IRSN views on challenges and research prospects to enhance SAMG in French NPPs

IRSN Views on Remaining Challenges and Research Prospects to Enhance SAMG in French NPPs D. Jacquemain (IRSN, France), G. Cenerino (IRSN, France), E. Raimond (IRSN, France), P. Giordano (IRSN, France), F. Barre (IRSN, France) SAMG objectives are to mitigate the consequences of a severe accident with keeping as low as possible the magnitude of radioactive material release in the environment and reaching and maintaining on the long term a controlled state of the damaged plant, i.e. with the damaged fuel cooled and sub-critical and the risks of energetic events and radioactive releases effectively mitigated. Though significant SAMG improvements have already been implemented or are planned in France for its operated generation II PWRs, SAMG enhancements are still being investigated for these reactors through research with the objective to approach as much as feasible safety objectives of the generation III French EPR in particular in terms of reduced magnitude of radioactive release. To identify where research could bring significant progress, IRSN has recently reviewed remaining challenges and issues to enhance SAMGs in French NPPS. This review is based on outcomes of recent safety assessments (periodic safety reviews, safety reviews addressing plant life extension, complementary safety evaluations after the Fukushima-Daiichi accident) covering in particular critical safety issues that have been identified in the aftermath of the Fukushima Daiichi accident as deserving further investigations, e.g. management of spent fuel pool (SFP) accidents, of accident resulting from major external events and involving more than one NPP unit, performance and reliability under SA conditions of safety systems and components - including passive systems and structures and components ensuring confinement -, instrumentation dedicated to SAM, human and organizational factors, effect of ageing on SAM, etc. Eleven main remaining challenges for SAMG enhancement have been identified related to (1) systems, structures, components and instrumentation behavior in SA (2) hydrogen combustion risk mitigation (3) in-vessel degraded fuel retention systems and strategies (4) ex-vessel degraded fuel retention systems and strategies (5) containment heat evacuation and pressure control systems and strategies (6) radioactive releases mitigation (7) mitigation in SFP accidents (8) mitigation strategies for extreme external and multi-units events (9) reliability and effects of SAMG strategies on the long term (10) human factors (11) SAMG validation. IRSN views on issues and challenges to be addressed for each topic will be presented as well as research prospects foreseen or undertaken at IRSN for topics where significant progress are expected. (author)