Process Heat Exchanger Options for Fluoride Salt High Temperature Reactor

Abstract

The work reported herein is a significant intermediate step in reaching the final goal of commercial-scale deployment and usage of molten salt as the heat transport medium for process heat applications. The primary purpose of this study is to aid in the development and selection of a heat exchanger for power production and/or process heat application, which would support large-scale deployment.vi vii SUMMARYThe strategic goal of the Advanced Reactor Concept Program for the fluoride high temperature reactor (FHR) is to broaden the environmental and economic benefits of nuclear energy in the U.S. economy by producing power to meet growing energy demands and demonstrating the FHRs applicability to market sectors not being served by light water reactors.The primary purpose of this study is to aid in the development and selection of a heat exchanger for power production and/or process heat applications for the Fluoride High Temperature Reactor (FHR), which would support large-scale deployment. Of primary importance is the transfer of heat from the reactor to the power generation and/or process heat application. Heat in the FHR is transferred from the reactor core by the primary liquid-salt coolant to an intermediate heattransfer loop through an intermediate heat exchanger. The intermediate heattransfer loop uses a secondary liquid-salt coolant through a secondary heat exchanger to move the heat to a power conversion system or a process heat industrial application.Three molten salt coolants were considered for use in the secondary coolant loop: LiF-NaF-KF (FLiNaK), KF-ZrF 4 , and KCl-MgCl 2 . The potential power conversion cycles identified are a super-critical Rankine steam cycle, a supercritical CO 2 cycle, a subcritical Rankine steam cycle, and a helium Brayton cycle. Each of these cycles achieves different values of thermal efficiency along with diverse operating conditions. The choice of the heat exchanger type will largely depend on the operating conditions of the power conversion cycle.Potential process heat applications were evaluated considering a maximum available temperature of 650ºC for use by the process heat applications. The current FHR design could provide process heat for the following applications in the near term:x Power production cycles (steam Rankine cycles, helium Brayton cycle, SCO 2 cycle)x Oil shale (in situ)x Oil shale (ex situ)x Oil sands.The characteristics of candidate molten salt coolants were extensively investigated in three different aspects: coolant thermal performance, coolant cost, and coolant chemistry (corrosion). Details of these characteristics, presented in Appendix A, are summarized as follows:x Thermal Performance: Six Figures of merit (FOMs) were developed in this study by an analytical approach to compare the thermal characteristics of various coolants. The FOMs were mathematically derived and the sensitivity of each property on the FOMs was also estimated. Overall, FLiNaK (LiFNaF-KF) showed superior thermal performance compared to the other candidate coolants, alt...

Strategic need for a multi-purpose thermal hydraulic loop for support of advanced reactor technologies

“…Therefore, it is very useful to develop figures of merit (FOMs) that can represent and quantify coolant thermal and chemical performance in the system of interest. The development of these FOMs is discussed in detail in reference [49]. A brief summary is provided here.…”

“… High heat transfer performance  Low pumping power Corresponding to the six requirements listed above, six FOMs were developed in [49]. For example, consideration of appropriate correlations for heat transfer coefficient and pumping power for turbulent pipe flows yields the following expression for FOM ht .…”

Development of a Multi-Loop Flow and Heat Transfer Facility for Advanced Nuclear Reactor Thermal Hydraulic and Hybrid Energy System Studies

“…Therefore, it is very useful to develop figures of merit (FOMs) that can represent and quantify coolant thermal and chemical performance in the system of interest. The development of these FOMs is discussed in detail in reference [13]. A brief summary is provided here.…”

“…A brief summary is provided here. Desirable characteristics for IHTL coolants include:  High heat transfer performance  Low pumping power  Low coolant volume  Low quantity of structural materials  Low heat loss  Low temperature drop Corresponding to the six requirements listed above, six FOMs were developed in [13]. For example, consideration of appropriate correlations for heat transfer coefficient and pumping power for turbulent pipe flows yields the following expression for FOM ht .…”