Sellafield: nuclear regulation

How the Environment Agency regulates discharges and radioactive waste disposals from Sellafield through environmental permitting.

Applies to England

Sellafield nuclear site is one of the most complex and hazardous industrial sites in Europe. Activities carried out at the site include:

  • retrieving waste from old (legacy) facilities
  • cleaning up (decommissioning) redundant buildings
  • managing spent fuel, including Magnox and oxide fuel reprocessing
  • safely managing and storing nuclear materials and radioactive waste

The site is operated by Sellafield Ltd.

The Environment Agency regulates Sellafield Ltd with the Office for Nuclear Regulation (ONR).

The two nuclear regulators provide reports to the West Cumbria Sites Stakeholder Group. This is an independent body whose role is to provide public scrutiny of the nuclear industry in west Cumbria.

Find out more about how the Environment Agency regulates nuclear sites.

Regulating through environmental permits

Nuclear sites must have an environmental permit to operate. Through the environmental permitting process, the Environment Agency regulates Sellafield’s radioactive discharges to air and water, and solid radioactive waste disposals.

Environmental permits contain strict conditions (rules) an operator must follow. These conditions are designed to make sure that the operator’s activities do not harm people or the environment.

The Environment Agency sets stringent discharge limits in Sellafield Ltd’s environmental permit. It makes sure the company minimises discharges and their impacts on people and the environment.

You can ask to see a copy of Sellafield Ltd’s current environmental permits in the public register.

Reviewing Sellafield Ltd’s environmental permits

In November 2018, radioactive fuel reprocessing ended at the Thermal Oxide Reprocessing Plant. Magnox fuel reprocessing ended in July 2022. The focus of the Sellafield site will change from reprocessing spent fuel to decommissioning. As a result, discharges into the environment have and will reduce.

We carried out a major review of Sellafield Ltd’s Radioactive Substances Activity (RSA) permit. This permit controls the receipt and disposal of radioactive waste. It also sets conditions and limits on the discharges to air and water. This is the most significant review of this permit since the early 2000s.

As part of the permit review, Sellafield Ltd applied to vary (change) its RSA permit in October 2018. We consulted on this application in 2018 and again on our draft decision in 2019.

We reached our final decision on Sellafield Ltd’s proposed changes, incorporating comments received from both consultations.

The main changes were to:

  • significantly reduce site discharge limits and introduce an upper and lower tier structure for site discharge limits
  • remove some site discharge limits where discharges have fallen below significant levels and no longer meet the Environment Agency’s criteria for setting limits
  • replace plant discharge limits with plant notification levels so that Sellafield Ltd can more effectively use the available discharge routes and treatment plants
  • remove discharge limits for the rate of fuel reprocessing (throughput) to reflect the end of reprocessing operations
  • introduce a specific tritium limit for solid waste disposals at the on-site landfill known as the Calder Landfill Extension Segregated Area (CLESA)
  • update the permit to the latest template so that it reflects recent guidance changes

This permit variation, reference KP3690SX (V009) was due to come into effect on 1 April 2020. As a result of the coronavirus pandemic, Sellafield Ltd was not able to make the changes needed to implement the variation (V009) on that date.

Sellafield Ltd then applied for (and we issued) another variation (V010) on 27 March 2020. This was to change the date on which they would implement the permit variation. The only change was to delay the effective date from 1 April to 1 October 2020.

We withdrew the previous variation (V009) and Sellafield Ltd continued to operate under its existing permit variation (V008) during the interim period.

On 24 September 2020 we issued a further variation (V011). This was to introduce a limit on the concentration of tritium activity for waste disposals to the CLESA landfill on the Sellafield site. The permit already has a limit for activity concentration for all consignments of waste to CLESA. This variation allows an activity concentration specifically for tritium that is higher than for other radionuclides. We are satisfied that the contribution of tritium to the total dose is within acceptable levels.

We agreed to this variation to allow greater flexibility when disposing of waste containing tritium to CLESA. This means decommissioning can progress more quickly. High tritium activity items will also be subject to Best Available Technique (BAT) assessments.

This change was part of the original permit variation that Sellafield Ltd applied for in October 2018. We consulted on and determined this as part of our decision on permit variation V009 but we did not implement it at the time.

This is because the Department of Business, Energy and Industrial Strategy (BEIS) must notify the European Commission (EC) about plans to change the permitted disposal of radioactive waste. They must do this to meet Article 37 of the Euratom treaty.

BEIS confirmed that it had formally notified the EC. Under Article 37 we do not need the EC to provide an opinion before we can permit the disposal. So we are now able to implement this permit variation.

This variation (V011) immediately superseded V010 as it had the same implementation date of 1 October 2020. There were no other changes between V010 and V011.

In March 2021, we issued a further variation to this permit (which came into force on 1 April 2021). This included a series of improvement requirements for the Magnox Swarf Storage Silo (MSSS).

Sellafield Ltd has detected a leak from the MSSS. ONR classified this event as a level 2 (incident) on the International Nuclear and Radiological Event Scale. Sellafield Ltd estimate that the leak started in July 2019. They formally reported it to the Environment Agency in November 2019. The leak rate has increased with time and the cause of the leak is unknown.

There is no risk to public water supply boreholes from the leak, nor is there a risk of them drawing any contaminated groundwater towards them. The boreholes are above the hydraulic gradient and far enough away from the site.

The improvement requirements in the permit target the MSSS leak. They aim to:

  • stop or minimise the current leak and its consequences
  • minimise the potential for further below ground leaks in the future

This permit variation does not change the permitted disposals of radioactive waste.

See all the documents for the original 2018 consultation – including the 2019 decision document and the subsequent permit variation documents for V009, V010, V011 and V012.

The Environment Agency’s formal investigation into this leak is on-going. Previous leaks from MSSS were detected in the late 1960s to the early 1980s. Sellafield Ltd believe these leaks were sealed by sludge contained in the silos. We continue to work closely with the ONR to reduce risks and support environmental remediation at Sellafield over the long term.

For information on Sellafield’s reported incidents you can read Sellafield Ltd incident reports and notices.

Sellafield Ltd also holds an installation environmental permit. In future, we may need to carry out a wider review of this permit as operations change on site.

Monitoring radiation from Sellafield

An environmental permit requires operators to monitor radiation levels from their discharges and any effects on the environment.

Sellafield Ltd carry out environmental monitoring around the Sellafield site. The Environment Agency assesses the results and suitability of Sellafield Ltd’s programme, including the company’s monitoring for radioactive objects on beaches in West Cumbria.

Find out more about:

The Environment Agency has also developed a Sellafield radioactive objects notification and intervention plan with other organisations involved in protecting the public. This plan explains how the different organisations will work together to:

  • protect the public and environment from any harm caused by radioactive objects on west Cumbria beaches
  • respond to a discovery of radioactive objects near the Sellafield site – a significantly unusual single find or a significant overall change in the find rate, activity or trends
  • check that the conclusions of a public health risk assessment for the radioactive objects are still valid

Monitoring the environment for radioactivity around nuclear sites is also done independently by the Environment Agency and other regulators. Find out more about monitoring radioactivity in the environment.


Nuclear Regulation Group (north)

Telephone: 020 3025 5873


Published 26 October 2018
Last updated 10 October 2022 + show all updates
  1. Updated to include information about the permit variations V009, V010, V011 and V012.

  2. Updated to reflect changes to environmental permits.

  3. We have removed the text: 'introduce a specific tritium limit for solid waste disposals at the on-site landfill – known as the Calder Landfill Extension Segregated Area'. This has not been implemented yet.

  4. Following public consultation, we have published our decision on changes to Sellafield Ltd's radioactive substances activities permit.

  5. Updates on the consultations about proposed changes to Sellafield Ltd's radioactive substances activities (RSA) permit. Also updated to include information about the review of Sellafield Ltd's installation permit.

  6. First published.