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Basis for Fluoride Salt–Cooled High-Temperature Reactors with Nuclear Air-Brayton Combined Cycles and Firebrick Resistance-Heated Energy Storage

Charles Forsberg, Per F. Peterson

Nuclear Technology / Volume 196 / Number 1 / October 2016 / Pages 13-33

Technical Paper /

First Online Publication:September 7, 2016
Updated:September 30, 2016

The fluoride salt–cooled high-temperature reactor (FHR) with a nuclear air-Brayton combined cycle (NACC) and firebrick resistance-heated energy storage (FIRES) is a new reactor and plant concept. The development of a new reactor is a large undertaking that requires a strong commercial case and a strong basis for government support to enable commercialization. The goals are (1) increase plant revenue by 50% to 100% relative to base-load nuclear plants with capital costs similar to light water reactors, (2) enable a zero-carbon nuclear renewable electricity grid, (3) no potential for major fuel failure and thus no potential for major radionuclide off-site releases in a beyond-design-basis accident, and (4) offer a pathway to more advanced energy systems. The approaches to achieve those goals are described herein.

The FHR uses liquid-salt coolants originally developed for molten salt reactors (MSRs) where the fuel is dissolved in the coolant. However, in the FHR the fuel is not dissolved in the coolant. Instead, the FHR uses graphite-based high-temperature gas-cooled reactor (HTGR) coated-particle fuel. This combination enables delivering heat to the power cycle between 600°C and 700°C that, in turn, enables the FHR to couple to NACC. Using an air-Brayton power cycle enables the FHR to operate as a base-load reactor and produce added electricity in a peaking mode with the addition of auxiliary heat (natural gas, stored heat, or hydrogen). The auxiliary heat-to-electricity production is a thermodynamic topping cycle with efficiencies of 66%. Because an FHR with NACC is more efficient in converting natural gas into peak electricity than a stand-alone natural gas plant (60%), it can economically compete with a natural gas plant for peak electricity production because it uses less fuel. NACC can also incorporate FIRES heat storage that enables buying electricity at low prices to later sell electricity at high prices. For every 100 MW(electric) of base-load capacity, the station output can vary from minus several hundred megawatts to +242 MW(electric) because of the capabilities of the NACC with FIRES. The FHR can be built in different sizes.

The use of high-temperature liquid-salt cooling and coated-particle fuel enables near-term reactor designs where large-scale fuel failure cannot occur, and thus, large-scale off-site releases of radionuclides cannot occur. Under extreme accident conditions decay heat can be passively conducted to the environment at temperatures below fuel failure temperatures and thus avoid the potential for large-scale radionuclide releases.

The FHR is the gateway technology to several advanced salt-cooled reactor systems that have additional capabilities. The MSR can be designed to enable breeding and actinide waste burning. New high-magnetic-field fusion systems may require liquid-salt cooling. The FHR would provide the required salt and power cycle technology for these advanced reactors. There are significant development challenges. The United States has a competitive advantage in developing the FHR because it leads in gas turbine technology, high-temperature materials, and HTGR fuels.