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

Sammanfattning

Heat pipes are efficient transporters of heat and are currently being considered innew microreactor designs. To support efforts in understanding the behaviour andlimitations associated with using heat pipes as primary heat removal componentsin microreactors, a reduced coupled model of a fuel assembly is developed in thisthesis. The model is based on publicly available information on the WestinghouseeVinci reactor, a prominent design currently under development. The reduced modelfunctions as an effective one-fuel-pin–one-heat-pipe model of a fuel assembly in aneVinci-like reactor and couples one-dimensional neutronics, two-dimensional heattransfer, and one-dimensional fluid flow. Applying the model to an estimated reactorconfiguration suggests that an eVinci-like reactor operating at the marketedpower output is within the heat-pipe limits considered in this thesis. The resultsalso indicate that the model complexity can be further reduced in normal operatingconditions, and partly in limiting conditions. Fixed-temperature approximations forthe neutronic data and the thermal conductivities have a small effect on the neutroniceffective multiplication factor, and do not alter the temperature and neutronfluxdistributions significantly. Furthermore, approximating the heat-pipe vapour asisothermal is acceptable under normal operating conditions, but breaks down nearthe sonic limit.