This study defines the design options for a secondary heat exchanger that couples the intermediate loop of a molten-salt-cooled nuclear reactor to a power production process. It is the first of several studies needed to select, develop, and demonstrate a secondary heat exchanger. In particular, it identifies design options affecting the functional and operational requirements of the secondary heat exchanger. The reference reactor design and configuration is a 3,400 MW(t) advanced high temperature reactor with three primary heat transfer loops. Multiple power conversion schemes are analyzed for a reactor outlet temperature of approximately 700°C. The applicability of other high temperature process heat applications that might eventually be coupled to the advanced high temperature reactor is also presented. An evaluation of viable secondary heat exchanger concepts is presented along with the parameters such as materials selection, system configuration, and coolant properties that will affect the secondary heat exchanger design. This study sets the stage for the two evaluations-a comparative analysis study and a feasibility study-that will follow. vi vii SUMMARYThe strategic goal of the Advanced Reactor Concept Program for the advanced high temperature reactor (AHTR) 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 an AHTR's applicability to market sectors not being served by light water reactors. This study is the first of three that will aid in the development and selection of the secondary heat exchanger (SHX) for power production from the AHTR, supporting large-scale deployment. The study identifies design options that will affect the functional and operational requirements of the SHX, and sets the stage for the comparative analysis and feasibility studies that will follow.Heat in the AHTR will be transferred from the reactor core by the primary liquid-salt coolant to an intermediate heat-transfer loop through an intermediate heat exchanger. The intermediate heat-transfer loop will circulate intermediate liquid-salt coolant through as many as three SHXs to transfer the heat to the power production process. Electric power generation was the principal process considered, but other processes were also evaluated because the heat transfer characteristics of molten salt coolants offer some advantages compared to high temperature gases produced by certain other reactor types.A broad comparison of molten salt coolants identified 11 for more detailed analysis, which led to the selection of three as potential intermediate loop coolants: LiF-NaF-KF (FLiNaK), KF-ZrF 4 , and KCl-MgCl 2 . Previous studies, which identified LiF-NaF-KF and KF-ZrF 4 as promising molten salt coolants, were confirmed. The high neutron cross-sections of KCl-MgCl 2 have generally disqualified it from use in the primary loop of thermal reactors, but do not disqualify its use as a coolant in the intermediate loop. Recent evaluations ...
This report documents the activities performed by Idaho National Laboratory (INL) during the fiscal year (FY) 2018 for the DOE Light Water Reactor Sustainability (LWRS) Program, Risk-Informed System Analysis (RISA) Pathway, Enhanced Resilient Plant (ERP) Systems research. The purpose of the RISA Pathway research and development is to support plant owner-operator decisions with the aim to improve the economics, reliability, and maintain the high levels of safety of current nuclear power plants over periods of extended plant operations. The concept of ERP refers to the combinations of Accident Tolerant Fuel (ATF), optimal use of Diverse and Flexible Coping Strategy (FLEX), enhancements to plant components and systems, and the incorporation of augmented or new passive cooling systems, as well as improved fuel cycle efficiency. The objective of the ERP research effort is to use the RISA methods and toolkit in industry applications, including methods development and early demonstration of technologies, in order to enhance existing reactors safety features (both active and passive) and to substantially reduce operating costs through risk-informed approaches to plant design modifications to the plant and their characterization.
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...
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