Fuel and cladding tests for fuel failure safety analysis

Three systems for testing fuel pin cladding were developed to support the determination of the mode and location of cladding failure during transient overpower events or transient undercooled overpower (TUCOP) conditions. The TUCOP FCTT system consists of exposing cladding specimens to thermal and loading conditions typical of TUCOP events. The Mandrel Loading Test (MLT) system was designed to produce cladding deformation and failure by internal mechanical interaction loading of a heated cladding specimen. The Cladding Rip propagation Test (CRPT) system measures the rip propagation behavior of cladding at different temperatures. Fuel deformation and fission gas release tests were performed to better understand fuel behavior. High temperature creep and hot pressing tests on mixed oxide fuel indicate that an enhancement in the creep rate occurs at temperatures above 23000C and that only a small proportion of the fabrication fuel porosity can be closed at temperatures above 25000C. Two fission gas induced modes of gross fuel behavior under transient thermal conditions have been demonstrated, i.e., brittle fracture along grain boundaries and massive plastic swelling of the fission-gas-containing fuel