<p>The next generation of nuclear power sources, Gen. IV, will include an emphasis on small modular designs, which allow for standardized operation, factory-based manufacturing and flexibility in designing power plants by utilizing a single or multiple modular reactor unit in parallel. A Small Modular Reactor (SMR) typically produces minimum 30 MWth per unit. One of the reactor concepts being investigated for Gen. IV is the Molten Salt Reactor (MSR) concept, which utilizes molten salt in either of two manners: dissolving the nuclear fuel into the salt flow loop or simply using the salt as the primary coolant. For both cases, the use of a supercritical carbon dioxide (sCO2) Brayton cycle is considered for power conversion. Carbon dioxide has several advantages as a working fluid, and its requirement of high turbine inlet temperature allows for several nuclear applications. At high inlet temperatures, the supercritical carbon dioxide power cycle has been shown to have higher efficiency hence perform better than traditional steam Rankine cycles and helium Brayton cycles. The liquid-adjacent density near the critical point allows for high power generation with relatively small turbomachinery as compared to steam. Additionally, the critical temperature of carbon dioxide is near ambient; 31oC, making it convenient to work with. One technical challenge is that the cycle requires very high operating pressures. This paper sought to optimize heat exchange between an MSR heat source and an sCO2 power cycle by thermal-hydraulically optimizing a Heat Exchanger (HEX) for this application. This was accomplished using a code written in Python programming language that solved for the geometry of a single pass shell-and-tube heat exchanger, as well as pressure loss, using inputs of operating parameters from an MSR technology assessment and for an optimized simple recompression (RC) sCO2 power cycle. Input parameters for HEX design include molten salt and CO2 inlet and outlet temperatures, mass flow rates, etc. Heat transfer correlations for both molten salt 2LiF-BeF2 (FLiBe) and CO2 were used to perform detailed calculations for designs of the molten salt reactor heat exchange concept with different boundary conditions, including those of a large reactor at 600 MWth and a SMR with 30 MWth. The HEX designs comprise of single shell and tubes with molten salt (FLiBe) flowing in the shell and sCO<sub>2 </sub>in the tubes.</p>

Optimization of a Primary Heat Exchanger for Flibe Molten Salt Nuclear Reactor With sCO2 Power System

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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