Fission product release in thoria and urania defective fuel experiments FDO-680 and FDO-681

Abstract

FDO-680 (thoria as ThO2-4%UO2) and FDO-681 (urania) were circa 1975 intentionally defected fuel experiments conducted in the National Research Experimental (NRX) reactor X-2 defect loop in Chalk River, Canada. The intent of these experiments was to determine the release rates of fission gases and radioiodines from a defected ThO2-4%UO2 element and to determine the extent to which a moderately powered ThO2-4%UO2 element would deteriorate when defected. Detailed analysis of the FDO-680 and FDO-681 fission product release data has only recently been undertaken. The objective of analyzing this data is to address a gap in defected thoria fuel behaviour knowledge enroute to commercialisation of thoria fuels. The analysis suggests: 1) thoria fuel has superior stability when defected relative to urania, 2) thoria results in a lower fission product burden in the Primary Heat Transport System (PHTS) than urania under steady-state conditions, and 3) the fission product transport models developed for urania cannot be directly applied to thoria.