Full-Fluence Tests of Experimental Thermosetting Fuel Rods for the High-Temperature Gas-Cooled Reactor

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Abstract
The irradiation performance of injected thermosetting fuel rods is compared to that of standard pitch-based rods for test conditions exceeding current high-temperature gas-cooled reactor requirements. Thermosetting rods have processing advantages in that they can be carbonized freestanding without loss of shape, but such rods have not performed well under irradiation in the past because of damage to coatings on fuel particles caused by coating-matrix interactions. No such damage was observed when the resin binder was diluted with polystyrene to reduce char yields, even for unusually porous Triso-coated particles used to maximize coating-matrix interactions. Moreover, these diluted thermosetting rods performed as well as standard rods with regard to particle retention, dimensional changes, and behavior of nonporous Biso-coated particle inclusions. However, penetration of resin binder into the porosity of Triso particles during rod injection apparently caused increased shrinkage failures of outer coatings at the highest fluences and temperatures. Additional testing is required to determine if this enhanced failure disappears for less porous particles.