Office for Nuclear Regulation

Fourth quarterly statement of nuclear incidents at nuclear installations

A statement on incidents at nuclear installations in Britain which meet Ministerial Reporting Criteria (MRC) is provided to the Secretary of State for the Department of Energy and Climate Change and the Secretary of State for Scotland, and is published each quarter by the Health & Safety Executive.

For the period 1 October 2010 to 31 December 2010 there was one incident at licensed nuclear installations, which met the MRC.

For the period 1 July 2010 to 30 September 2010 we said there were two incidents that may meet the MRC, only one of these incidents, which occurred at the Sellafield site in August 2010, is considered to meet the MRC and an update is provided below.

Sellafield - Calder Hall

On the 24 August 2010 an incident occurred when one of two gas analysers serving Magnox Swarf Storage Silo Compartment No.7, was found to be disconnected from its sample pipe, and the other analyser was out of service. As a result no analysis of the air space in Compartment No. 7 to detect hydrogen content was carried out for a period of 6 days. There was no release of radioactivity, no personal injury and no requirement for the equipment to have operated.

The safety case requires two diverse hydrogen analysers per compartment to provide the means of measuring hydrogen concentration in the extract flow from the compartments. It is also required that one analyser must be in service before the second one may be taken out of service.

Sellafield Ltd (SL) launched an immediate Board of Inquiry into the circumstances preceding and during the incident. HSE carried out a separate investigation in to the event during September 2010. Subsequent consideration of the incident, and application of the HSE Enforcement Management Model, resulted in HSE serving an Improvement Notice under Section 2 of the Health and Safety at Work Act 1974.

SL has responded positively to the incident and has developed an improvement programme to address its Board of Inquiry findings and the requirements of the Improvement Notice.

HSE is monitoring SLs performance in responding to the learning opportunities from the incident, and implementation of its improvement programme.

This incident has been rated at Level 1, an anomaly, on the 7 level International Nuclear and Radiological Event Scale (INES).

Sellafield Calder Hall

Sellafield Ltd (SL) is pursuing a programme of work to identify and record areas of local radiological contamination adjacent to ventilation ductwork and pipework in the Magnox Reprocessing Plant. The analysis of samples taken in support of this work identified an area of ground that is contaminated with plutonium bearing liquors.

The area of contaminated ground is relatively small and is located within a controlled area (known as the Separation Area) towards the centre of the licensed site. No emergency response was necessary, although access to the immediate area is being controlled. No workers are reported to have been affected.

SL has made an estimate of the amount of radioactive material present at the location based on sample results. The estimate indicates the event is reportable to HSE, in accordance with the Ionising Radiation Regulations 1999. However, the confirmed figure will not be known until the contaminated material has been removed and examined.

HSE has followed up this event and is content with SLs response to date. However, in conjunction with the Environment Agency, our inspectors will continue to monitor the licensees response to ensure the area is appropriately remediated and, workers and the environment are protected.

SL identified this contamination during a programme of work to improve knowledge of legacy contamination on the site, and in response to past events (including an event which occurred in January 2009 which was investigated by HSE and Environment Agency). The HSE welcomes the commitment by SL to resolve shortfalls in contamination control, which are attributed to previous incidents on the site.

This incident has been provisionally rated at Level 1 on INES, which is an anomaly on the 7 level scale.

Single copies of statements are available free from the Health and Safety Executive, Nuclear Directorate, Division 3, Building 4.N2, Redgrave Court, Merton Road, Bootle, L20 7HS,