Computational Modeling of Coupled Thermomechanical and Neutron Transport Behavior in a Godiva-Like Nuclear Assembly

The primary shutdown mechanism of all-metal nuclear assemblies engaging in pulsed operations is thermal expansion of the fuel material. Typically, a fuel temperature coefficient of reactivity is acquired by building the apparatus and fitting the operational data to the Nordheim-Fuchs kinetics equations. This value may vary as a function of reactivity insertion because of thermomechanical effects in the fuel material, which leads to uncertainty regarding untested reactor designs. This paper presents a computational method for modeling power, temperature, and thermoelastic displacement behavior of a spherical Godiva-like assembly during a prompt supercritical excursion and provides a way of determining fuel temperature coefficients of reactivity without the use of operational data.