Numerical analysis on the dynamic behaviors of a graphite-moderated molten salt reactor based on MOREL2.0 code

Molten salt reactors (MSRs) are selected as one of six generation-IV nuclear power systems due to its remarkable advantages in terms of inherent safety, nuclear non-proliferation and economy. Liquid fuel makes the neutronics and thermal-hydraulics characteristics of MSRs different from those of conventional solid fuel reactors. In this study, transients perturbed by control rod ejection, local perturbation and over feeding U235 were analyzed for a graphite-moderated MSR based on a 3D coupled neutronics/thermal hydraulics code MOREL2.0. The effective delayed neutron fraction decreased with the rise of fuel mass flow. The core power changed more fiercely and even occurred supercritical phenomenon for larger fuel mass flow when the same reactivity was introduced. Local blockage introduced negative reactivity, and MSR maintained a safety state. While local overcooling resulted in positive reactivity introduction, and core power increased first then tended to be stable due to the negative temperature feedback. Furthermore, the response of core power at the transient of over feeding fissile isotopes was simulated. Those numerical results provide valuable information for the research and design of this new generation reactor.