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Experience has shown that the most valid test for HTGR fuels is one in which the fuel particles are bonded into a matrix and tested with temperatures and temperature gradients simulating those which will exist in the real reactor. A series of tests was conducted in the removable beryllium positions of the High Flux Isotope Reactor (HFIR) in which the above criteria were met. Although the original purposes of the tests varied, some insight was gained on the performance of various fissile and fertile particles under HTGR conditions. several different bonding matrices was also determined. as a fertile particle for the HTGR, but it does exhibit amoeba migration after a burnup exceeding 7% FIMA. Biso-coated (4Th,U)02 fissile particles containing either 3U or highly enriched 'U showed amoeba migration under conditions where Tho2 showed none, indicating that the threshold conditions of burnup and temperature had been exceeded by the fissile particles, but not by the fertile particles. Both 35Uand 3U-bearing particles showed about the same migration rates. A comparison of rods made by extrusion and slug-injection with approximately identical fuel loadings, neutron fluxes, and surface temperatures showed that extruded rods had a significantly better fuel performance than slug-injected rods, presumably because of a higher thermal conductivity. migration, but moderate to severe fission producHiC interactions were observed in the Triso coatings. Both palladium (arising primarily from plutonium fissions) and rare earths were identified in different reaction zones. Indications of a liquid phase were found where palladium reacted with Sic and in some of the kernels. More work is required to explain these observations. The comparative performance of Results showed that Biso-coated Tho2 continues to be promising Fissile particles made from ion exchange resins showed no amoeba |
