- Date released: 2 July 2025
- Request Number: 202506003
- Release of information under: Environmental Information Regulations (EIR)
Information requested
I am writing to request information under the Freedom of Information Act 2000 and/or the Environmental Information Regulations 2004 regarding the ongoing leak of radioactive liquor from the Magnox Swarf Storage Silo (MSSS) at the Sellafield site.
Public reports and statements from various bodies, including the Nuclear Decommissioning Authority and parliamentary committees, indicate that the MSSS has been leaking radioactive water into the ground since approximately 2018. The reported volume of this leakage is stated to be in the region of 2 to 2.5 cubic metres per day.
As the UK's independent nuclear regulator, the Office for Nuclear Regulation (ONR) monitors Sellafield Ltd's management of this facility and the associated risks. I therefore request the following specific information that the ONR holds or has access to:
- Quantification of Radioactivity in the Leakage:
a) What are the average and/or most recently recorded concentrations of specific radionuclides (e.g., Caesium-137, Strontium-90, Plutonium isotopes, Americium-241, and any other significantly present radionuclides) in the liquor leaking from the MSSS? Please provide this information in Becquerels per litre (Bq/L) or Becquerels per cubic metre (Bq/m³).
b) Based on the reported leakage volume of 2-2.5 m³ per day, what is the ONR's understanding or assessment of the estimated total daily, monthly, and annual amount of radioactivity (in Becquerels or Terabecquerels) for each of these key radionuclides being released to the ground from the MSSS?
- Period of Data:
a) Please provide this data for the most recent period for which it is available to the ONR.
b) If available, please provide any data or summaries held by the ONR regarding the annual levels of radioactivity released via this leak since it was first quantified. I am aware of some historical data (e.g., an estimate of 35 TBq of Caesium-137 and 2 TBq of Strontium-90 over a 14-month period from July 2019, as mentioned in Environment Agency documentation) and am seeking the most current and ongoing measurements and assessments available to the ONR.
- Regulatory Assessment and Compliance:
a) Please provide copies of any reports, summaries, or formal correspondence held by the ONR that detail its assessment of the radiological risks associated with this ongoing ground contamination within the Sellafield site boundary.
b) Please provide information on how Sellafield Ltd is demonstrating compliance with relevant Licence Conditions (such as LC34 regarding leakage and escape of radioactive material) in relation to this specific ongoing leak, and the ONR's view on this compliance.
Information released
We confirm that we hold some of the information you have requested. Please find our response to each of your questions in turn below.
- Quantification of Radioactivity in the Leakage:
a) I confirm that we do not hold this information as the information does not exist. This is because it has not been possible to directly sample the MSSS Original Building (OB) leaking liquor. In its place, Sellafield Ltd. models the liquor composition. Although we are aware of Sellafield Ltd.’s liquor balance model and have access to it, we do not hold any of this data on ONR’s systems.
b) I confirm that we hold some of this information. In November 2019 Sellafield Ltd. reported to regulators (ONR and the Environment Agency) that the MSSS OB liquor balance model identified that the liquor loss rate had progressively exceeded the 5.0m3/month trigger level for four successive months since July 2019. As of 11 March 2025, Sellafield Ltd. reported an OB gross loss rate of 2.0m3/day. Since July 2019, it is estimated that for the period up to the end of February 2025, the cumulative volume of liquor lost to ground totals 4176.3 m³, with an associated activity of 130.6TBq Cs-137 and 15.7TBq Sr-90. It is important to note that Sellafield Ltd. provides us with updates on OB gross loss rate quarterly. We do not receive daily or monthly updates. We maintain regulatory oversight of the OB leakage as part of our legacy silos safety inspector’s routine engagements with Sellafield Ltd. This includes the company’s assessment and monitoring of leakage characteristics, including modelled chemistry, groundwater monitoring in ground and above ground monitoring.
- Period of Data:
a) Please see answer to 1 b).
b) Please see answer to 1 b).
- Regulatory Assessment and Compliance:
a) I confirm that we do hold this information however we are refusing this element of your request under Regulation 12(4)(b) of the EIR – manifestly unreasonable requests. ONR is committed to being an open and transparent regulator. We will use openness and transparency to achieve our objective of developing and maintaining stakeholder trust in ONR as an effective independent regulator. However, your request is broad and covers a wide-range of information, and following a search of ONR’s document management system, we have identified over 400 documents associated with the MSSS OB leak. Due to the volume of documents and the way the information is held on our systems, gathering the information together would place a disproportionate burden on ONR’s resources and would be considered manifestly unreasonable. Under Regulation 9 of the EIR, we have a duty to provide advice and assistance when refusing a request. We believe the following Project Assessment Report setting out ONR’s Regulatory Position on MSSS OB Leak to Ground ONR-SDFW-PAR-22-003 – Revision 3 will provide you with the information you require.
b) Please see ONR-SDFW-PAR-22-003 – Revision 3.
Exemptions applied
N/A
PIT (Public Interest Test) if applicable
N/A