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 Office for Nuclear Regulation ONR, an Agency of HSE.
For the period 1 July 2011 to 30 September 2011 there was one incident at licensed nuclear installations, which met the MRC.
At Dungeness B power station uranium dioxide fuel clad in stainless steel, is used to produce electricity. Before a specific fuel assembly reaches a defined irradiation limit, it is removed from a reactor using a fuelling machine and replaced by new fuel. Handling and initial storage of Irradiated Fuel Assemblies (IFAs) is normally carried out in a carbon dioxide atmosphere. This limits the radiological consequences arising from oxidation of any exposed uranium dioxide fuel if an IFA is accidentally dropped or if the IFA contains fuel, with the cladding having failed in the reactors.
On 3 August 2011 an IFA was loaded into the fuelling machine which had an air rather than a carbon dioxide atmosphere. EDF Energy Nuclear Generation Ltd (NGL) reported this incident as a breach of one of the Dungeness B Technical Specifications. There were no injuries and no release of radioactive material.
In response to the incident, NGL held a number of Operational Decision Meetings to establish the best way to restore the plant to a sustainable safe position. The plant was duly placed in such a state. This was facilitated by the low decay heat of the IFA and the fact that the IFA contained no failed fuel. Further fuel route activities were embargoed by NGL without the specific agreement of the Station Director. NGL has now completed a full investigation into this incident, including the establishment of root causes and production of a corrective action programme.
ONR has carried out its own investigation establishing key facts and satisfying itself of the adequacy of the immediate remedial actions put in place by NGL to return the fuel route to service in a safe manner. ONR will now review the outcome of NGL’s full investigation before deciding whether further regulatory intervention is required beyond the monitoring NGL’s progress in closing out the actions from its investigation.
This incident has been rated at Level 1 on INES, which is an anomaly on the 7 level scale.