THE HEVA EXPERIMENTAL PROGRAM

Between 1983 and 1989, the Fuel Behavior Studies Branch of the Commiss ariat it l'Energie Atomique-Grenoble performed eight tests in the HEVA (helium and vapor) program. This program, which is a part of the gene ral French Institute for Nuclear Protection and Safety program concern ing severe accident studies, is devoted to the measurement of fission product (FP) re(ease rates under severe accident conditions. Each test was performed with a small section (three pellets) of a standard pres surized water reactor fuel rod in its original cladding, heated in a h igh frequency furnace, at temperatures up to 2300 K, in a steam and hy drogen environment. The volatile FP release rates were measured by gam ma spectrometry. Posttest examinations supplied further information ab out the behavior of the FP, mainly concerning the aerosol sizing and t he chemical speciation of the deposits. The results were compared with those obtained by other laboratories and with the calculated values. The measured release rates are generally lower than those calculated u sing the CORSOR model. A large influence of the environment is evidenc ed. The aerosol mean aerodynamic diameter is similar to 0.3 mu m. The HEVA program is extended by the VERCORS program mainly devoted to low volatile FP release rates and kinetics.