A statement on incidents at nuclear installations in Great Britain and during the transport of radioactive material, which meet Ministerial Reporting Criteria (MRC), is provided to the Secretary of State for Business, Energy and Industrial Strategy and the Secretary of State for Scotland and Wales, and is published each quarter by the Office for Nuclear Regulation.
For the period, 1 January 2018 to 31 March 2018, there was one incident which met the MRC.
Ministerial Reporting Criterion – Abnormal occurrences leading to a release or suspected release or spread of radioactivity on or off site, which requires special action or special investigation by the operator.
On the 1 March 2018, during a period of extremely cold weather, an overhead external raw water supply (i.e. an uncontaminated raw water process supply) pipe failed and water subsequently flowed into an active pipe trench and the basement of a contaminated redundant building. This resulted in contaminated water from the flooded basement flowing into a concrete compound on the side of the building and along a redundant sealine trench. The contaminated water discharged to ground within the site at these two locations. The remainder of the contaminated water was pumped, by installed systems and the fire brigade, to existing effluent management systems and discharged to sea by the approved route.
Sellafield Ltd. has made a series of estimates to assess discharges to sea and ground based on the estimated volume of water discharged and the results of sample analysis. The total volume of leaked water is estimated as 680m3 and 565m3 of this is estimated to have become contaminated. We believe that these estimates are conservative.
The estimates of radioactive discharges are based on nine sample results taken from water in the basement of the contaminated building, the sump in the compound at the rear of the building and the sealine trench. All nine total beta radiation results and three of the nine total alpha radiation results are less than the instrument detection limits and hence negligible. The other six samples indicate that the main alpha radiation emitters (Am-241 and Pu-238,239, 240) have exceeded the limits set out in column 5 of schedule 7 to the IRR17 by a factor of four. The radionuclides detected are consistent with our expectations and the level of release is considered to be low. For example, if all of this contaminated water was assumed to have been discharged to the sea, this would equate to less than 1/50,000 of the annual total authorised discharges to sea for the Sellafield site.
This event falls primarily in the vires of the Environment Agency who are the regulatory lead, with ONR monitoring the outcome. ONR will work with the Environment Agency to ensure that appropriate steps are taken by Sellafield Ltd to prevent a reoccurrence.