The HEVA Experimental Program

Between 1983 and 1989, the Fuel Behavior Studies Branch of the Commissariat à l’Energie Atomique-Grenoble performed eight tests in the HEVA (helium and vapor) program. This program, which is a part of the general French Institute for Nuclear Protection and Safety program concerning severe accident studies, is devoted to the measurement of fission product (FP) release rates under severe accident conditions. Each test was performed with a small section (three pellets) of a standard pressurized water reactor fuel rod in its original cladding, heated in a high frequency furnace, at temperatures up to 2300 K, in a steam and hydrogen environment. The volatile FP release rates were measured by gamma spectrometry. Posttest examinations supplied further information about the behavior of the FP, mainly concerning the aerosol sizing and the 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 using the CORSOR model. A large influence of the environment is evidenced. The aerosol mean aerodynamic diameter is ∼0.3 µm. The HEVA program is extended by the VERCORS program mainly devoted to low volatile FP release rates and kinetics.