High-Temperature Gas-Cooled Reactor Fuel Pressure Vessel Performance Models

A Triso-coated particle stress model was used to describe pressure vessel failure in high-temperature gas-cooled reactor fuel particles. Two separate failure modes were treated, namely, category I, which applies to standard particles characterized by a load-bearing silicon carbide (SiC) layer and instantaneous pyrolytic carbon (PyC) and SiC failure, and category II, which applies to particles with a defective SiC layer incapable of supporting a tensile load. Closed-form solutions, which describe PyC and SiC coating layer stresses as a function of irradiation conditions and particle geometry, were adapted to Monte Carlo calculational routines. The PyC and SiC stresses were calculated for a large number (10⁴ to 10⁶) of particles, and particle failure was predicted to occur when the calculated coating layer tensile stresses exceeded either the SiC (category I failure) or PyC (category II failure) fracture lengths. Model predictions are generally consistent with irradiation test results and serve as a useful guide for particle design optimization studies and in-core fuel performance evaluations.