Research on Severe Accidents in Nuclear Power Plants

Abstract

Severe accidents (SA) in nuclear power plants (NPPs) are unlikely events but with serious consequences, as recently shown by the accident that occurred in April 2011 in the Fukushima Japanese NPPs. SA research started originally in the seventies with initial risk assessment studies and later on with experimental programs, development of numerical simulation codes, and Level 2 Probabilistic Safety Assessments (PSA2). A huge amount of research and development (RD then in the Chernobyl RBMK (Watercooled channel-type reactors with graphite as moderator, designed by Soviet Union) reactor in Ukraine. Large progress has been reached in recent years on the understanding of SA but several issues still need research activities to reduce uncertainties and consolidate the accident management plans. Along with the progress of understanding and the limited amount of the national budgets on SA RD Micaelli et al., 2005), in the framework of the 6th Framework Programme (FP6) of the European Commission, gathering most worldwide actors on R&D SA. One of the main outcomes was the identification of the highest priority SA issues still to be solved. A second phase of the network (SARNET2 project) has started in April 2009, again supported by EC in the FP7 for four years, again coordinated by IRSN. Section 2 describes shortly what a severe accident is (most of the material described in this section is issued from the reference IRSN-CEA, 2007). Section 3 presents the general approach on SA R&D. Section 4 explains in details the approach that was adopted in SARNET to rank the R&D priorities. Section 5 describes the current SARNET2 FP7 project and the common research programmes, and finally Section 6 focuses, for the sake of illustration, on the important issue of coolability of a degraded core during reflooding.