Guidance

Computer Modelling, Software Development and Calculation Checking

Published 27 October 2026

Purpose and Scope

This Nuclear Waste Services Standard Operating Procedure (NWSSOP) is part of the Nuclear Waste Services Integrated Management System (IMS). This procedure defines instructions and responsibilities for computer modelling, software development and calculation checking.  Specifically, it covers conceptual and mathematical model development and their implementation in software, model application and checking of calculations, in line with NWS’s aims and principles for computer modelling and related activities. 

It is possible to distinguish a ‘model’ from a ‘toolkit that performs some calculations’ in the following way.  For a toolkit, if the input data are correct and the mathematical formulae are correct, the output will be fit for purpose.  For a model, if the input data are correct and the mathematical formulae are correct, the output may still not be fit for purpose because a model has an element of approximation, abstraction or conceptualisation of reality that may be flawed.  Simpler quality assurance activities may be more applicable for toolkits than models.  However, for the purposes of these procedures, both models and toolkits have the potential for error and are not distinguished and are both referred to throughout as ‘models’.   

It is also possible to distinguish a model from simple ad-hoc calculations.  A simpler checking procedure exists for simple ad-hoc calculations which are not part of a maintained toolkit or model that requires longer-term controls.   

It is important to distinguish between a piece of modelling software (such as GoldSim) and the model that is built within it.  Checking and verification measures must therefore recognise that errors can be introduced by the two separate aspects: through the mathematical model and the input data associated with it and through the software code.  Checking and verification measures must therefore explicitly address both these aspects.  When using proprietary packages such as GoldSim we can examine verification evidence supplied by the manufacturer that the software code does indeed do what it is supposed to.  We need separately to check that the model that we (or a supplier) have built within the software platform is appropriately modelling the situation defined and that we can have confidence in the outputs.

Responsibilities

Model Senior Responsible Owner (MSRO)

A Model Senior Responsible Owner (MSRO) for a model is a member of NWS staff in a sufficiently senior position that they are able to understand the strategic importance to the business of what the model is being used for and the associated business risk.  A MSRO does not require a detailed technical understanding of how the model works – that is the responsibility of the Model Technical Owner (MTO).  The responsibilities of a MSRO are as follows: 

• When a model is being developed – either for the first time or as a modification – either in-house or in the supply chain – to carry out a risk assessment as to the likelihood and impact of a significant error in the model upon products in which it will be used.

• To prepare a summary of the uncertainties and caveats that will need to be communicated along with the model results in any reported work. 

• In conjunction with the MTO, to produce a quality plan, informed by the risk assessment, detailing the approach to quality assurance that will be applied to the development and use of the model and its input data and to ensure that it is followed.   

• To document the above three requirements using the Model Risk Assessment and Quality Plan form NWSF 30.02.03_003, and to ensure this is communicated to the appropriate managers for products that make use of any model results, and, if appropriate, the Executive.   

• To ensure that the model details are included on the register of models maintained by the Senior Modelling Manager. 

• During the lifetime of the model, to provide constructive challenge to the MTO and Model Users on the approach to quality assurance and request additional resources if necessary. 

• To re-visit and where necessary update the Model Risk Assessment and Quality Plan as necessary, as a minimum each time the model is used for a different product (because the risks, and therefore quality requirements, may be different).   

• The MSRO is appointed by the Director of the relevant function in NWS.

Model Technical Owner (MTO)

A Model Technical Owner (MTO) is a member of staff responsible for taking technical ownership of a model.   

• For a model developed or used in-house, the MTO is a specialist with the appropriate competency who must have full knowledge of how the model works, i.e. full knowledge of the conceptual and mathematical model. 

• If the model is used only in the supply chain, the MTO must have the appropriate competency to act as the Intelligent Customer for the work, i.e. qualified to specify and review the modelling activities carried out by the contractors.    

• The MTO is appointed by the MSRO for the model.

Model User

A Model User is a suitably qualified member of staff or a contractor responsible for applying a computer model to produce output that feeds into reported work or that is used by others in the company.  It is the responsibility of the Model User to ensure these model calculations are adequately checked, and that the input data for the model are appropriately approved as per procedure NWSSOP 30.02.07.

Model Checker

A Model Checker is a member of staff or a contractor (other than the Model User) responsible for checking that calculations carried out by applying a computer model are correct and can be approved for use.

Senior Modelling Manager

The Senior Modelling Manager is the member of staff responsible for maintaining a register of models used in NWS.  This Senior Modelling Manager has responsibility for maintaining an overview of modelling activities across NWS and providing advice on good practice for appropriate quality assurance.

Calculation Originator

A Calculation Originator is member of staff or a contractor carrying out a simple ad-hoc calculation (as opposed to a more complex modelling activity) the results of which are to be used elsewhere in the company or feed into reported work.

Calculation Checker

A Calculation Checker is a member of staff or a contractor (other than the Calculation Originator) responsible for checking a simple ad-hoc calculation.

Work Package Manager

A Work Package Manager is a member of staff responsible for managing a work package in the supply chain.

NWS Executive Directors

The NWS Executive Directors are responsible for appointing an individual as MSRO for each model or toolkit used within the functions for which they have responsibility.

References

This procedure has five associated work instructions: 

• NWSSOP 30.02.03_001 – In-house Model Development. 

• NWSSOP 30.02.03_002 – Control and Checking of Model Calculations. 

• NWSSOP 30.02.03_003 – Checking of Spreadsheets and ad-hoc Calculations. 

• NWSSOP 30.02.03_004 – Managing Modelling Activities in the Supply Chain. 

• NWSSOP 30.02.03_005 – Software Tool Development in the Supply Chain.

This procedure has three associated forms: 

• NWSF 30.02.03_001 – Computer Model Check Sheet.

• NWSF 30.02.03_002 – Calculation Check Sheet. 

• NWSF 30.02.03_003 – Model Risk Assessment and Quality Plan. 

Staff developing models should be aware of the following NWS procedure: 

• NWSSOP 30.02.07 – Data Management Procedure. 

Staff working on model development projects should be aware of the following NWS procedure: 

• NWSSOP 17.10.01 – NWS Competence Management System. 

Staff using models reported in documents that are subject to change control should be aware of the following RWM procedure: 

• NWSSOP 30.04.03 – Geological Disposal System Change Management Procedure. 

Staff working with models and spreadsheets relating to financial information should be aware of the following NDA procedure: 

• FNPR09 – Critical Spreadsheets and Models Procedure. 

General guidance on modelling activities, including NWS’s strategy for modelling, is available in the Modelling Framework report: 

• Nuclear Decommissioning Authority, Framework for Application of Modelling in the Radioactive Waste Management Directorate, NDA Report NDA/RWMD/101, September 2013.

Procedure

The work instructions associated with this procedure describe the following processes in detail: 

NWSSOP 30.02.03_001 – In-house Model Development – This procedure covers: 

• Specification and documentation of requirements. 

• Modelling approach to be used. 

• Need for and approach to verification, validation or benchmarking. 

• Assessment of risks to the business associated with the proposed use of the model, and production of a Model Risk Assessment and Quality Plan by the MSRO.  This document must explain concisely how the project will demonstrate compliance with these work instructions. 

• Model management issues. 

• Software solution issues. 

NWSSOP 30.02.03_002 – Control and Checking of Model Calculations – This procedure covers aspects of application of models for various purposes, including: 

• Checking calculations carried out with models in-house – including the need for independent checker, intelligent user, level of checking for new model vs variants of same model. 

• Version control – the level of control will depend on how the model output is used. 

• Change control – where model output is used in documents subject to change control. 

NWSSOP 30.02.03_003 – Checking of Spreadsheets and ad-hoc Calculations – This procedure is a simpler QA procedure than NWSSOP 30.02.03_002, designed for ad-hoc calculations and spreadsheets, to ensure that non-trivial calculations, when used in any work reported or used by others, are formally checked and that the check is recorded.   

NWSSOP 30.02.03_004 – Managing Modelling in the Supply Chain – If a contractor is also required to develop new bespoke software to implement a model, then NWSSOP 30.02.03_005 will also apply.  This procedure covers: 

• Specification of model development activities, including approach to be used. 

• Specification of requirements for a contractor to apply an existing/provided model. 

• Assessment of risks to the business associated with the proposed use of the model, and production of a Model Risk Assessment and Quality Plan by the MSRO.  This document must explain concisely how the project will demonstrate compliance with these work instructions. 

• Requirements for inclusion in contracts for modelling activities. 

• The extent to which NWS staff need to be involved in development of the model. 

• Issues relating to Intellectual Property Rights (IPR) relating to models developed, or models provided to the contractor for use. 

• Need for verification, approach to validation or benchmarking. 

NWSSOP 30.02.03_005 – Software Tool Development in the Supply Chain – This procedure covers specification, testing requirements and acceptance procedures for software development.  If the proposed software development also includes development of a model, then NWSSOP 30.02.03_004 will also apply.    

For many applications of modelling, the work instructions listed above can be followed directly.  However, for more complex modelling activities in NWS a team may facilitate compliance with this procedure by writing a Local Operating Procedure which describes additional detail relevant to their application but not of interest to other activities in the company.  Such procedures may cover, for example, electronic storage of model runs, version control arrangements and data management issues specific to the particular type of modelling carried out.

Documentation & Records

This procedure has three associated forms which will be generated every time a model or calculation is developed or checked and are therefore identified as records: 

• NWSF 30.02.03_001 – Computer Model Check Sheet. 

• NWSF 30.02.03_002 – Calculation Check Sheet. 

• NWSF 30.02.03_003 – Model Risk Assessment and Quality Plan.

Document/record	Responsible	Retention period
Completed NWSF 30.02.03_001 forms	Model User	Indefinite
Completed NWSF 30.02.03_002 forms	Calculation Originator	Indefinite
Completed NWSF 30.02.03_003 forms	MSRO	Indefinite