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Fission-product contamination of the helium coolant of High-Temperature Gas-Cooled Reactors (HTGR) is strongly influenced by the end-of-life (EOL) failed-particle fraction. Knowledge of the EOL-failure fraction is the basis for model calculations to predict the total fission product release from the reactor core. After disintegration of irradiation fuel rods, fuel particles are placed in individual holes of a graphite tray. During a 5-h heat treatment at 1000/sup 0/C in a helium atmosphere failed particles leak fission products, especially the volatile cesium, into the graphite. After unloading a ..beta..-autoradiograph of the tray is made. Holes that housed defective particles are identified from black spots on the ..beta..-sensitive film. The EOL-failure fraction is the ratio of defective particles to the total number of particles tested. The technique is called PIAA, PostIrradiation Annealing and Autoradiography. The PIAA technique was applied to particles of a Trisocoated highly-enriched UO/sub 2/ fissile batch irradiated to a burnup of 35% FIMA at an irradiation temperature of 1250/sup 0/C. Visual examination showed all particles to be intact. From 11 to 47% of the particles had failed, as determined by PIAA. Further, postirradiation examination showed that localized corrosion of the silicon carbide coating by fission-product rare-earth chlorides had occurred.

Determination of end-of-life-failure fractions of HTGR-fuel particles by postirradiation annealing and beta autoradiography