One of the concepts being investigated for Generation IV nuclear reactors is the Molten Salt Reactor (MSR), with designs utilizing molten salts as both fuels and/or coolants. Historic development focused on large reactors, but contemporary efforts are likely to be small and modular, with this analysis considering 30 MWth per reactor unit For both cases, the use of a supercritical carbon dioxide (sCO2) Brayton cycle is being considered for power conversion. Compatibility of sCO2 power cycles with high turbine inlet temperature among several other advantages allows for several nuclear applications.

This paper sought to optimize heat exchange between an MSR heat source and an sCO2 power cycle by thermalhydraulically optimizing a salt-heat exchanger sCO2 (HEX). This is accomplished using a one dimensional (1D) heat transfer code that solves for the geometry of a single pass shell-and-tube HEX, as well as pressure loss. Input to the HEX code are derived from a MSR technology assessment and from an optimized recuperated recompression (RRC) sCO2 power cycle. The HEX designs comprise of single shell and tubes with molten salt 2LiFBeF2 (FLiBe) flowing in the shell and sCO2 in the tubes. Hastelloy N is chosen for HEX material due to its tested compatibility with in nuclear application with FLiBe. Shell diameter and number of tubes are varied to optimize length of the HEX. Initial estimate for the weight of the HEX is then compared against the heat transfer area to further converge on an optimized design.

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