• applicable lifecycle stages and operating modes
• GDA submissions within the safety, security and environmental case (SSEC), and the relationship with the GDA topic activities, which defines the scope of the submissions

The GDA scope consists of the operations that occur within the nuclear island (NI) plus the on-site fuel store, which includes the following buildings:

• containment enclosure structure (CES)
• containment structure (CS)
• reactor auxiliary building (RAB)
• intermediate building (IB)

During Step 2, the RP submitted several updates to the GDA scope and DRP, which included removing the radioactive waste building (RWB) and incorporating the functions of this into the RAB, following a modification to the SMR-300 design. The RP also reduced the GDA scope for the storage module underground maximum safety (UMAX) system in the independent spent fuel storage installation (ISFSI).

There are some aspects of reactor design excluded from the GDA scope which are relevant to the Environment Agency assessment. For example, the balance of plant consists of the following main structures, which are excluded from the scope of the GDA:

• annex building
• turbine building
• diesel generator building
• waste heat cooling tower or air-cooled condenser

Site-specific assessments are also excluded from the scope of this 2-step GDA. These aspects will be assessed at a future stage, during the environmental permitting process, when more information becomes available.

For specific inclusions and exclusions of scope, see each assessment topic in sections 5.1 to 5.7.

The scope indicates that the RP is intending to progress to the end of GDA Step 2 only and that the GDA will be carried out for a twin-unit reactor arrangement.

At the end of Step 1, we issued a Step 1: statement of findings concluding that there would be enough information for a meaningful GDA, subject to acceptable document content and quality.

3.3 Documents submitted for this GDA

Documents that form the GDA submission are recorded in the MDSL (HOLTEC BRITAIN, 2025ac). These documents are organised into 4 tiers of information:

1. SSEC documents that set out the overall claims, arguments and evidence (CAE) for the SMR-300.
2. Fundamental design documents that set the scope and strategy.
3. Topic reports (safety and environmental justification in an individual topic area). These reports provide a summary of CAE.
4. Supporting documents to topic reports providing detailed technical justifications.

The MDSL contains the latest revision of each submission made by the RP and is updated during the GDA process to reflect any additional work. Regulatory Queries (RQs) and Regulatory Observations (ROs) and the responses provided by the RP are included in the MDSL.

The tier 1 documents form the SSEC case and consist of the:

• preliminary safety report (PSR)
• preliminary environmental report (PER)
• generic security report (GSR)
• preliminary safeguards report (PSgR)

Most of the information required by the Environment Agency can be found in the PER, which consists of 6 chapters:

• PER Chapter 1 - Radioactive Waste Management Arrangements (HOLTEC BRITAIN, 2025i)
• PER Chapter 2 - Quantification of Effluent Discharges and Limits (HOLTEC BRITAIN, 2025j)
• PER Chapter 3 - Radiological Impact Assessment (HOLTEC BRITAIN, 2025k)
• PER Chapter 4 - Conventional Impact Assessment (HOLTEC BRITAIN, 2025l)
• PER Chapter 5 - Monitoring and Sampling (HOLTEC BRITAIN, 2025m)
• PER Chapter 6 - Demonstration of Best Available Techniques (HOLTEC BRITAIN, 2025n)

However, relevant information can also be found in chapters of the PSR, for example:

• PSR Part A Chapter 1 - Introduction (HOLTEC BRITAIN, 2025o)
• PSR Part A Chapter 2 - General Design Aspects and Site Characteristics (HOLTEC BRITAIN, 2025p)
• PSR Part A Chapter 4 - Lifecycle Management of Safety and Quality Assurance (HOLTEC BRITAIN, 2025q)
• PSR Part B Chapter 2 - Reactor (HOLTEC BRITAIN, 2025u)
• PSR Part B Chapter 5 - Reactor Supporting Facilities (HOLTEC BRITAIN, 2025d)
• PSR Part B Chapter 10 - Radiological Protection (HOLTEC BRITAIN, 2025r)
• PSR Part B Chapter 11 - Environmental Protection (HOLTEC BRITAIN, 2025s)
• PSR Part B Chapter 13 - Radioactive Waste Management (HOLTEC BRITAIN, 2025t)
• PSR Part B Chapter 23 - Reactor Chemistry (HOLTEC BRITAIN, 2025v)
• PSR Part B Chapter 24 - Fuel Transport and Storage (HOLTEC BRITAIN, 2025w)
• PSR Part B Chapter 26 - Decommissioning Approach (HOLTEC BRITAIN, 2025x)

There are also some tier 2 and 3 documents important for our assessment, in particular:

• Integrated Waste Strategy (HOLTEC BRITAIN, 2025aa)
• Requesting Party Response to NWS Expert View on Disposability (HOLTEC BRITAIN, 2025y)
• Decommissioning Strategy Assessment (HOLTEC BRITAIN, 2024a)
• Generic Site Envelope Report (HOLTEC BRITAIN, 2025c)
• Approach and Application of the Demonstration of BAT (HOLTEC BRITAIN, 2025a)
• SMR-300 GDA RSR-BAT Guidance (HOLTEC BRITAIN, 2025ad)
• Environmental Protection Functions Report (HOLTEC BRITAIN, 2025g)

The procedures that detail the production, governance and management of documents for GDA are considered as part of our assessment of management for safety and quality assurance (MSQA) (see section 5.1).

3.4 Design developments during GDA

3.4.1 Design reference and design reference point

The SMR-300 is a developing design that is not yet in operation, therefore, there is no as-built reference plant that forms the basis for this GDA. Holtec has started a programme to build the first SMR-300 reactor units at the Palisades site in Michigan, USA. The US Reference SMR-300 Plant is the GDA Input Reference Design. The SSEC submitted by the RP is specific for the UK. However, it is based on information and analysis under development for the Palisades SMR-300 project.

The design reference (DR) for the UK SMR-300 GDA at the identified DRP is based on the Holtec SMR-300 plant design as of May 2025. This includes some design developments and design changes which occurred following a review of the DRP in January 2025. The DRP report (HOLTEC BRITAIN, 2025b) provides a list of the SSCs which are included in the scope of the GDA, and their relevant GDA reference design documents. The DRP is a design development point on which the SSEC are based. DRP1.1 is the plant configuration control point, chosen by the RP, upon which its analysis and our assessment is based.

A GDA carried out at this early stage of the design presents opportunities for environmental and sustainability aspects to be considered early and to be included within detailed optioneering and decision-making. This should result in well balanced optimisation and improved recording of information needed to substantiate the SSEC case as it develops.

3.4.2 Design change

During the GDA process, it is normal practice for the reference design to continue to develop, as changes will inevitably occur during the evolution of the design. This has resulted in a design change acceptance process for bringing design changes into GDA, accompanied by a revision of the DR and DRP. During the GDA process, prospective design changes to the DRP are managed by the RP’s design management process. Design challenges and prospective design changes have been captured within each relevant chapter of the SSEC, with GDA commitments raised as appropriate, where there is either further work required to resolve the challenge or a potential design change has been identified. Commitments are captured within the commitments, assumptions and requirements (CAR) register (HOLTEC BRITAIN, 2025ae). Our assessment of the control of design configuration is considered in our assessment of MSQA (see section 5.1).

3.4.3 Commitments, assumptions and requirements

The SMR-300 is a developing design and as a result work is ongoing both on the design and underpinning evidence for the design. This is business as usual for any design at this stage of maturity. Many actions are part of the normal process for development of the design and the associated SSEC. However, where specific actions arise from this GDA that are required to progress the SMR-300 to a site-specific design for the UK, the RP has opted to capture these actions as CAR, as follows (HOLTEC BRITAIN, 2025z).

GDA commitment

A stated intent or undertaking made by the RP that affects the SMR-300 design intended for deployment to a UK site. A commitment is a statement concerning a change to an aspect of the GDA SMR-300 design or operational characteristics needed to meet the requirements of UK context.

GDA assumption

Underlying conditions upon which certain decisions or analyses within the SSEC are based.

GDA requirements

Design and performance requirements are defined as part of the design development of the SMR-300. Requirements also include mandatory and regulatory requirements that ensure the safety, security and environmental protection of nuclear facilities.

CARs may originate from multiple sources, including (HOLTEC BRITAIN, 2025z):

• production and delivery of the PSR, PER, PSgR and GSR – commitments will be identified in the SSEC reports
• design challenges or prospective design changes
• RQs, ROs, Regulatory Issues (RIs) or their associated resolution plans
• production of documentation that supports the SSEC
• preliminary UK optioneering studies or design reviews, including those driven by SMR-300 design changes
• OPEX

The identified CARs are documented in relevant chapters of the SSEC documents, with their additional context endorsement onto the CAR register (HOLTEC BRITAIN, 2025ae). The RP has a defined process to capture and manage CARs made within the SSEC and supporting documentation (HOLTEC BRITAIN, 2025z). Our assessment of the RP’s process to manage CARs is considered in the topic relating to MSQA (see section 5.1). Beyond GDA, the environmental aspects will continue to develop in line with the developing maturity of the generic SMR-300 design, as well as site-specific site requirements of nuclear site licensing and environmental permits. The RP has captured these as future evidence in the relevant PER chapters.

4. Our assessment

4.1 Standards and guidance

We assessed the design against our regulatory requirements and expectations as detailed in our Environment Agency: Guidance for Requesting Parties. This includes identifying any fundamental environmental protection shortfalls that could prevent the design from being potentially acceptable to build and operate at sites in England and Wales. We have considered the methods, approaches, standards and philosophies that the RP used to underpin the design and form its environment case. We have applied lessons learned from Step 1 of this GDA and from previous GDAs.

We made our assessment using our internal operational instruction and technical guides. We reviewed whether our Radioactive substances regulation (RSR): objective and principles and relevant RSR generic developed principles were considered by the RP. Where relevant, other international standards and guidance were considered, for example, from the International Atomic Energy Agency (IAEA), International Commission on Radiological Protection (ICRP) and the International Standards Organisation (ISO).

4.2 Scope of our assessment

The assessment scope during Step 2 of GDA is a fundamental assessment of the design. There are 7 assessment topics for the environment. These are:

1. MSQA – this considers the arrangements and process in place to manage and control the GDA submission made to regulators and the design configuration as it evolves, and to ensure environmental leadership within the RP organisation.
2. Radioactive waste management arrangements (RWMA) and best available techniques (BAT) – considers the strategic thinking behind the waste management and disposal choices and the process and structure of the demonstration of BAT, considering waste and impact minimisation aspects of the design. At Step 2 GDA, we are interested in the method and structure of the approach, with evidence being reviewed in Step 3 GDA or prior to or during the application for an environmental permit.
3. Solid waste, spent fuel and disposability – considers the derivation of solid waste estimates and their acceptability for disposal with existing UK infrastructure.
4. Discharges – considers the derivation of gaseous and liquid estimates and their acceptability for disposal to the environment.
5. Sampling and monitoring – considers sampling or monitoring of all radioactive wastes which would demonstrate compliance with an environmental permit, and also in-process monitoring acceptability, where relevant to the demonstration of BAT.
6. Generic site and radiological impact – considers the method and parameters used to determine the impact of radioactivity on both human and non-human species and the impact assessment outcome.
7. Other environmental regulations – considers how the design is managing the requirements of environmental legislation other than for the regulation of radioactive substances.

Other environmental regulations include:

• water use and abstraction
• discharges to surface water
• discharges to groundwater
• operation of combustion plant and incinerators
• Control of Major Accident Hazards Regulations (COMAH)
• fluorinated greenhouse gases (F-Gases) and ozone-depleting substances (ODS)

The topic-specific scope and findings are detailed in sections 5.1 to 5.7. Sustainability is considered in a number of chapters within the PER and PSR, for example, management of spent fuel. Consideration of sustainability aspects of the design is detailed within the PER chapter 4 and assessed within our topic assessment of other environmental regulations (see section 5.7).

4.3 Working with other regulators

GDA is a joint regulatory process. We work alongside the ONR, which considers nuclear safety, conventional health and safety, security and safeguards during GDA. We have also worked jointly with NRW on the environmental aspects of the design. This included joint meetings on matters of regulatory interest to each regulator, particularly at project level, on the joint assessment area of MSQA and in some aspects of ONR’s nuclear liabilities regulation (NLR) and radiological protection assessment areas. ONR has reported its assessment on the ONR GDA website.

4.4 Public comments

As required in our Guidance for Requesting Parties, Holtec Britain launched its Holtec Britain GDA website and public comments process at the start of Step 2 of the GDA. It also published the main submissions (excluding any sensitive nuclear information or commercially confidential information) on that website. The comments process enables the public to contribute to GDA by asking questions or making comments on the GDA submissions published on the website. The RP is expected to respond to each comment received as part of this process. We would respond to any comments made that are relevant only to the regulators. 

As part of our assessment, we review all public comments and the RP’s responses. We use them to inform our assessment, where applicable. We have considered all comments and responses made up to 14 November 2025. The public comments process began at the start of Step 2 of the GDA, in August 2024. Between then and 14 November 2025, the process received 9 comments from the public. A number of these comments related to matters that were not within the remit of this GDA for the Environment Agency and NRW, including:

• 3 comments relating to technical queries regarding aspects of the SMR-300 design, including the heat removal systems, the performance of natural circulation, construction (design and management) regulation (CDM) principles and the use of a combined steam generator and pressuriser in the design – the RP responded by directing these enquiries to the PSR documents available on its website
• one comment on the overall design of the SMR-300
• one general comment relating to the future deployment of SMRs in the UK
• one comment regarding security
• one comment relating to a request for documentation to which the RP responded by signposting to documents available on its website

Two of the comments received related to environmental queries, one of which related to the RP’s RWMA. We have carefully reviewed this comment and the RP’s response. Although we are satisfied that the RP has provided GDA documentation relating to RWMA, we conclude that it could have provided a more detailed response to this query. The RP could have referred to the relevant parts of the PSR and PER which support this topic area as well as supporting documentation regarding an expert view from Nuclear Waste Services (NWS).

Another comment related to the potential impact of the SMR-300 on conservation, specifically protected species. This is outside the scope of GDA and would be considered as part of a site-specific assessment prior to or during application for an environmental permit.

4.5 Internal governance during GDA

Our internal process for carrying out a GDA is set out in our operational instruction on GDA of candidate nuclear power plant designs (Environment Agency, 2020). This describes the GDA process we use and links to guidance. It describes how the project should be set up and run, the regulatory tools we use, how we should record the assessment and how we should work with others. The project governance is recorded in an audit trail document.

As part of our continuous improvement, we took into account lessons learned at the end of each previous GDA, and we have used the outcomes to modify and update our GDA processes and governance over time.

Our Step 2 assessment has been through a rigorous peer review process, consisting of a technical review with input from NRW, a technical edit to ensure compliance with accessibility requirements, consistency checks with ONR, and a factual accuracy check by Holtec Britain. It has been endorsed by the relevant Environment Agency and NRW Programme Boards. This ensures that the outcomes are appropriate, factually and technically correct, and are consistent with our requirements and ONR assessments.

We followed the government accessible documents policy - Department for Environment, Food & Rural Affairs to ensure the reports are accessible and can be published.

5. Fundamental assessment outcomes

Our GDA Guidance for Requesting Parties requires a fundamental assessment during Step 2 of GDA. This involves examining the aspects of the submission that could potentially affect the environment. The assessment aims to identify any potential fundamental environmental shortfalls in the protection of the public and the environment from the deployment of the Holtec SMR-300 in England or Wales.

The assessment, scope, method and outcomes for each of the topics assessed, as listed in section 4.2, are presented in the following sections of this report (see sections 5.1 to 5.7).

5.1 Management for safety and quality assurance

Our aim in assessing management arrangements and quality assurance during GDA is to gain confidence in the quality of the RP’s GDA submission, and to confirm that adequate processes are in place to transfer the RP’s GDA information to a future operator. We work jointly with ONR to consider how the design has been controlled and how the GDA submissions are produced and managed.

We carried out our assessment mainly by reviewing documents submitted by the RP, via scheduled meetings on specific MSQA topics, and by carrying out inspections (MSQA evaluation) of the RP’s use and implementation of its arrangements for the GDA. Both the meetings with the RP and the inspections were carried out jointly with ONR.

The main conclusions of our assessment are that the:

• RP has a clear organisational structure in place to implement GDA, with identified roles and responsibilities to develop the GDA design, the PER and the PSR
• RP has defined arrangements in place for providing sufficient suitably qualified and experienced persons (SQEP) to carry out GDA roles, including leadership, governance and decision-making, design development, PER and PSR authoring, and assurance roles
• RP has developed structured management arrangements that integrate safety, security and environmental requirements for the delivery of GDA
• RP’s GDA management system is certified to the ISO9001:2015 quality management standard
• RP has appropriate and mature design management processes for the development of the reactor design, including suitable checks, reviews and approvals for design changes
• RP has put in place formal arrangements for engaging and corresponding with regulators – our experience through Step 2 is that these arrangements are effective
• RP has documented procedures in place for the production, control and review of GDA documents and records

During Step 2, we and ONR raised 5 RQs that were relevant to MSQA. These have been closed, with a response provided during Step 2. Where applicable, relevant information arising from RQ responses has been incorporated into the PER to provide additional context.

During Step 2, the RP provided us with enough information to carry out our assessment. It demonstrated that the RP operates an appropriate and adequate management system, which includes and integrates aspects that control the content and accuracy of its GDA submissions. As a result, we have confidence that the production and update of submissions will be adequately controlled for this stage of the design, and that any issues raised will be managed appropriately. We did not identify anything unacceptable with the RP’s arrangements during our fundamental assessment. Overall, our conclusion is that RP’s GDA management and quality arrangements are adequate for this stage of GDA.

5.2 Best available techniques (BAT) and radioactive waste management arrangements

Our Guidance for Requesting Parties sets out the process we follow during GDA and the information required from the RP to complete our assessment of BAT and the RP’s RWMA. BAT is the method by which we expect operators to prevent the unnecessary creation of wastes or discharges, minimise waste generation and minimise the radiological impact of discharges on people and the environment. We expect the impacts to be minimised (or ‘optimised’) by taking into account the environmental, social and economic factors. Our expectations for optimisation can be found in our RSR: Principles of optimisation.

The RP is responsible for defining the scope of GDA. During Step 2, the scope for the dry spent fuel store was refined and the level of assessment was revised. The design was also developed to integrate the RWB functions into the RAB, and the active drains were removed from the scope. We would expect these out-of-scope parts of the facility to be addressed in future regulatory processes.

During Step 2, we conducted a thorough assessment of the RP’s approach to the demonstration of BAT, which included reviewing worked examples demonstrating how BAT is applied to the SMR-300 design. We also assessed the ‘BAT case’ as set out in chapter 6 of the PER (HOLTEC BRITAIN, 2025n). This provides the CAE for how BAT is applied to the SMR-300 design to minimise the generation and disposal of radioactive wastes.

Based on our Step 2 assessment, we found no fundamental environmental protection shortfalls in the design that could prevent the design from being acceptable to build and operate at sites in England and Wales. The design is still evolving, and future work has been identified by the RP for it, or a prospective operator, to complete to meet our regulatory requirements. A summary of our findings for each of the assessment areas related to BAT and RWMA included within this report is provided in the following sections.

5.2.1 Assessment of the optimisation process

The SMR-300 has been initially designed to meet USA regulatory requirements, primarily those of the US Nuclear Regulatory Commission (NRC). Although BAT was not specifically considered in the design, it has been produced using engineering principles including codes and standards that are, in many instances, similar to the UK regulatory system. We have not closely examined these requirements, but they should provide a good baseline for the design to be able to demonstrate BAT.

The RP’s approach is to ascertain whether a BAT case can be made for the current design by collecting evidence to satisfy the environmental claims in a CAE format. Where this is not possible, an ‘options appraisal approach’ will be used to identify BAT, and design modifications may be proposed. We assessed whether these 2 complementary approaches would be likely to be sufficient to identify and demonstrate BAT at the site-specific permitting stage.

The RP’s overarching approach to optimisation (HOLTEC BRITAIN, 2025a) covers the principles we would expect, including the waste management hierarchy, precautionary principle, polluter pays principle and sustainability. It also describes the regulatory framework for the UK, our guidance and principles. The optimisation process presented by the RP meets our expectations for the current stage and maturity of the SMR-300 design. We did not find any significant omissions or areas where further development of this overall strategy is needed.

5.2.2 Assessment of the best available techniques claims, arguments and evidence

PER chapter 6 - Demonstration of BAT uses a CAE model to demonstrate BAT for the generic SMR-300. The claims align with the main considerations in our GDA guidance, covering both the implementation of environmental principles into the design and radioactive and non-radioactive aspects of environmental protection. There do not appear to be any significant omissions in the claims defined.

Arguments and sub-arguments are expressed in a level of detail that is commensurate with the level of design maturity. A large amount of evidence has been provided to support the arguments, but the RP recognises that there are some gaps because the design is still developing. These have been captured as ‘future evidence’ against each argument. In addition to future evidence, the RP has made ‘GDA commitments’ to record stated intents that will affect the SMR-300 design to be deployed in the UK. No GDA commitments have been raised specifically within the BAT topic area, but several that interface with BAT are recorded elsewhere in the SSEC. These include, for example, RWMA quantification of effluent discharges and limits, and sampling and monitoring.

The BAT claims and arguments structure meets our expectations for the current stage of the SMR-300 design. It provides a suitable basis for the RP or a future operator to develop the BAT case for the SMR-300. Some of the arguments require further development, and we expect this will be possible as the design matures. Evidence supporting claims and arguments was sampled and assessed at Step 2 of GDA. Evidence not assessed would be part of either a future Step 3, pre-application engagement or site-specific permit determination.

During our assessment, 2 RQs were raised to understand how BAT had been considered in specific areas of the design – the reactor core design (RQ-01567) and the choice of ILW containers (RQ-01934). We were satisfied that BAT could be demonstrated for these areas through the CAE that was shared in Step 2.

We had concerns that the radioactive waste systems (liquid and gaseous) were being designed by a contractor working to USA standards. During Step 2, we did not receive evidence that BAT has been considered for these safety and environmentally significant systems. However, the design uses recognised methods that follow the principles of concentrate and contain, and segregation of different waste types. The RP has identified this gap as future evidence in the BAT case. At this stage in the development of the design, there are no indications that the proposed systems will lead to unacceptable quantities or activities of radioactive waste. There are no fundamental reasons why these systems cannot be designed in a way that demonstrates BAT.

5.2.3 Assessment of the options appraisal approach

The RP set out its BAT approach for the SMR-300 through its BAT guidance submission (HOLTEC BRITAIN, 2025ad). This approach is used to evaluate different options to decide which one represents BAT. It uses a structured method that is designed to be proportionate to the potential environmental impact. The approach was improved during GDA to incorporate our feedback and lessons learned from the worked examples.

We raised RQ-01736 based on a concern that depending on the issue being considered the RP would only use the as low as reasonably practicable (ALARP) guidance (HOLTEC BRITAIN, 2024f) for radiological protection issues. We were concerned that this guidance did not contain comprehensive environmental criteria such as sustainability considerations, which may have led to sub-optimal environmental outcomes. In response to our RQ, the RP confirmed that if an issue had both a safety and environmental consideration, both the BAT and ALARP guidance would be used. The revised BAT guidance (revision 1) confirmed that any conflicts or issues between BAT and ALARP will be raised to the Head of Licensing at Holtec Britain to resolve. We are satisfied with this approach for Step 2. However, this is a process that we will follow up on at a potential Step 3 of GDA, pre-application engagement or site-specific permit determination.

In Step 2 we have seen how the BAT statement and BAT assessment approach have worked, as both were submitted as worked examples (see section 5.2.5). We note that we have not seen how the BAT study process works in practice. However, we have seen how well the BAT assessment approach works, and if it is a smaller, simpler process it should work equally as well. Again, this is a process we will follow up on at a future stage.

Overall, we consider that the RP’s BAT approach meets the criteria from our Guidance for Requesting Parties and our Radioactive substances management: generic developed principles (RSMDP4 – BAT methodology). We have identified that the RP’s BAT guidance has outlined criteria for when to review the demonstration of BAT, however, there is no set period identified on when to review the demonstration. This is important because some of the BAT design decisions made now may not come into fruition for several years. Depending on the site selection, other design decisions and new technologies arising during this time, the option chosen may no longer be BAT. The RP has identified this gap and stated that the BAT demonstration document shall be reviewed at appropriate milestones (to be defined post-GDA).

5.2.4 Assessment of design change management

The RP has established a design management process to identify prospective changes to the GDA DRP. This process can be used to ensure that changes originating in the USA do not adversely impact BAT, and that any potential UK compliance gaps are identified and fed back into the generic SMR-300 design.

The RP’s processes in this area were being developed during the GDA. We raised RQ-01466 to capture our questions about categorisation and scoring of changes since we were concerned that minor changes or those only impacting the environment (not safety or security) would not be assessed for BAT, that novel technologies may be avoided, and that cumulative effects of several smaller changes may be missed. The design management process (HOLTEC BRITAIN, 2024b), which was produced after this RQ was raised, adequately answered these concerns. We expect this process to evolve post GDA to consider learning from experience to ensure it remains fit for purpose.

Because the design is immature in some areas, producing design solutions is generally not possible within the GDA timescales. Therefore, potential compliance gaps are logged on a register. Design changes originating from the USA are assessed against UK requirements. Any forward actions agreed from this process are added to the CAR register (HOLTEC BRITAIN, 2025ae). Post GDA it will be necessary for the RP to review all prospective design changes identified and decide whether to alter the UK reference design.

The RP has also produced guidance on the consideration of design stability when demonstrating risks are reduced to ALARP and the use of BAT (HOLTEC BRITAIN, 2024e). It appears the aim of this guidance is to minimise the number of changes made to the generic SMR-300 design to protect the RP’s claimed benefits of a fleet deployment. While this approach seems broadly justifiable, if any arguments are made that give a weighting to maintaining the existing design, even if another approach would be considered BAT in a UK-only context, this will have to be carefully evaluated. No such arguments have been made within Step 2.

5.2.5 Assessment of the best available techniques worked examples

We assessed 3 worked examples of the RP’s options appraisal to identify BAT. Two of these covered design decisions: a BAT statement for the choice of lithium hydroxide (LiOH) used to maintain pH of the primary coolant (HOLTEC BRITAIN, 2025e), and a BAT assessment of the NFW packaging (HOLTEC BRITAIN, 2025h). The third example was a BAT statement for changes to the CES and CS (HOLTEC BRITAIN, 2025f), which was driven by the requirements of the Palisades site in the USA. 

The BAT statement on the use of LiOH was logical, clear and similar to BAT assessments we have observed at operating power stations. We noted that the final decision on the use of LiOH would be made by the operator, but this is not foreclosed by the design. The BAT statement for the CES and CS design change identified the claims and arguments in the BAT case that could be impacted by this change. Although the evaluation of the options was clear, there was uncertainty over the quantities of radioactive waste since the design was immature. It was also not possible to say whether any equipment fulfilling EPFs would be affected since these have not yet been identified for this part of the design. Although, at this stage in the design, the BAT case is not challenged by the design change, this will need to be re-evaluated once the uncertainties mentioned above have been resolved.

The BAT assessment for NFW container selection was a much more in-depth undertaking by the RP. It involved an optioneering workshop, with briefing material and a comprehensive output report. We carried out a detailed review of the criteria for optimisation outlined in our Guidance for Requesting Parties.

At a fundamental level, most considerations for optimisation were met. We noted that there was not much detail on discharges and no consideration of the radiological impact to the public and other species for the different containers. We consider this acceptable at this stage due to the level of design detail and maturity available at the time of assessment. However, a further assessment of radiological impact from NFW containers and any subsequent storage facilities and impacts from discharges is required to support the BAT assessment at the site-specific stage.

The worked examples were used to improve the BAT method. They demonstrated that the RP’s optimisation process is adequate for identifying and recording BAT.

5.2.6 Assessment of environmental protection functions and measures (Radiological)

Our Engineering: generic developed principles (specifically ENDP4) set out our expectation that EPFs under normal and fault conditions should be identified, and adequate environmental protection measures (EPMs) be in place to carry out these functions.

We observed that the method for identifying EPFs and EPMs is a logical process which takes account of our generic developed principle ENDP4. We also observed that the approach identifies the interactions with BAT, safety functions and broader management arrangements, such as asset management and design change control. The framework for EPFs is suitable to be used post GDA for a site-specific project.  

The RP acknowledges that the EPM identification method lacks details on an environmental risk assessment to categorise environmental SSCs. There is currently no consideration of defence in depth or methods of operation (human factors) for environmental SSCs that would impact on the risk assessment. The RP’s approach was explored in a pilot study for the liquid radwaste system (LRW), which provided some confidence that these aspects could be successfully incorporated in future. We also observed that the method is not linked to fault studies for the SMR-300 which could be used to identify EPFs and EPMs required under fault conditions. These gaps are commensurate with a concept design and sufficient for a 2-step GDA. The RP identified several forward actions to review and improve the EPF and EPM approach post GDA. These actions need to be completed to allow a fully developed list of EPFs and EPMs to be produced.

Based on our Step 2 assessment of EPFs and EPMs, we have found no fundamental environmental protection shortfalls at this stage that could prevent the design from being acceptable to build and operate at sites in England and Wales.

5.2.7 Radioactive waste management arrangements (RWMA)

During Step 2 of GDA we assess strategic considerations for the management of radioactive waste and spent fuel, including the RP’s IWS and any relevant strategic documents. We expect these documents to identify the strategic considerations for radioactive waste management which underpin the design. We also expect these to identify radioactive wastes and spent fuel arisings from the Holtec SMR-300 throughout the nuclear power plant’s lifecycle and how they will be managed and disposed of.

The RWMA and IWS broadly meet our expectations for the current stage and maturity of the SMR-300 design. Strategic considerations, including relevant policy, legislation, regulation, guidance and principles are clearly defined in relation to radioactive waste management.

The commitments by the RP will address gaps in information that would be required at the site-specific permitting stage.

The RP explicitly lists the assumptions behind the development of the waste management strategy and the uncertainties and opportunities associated with management of waste and spent fuel. The RP acknowledges the option of decay storage of boundary wastes and that new disposal routes may become available during reactor operations or decommissioning.

Based on our Step 2 assessment of RWMA, we have found no fundamental environmental protection shortfalls at this stage that could prevent the design from being acceptable to build and operate at sites in England and Wales.

5.2.8 Decommissioning

During Step 2 of GDA we assess the RP’s submissions against the relevant regulatory expectations for the decommissioning strategy and the decommissioning and waste management plan (DWMP). This includes the RP’s considerations at the design stage for meeting our guidance for nuclear sites undergoing decommissioning (Environment Agency & Natural Resources Wales, 2024) and our guidance on requirements for release from radioactive substances regulation, known as ‘GRR’ (Environment Agency, Scottish Environment Protection Agency and Natural Resources Wales, 2018).

We conclude that the RP has taken our guidance and UK government policy into account when developing the decommissioning strategy. The RP has provided information on its decommissioning strategy and how the design of the SMR-300 will facilitate decommissioning at the end of operations.

The decommissioning waste inventory supplied by the RP (HOLTEC BRITAIN, 2024h) is qualitative and because a source term has not yet been calculated, there is some uncertainty around the type and quantity of decommissioning wastes that will be generated. Arrangements for the management of higher activity wastes (HAW) arising from decommissioning work have not yet been confirmed. However, the RP has supplied an acceptable level of information for the purposes of our fundamental assessment at Step 2 of GDA, and we:

• accept that decommissioning of the SMR-300 is unlikely to generate orphan wastes
• have not identified aspects of the reference design or design approach that would foreclose the use of BAT when decommissioning the SMR-300

Based on our Step 2 assessment of the RP’s proposals for decommissioning the SMR-300, we have found no fundamental environmental protection shortfalls at this stage that could prevent the design from being acceptable to build and operate at sites in England and Wales.

5.3 Solid waste, spent fuel and disposability

This section documents the GDA Step 2 fundamental assessment of solid waste, spent fuel and disposability for the SMR-300, including the treatment, packaging, storage and disposal of solid wastes and spent fuel arising from the operations and decommissioning of the SMR-300. We present our assessment outcomes specifically in relation to:

• identifying and quantifying solid radioactive waste and spent fuel
• proposed disposal routes for the radioactive wastes identified
• how waste records will be managed to enable disposal
• forward action plans relating to this topic area

Solid radioactive waste will start being generated by the SMR-300 from the point at which nuclear fuel is brought to site and commissioning takes place. It will then be generated throughout the operational phase (design life is estimated to be at least 80 years) and decommissioning phases of the nuclear reactor. Spent fuel will be generated throughout the operational phase of the SMR-300.

The RP describes the following waste categories in its GDA submissions:

• HAW, including spent fuel – HAW includes high-level waste (HLW), ILW and some LLW that is unsuitable for disposal in the Low Level Waste Repository (LLWR)
• lower activity wastes (LAW) – includes LLW and VLLW
• decommissioning wastes

5.3.1 Our fundamental assessment of solid waste, spent fuel and disposability

The main goal of our assessment for this topic area is to ensure that any wastes identified are quantified and are disposable. Our conclusions on disposability are considered in the context of the disposal facilities currently available in the UK.

We assess the RP’s submission against best practice guidance and Environment Agency guidance, including our RSR objective and principles and RSR generic developed principles. We base our assessment on published Environment Agency guidance and any relevant international guidance. The scope of our assessment is defined by our Guidance for Requesting Parties and what the RP defines as the scope of what it wants us to assess.

During Step 2, our assessment has covered spent fuel and waste management, including waste generation, pre-treatment, treatment, conditioning, storage and disposal. Solid radioactive wastes produced by the SMR-300 include HAW and LAW.

A high-level description of the scope of this GDA can be found in section 3. For solid waste, spent fuel and disposability, the scope includes:

• a high-level estimate of the nature and quantities of radioactive wastes anticipated to be generated during operations and decommissioning
• a description of the strategy for the management of each waste category
• a demonstration that it will be possible to design and operate capabilities for the safe and compliant management of ILW and spent fuel until such time as a GDF becomes available
• evidence of disposability of HAW streams based on NWS expert view
• demonstration of disposability for LAW streams

The RP has specified that the following are out of scope of the SMR-300 GDA:

• detailed estimates of the nature and quantities of radioactive wastes anticipated to be generated during decommissioning
• design and associated analysis of systems outside the NI for the management of ILW
• on-site ILW processing capability
• on-site ILW storage facility

Radioactive substances management: generic developed principles RSMD15 highlights our expectations with regards to the disposal of wastes. We expect the RP to demonstrate that it is starting to address these requirements as part of our fundamental assessment of the SMR-300.

We assessed several documents from the RP’s GDA submission for this topic area. However, we also worked closely with the BAT topic assessment area and ONR’s NLR assessment area. Main documents submitted by the RP in support of this topic area included:

• PER Chapter 1, Radioactive Waste Management Arrangements, HI-2240360 (HOLTEC BRITAIN, 2025i)
• Integrated Waste Strategy, HI-2241151 (HOLTEC BRITAIN, 2025aa)

NWS has developed a disposability assessment process to reduce the risk of the generation of waste that is incompatible with geological disposal. For a Step 2 GDA, NWS provides an expert view on disposability intended to highlight any inherent, unmitigated risks to the disposability of HAW based on a high-level review.

5.3.1.1 Higher activity wastes (HAW)

Identifying and quantifying higher activity wastes

The RP has classified wet solid HAW in terms of its source and physical properties. ILW streams consist of spent ion-exchange resins, spent filter media (activated charcoal) and spent filter cartridges. Annualised HAW volumes and composition, for a single SMR-300 reactor, are expected to be 7.5 cubic metres per year (m³/year). The main non-radioactive contaminants present in the wet wastes are expected to be boron and chromium, based on available UK OPEX data (HOLTEC BRITAIN, 2025aa). The RP does not expect any operational dry-route ILW to be produced.

The RP has estimated the quantity of spent fuel that would be produced by the SMR-300 based on OPEX from nuclear reactors using the same fuel type (Framatome GAIA) that will also be used by the SMR-300. The RP provided details of the length of the fuel cycle, the expected average and maximum fuel burn-up rate, the number of refuelling cycles and total spent fuel elements expected to be generated over the 80-year lifetime of a twin unit SMR-300. A design specific radionuclide inventory of the spent fuel was not available within the timescales of GDA Step 2.

NFW is expected to comprise high-dose rate redundant metallic components, including rod cluster control assemblies (RCCA) and in-core instrumentation, that have been activated in the reactor core. The RP did not supply a detailed physical, chemical and radionuclide inventory of items that are classed as NFW for Step 2 of the GDA.

The RP identified ion-exchange after-filters originating in the LRW as a potential boundary waste. Current estimates suggest this would be a small waste stream of about 0.3 m³/year per twin SMR-300 unit.

We are satisfied that the waste types and categories identified and the estimates of waste volumes provide a sufficiently accurate picture of the performance of the SMR-300 in the context of the requirements of GDA Step 2. Where quantitative data was provided, the modelling approach seems reasonable, and the source data and assumptions are clearly described. This is deemed to be good practice.

While an improved understanding of the spent fuel inventory would increase our confidence in the disposability of the spent fuel, this is not a fundamental concern at Step 2 of GDA. This will be required at the site-specific permitting stage.

Management and disposal of HAW

The RP has carried out a high-level, qualitative assessment of the options available for packaging and interim storage of HAW prior to disposal. The preferred or ‘opportunity’ option selected by the RP is to store unencapsulated waste in a high integrity container (HIC). The alternative or baseline option for operational solid ILW would be to package the waste in an unencapsulated form in a package adopted by NWS as standard for low heat generating waste. The RP has selected the robust shielded container (RSC) for this application. The design of the storage facility for these packages is outside the scope of the GDA.

Spent fuel will be stored within the SFP for a cooling period then removed from the storage racks and packaged. The RP’s preferred packaging for spent fuel is the single wall MPC-37 multi-purpose container. Damaged fuel will be placed within a damaged fuel canister and then placed in an MCP-37 together with undamaged fuel elements. The preferred strategy for NFW is to store it in SFSRs in the SFP until sufficient NFW has been accumulated to fill a NFW canister. Once filled, canisters will be dried, sealed and transferred to the ISFSI for interim storage.

Government policies in England and Wales for the long-term management of HAW and spent fuel are based on disposal in a GDF. This is on the assumption that a suitable GDF or disposal facility will be available. Assumptions regarding the availability of a GDF have been captured in the RPs CAR register (HOLTEC BRITAIN, 2025ae). In advance of the availability of an operational GDF, the wastes and spent fuel produced from the SMR-300 would be stored in interim storage facilities on the site. Interim storage is outside the scope of this GDA.

The RP has engaged with NWS early in the GDA process and sought an expert view (HOLTEC BRITAIN, 2024d). NWS provided an expert view (Nuclear Waste Services, 2025) and the RP has produced its Disposability Assessment Review (Gap Analysis) (HOLTEC BRITAIN, 2024c) to support this.

The RP presented NWS with 2 packaging options:

• a baseline case whereby spent fuel would be disposed of to a GDF using a NWS reference disposal container
• a second option consisting of direct disposal of spent fuel in MPC-37 containers, which are novel containers in a UK context

In its assessment, NWS considered the disposability of wastes and spent fuel from the SMR-300 against the baseline case. It concluded that the nature of the wastes and spent fuel from the SMR-300 would not significantly differ from those which would arise from existing and planned reactors. This provides NWS with the confidence to consider that a disposability case for the wastes and spent fuel from the SMR-300 could be made for the baseline case (Nuclear Waste Services, 2025).

However, NWS noted that the physical size and mass of the novel containers or overpacks would be too large for routine transport on the UK rail and road network and for the anticipated openings in a GDF. Furthermore, the heat output from the MPC-37, would be too great to comply with GDF thermal limits without extending the prior interim storage period to impractical timescales (Nuclear Waste Services, 2025). NWS, therefore, considers that direct disposal of spent fuel in novel containers is not feasible. At the site-specific permitting stage, it will need to be demonstrated that any packages used for disposal of spent fuel are compatible with the UK. The RP has captured this requirement within a GDA commitment in its CAR register (HOLTEC BRITAIN, 2025ae).

In its assessment, NWS identified 6 low risks associated with uncertainties that would need to be resolved before a full disposability case could be made. NWS considered that the current baseline prompt decommissioning strategy posed a high risk to disposability and that a period of interim storage may be required for HAW decommissioning wastes. Considering the design challenges highlighted in this section, requirements beyond GDA timescales have been captured within a GDA commitment in its CAR register [HOLTEC BRITAIN, 2025ae].

We raised RQ-02237 on the effect of the use of Metamic racks in the fuel pond on discharges and solid waste and whether this represents BAT. The RP has provided information explaining how the use of Metamic may reduce aqueous radioactive discharges when compared to using other material such as Boraflex. However, the RP has recognised that further substantiation of the use of Metamic is required.

From our assessment, we conclude that the management arrangements for solid wastes and spent fuel have not yet been optimised and assessed against BAT to minimise the impact of waste disposals on the environment. However, the RP has provided examples of the process it will apply to optimise its waste management arrangements in the future. Based on our Step 2 assessment of RWMA, we have found no fundamental environmental protection shortfalls at this stage that could prevent the design from being acceptable to build and operate at sites in England and Wales.

We are satisfied that the RP has presented sufficient information about the management of solid wastes and spent fuel to satisfy the requirements of Step 2 of GDA, noting that further work is required at the pre-application and site-specific permitting stage to provide a full disposability case. The RP has demonstrated an awareness of the relevant policy, regulations and standards on waste management in the UK and of the waste routes available for the disposal of radioactive waste.

5.3.1.2 Lower activity wastes (LAW)

Identifying and quantifying LAW

The RP has identified relatively low volumes (less than 2 m³/year) of spent ion-exchange resins expected to be generated as LLW, per reactor unit.

Dry solid wastes volumes were estimated based on typical PWR OPEX. The RP has estimated that the bulk of the dry LLW will be combustible: 85 m³/year of dry active wastes (for example, rags, wipes and PPE) and a smaller quantity approximately 0.84 m³/year of combustible oily waste or chemical wastes. Non-combustible waste will consist of filters (9.3 m³/year) and a small metallic waste stream consisting of failed equipment components and contaminated tools (0.45 m³/year).

Management and disposal of LAW

The RP has not provided detail on the techniques that will be used to manage LAW but lists the principles that will be followed. For example, segregation at source, volume reduction where practicable, and disposal at an authorised facility as soon as practicable, through use of the NWS waste services contract.

Waste will initially be segregated at source by provenance, before being transferred to the waste management area in the RAB for sorting and segregation according to the intended disposal route. In the IWS, the RP has stated its intention to “apply the waste hierarchy, evaluate all viable on-site or off-site options for the treatment of dry solid wastes and select optimised waste disposal routes based on the properties of the LAW and taking into account the principles of BAT, ALARP, and the proximity principle” at the site-specific permitting stage (HOLTEC BRITAIN, 2025aa).

The RP has provided some detail on the design of the facility for treating LAW, outlining that the design of the LLW buffer storage meets US good practice for PWRs as set out in the Electric Power Research Institute: Utility Requirements Document (Electric Power Research Institute, 2014).

In its assessment, NWS noted that boron is a capacity-controlled material at the LLWR and this would currently act as a constraint on the amount of Metamic that could be consigned there. Based on NWS’s current understanding, the material appears similar to high boron-containing metallic items already consigned to the LLWR from Sellafield, however more information would be needed on the exact composition of the Metamic itself. NWS acknowledges the RP’s intention to manage LLW via an appropriate route once the waste inventory for the SMR-300 has been determined and appropriately categorised.

We have noted that the LLW disposal routes are not yet optimised at this time but acknowledge that the wastes generated by the operation of the SMR-300 are likely to be disposable. We have also noted that the RP’s approach for managing LLW and its intended use of the NWS waste services contract is likely to result in the disposal of wastes by an appropriate route.

5.3.1.3 Decommissioning wastes

Decommissioning is the administrative and technical actions taken to allow the removal of some or all of the regulatory controls from a nuclear facility or site. Decommissioning is a transitional phase where operations have finished but radioactive substances activities are still required to clean out radioactive waste and to dismantle nuclear facilities. The final decommissioning phase ends when all planned work involving radioactive substances has stopped (Environment Agency & Natural Resources Wales, 2024).

Identifying and quantifying decommissioning wastes

Sources of information provided by the RP included Decommissioning Waste Inventory for the Generic SMR-300 Design, HI-2241428 (HOLTEC BRITAIN, 2024h).

The SMR-300 design is still at an early stage and, therefore, not mature enough to provide specific data on the masses, volumes or radionuclides inventories of waste likely to be generated from decommissioning and dismantling activities.

The RP has used OPEX data from the selected PWR designs as a basis for deriving a qualitative decommissioning waste inventory for the SMR-300 design. This is based on the similarity between fuel and core properties of the SMR-300 design and those of the other selected PWR designs – including fuel cycle, fuel type, fuel assembly and core coolant or neutron moderator. The RP states that where PWRs are characterised by similarities in fuel and core design features, it can be argued that those downstream impacts will follow similar trends in terms of reactor chemistry, material activation and secondary waste generation (HOLTEC BRITAIN, 2024h). The RP has presented qualitative information on the origin and provenance of radioactive waste, waste types and matrix materials, and estimated waste category. We accept that qualitative estimates of decommissioning wastes quantities and waste types are adequate for the purpose of assessing the decommissioning strategy at this stage of development of the SMR-300 design.

We consider that, as the design develops, further work will be required to better define the full extent of decommissioning wastes. Estimates will also need to include waste resulting from the decommissioning of the ancillary buildings that have not been included within the scope of this GDA. Under Section 45 of the Energy Act 2008, applications for a nuclear site licence to operate a nuclear power station must prepare and submit a Funded Decommissioning Programme (FDP) for approval, which includes a detailed DWMP. The RP has captured this requirement as ‘future evidence’ in PER Chapter 1 (HOLTEC BRITAIN, 2025i).

Disposal of decommissioning wastes

A future operator may decide to adopt other waste processing systems that differ from the RP’s current proposals. However, we expect the RP to demonstrate, in principle, that the decommissioning HAW can be conditioned, packaged and disposed of.

The RP has not provided any details regarding its arrangements for managing decommissioning wastes. However, it has stated its intention that it will consider the same regulatory regime and waste management principles when managing decommissioning wastes as when operating the plant. The RP has outlined techniques that might be used to treat various types of waste, expected to be generated by decommissioning activities. We acknowledge that this is a sufficient level of detail for a Step 2 GDA and that further work is required at a future stage to provide sufficient information for a permit application. The wastes resulting from the decommissioning of PWRs are well understood and, therefore, we do not have any fundamental concerns about the disposability of wastes generated by decommissioning of the SMR-300.

5.3.2 Records and knowledge management for waste disposal

The RP’s IWS aims to describe the management strategies for radioactive waste, non-radioactive waste and spent fuel in line with UK legislation, policies and standards. The information with respect to the management and disposal of radioactive waste should be sufficiently recorded and maintained over the lifecycle of the plant under appropriate quality assurance arrangements (HOLTEC BRITAIN, 2025aa). The RP has recognised the requirement to adequately record and maintain all relevant documentation and information, including environmental and safety case documentation, waste information, commitments, decision-making records, assumptions, uncertainties and operation history using an appropriate information management system. The RP has stated that this will be developed at the site-specific stage.

The RP has listed in the IWS the typical information that would be recorded, and makes reference to relevant industry guidance (Nuclear Waste Services, 2015) and to the RP’s MSQA procedures defined in PSR Part A Chapter 4 (HOLTEC BRITAIN, 2025ab). The RP states that this information will form part of any hand-over package post GDA (HOLTEC BRITAIN, 2025aa). We consider the RP’s proposals on waste records adequate for a Step 2 GDA, recognising that a records management system will need to be developed to a more advanced state by the developer or future operator for a site-specific permit application.

5.3.3 Commitments, assumptions and requirements

Two commitments relevant to this topic are recorded in the RP’s CAR register (HOLTEC BRITAIN, 2025ae). Commitments are managed under the RP’s CAR management procedure (HOLTEC BRITAIN, 2025z) within the GDA process and are to be completed as part of the issue of a pre-construction SSEC.

The first commitment is to further quantify and categorise radioactive waste inventories. This includes selecting ILW management options to produce detailed designs of facilities for ILW storage and LLW handling to optimise the design of the facilities for managing solid radioactive waste. It also includes a commitment for further engagement with NWS on a disposability assessment of ILW packages, following down-selection of containers and further development of radioactive waste inventories.

The second commitment is to perform a comparative assessment of the preferred prompt decommissioning strategy against a strategy for deferred decommissioning. This will integrate considerations from a quantitative decommissioning inventory and identify enduring plant and equipment required for decommissioning that will require maintenance beyond the plant’s operational period.

As the SMR-300 design is not fully mature, the completion of these CARs is crucial to the development of a design that minimises the generation of radioactive waste or spent fuel and enables the impact of disposal of waste to be minimised.

5.3.4 Conclusions to our fundamental assessment of solid waste, spent fuel and disposability

We are satisfied that the waste types and categories identified and the estimates of waste volumes provide a sufficiently accurate picture of the performance of the SMR-300 in the context of the requirements of a Step 2 GDA. We accept that qualitative estimates of decommissioning wastes quantities and waste types are adequate for the purpose of assessing the decommissioning strategy at this stage of development of the SMR-300 design.

At this stage of the design, specific waste inventories were not available, and therefore, the performance of the SMR-300 could not be compared with other nuclear power stations (both operational and in the design phase). We expect the RP to provide data to enable these performance comparisons to be made at the site-specific permitting stage. We recognise that the RP has put a framework in place to calculate accurate waste inventories in future, once the design-specific SMR-300 waste source term is known. This will enable waste disposal impacts to be determined and provide information on which to assess waste management arrangements against BAT requirements.

The management arrangements for solid wastes and spent fuel have not yet been optimised and assessed against BAT, to minimise the impact of waste disposals on the environment. However, the RP has provided examples of the process it will apply to optimise its waste management arrangements in the future. We consider that application of this process is likely to result in the development of arrangements that will comply with environmental permitting requirements once the SMR-300 is permitted and operational.

On the basis of the expert view from NWS and the RP’s CARs, we don’t have any fundamental concerns about the disposability of wastes generated by the operation or decommissioning of the SMR-300, noting that further work is required to provide a full disposability case. At the site-specific permitting stage, it will need to be demonstrated that any packages used for disposal of spent fuel are compatible with the UK.

The RP has presented sufficient information about the management of solid wastes and spent fuel to satisfy the requirements of Step 2 of GDA. The RP has demonstrated an awareness of relevant policy, regulations and standards on waste management in the UK and of the waste routes available for the disposal of radioactive waste.

Based on the information provided so far and our Step 2 assessment, we have found no fundamental environmental protection shortfalls at this stage that could prevent the design from being potentially acceptable to build and operate at sites in England and Wales.

5.4 Discharges of liquid and gaseous radioactive waste

The scope of the assessment includes radioactive discharges from normal operations, which includes start-up, at power, shutdown, maintenance and testing, outage and discharges resulting from any other reasonably foreseeable events expected to occur during the lifetime of the reactors (‘expected events’). Excluded from the scope are discharges resulting from commissioning and decommissioning.  

Our assessment has considered the RP’s submission in relation to relevant policy, legislation and guidance, including our Guidance for Requesting Parties and against Environment Agency expectations in our RSR objective and principles and RSR generic developed principles​, the main one being RSMDP12 – Limits and levels on discharges. 

Our assessment seeks to ensure that:  

• all sources of gaseous and liquid radioactive waste have been identified
• all routes for gaseous and liquid radioactive waste to the environment have been identified
• the monthly discharge estimates are quantified for an appropriate range of radionuclides
• all significant radionuclides relating to gaseous and liquid radioactive waste are identified, quantified and assigned an appropriate proposed discharge limit
• all the assumptions in the submission relating to gaseous and liquid radioactive waste are clearly visible, appropriate and justified
• annual limits proposed by the RP should have:
  • been clearly derived
  • been given acceptable headroom
  • taken account of our limit setting guidance
• the proposed discharges from the Holtec SMR-300 do not exceed those of comparable nuclear power stations around the world

We held technical meetings with the RP to clarify our understanding of the information presented and explain any concerns we had with that information. We raised 2 RQs as part of our assessment.

RQ-01575 – Supporting submissions for PER Chapter 2 - Quantification of Effluent Discharges and Limits (QEDL)

This RQ was to address information not present in PER Chapter 2 (HOLTEC BRITAIN, 2025j) ​at the start of Step 2 or expected changes to the planned supporting submissions, to ensure that the aims of our Step 2 assessment plan could still be met. The RP’s response provided updates on the intended submission titles, a summary of their content and their delivery dates, as well as outlining its approach to deriving a source term and discharge estimates.

RQ-02464 – Clarifications for the QEDL topic

This RQ was to confirm whether a single or twin reactor is represented in the discharge estimates for the Holtec SMR-300, as this appeared to vary between submissions. The RQ also required confirmation of some other values in PER Chapter 2 (HOLTEC BRITAIN, 2025j) and an explanation of what is meant by the term ‘dilution’ under 2 different contexts. The RP’s response provided updated values and the necessary clarifications. 

Through our assessment work we have established that the RP understands the regulatory framework and legislative requirements, and we are satisfied that it has addressed the following assessment objectives at an acceptable level of detail for this Step 2 fundamental assessment: 

• the main sources of gaseous and aqueous radioactive effluent have been identified, along with their routes for discharge to the environment – there may be additional sources, but these are not expected to contribute significantly to discharge estimates
• an appropriate range of radionuclides has been identified for estimating discharges – the method for estimating effluent discharges is clearly demonstrated, as is the selection of significant radionuclides for limit setting
• expected events have been identified and a contribution to discharge estimates is included – the RP recognises that further work is needed to ensure the approach adequately factors in contributions to discharges from expected events
• headroom factors have been determined, using a statistical approach
• proposed annual limits, in giga-Becquerels per year (GBq/y), are derived from the discharge estimates with the appropriate application of the headroom factors – these are presented in Table 1 and Table 2
• details of any assumptions are included in the submissions, with corresponding justification – the RP understands that there are limitations with aspects of its chosen approaches, some of which introduce overly conservative inputs
• a comparison of discharge estimates and limits with OPEX and previous GDAs is presented, with reasonable explanations for any significant differences

Table 1: Proposed gaseous emission limits for a twin-unit Holtec SMR-300 

Radionuclide/radionuclide group	Proposed discharge limit (GBq/y)
Tritium	4.34E+04
Carbon-14	5.03E+02
Noble gases	6.28E+04
Iodine-131	4.32E-03
Other beta-emitting particulates	6.03E-01

Table 2: Proposed aqueous emission limits for a twin-unit Holtec SMR-300 

Radionuclide/radionuclide group	Proposed discharge limit (GBq/y)
Tritium	1.82E+04
Carbon-14	5.70E+01
Caesium-137	4.11E-01
Other beta/gamma emitting radionuclides	1.27E+00

We recognise that the discharge estimates and proposed limits are Step 2 figures, and we expect to see refinement of these as part of normal design development. Commitments and future evidence are in place to address aspects that will need to be reviewed when reactor-specific design values and site-specific considerations are available. These cover: 

• detailed assessment of estimated discharge source terms
• contributions from all components of normal operation, including expected events, as well as load following
• the calculation of maximum monthly discharge estimates to reflect the peak discharges under normal operations
• specific reviews of the methods for estimating discharges of argon-41 and tritium, supplemented with further work to ensure that tritium discharge estimates are representative
• further consideration of whether use of the GALE-PWR 3.2 code is relevant good practice (RGP) for the Holtec SMR-300
• reconsideration of the selected significant radionuclides for proposed permit limits

We will follow up on the development of this detail and subsequent updates and refinements to the discharge estimates and proposed limits, along with their use for comparison purposes, under any future detailed assessment work. 

Under the response to RQ-02464, the RP confirmed that the discharge estimates presented in PER Chapter 2 (HOLTEC BRITAIN, 2025j) represent a single reactor rather than the intended twin unit Holtec SMR-300 design. We are satisfied that the updated data provided in the RQ response do not change any of the RP’s findings or our conclusions. We expect that the detailed work already planned under commitments and future evidence will include steps to update any inputs that should reflect the twin units. 

Overall, our conclusion is that the calculation of discharges and proposed limits is thorough, systematic and appropriate for Step 2 of GDA, subject to further refinement as a result of ongoing work. We have found no fundamental environmental protection shortfalls at this stage that could prevent the design from being potentially acceptable to build and operate at sites in England and Wales.

5.5 Sampling and monitoring

Our information requirements for a GDA are given in our Guidance to Requesting Parties (2023). For sampling arrangements, techniques and systems for measuring and assessing discharges and disposals of radioactive waste, our assessment covers:

• in-process monitoring
• monitoring final discharges of gaseous and aqueous wastes
• monitoring disposals of non-aqueous liquid and solid wastes

The RP must also demonstrate that its proposals represent BAT for monitoring and confirm that the sensitivity is sufficient to:

• readily demonstrate compliance with the proposed limits
• meet the levels of detection specified as good practice recommended by the EU in 2004/2/Euratom (EU, 2004)

The RP must describe the facilities provided for independent periodic sampling (by the regulator) of final discharges of gaseous and aqueous wastes.

We have assessed the RP’s approach to sampling and monitoring as part of our GDA Step 2 Fundamental Assessment of the generic SMR-300 design. Overall, our conclusion is that the considerations for sampling and monitoring are adequate for this stage of GDA.

The RP has provided the information required for a Step 2 GDA. It has acknowledged gaps which will be addressed either by delivery of a GDA commitment or future evidence requirement in line with the Holtec SMR-300 GDA capturing and managing commitments, assumptions and requirements process (HOLTEC BRITAIN, 2025z).

Our Step 2 assessment has focused on information provided by the RP, how it has defined appropriate requirements, considered good practice, OPEX, guidance and standards, and identified where further work would be required to meet our requirements. Overall, our conclusion is that the considerations for sampling and monitoring are adequate for this stage of GDA.

There are several areas that due to currently limited information require future determination and assessment to ensure they meet our requirements. The RP has identified these in 2 GDA commitments and 17 future evidence requirements. These are detailed in the CAR register (HOLTEC BRITAIN, 2025ae) and summarised as:

• detailed design of the monitoring and sampling systems
• detailed arrangements for in-process sampling and monitoring
• provision and equipment for flow monitoring of gaseous and aqueous discharges, including fulfilment of relevant standards
• instrumentation, sampling techniques, analytical methods, laboratory facilities and how required sensitivity will be achieved
• arrangements for how representative sampling of gaseous effluent will be achieved in line with ISO 2889:2023
• arrangements for how representative sampling of aqueous effluent will be achieved in line with ISO 5667-1:2023
• provision and arrangements for sample return requirements
• provision and arrangements of alarm systems for discharge and in-process sampling and monitoring
• arrangements for plant condition monitoring
• provisions for independent periodic sampling of gaseous and aqueous discharges
• access arrangements for calibration and maintenance in line with BS EN 14181:2004
• detailed arrangements for sampling, monitoring and characterisation of solid radioactive wastes and non-aqueous liquid wastes

There were no RIs, ROs or RQs raised for the sampling and monitoring topic during this GDA. However, through regular engagement with the RP, we sought clarification where necessary, and informal feedback has been provided to the RP during Step 2.

We are satisfied that the RP understands the requirements associated with sampling and monitoring. We have considered the claims, arguments and sub-arguments presented by the RP applicable to this topic and, where presented, the level of evidence provided is adequate for this stage of GDA. The RP has acknowledged current gaps in evidence and has included these as either a GDA commitment or future evidence requirement. This approach provides us with assurance that the RP has a suitable plan in place to provide evidence in future assessment stages.

5.6 Generic site and radiological impact assessment

5.6.1 Generic site description

As part of the GDA process, the RP is required to provide a description of the type of sites where the power plant could be built. We call this the generic site (or sites). The RP provided details of 2 generic sites in its generic site envelope report (HOLTEC BRITAIN, 2025c).

The generic site envelope (GSE) covers the parameters of the generic site needed to perform safety assessments (external hazards, natural or manmade hazards external to the facility which may affect the operation of the facility; generic site information, including features of a site that can be defined on a qualitative basis). The GSE also includes the generic site description (GSD), providing the features and characteristics of a site needed to undertake environmental assessments.

These assessments are used to predict radionuclide behaviour and fate in the environment following discharge. As GDA is carried out before site-specific parameters are available, the RP must provide a description of the generic site parameters and justify why the parameters selected are suitable for the SMR-300 generic site.

The GSD has been based on the 8 sites listed in EN-6 (Department for Energy and Climate Change, 2011), in addition to Trawsfynydd which has been considered by the UK government as a candidate site for a nuclear power plant. Two potential siting scenarios were identified in the GSD: a coastal site discharging into a marine environment and an inland lakeside site discharging into a lake.

Based on our assessment of the GSE report (HOLTEC BRITAIN, 2025c) against our expectations at Step 2 of GDA, we have concluded that the:

• GSD is consistent with the characteristics of existing nuclear sites in the UK and takes into account climate change
• parameters provided to define the generic site are sufficient for the purpose of carrying out a radiological impact assessment (consistent with expectations for Step 2 of GDA)
• parameters provided to define the generic site are consistent with the parameters defined in the detailed radiological impact assessment method
• parameters provided to define the generic site are suitably bounding for an initial radiological impact assessment of the SMR-300 design

During the progression of the GDA, Great British Nuclear (now Great British Energy – Nuclear) discounted Trawsfynydd as a potential site for initial SMR deployment due to the size of the site and limited volume of cooling water. As a result of the pessimisms in the assumptions and carbon-14 accumulation in the RP’s initial radiological impact assessment, it was not possible to demonstrate that doses resulting from aqueous discharges into Llyn Trawsfynydd would be acceptable for the generic SMR-300 (or other similar PWRs) without significant additional abatement of carbon-14. Therefore, only the coastal generic site was used for the radiological impact assessment presented in the PER. A more detailed assessment would be required to demonstrate if discharges into a larger lake system would result in doses below the source dose constraint.

5.6.2 Initial radiological impact assessment

The RP carried out a staged initial radiological impact assessment at the proposed discharge limits for one SMR-300 unit during normal operations. The Environment Agency’s initial radiological assessment tool (IRAT2) was used to carry out Stage 1 and Stage 2 initial assessments.

We reviewed the outcomes of the initial radiological impact assessment presented by the RP against our Radiological protection of people and the environment: generic developed principles, specifically:

• RPDP2, which states that radiation doses to individual people shall be below the relevant dose limits and, in general, should be below the relevant constraints
• RPDP3, which states that non-human species should be adequately protected from exposure to ionising radiation

The relevant dose limits and constraints for the public are:

• 1,000 micro-Sieverts per year (µSv/y) effective dose for members of the public (from all sources of radiation, excluding nuclear accidents or radiological emergencies, natural background radiation and medical irradiation)
• 300 µSv/y for proposed discharges and direct radiation from any new single source
• 500 µSv/y for discharges from any single site

The source and site dose limits are sometimes referred to as constraints. Dose constraints are part of the optimisation process. They are a tool to help restrict, as far as is reasonably practicable, an individual’s exposure to ionising radiation that might arise from a particular activity (Department for Energy Security & Net Zero, 2024).

The relevant dose constraint for wildlife is a combined dose rate of 40 micrograys per hour (µGy/h), below which the Environment Agency and Natural England have agreed there would be no adverse effect to the integrity of a protected site.

The RP’s initial radiological assessment, carried out using parameters from the generic site, resulted in doses to the public and dose rates to wildlife:

• 13 (µSv/y) to a member of a fishing family from discharges to sea
• 0.003 micrograys per hour (µGy/h) to marine wildlife from discharges to sea
• 44 µSv/y to a local resident from discharges to air
• 0.011 µGy/h to terrestrial wildlife from discharges to air

The methods presented for calculating dose impacts for members of the public and wildlife are adequate for this stage of GDA and we found no fundamental shortfalls in the RP’s submissions. The initial assessment undertaken using the preliminary discharge limits resulted in doses to people and dose rates to wildlife that were all below the relevant dose limits and source and site dose constraints.

We verified the outcomes of the initial radiological assessment carried out by the RP by performing our own Stage 1 and Stage 2 assessment using IRAT2. The same preliminary bounding discharge source term and assumptions regarding stack height (effective release height) and coastal dispersion were included. Our assessment resulted in the same dose outcomes to the public and wildlife.

The assessments presented by the RP were carried out for a single SMR-300 unit and will, therefore, be higher for the DR of a twin-unit deployment. In response to RQ-02464, the RP stated that doubling the doses presented in the PER chapter would be bounding. Our assessment findings are not changed by doubling the doses to the public and wildlife.

5.6.3 Detailed radiological impact assessment

IRAT2 is a conservative screening tool and is suitable for this early stage of GDA to demonstrate if a more detailed assessment is required. As the SMR-300 GDA will conclude following Step 2, a refined radiological impact assessment was not provided during GDA. The RP outlined its proposed method for a refined radiological assessment to be carried out post GDA in the PER (HOLTEC BRITAIN, 2025k). The method includes:

• a detailed site characterisation, including habits of local residents, identification of appropriate non-human reference organisms, determining local meteorological conditions and radiological baseline for the site
• selection and justification of models to be used to model dispersion and build-up of gaseous and aqueous radioactive wastes discharged into the environment
• doses due to a build-up of radioactivity in the environment during operations
• anticipated short-term discharges from the facility during normal operation which may contribute to public dose estimates
• collective doses to the UK, European and world populations (truncated at 500 years)
• a sensitivity analysis of parameters for the Stage 3 assessments to identify which variables have the most significant impact on the results, thereby showing how sensitive the results are to change in input parameters

The proposed approach is in line with our principles for assessment of prospective public doses and the RP presented adequate justification of the models, methods and data proposed. The parameters used in the detailed radiological impact assessment method are consistent with the GSD provided.

As such, we also consider that the method aligns with our generic developed principles, in particular:

• RSMDP13 – monitoring and assessment, which states that BAT, consistent with relevant guidance and standards, should be used to monitor and assess radioactive substances, disposals of radioactive wastes and the environment into which they are disposed
• RPDP4 – prospective dose assessments for radioactive discharges into the environment, which states that assessments of potential doses to the public and to non-human species should be made prior to granting any new or revised permit for the discharge of radioactive wastes into the environment

5.7 Other environmental regulations

Sections 5.1 to 5.6 of this report focus on RSR. This section considers how the Holtec SMR-300 is managing the requirements of environmental regulations other than RSR. The other environmental regulations assessment considers the following conventional (non-radioactive) topics:  

• water use and abstraction
• discharges to surface water
• discharges to groundwater
• operations of installations (combustion plants)
• Control of Major Accident Hazard Regulations (COMAH)
• F-gases and ODS

We completed our assessment by reviewing the relevant chapters of the RP’s submissions and had several meetings to discuss the information in more detail. For this topic, we have not found any fundamental environmental protection shortfalls that would mean that the design could not be safely operated in line with relevant environmental legislation, policies and guidance.

The early stage of the SMR-300 design during the GDA Step 2 meant that conventional environmental systems were yet to be fully specified. This has resulted in information gaps in the submissions we have received and assessed. For example, the chemical inventory and types of fluorinated gas (F-gas) to be used in conventional environmental systems have not been specified.

While there were information gaps, we found that the details provided were sufficient to enable a fundamental assessment of the SMR-300 design. The RP has committed to carry out further work to specify and develop conventional environmental systems beyond GDA Step 2 as the design of the SMR-300 progresses. A summary of our findings for each of the assessment areas is provided below.

With regard to F-gas and ODS, the SMR-300 will utilise F-gases in the heating, ventilation and fire protection systems, but these are yet to be specified. However, information provided confirmed that ODS will not be used in the SMR-300.

Hazardous chemicals are to be stored and used in the SMR-300 for preventing biofouling, corrosion, scaling and for pH control. The RP has not specified a comprehensive chemical inventory for the SMR-300 during Step 2 of the GDA. However, comparison with recently concluded GDAs for PWRs has concluded that the SMR-300 will likely be a lower tier COMAH establishment due to an estimated quantity of the chemical hydrazine. It is possible that this may change, depending on the quantity of hydrazine required to meet site-specific operational needs.

Combustion activities in the twin-unit SMR-300 will involve 4 diesel generators and one auxiliary boiler. The total thermal input for the combustion plants is under 50 MWth, which means that combustion activities will likely be subject to Medium Combustion Plant Directive (MCPD) rules. If more combustion plants are added and the total thermal input exceeds 50 MWth, then Large Combustion Plant Directive (LCPD) rules may apply. The proposed sources of fuel are diesel, natural gas and propane, but this does not foreclose specification of other fuel sources by the operator at the site-specific permitting stage. The intention is to use low sulphur diesel in the SMR-300 combustion plant to minimise air quality impacts. An assessment of how the combustion activities would likely impact air quality will be conducted at the site-specific stage.

Water abstraction estimates indicate that the SMR-300 will require an abstraction licence if it is to be sited next to an inland freshwater source. Design considerations associated with the protection of aquatic organisms during abstraction will be developed if required using the output from site-specific assessments. Protective measures for fish and other marine or freshwater biota may be required for abstraction or impoundment structures. If required, the design will consider the requirements of the local water ecology and relevant legislation.

The main sources of non-radioactive effluent discharges are the wastewater treatment system, the annular reservoir and the mechanical draft cooling tower. The annular reservoir, cooling tower and some other water use systems will be dosed with chemicals for chemistry control purposes (these are still to be specified). These chemicals fall under the following categories: corrosion inhibitors, anti-scaling agents, biocides, and pH control agents, and their use for such purposes is considered normal practice. Based on the categories of chemicals and the temperature of effluents, the SMR-300 will likely require a water discharge activity permit (WDAP) to enable discharges into surface water. There are no planned discharges to groundwater.

The RP developed a framework for specifying EPFs for conventional environmental systems. The RP also developed an approach for identifying EPMs that enable delivery of EPFs. This approach was piloted on a single system, and we are satisfied with the approach used, noting that further work is required to refine it for application across all conventional systems.

Based on our Step 2 assessment, we have found no fundamental environmental protection shortfalls at this stage that could prevent the design from being potentially acceptable to build and operate in England and Wales. However, there are information shortfalls that need to be resolved in the future to demonstrate compliance with relevant legislation and Environment Agency guidance. These are:

• confirmation of the names and quantities of F-gases that will be used in relevant systems and specification of the measures taken in the design to prevent and minimise leakages of such substances
• specification of a chemical inventory to facilitate an assessment against COMAH regulations and subsequent description of measures taken in the design to prevent a major accident to the environment if a COMAH threshold is exceeded
• final confirmation of the aggregated thermal input of all combustion plants to determine whether they:
  • are classed as MCP or LCP
  • would require a greenhouse gas emissions monitoring permit
  • would need a comparison of the proposed technology against BAT reference document for LCP (European Commission Joint Research Centre, 2017) if thermal input exceeds 50 MW
• confirmation of the air quality impact assessment results for the combustion plants
• specification of the volumes of fresh and cooling water requirements, including final confirmation of water abstraction volumes
• confirmation of the chemistry control regime for systems using water, including the chemical composition and temperature of effluents to enable assessment of permitting requirements for effluent discharges to surface waters

Further work is also required to improve the clarity of the descriptions of EPFs to identify appropriate EPMs. In addition, more work to identify EPMs across all relevant systems is necessary to fully develop the EPM repository for effective delivery of EPFs.

5.7.1 Sustainability

The UK policy framework for managing radioactive substances and nuclear decommissioning (2024) requires sustainability to be hard wired into thinking on the management of radioactive substances and how nuclear decommissioning is carried out. The Environment Agency and NRW have statutory duties for sustainability set out in the Environment Act 1995 and the goals and principles of the Well-being of Future Generations (Wales) Act 2015 and Part 1 of the Environment (Wales) Act 2016, respectively. This policy and legislation has shaped our organisational plans (EA2025 and now EA2030 and NRW Well-being statement). Throughout these documents, our expectations are influenced by the UN Sustainable Development Goals (UNSDG), which require sustainability to be incorporated into the management of radioactive substances.

For GDA, our Guidance to Requesting Parties states that we expect to see sustainability considered in the design of new nuclear power stations. During our Step 1 engagements with the RP, we shared our considerations of why sustainability is important in GDA and how sustainability aspects should be embedded as a principle of design and decision-making. The RP set out a high-level sustainability case for the generic SMR-300 within PER Chapter 4: Conventional Impact Assessment (HOLTEC BRITAIN, 2025l).

The RP has developed a sustainability strategy which sets out how sustainability measures will be implemented in the SMR-300 design. Key to incorporating sustainability principles is the embedding of BAT within the SMR-300 design. The design management process will be used to ensure that BAT is used to mitigate design risks. The intention is to reflect BAT throughout the lifetime of the SMR-300.

The sustainability strategy needs to be better defined so that sustainable development can be delivered throughout the lifetime of the SMR-300. Incorporating short to long-term objectives in the strategy may be useful for tracking the sustainability performance of the SMR-300. The RP has committed to updating the sustainability strategy for a site-specific project to ensure its scope takes into account local stakeholders and site-specific factors. This has been captured as future evidence in PER Chapter 4 (HOLTEC BRITAIN, 2025l).

6. Conclusions

Our Step 2 assessment of the Holtec SMR-300 design has focused on identifying any fundamental environmental protection shortfalls that could prevent the design from being potentially acceptable for deployment in England or Wales. Based on our assessment across all topic areas, we have found no fundamental environmental protection shortfalls at this stage.

The RP has demonstrated an understanding of UK regulatory requirements and provided sufficient information to enable a meaningful assessment. Our main findings are as follows.

The RP has established robust governance and quality management systems, ensuring control over design development and GDA submissions. We are confident these arrangements are adequate for this stage of GDA.

The RP’s BAT approach and radioactive waste management strategy meet our expectations for Step 2. We are satisfied that the RP has a systematic optimisation process and that the structure of the demonstration of BAT provides a suitable basis to be taken forward by any future developer. While some evidence gaps remain due to design immaturity, the RP has committed to addressing these through future commitments and actions.

The RP has presented sufficient information about the management of solid wastes and spent fuel to satisfy the requirements of Step 2 of GDA, noting that further work is required at the pre-application and site-specific permitting stage, to provide a full disposability case. We recommend continued consideration of decommissioning throughout the detailed design work to ensure there is sufficient information for any future permit application.

Calculation of discharges and proposed limits for gaseous and liquid discharges presented in GDA is thorough, systematic and appropriate for this stage, subject to refinement as the design matures. Commitments and future evidence are in place to address aspects that will need to be reviewed when reactor-specific design values and site-specific considerations are available.

Sampling and monitoring provision is still in the early stages of development. However, we are satisfied that the RP understands the requirements associated with sampling and monitoring and that its considerations for sampling and monitoring are adequate for this stage of GDA.

Methods presented for calculating dose impacts for members of the public and wildlife are adequate for this stage of GDA, and we found no fundamental shortfalls in the RP’s submissions. The initial assessment undertaken using the preliminary discharge limits resulted in doses to people and dose rates to wildlife that were all below the relevant dose limits and source and site dose constraints. The assessments presented by the RP were carried out for a single SMR-300 unit and will, therefore, be higher for the DR of a twin-unit deployment. In response to RQ-02464, the RP stated that doubling the doses presented in the PER chapter would be bounding. Noting that IRAT2 is a conservative screening tool, our assessment findings are not changed by doubling the doses to the public and wildlife. A refined radiological impact assessment will be required at the pre-application and site-specific permitting stage, and we are satisfied with the approach developed.

The twin-unit SMR-300 will require 4 diesel generators and one auxiliary boiler and will, therefore, likely require an environmental permit under the MCPD as the thermal input is above one MWth and below 50 MWth. Further specification of conventional environmental systems, chemical inventories and combustion plant details will be required at the site-specific permitting stage.

We agree that the RP is applying relevant legislation, regulatory requirements and RGP in its design decisions.

Overall, the SMR-300 design appears to be capable of meeting UK environmental regulatory requirements provided that the RP delivers on its commitments and resolves identified gaps post GDA and at the site-specific permitting stage. While the design is still evolving, the frameworks and methods presented give us confidence that environmental protection objectives can be achieved.

This assessment is made based on the scope and information submitted in the following documents, the:

• SMR-300 UK Generic Design Assessment Scope (HOLTEC BRITAIN, 2024g)
• Preliminary Safety Report Part A Chapter 1 (HOLTEC BRITAIN, 2025o) and Part A Chapter 2 (HOLTEC BRITAIN, 2025p)
• GDA Design Reference Report (HOLTEC BRITAIN, 2025b)
• MDSL for GDA (HOLTEC BRITAIN, 2025ac)

We have not been requested to carry out a Step 3 of GDA (Detailed Assessment), and so this conclusion is subject to carrying out a detailed assessment and any future developer gaining the necessary site-specific permissions. The detailed assessment work would include the further work identified in the RP’s CAR register. Our conclusion is without prejudice to us identifying further regulatory concerns and shortfalls during any future detailed assessment.

7. References

Department for Energy and Climate Change, 2011. National Policy Statement for Nuclear (EN-6), June 2011.

Department for Energy Security & Net Zero, 2024. Managing Radioactive Substances and Nuclear Decommissioning: UK policy framework, May 2024.

Electric Power Research Institute, 2014. Advanced Nuclear Technology: Advanced Light Water Reactor Utility Requirements Document, Revision 13, December 2014.

Environment Agency & Natural Resources Wales, 2024. RSR guidance for nuclear sites undergoing decommissioning, February 2024.

Environment Agency, Scottish Environment Protection Agency and Natural Resources Wales, 2018. Management of radioactive waste from decommissioning of nuclear sites: Guidance on Requirements for Release from Radioactive Substances Regulation, July 2018.

Environment Agency, 2020. Operational Instruction - Generic design assessment of candidate nuclear power plant designs, LIT11573, August 2020.

EU, 2004. Commission Recommendation on standardised information on radioactive airborne and liquid discharges into the environment from nuclear power reactors and reprocessing plants in normal operation (2004/2/Euratom). Official Journal of the European Union, L 2, 36-46. Commission of the European Communities, 2004.

European Commission Joint Research Centre, 2017. Best Available Techniques (BAT) Reference Document for Large Combustion Plants; EUR 28836 EN, 2017.

HOLTEC BRITAIN, 2024a. Decommissioning Strategy Assessment, HI-2241256, Revision 0, November 2024.

HOLTEC BRITAIN, 2024b. Design Management, HPP-3295-0017, Revision 1, December 2024.

HOLTEC BRITAIN, 2024c. Disposability Assessment Review (Gap Analysis), HI-2240781, Revision 0, October 2024.

HOLTEC BRITAIN, 2024d. NWS Expert View Submission, HI-2240759, Revision 1, October 2024.

HOLTEC BRITAIN, 2024e. SMR-300 GDA Design Stability Toolkit, HI-2241147, Revision 0, November 2024.

HOLTEC BRITAIN, 2024f. SMR-300 UK GDA ALARP Guidance Document, HI-2241304, Revision 0, November 2024.

HOLTEC BRITAIN, 2024g. SMR-300 UK Generic Design Assessment Scope, HI-2240121, Revision 1, May 2024.

HOLTEC BRITAIN, 2024h. UK GDA Decommissioning Waste Inventory for the Generic SMR-300 Design, HI-2241428, Revision 0, December 2024.

HOLTEC BRITAIN, 2025a. Approach and Application of the Demonstration of BAT, HI-2240359, Revision 1, May 2025.

HOLTEC BRITAIN, 2025b. GDA Design Reference Point, HI-2240648, Revision 2, May 2025.

HOLTEC BRITAIN, 2025c. Generic Site Envelope Report for SMR-300 UK GDA, HI-2240069, Revision 2, January 2025.

HOLTEC BRITAIN, 2025d. Holtec SMR GDA PSR Part B Chapter 5 Reactor Supporting Facilities, HI-2240777, Revision 1, June 2025.

HOLTEC BRITAIN, 2025e. Holtec SMR-300 GDA BAT Statement - Li Enrichment, HI-2241563, Revision 0, January 2025.

HOLTEC BRITAIN, 2025f. Holtec SMR-300 GDA BAT Statement - Prospective Design Change CES & CS, HI-2250414, Revision 1, July 2025.

HOLTEC BRITAIN, 2025g. Holtec SMR-300 GDA Environmental Protection Functions, HI-2250394, Revision 1, July 2025.

HOLTEC BRITAIN, 2025h. Holtec SMR-300 GDA- Non-Fuel Waste Packaging BAT Workshop Output Report (worked example), HI-2241494, Revision 0, March 2025.

HOLTEC BRITAIN, 2025i. Holtec SMR-300 GDA PER Chapter 1 Radioactive Waste Management Arrangements, HI-2240360, Revision 1, June 2025.

HOLTEC BRITAIN, 2025j. Holtec SMR-300 GDA PER Chapter 2 Quantification of Effluent Discharges and Limits, HI-2240361, Revision 1, June 2025.

HOLTEC BRITAIN, 2025k. Holtec SMR-300 GDA PER Chapter 3 Radiological Impact Assessment, HI-2240362, Revision 1, July 2025.

HOLTEC BRITAIN, 2025l. Holtec SMR-300 GDA PER Chapter 4 Conventional Impact Assessment, HI-2240363, Revision 1, June 2025.

HOLTEC BRITAIN, 2025m. Holtec SMR-300 GDA PER Chapter 5 Monitoring and Sampling, HI-2240801, Revision 0, June 2025.

HOLTEC BRITAIN, 2025n. Holtec SMR-300 GDA PER Chapter 6 Demonstration of Best Available Techniques, HI-2241253, Revision 0, July 2025.

HOLTEC BRITAIN, 2025o. Holtec SMR-300 GDA PSR Part A Chapter 1 Introduction, HI-2240332, Revision 1, July 2025.

HOLTEC BRITAIN, 2025p. Holtec SMR-300 GDA PSR Part A Chapter 2 General Design Aspects and Site Characteristics, HI-2240333, Revision 1, July 2025.

HOLTEC BRITAIN, 2025q. Holtec SMR-300 GDA PSR Part A Chapter 4 Lifecycle Management of Safety and Quality Assurance, HI-2240335, Revision 1, July 2025.

HOLTEC BRITAIN, 2025r. Holtec SMR-300 GDA PSR Part B Chapter 10 Radiological Protection, HI-2240341, Revision 1, June 2025.

HOLTEC BRITAIN, 2025s. Holtec SMR-300 GDA PSR Part B Chapter 11 Environmental Protection, HI-2240342, Revision 1, June 2025.

HOLTEC BRITAIN, 2025t. Holtec SMR-300 GDA PSR Part B Chapter 13 Radioactive Waste Management, HI-2240344, Revision 1, June 2025.

HOLTEC BRITAIN, 2025u. Holtec SMR-300 GDA PSR Part B Chapter 2 Reactor, HI-2240776, Revision 1, June 2025.

HOLTEC BRITAIN, 2025v. Holtec SMR-300 GDA PSR Part B Chapter 23 Reactor Chemistry, HI-2240352, Revision 1, June 2025.

HOLTEC BRITAIN, 2025w. Holtec SMR-300 GDA PSR Part B Chapter 24 – Fuel Transport and Storage as an applicable reference document, HI-2240353, Revision 1, June 2025.

HOLTEC BRITAIN, 2025x. Holtec SMR-300 GDA PSR Part B Chapter 26 Decommissioning Approach, HI-2240355, Revision 1, June 2025.

HOLTEC BRITAIN, 2025y. Holtec SMR-300 GDA Requesting Party Response to NWS Expert View on Disposability, HI-2240760, Revision 0, March 2025.

HOLTEC BRITAIN, 2025z. Holtec SMR-300 Generic Design Assessment Capturing and Managing Commitments, Assumptions and requirements, HPP-3295-0013, Revision 1, January 2025.

HOLTEC BRITAIN, 2025aa. Integrated Waste Strategy, HI-2241151, Revision 0, January 2025.

HOLTEC BRITAIN, 2025ab. PSR Part A Chapter 4 Lifecycle Management of Safety and Quality Assurance, HI-2240335, Revision 1, July 2025.

HOLTEC BRITAIN, 2025ac. SMR-300 GDA Master Document Submission List for GDA, HI-2240061, Revision 16, September 2025.

HOLTEC BRITAIN, 2025ad. SMR-300 GDA RSR-BAT Guidance, HI-2241319, Revision 1, April 2025.

HOLTEC BRITAIN, 2025ae. UK GDA - Commitments, Assumptions and Requirements Register, HI-2251168, Revision 0, July 2025.

Nuclear Waste Services, 2015. WPS/850/03, Geological Disposal: Waste Package Data and Information Recording Requirements: Explanatory Material and Guidance, 2015.

Nuclear Waste Services, 2025. LTR/WMIDA-582826885-12687 (HI-2250267), GDA Step 2 Expert View on the Disposability of Wastes and Spent Fuel arising from the Holtec SMR-300, February 2025.