Irradiation performance of HTGR fuel in HFIR capsule HT-31

Abstract
The capsule was irradiated in the High Flux Isotope Reactor at ORNL to peak particle temperatures up to 1600/sup 0/C, fast neutron fluences (0.18 MeV) up to 9 x 10/sup 25/ n/m/sup 2/, and burnups up to 8.9% FIMA for ThO/sub 2/ particles. The oxygen release from plutonium fissions was less than calculated, possibly because of the solid solution of SrO and rare earth oxides in UO/sub 2/. Tentative results show that pyrocarbon permeability decreases with increasing fast neutron fluence. Fission products in sol-gel UO/sub 2/ particles containing natural uranium mostly behaved similarly to those in particles containing highly enriched uranium (HEU). Thus, much of the data base collected on HEU fuel can be applied to low-enriched fuel. Fission product palladium penetrated into the SiC on Triso-coated particles. Also the SiC coating provided some retention of /sup 110m/Ag. Irradiation above about 1200/sup 0/C without an outer pyrocarbon coating degraded the SiC coating on Triso-coated particles.

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