IRSN, Institut de radioprotection et de sûreté nucléaire

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Post-Fukushima Complementary Safety Assessments: IRSN analysis and conclusions following an expert review of the reports submitted by operators to ASN

Following the accident that occurred on the Fukushima Daiichi nuclear power plant on 11th March 2011, the French prime minister asked the French nuclear safety authority (ASN) to carry out an audit on the safety of French nuclear facilities. On 5th May 2011, ASN required the French nuclear operators to perform Complementary Safety Assessments (CSAs) of their facilities.

The CSAs evaluate the capacity of French nuclear facilities to withstand extreme situations beyond design basis assumptions. In 2011, these evaluations included the power reactors in operation or under construction, as well as certain nuclear facilities considered by ASN to be priority.

The operators submitted their CSAs reports to ASN on 15th September 2011. IRSN’s review and of these reports was transmitted to ASN and to the Nuclear Safety Advisory Committees on 4th November 2011.

Based on IRSN's critical assessment, the Nuclear Safety Advisory Committees met the 8th, 9th and 10th November 2011 to review these Complementary Safety Assessments and the relevance of the improvements proposed by the operators to enhance the safety of their facilities in the event of extreme situations (earthquake, flood, loss of electrical power supply, loss of heat sinks).

On 17th November 2011, during a conference jointly organised by ASN and IRSN, IRSN presented its analysis and conclusions to the press and made public its CSAs report. And on 3rd January 2012, ASN’s report on the CSAs was submitted to the Prime Minister and made public.

The review conducted by IRSN of the CSAs reports submitted by operators revealed three main observations:

  • 1. A small number of nuclear facilities have compliance gaps in terms of requirements, which weaken their safety within the framework of events taken into account for their design. Corrective actions are already in progress and are to be accelerated.
  • 2. Developments in knowledge must lead to some requirements being re-examined in advance. This is especially the case with the integration of earthquakes, for which knowledge has advanced massively over the last years.
  • 3. The issue of the behaviour of nuclear facilities in the event of a conceivable extreme natural disaster is raised since, in the current situation, this could have unavoidable consequences, ending up in core meltdown and radioactive release.

To confront these exceptional - but nonetheless conceivable - scenarios, IRSN recommends adopting an additional safety requirement level, entitled “hardened safety core”, which would guarantee that the vital basic functions of nuclear facilities are sustained over several days, thus enabling off-site resources to intervene.

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