At the Heat-Pipe Limit – Coupled Modelling and Operating-Limit Assessment of a Heat-Pipe-Cooled Microreactor

Abstract

Heat pipes are efficient transporters of heat and are currently being considered in new microreactor designs. To support efforts in understanding the behaviour and limitations associated with using heat pipes as primary heat removal components in microreactors, a reduced coupled model of a fuel assembly is developed in this thesis. The model is based on publicly available information on the Westinghouse eVinci reactor, a prominent design currently under development. The reduced model functions as an effective one-fuel-pin–one-heat-pipe model of a fuel assembly in an eVinci-like reactor and couples one-dimensional neutronics, two-dimensional heat transfer, and one-dimensional fluid flow. Applying the model to an estimated reactor configuration suggests that an eVinci-like reactor operating at the marketed power output is within the heat-pipe limits considered in this thesis. The results also indicate that the model complexity can be further reduced in normal operating conditions, and partly in limiting conditions. Fixed-temperature approximations for the neutronic data and the thermal conductivities have a small effect on the neutronic effective multiplication factor, and do not alter the temperature and neutronflux distributions significantly. Furthermore, approximating the heat-pipe vapour as isothermal is acceptable under normal operating conditions, but breaks down near the sonic limit.