Third ten-year inspection of French 1300 MWe reactors: IRSN's conclusions on EDF's proposed additional measures for severe accidents

As part of the third ten-year inspection of 1,300 MWe reactors, IRSN has published a summary (in French) of its assessment of actions taken by EDF regarding severe accidents, on the basis of which ASN has issued a position in letters addressed to EDF on November 25, 2013 and January 20, 2014.

Rather logically, in connection with the third ten-year inspection of these reactors and with respect to severe accidents, EDF is proposing to focus on improving radioactive materials containment and on reducing the probability of scenarios likely to lead to early or significant radioactive releases.

While finding the facility modifications proposed by EDF to be pertinent in principle, IRSN's assessment identified several potential avenues for improvement, in particular concerning EDF’s planned measures to eliminate any possibility of a steam explosion in the event of a reactor vessel breach following a core meltdown.

In the field of level 2 probabilistic safety assessments, used to assess the probability of occurrence of an undesirable event and its potential consequences in terms of radioactive releases to the environment, IRSN noted that EDF's initiative was generally consistent with the practices of other countries. However, the Institute also found that certain risks – such as hydrogen combustion in the space between the two superposed containment buildings (a specificity of these reactors) – were not taken into account and considered that additional studies were needed to give a more realistic grasp of certain environmental release risks. For the operator, the challenge is to demonstrate that its proposals help achieve the lowest level of risk possible, given the intrinsic technological characteristics of these reactors.

More information in French: IRSN's summary of assessment of actions taken by EDF regarding severe accidents