One issue of concern is the response of high burnup cladding to a reactivity insertion accident (RIA). In the case of a control-rod drop or control rod ejection accident, a sudden insertion of reactivity deposits a large amount of energy in the fuel, leading to fission gas release and fuel expansion. The cladding has to be able to withstand this sudden deformation without failing to avoid possible fuel dispersion and loss of coolable geometry. The U.S. Nuclear Regulatory Commission has set minimum energy deposition limits that the fuel cladding must be able to withstand, based on experiments conducted on fresh cladding.

Recent results have shown that the ability of the cladding to withstand the RIA accident is severely degraded with neutron fluence. This could be due to the several fuel degradation factors present in high burnup fuel, including severe oxidation and hydriding, radiation damage and to the special characteristics of cladding deformation during an RIA, including high strain rates and plane strain deformation. At Penn State we are conducting an experimental study of how the fracture behavior of Zircaloy changes under these severe loading conditions.

Researchers : T.M.Link, D.A.Koss and A.T.Motta.

Funding: NuclearRegulatory Commission.