- 191 - In the case of an accident involving loss of pool cooling, this would lead to boiling of the water in the pool. Dynamic containment would then no longer be effective, as DVK system filtration is ineffective in the presence of the steam given off by spent fuel pool boiling. Furthermore, the fuel building consists of a metal cladding roof and a thin concrete wall (about 30 cm), for the entire fleet in operation and the EPR. The fuel building is not therefore designed to ensure static containment in the event of a pressure rise following a release of steam owing to boiling of the spent fuel pool. Given the difficulty, if not the impossibility, of implementing effective means to limit the consequences of prolonged uncovering of fuel assemblies, ASN will issue requirements demanding that EDF reinforce the prevention measures and robustness of the facility to limit the possibility of such an accident, thus ensuring that this risk remains residual (see above). Instrumentation necessary for accident management As part of the CSAs, ASN asked EDF to analyse the adequacy and availability of the required instrumentation for monitoring the parameters of the spent fuel pool in the event of a severe accident. For the NPPs in operation and the EPR, EDF proposes studying the steps to be taken to reinforce the robustness of the instrumentation in the spent fuel pool (water temperature, water level, dose rate in the hall) to ensure management of the situation and in particular management of makeup. ASN considers that such modifications are essential in order to guarantee a clear picture of the status of the facility during a severe accident. Furthermore, the implementation of such modifications will not entail any major difficulties and should thus take place rapidly. ASN will issue a technical requirement on this subject. Accessibility and habitability of the control room In the event of an accident in the spent fuel pool, ASN asked EDF to evaluate the adequacy of the existing management measures, including the severe accident management guides and the possible additional measures. The accessibility and habitability of the control room were among the particular points to be examined by EDF. In the CSA reports, the EDF analysis concludes that releases into the environment in the event of boiling of the BK spent fuel pool, without deterioration of the fuel assemblies, remain below those involved in a loss of coolant accident (LOCA) of category 4 in the baseline safety requirements. Consequently, the habitability of the control room remains guaranteed for the loss of cooling accident or the loss of water inventory in the BK spent fuel pool. As mentioned above, an accident leading to deterioration of the fuel assemblies, subsequent to their uncovering in the BK spent fuel pool could lead to significant releases in the fuel building, against which it is hard or even impossible to implement effective means of mitigation. Following the CSAs, EDF will examine the feasibility for the NPPs in operation and the EPR, of remote transmission of the makeup system controls to areas completely protected from the propagation of steam and of improving the operation of the steam outlet. ASN considers this approach to be pertinent. 6.4.3 Conclusions concerning the steps taken to limit radioactive releases in the event of a severe accident In the CSA specifications, ASN asked EDF to look at the possible areas for improvement to limit radioactive releases. Following the CSAs, EDF will examine the modifications necessary to systematically ensure an alkaline pH in the sumps of the reactors in service in the event of a core melt, in order to limit iodine releases and further reduce the short-term impact on the site and on the surrounding populations in a severe accident situation.
RkJQdWJsaXNoZXIy NjQ0NzU=