Fission product release under severe accidental conditions: general presentation of the program and synthesis of VERCORS 1-6 results

The French Nuclear Protection and Safety Institute (IPSN) launched the HEVA-VERCORS program in 1983, in collaboration with Electricite de France (EDF). This program is devoted to the source term of fission products (FP) released from PWR fuel samples during a sequence representative of a severe accident. The analytical experiments are conducted in a shielded hot cell of the LAMA facility of the Grenoble center of CEA (Commissariat a l'Energie Atomique); as simplified tests addressing a limited number of phenomena, they give results complementary to those of the more global in-pile PHEBUS experiments. Six VERCORS tests have been conducted from 1989-1994 with higher fuel temperatures (up to 2600 K) compared with the earlier HEVA tests in order, in particular, to quantify better the release of lower volatile FPs. This paper gives an overview of the experimental facility, a synthesis of FP release from these tests and exhibits, as an example, some specific results of the VERCORS 6 test, performed with high burn-up fuel (60 GWd tU-1). The on-going VERCORS HT-RT program, designed to reach fuel liquefaction temperatures, is described before conclusions are drawn