First high temperature safety tests of AGR-1 TRISO fuel with the Fuel Accident Condition Simulator (FACS) furnace

Abstract

Three TRISO fuel compacts from the AGR-1 irradiation experiment were subjected to safety tests at 1600 and 1800°C for approximately 300h to evaluate the fission product retention characteristics. Silver behavior was dominated by rapid release of an appreciable fraction of the compact inventory (3–34%) at the beginning of the tests, believed to be from inventory residing in the compact matrix and outer pyrocarbon (OPyC) prior to the safety test. Measurable release of silver from intact particles appears to become apparent only after ∼60h at 1800°C. The release rate for europium and strontium was nearly constant for 300h at 1600°C (reaching maximum values of approximately 2×10−3 and 8×10−4 respectively), and at this temperature the release may be mostly limited to inventory in the compact matrix and OPyC prior to the safety test. The release rate for both elements increased after approximately 120h at 1800°C, possibly indicating additional measurable release through the intact particle coatings. Cesium fractional release from particles with intact coatings was <10−6 after 300h at 1600°C or 100h at 1800°C, but release from the rare particles that experienced SiC failure during the test could be significant. However, Kr release was still very low for 300h 1600°C (<2×10−6). At 1800°C, krypton release increased noticeably after SiC failure, reflecting transport through the intact outer pyrocarbon layer. Nonetheless, the krypton and cesium release fractions remained less than approximately 10−3 after 277h at 1800°C.