Life-limiting aspects of GCFR core assembly designs

A review is made of the various potential life-limiting effects of current consideration in the GCFR core assemblies. The most life-limiting aspects are not related to individual fuel rod behavior characteristics, but rather to distortions within the rod bundles. Fuel rod internal fission gas is not limiting, as it is in most fast reactors, because of the GCFR pressure-equalization system. The life-limiting bundle distortions are the result of neutron-flux-enhanced creep and fast-fluence-induced metal swelling. These effects are somewhat unique to fast reactors and are material dependent. The current evaluations apply to the use of 20% cold-worked type 316 stainless steel as the core structural material. Alternate structural materials having lower neutron-fluence-induced metal swelling would reduce the distortions, in which case, the most life-limiting effect would likely be one of the more traditional effects such as fuel-clad mechanical interaction