DISSOLUTION OF UO2 IN MOLTEN ZIRCALOY-4 .1. SOLUBILITY FROM 2000-DEGREES-C TO 2200-DEGREES-C

This paper reports solubility measurements for unirradiated UO2 fuel a t 2000, 2100 and 2200-degrees-C in initially 0-free Zircaloy-4 and at 2100 and 2200-degrees-C in Zircaloy-4 with an initial 25 at% 0 content . The Zircaloy/25% 0 was used to represent the 0-saturated Zircaloy co mponent of steam-oxidized cladding. A UO2/Zircaloy mass ratio of appro ximately 10.9 was used in most experiments to simulate the quantities present in a CANDU-PHW (CANada Deuterium Uranium Pressurized Heavy Wat er) reactor fuel bundle. At each temperature, the UO2 solubility reach ed a maximum with initially 0-free Zircaloy, indicating that fuel diss olution in previously unoxidized cladding represents a worst-case scen ario during a severe fuel damge (SFD) accident. Thus, Use Of UO2 solUb ilities to model SFD accidents allows upper limits to be placed on pos sible release of volatile fission products at any one temperature and may be more defensible than the use of kinetic data for modeling fuel dissolution.