Release of short-lived noble gases from HTGR fuel with failed coated fuel particles and contaminated matrix

Fuel compacts of the high-temperature gas-cooled reactor may contain a fraction of exposed uranium as defective coated fuel particles and a contamination of graphite matrix. Releases of short-lived noble gases were measured on the fuel compacts containing artificial failed particles as well as those having a highly contaminated matrix. The results were compared with the prediction by the JAERI model of short-lived gas release, which has been generated from previous irradiation testings. The release from the compacts with artificial failed particles agreed with the prediction except at lower temperatures where the fission-induced diffusion would predominate. The release from the matrix-contaminated compacts was different from the model prediction: The model fairly accurately predicted R/B of Xe, but significantly overpredicted that of Kr.