Office for Nuclear Regulation

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ONR respond to graphite weight loss coverage

11 July, 2014

In response to today’s article in the Times, ‘Safety regulations could be relaxed to keep nuclear power stations open’, ONR have released the following statement:

ONR’s primary concern is the continued safe operation of the UK fleet of nuclear reactors, and we would not allow the continued operation of any nuclear reactor unless it was safe to do so.

As the independent safety and security regulator for the nuclear industry, ONR is neutral on the contribution that nuclear power may make to UK electricity generation. ONR’s role is to regulate the nuclear industry, holding the operators of nuclear sites to account against the high safety and security standards required by law.

No safety regulations are being relaxed to keep nuclear power stations open. The limits for graphite weight loss in reactor cores are not safety regulations, and are not prescribed by ONR or by law. They are set by the operator based on extensive research and on their surveillance and analysis of the graphite. The operator can use this information to revisit their case for the limits they themselves impose on graphite weight loss, and must submit an underpinning justification to ONR that demonstrates it is safe to increase the limits. Following a detailed assessment, if we are satisfied by the evidence and the case submitted by the operator we will agree to it. If we are not satisfied, or have any safety concerns, we would not permit the increase.

In the case of Dungeness B, ONR’s regulatory approach requires that EDF provide ONR with assurance that they are able to continue to operate the reactor at Dungeness B safely. ONR require EDF to carry out regular inspections and surveillance of the graphite and to analyse the results to determine the extent of cracking and weight loss within the graphite cores. As part of the safety case submitted by EDF to justify the return to service of Reactor 21 after its latest periodic shutdown, ONR received a submission from EDF which sought to justify an increased weight loss limit of the graphite from 6.2% to 8%.  After completing our assessment of the submission, ONR were satisfied that the licensee had provided an adequate demonstration that the safe operation of Reactor 21 could continue, with this increased weight loss limit, until its next periodic shutdown in three years time. ONR therefore issued its consent for the return to service of Reactor 21 on 18 June.

If EDF wish to increase weight loss limits for other reactors in its fleet, it will first need to provide us with sufficient evidence that increasing the limits will not impact on the safe operation of the reactors.