Performance Analysis of Silicon Carbide Composite Clad Uranium Carbide Fuel for a Long-Life Gas-Cooled Fast Reactor Under Normal Operation—Part II: Modeling and Simulation

Fuel performance analysis was conducted for silicon carbide (SiC) composite clad uranium carbide (UC) fuel of a 500-MW(thermal) gas-cooled fast reactor, specifically the energy multiplier module (EM²) under normal operation. The analysis consists of two parts: Part I includes a description of design bases and criteria, fuel element design specifications, and material properties and models, while Part II (this paper) includes the fuel modeling approach, computer code, and the fuel design evaluation. In Part II, the FRAPCON-4.0 code was updated to include material properties and models of UC fuel, SiC composite cladding, and helium coolant, and named FRAPCON-4.0GA. The analysis was performed using the hot rod power envelope and burnup history. The results show that the present design of the EM² fuel element has ample margin to melting owing to the high thermal conductivity of the UC fuel and annular pellet configuration. The operating temperature of the fuel element also minimizes the radiation-induced deformation of the SiC composite cladding. The simulation results show that the hoop stress of the cladding is below its tensile stress limit, i.e., one-third of ultimate tensile stress, while the cladding hoop strain limit is reached at 22.5 year, which is less than its design life of 32 years. However, sensitivity calculations of the swelling rate and design parameters indicate that it is feasible to reduce the cladding hoop strain by accommodating the fuel swelling into the open pore. Considering uncertainties associated with the material properties and models, it is highly recommended to experimentally verify the UC swelling and SiC composite creep, which are critical properties in analyzing the long-life fuel behavior.