IRSN source term: LOCA program
Alain Mailliat, Georges Hache, Claude Grandjean, Bernard Clément, Joëlle Papin, Jean-Claude Mélis. OECD expert Group on PHEBUS-LOCA Project 19-20 November 2003, Madrid, Spain.
Studies performed in IRSN and elsewhere pointed out that modern alloys used for rod cladding and high burn up fuels induce specific effects under LOCA conditions. This paper is devoted especially to those related with bundle flow blockage geometry and accumulation of heat sources induced by fuel relocation. Uncertainties exist regarding how much these effects affect the evolution of the accident transient and the applicability of the current LOCA regulatory safety criteria. The main question marks are related with increases of peak cladding temperature and of equivalent cladding reacted and whether the resulting flow blockage geometry is coolable. In addition to the existing or planned programmes related to several pending LOCA issues, IRSN proposes to address the points which are not explored elsewhere through two in pile bundle tests of the LOCA part of its STLOC program. The test objectives are to produce data for realistic flow blockage geometry using a multirod configuration and to determine the accumulation of heat source associated to both fuel relocation and the balloon size variability due to rod interactions at burst. Such a piece of information is required for answering the main issues: will the resulting flow blockage with fuel accumulation be still coolable, when using modern clad alloys and high burn up fuel. IRSN is proposing this program to the main partners of the nuclear community in a consistent way with the present effort of both in pile and separate effects experimental programmes for strengthening power plant operations with high burn up and MOX fuels and the associated safety.