The Thorp reprocessing plant at Sellafield in the UK’s Cumbria has been issued with two improvement notices by the Nuclear Installations Inspectorate (NII) following a leak.

The notices were served part way through an NII investigation at the plant, which began after 83,000 litres of uranium and plutonium dissolved in nitric acid was found to have leaked from a ruptured pipe into a sealed cell.

Operators British Nuclear Group Sellafield (BNGS) produced a board of enquiry report for Sellafield’s owner the Nuclear Decommissioning Authority a summary of which was made available by BNG. The full report is ‘for internal use only’ and has not yet been made public.

The summary explained that while the leak was discovered in April, it may have remained undetected for up to nine months. BNG admitted that opportunities which could have shown that material was escaping (such as cell sampling and level measurements) were missed and that the quantities of escaped material dould have been significantly reduced.

The NII told Nuclear Engineering International that their investigation was ongoing and it would be inappropriate to comment on emerging findings until the information obtained to date has been confirmed.

However, the NII could confirm that NII inspectors judge that sufficient evidence of significant deficiencies has already been gathered to call for the serving of two improvement notices, to ensure that British Nuclear Group Sellafield (BNGS) takes prompt action to prevent similar events recurring. This does not preclude further enforcement action, should this prove necessary.

The first improvement notice relates to licence conditions 34(2) (to ensure that no leak or escape of radioactive material can occur without being detected) and 28(1) (to make and implement adequate arrangements for the regular and systematic examination, inspection, maintenance and testing of all plant which may affect safety). The notice requires BNGS to ensure leaks are adequately detected, and that any means of detection is adequately maintained and tested.

The second notice relates to licence conditions 24(1) (to ensure that all operations which may affect safety are carried out in accordance with written instructions) and 25(1) (to ensure that adequate records are made of the operation, inspection and maintenance of any plant which may affect safety). This notice requires BNGS to have adequate instructions for sampling the containment sumps for leaks and responding to sump level alarms, and to ensure adequate records are kept.

Both improvement notices were served at Sellafield on 17 June, and BNGS has until 8 October to comply, although it could appeal.

The NII also confirmed that their parent department, the Health and Safety Executive is satisfied that the plant has been, and remains, in a safe state and there have been no harmful effects to people or the environment.

Although no radioactive material left the site and no-one was injured in the incident, the aftermath of the leak could see the plant remain closed for as long as six months, a situation that would cause the NDA to forego up to £300 million ($547 million) in lost revenue.