Molten Salt Reactor Loss of Flow Accident Analysis using the NERTHUS Dynamic Model

Abstract

Background Molten salt reactors (MSRs) can have different behavior to various types of accidents compared to conventional reactors. MSRs also have different safety limitations that many are unfamiliar with. With limited operating time, simulations with a dynamic model are a valuable method of analyzing the effects of potential accidents scenarios. Methods The model used in this work is the NERTHUS Dynamic Model in MATLAB-Simulink, which is a generic MSR design agnostic to any specific reactor design. The type of accident investigated in this work are pump failures in each of the fluid loops (i.e., primary, secondary, and tertiary) with no control rod movement and the only response being a trip to the once-through steam generator feedwater at different delay times. Pump failure was modeled as an exponential decay curve to represent the effects momentum would have on the resulting flow coastdown. Results The results of these simulations show that an MSR could be safely powered down in the event of a pump failure by decreasing the feedwater flow rate to the steam generator in a timely manner. A delayed response leads to fluid temperatures in the loops rapidly decreasing to the point where freezing of the coolant salts can become a concern. Conclusions The trending behavior across the simulations is that the temperatures between the reactor core outlet and the location of the pump failure increase compared to pre-transient conditions. The temperatures of the loops further downstream than the pump failure will decrease unless action is taken.