Development, Optimization and Verification of Simulation Tools for a Self-sustaining Thorium-fueled BWR
The RBWR-Th is a sustainable, near-term, novel reactor concept based upon Hitachi’s resource-renewable BWR (RBWR-AC), which is compatible with today’s BWR technology. The RBWR-Th’s high average coolant void fraction and hard neutron spectrum allow it to operate as a self-sustaining breeder reactor using thorium as its only feed fuel. The strong inter-dependence between the spatial variation of the fission power density and the coolant density mandates tight coupling between the neutronic and thermal/hydraulic simulations. Current analysis focuses upon the equilibrium cycle, which is found after many depletions and recycles.
The MocDown code is being developed to efficiently perform such a coupled simulation; it consists of a Monte Carlo depletion simulation tool with online T/H coupling and accelerated recycling. MocDown is able to find the RBWR-Th equilibrium composition in a couple days—a task that previous tools performed in weeks—with the same or higher numerical rigor as previous tools. Variants of the RBWR-Th core design exhibit an axially negative/positive void reactivity coefficient, which may result in unstable power oscillations. This and other unique features of the RBWR-Th core design warrant further investigation of the physics and development, optimization, and verification of the simulation tools.