Dissolution of UO 2 in molten Zircaloy-4 Part 1: Solubility from 2000 to 2200°C

Abstract

This paper reports solubility measurements for unirradiated UO 2 fuel at 2000, 2100 and 2200°C in initially O-free Zircaloy-4 and at 2100 and 2200°C in Zircaloy-4 with an initial 25 at% O content. The Zircaloy/25% O was used to represent the O-saturated Zircaloy component of steam-oxidized cladding. A UO 2/Zircaloy mass ratio of ~ 10.9 was used in most experiments to simulate the quantities present in a CANDU-PHW ( CAN ada D euterium U ranium P ressurized Heavy Water ) reactor fuel bundle. At each temperature, the UO 2 solubility reached a maximum with initially O-free Zircaloy, indicating that fuel dissolution in previously unoxidized cladding represents a worst-case scenario during a severe fuel damge (SFD) accident. Thus, use of UO 2 solubilities to model SFD accidents allows upper limits to be placed on possible release of volatile fission products at any one temperature and may be more defensible than the use of kinetic data for modeling fuel dissolution.