Fluoride-Salt-Cooled High-Temperature Reactor (FHR) Using British Advanced Gas-Cooled Reactor (AGR) Refueling Technology and Decay Heat Removal Systems That Prevent Salt Freezing

Abstract

The flouride-salt-cooled high-temperature reactor (FHR) uses graphite-matrix coated-particle fuel [the same as high-temperature gas-cooled reactors (HTGRs)] and a clean liquid salt coolant. It delivers heat to the industrial process or the power cycle at temperatures between 600°C and 700°C with average heat delivery temperatures higher than for other reactors. The melting point of the liquid salt coolant is above 450°C. The high minimum temperatures present refueling challenges and require special features to control temperatures, avoiding excessively high temperatures and freezing of the coolant that could impact decay heat cooling systems. This paper describes a preconceptual FHR design that addresses many of these challenges by adopting features from the British advanced gas-cooled reactor (AGR) and alternative decay heat cooling systems. The bases for specific design choices are described.The AGRs are carbon dioxide-cooled and graphite-moderated reactors that use cylindrical fuel subassemblies with vertical refueling at 650°C, which meets the FHR high-temperature refueling requirements. Fourteen AGRs have operated for many decades. The AGR uses eight cylindrical fuel subassemblies, each 1 m tall coupled axially together by a metal stringer to create a long fuel assembly. The stringer assemblies are in vertical channels in a graphite core that provides neutron moderation. This geometric core design is compatible with an FHR using graphite-matrix coatedparticle fuel. The FHR uses a once-through fuel cycle. The design minimizes used nuclear fuel volumes relative to other FHR and HTGR designs. The primary system is inside a secondary liquid salt-filled tank that (1) provides an added heat sink for decay heat, (2) helps to ensure no freezing of primary system salt, and (3) helps to ensure no major fuel failures in a beyond-design-basis accident. The refueling standpipes above each stringer fuel assembly in the AGR core with modifications can be used in an FHR for refueling and can provide efficient heat transfer between the primary system and the secondary liquid salt-filled tank. The passive decay heat removal system uses heat pipes that turn on and off at a preset temperature to avoid overheating the core in a reactor accident and to avoid freezing the salt coolant as decay heat decreases after reactor shutdown.

Fusion Blankets and Fluoride-Salt-Cooled High-Temperature Reactors with Flibe Salt Coolant: Common Challenges, Tritium Control, and Opportunities for Synergistic Development Strategies Between Fission, Fusion, and Solar Salt Technologies

“…Sodium heat pipes are proposed to transfer heat from the flibe salt to the power cycle 52,53 with three additional objectives: (1) isolate low-pressure flibe reactor system from highpressure power cycle, (2) prevent accidental freezing of flibe salt, and (3) capture tritium. Each heat pipe (Fig.…”

Heat-Pipe Heat Exchangers for Salt-Cooled Fission and Fusion Reactors to Avoid Salt Freezing and Control Tritium: A Review

“…The FHR has a passive decay heat cooling system where the goals are to minimize heat losses during normal operations, remove heat if the salt coolant temperature increases such as after reactor shutdown, and avoid freezing the salt. Several alternative systems 33,34 have been proposed to meet these goals. A direct reactor auxiliary cooling system (DRACS) with heat pipes can be used as shown in Fig.…”

Extending Transuranus Burnup Model for Agr-Like Fhr Fuel Design

“…The new design uses Hastelloy-N cladding in a low-pressure molten lithium fluoride and beryllium fluoride (FLiBe) salt environment, instead of the standard high-pressure carbon dioxide (CO 2 ) coolant used in the AGR. In this paper, the term ''AGR-like FHR reactor'' (Forsberg et al, 2015) refers to this FHR concept that incorporates AGR features. Previous work performed on the design of such AGR-like FHR has studied different configurations based on a reference AGR fuel assembly that could potentially achieve a better performance than AGRs while complying with the required safety limits (Xing, 2022;Margulis and Shwageraus, 2021).…”