An Assessment of Fuel Damage in Postulated Reactivity-Initiated Accidents

In late 1993 and early 1994, tests in France and Japan showed that cladding damage in fuel rods with burnups above 50 GWd/ton occurs at much lower energies than in unirradiated fuel rods when exposed to large power pulses. During the last decade, significant additional test results have become available to permit an interim assessment of potential cladding failure in reactivity-initiated accidents (RIAs) in reactors with fuel burnups above 40 GWd/ton, which is generally regarded as high-burnup fuel. These data are summarized, and systematic biases due to atypical test conditions are identified. The magnitude of biases in the fuel enthalpy for failure are estimated to range from –19 to +27 cal/g for the cases analyzed. With these adjustments, a lower bound of the enthalpies for experimentally observed cladding failure is compared with potential enthalpies in pressurized water reactors and boiling water reactors. Based on available information on control rod worths, it is concluded that current operating reactors in the United States are not likely to experience cladding failure during the worst postulated RIAs.