An evaluation of viable secondary heat exchanger concepts for use with a molten salt nuclear reactor is presented based on thermal design studies using KF-ZrF 4 as the secondary coolant. Along with the potential issues related to materials, fabrication methods, system configuration, coolant properties and hot corrosion, a discussion of challenges associated with integrating a steam power cycle with the reactor is also presented. The reference reactor design and configuration is a 3,400 MW t advanced high temperature reactor utilizing Rankine subcritical or supercritical cycles for power production.
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SUMMARYAdvanced High Temperature Reactors (AHTRs) will produce high outlet temperatures (704°C) using coated particle fuel, which provides for improved efficiency in power production or process heat for a variety of industrial applications. The AHTR is part of the fluoride-salt-cooled high temperature reactor (FHR) class of nuclear reactors included in the advanced reactor concept program. Early design decisions for the AHTR include use of an intermediate heat exchanger (IHX) to couple the primary loop to an intermediate loop. Heat from the IHX will be circulated in the intermediate loop through a secondary heat exchanger (SHX) and transferred to a power cycle that produces electricity or transferred to an industrial process. The feasibility of design options for the SHX is the subject of this study, and for the purposes of this study, the following preliminary decisions were made as a baseline for comparison:x The reactor outlet temperature is 704°C, from which the primary, secondary and tertiary fluid temperatures are derived. x The intermediate loop fluid is KF-ZrF 4 , which determines the SHX upstream side fluid and fluid conditions. x A supercritical or subcritical steam cycle is connected downstream of the SHX for power production, setting the fluid conditions on the downstream side. x The SHX is either a helically coiled tube and shell design or a printed circuit heat exchanger (PCHE) design. x The baseline material of construction is Alloy N.Alternative parameters are evaluated in this study and compared to the baseline based on the feasibility of their implementation.Heat exchangers are considered key components that need to be extensively investigated because they are operated under a severe environment and their performance is directly related to the overall system efficiency and safety. Previous analysis (INL/EXT-11-21584) of the power conversion system showed that Rankine subcritical and supercritical cycles with a turbine inlet temperature of 679°C can yield conversion efficiencies of 42% and 44% respectively, with KF-ZrF 4 as the secondary salt coolant.Fluoride salts such as KF-ZrF 4 have highly desirable characteristics for high temperature nuclear reactor heat transport. A characteristic of molten fluoride salts is that they can easily dissolve passive oxide layers such as the chromia oxide film (Cr 2 O 3 ) that provides the corrosion resistance for stainless steels and nickel based alloys...