Shortly after the Fukushima disaster in March, the European Council (EC) requested that each member state with nuclear power facilities ensured that operators conduct ‘stress tests’ of each facility.

The tests are led by questions that have been raised following the events at the Fukushima Dai-ichi plant, which was struck by an earthquake, and subsequently overwhelmed by the resultant tsunami, causing a loss of power and loss of cooling.

They will seek to ensure that the ‘design basis’ of each plant – the way that flooding and seismic hazards were considered in the plants’ design and construction and subsequent 10 yearly safety reviews – are correct and remain valid in the light of events in Japan.

The tests will also look at the safety margins against these hazards to identify potential ‘cliff edges’ and they will also look at the robustness of the sites against loss of off-site power and implications for loss of cooling. The tests also ask operators to review arrangements for severe emergencies, to identify potential modifications which would improve the margins of safety.

In the UK, we’ve gone further than the EC required. In addition to the operating and defuelling nuclear power stations, ONR has asked operators of reprocessing, fuel and waste, defence and defuelled facilities to also conduct stress tests, relevant to their operation.

ONR received submissions from the UK power plant operators as required in advance of its progress report to the EC, which was delivered, as requested by mid September.

Our progress report, which will be followed by a full report before the end of the year, confirms that stress tests have been initiated at all UK nuclear power stations, as required. Submissions and reports on other nuclear facilities will follow.

To date, none of the stress test work by the licensees, or other work and reviews undertaken in the UK, has indicated any fundamental weaknesses in UK nuclear power plants.

However, in line with the continuous improvement culture we adopt in this country, lessons are being learnt from Fukushima to improve safety. Fukushima is a warning against complacency, and we are finding things that we could do to improve resilience. Licensees are already responding well, identifying practical measures to take forward.

ONR’s ambition is to conduct our work with openness and transparency, so subject to security and other constraints, we will be publishing licensee submissions and our reports online in due course, and we will use ONR’s Quarterly Report and other channels to discuss this work and invite questions in the near future.

www.hse.gov.uk/nuclear/ fukushima