Fluoride-Salt-Cooled High-Temperature Reactor (FHR) Temperature Control Options: Removing Decay Heat and Avoiding Salt Freezing

Report Date: January 2019
Appendices: No

The FHR uses graphite-matrix coated-particle fuel (same as high-temperature gas-cooled reactors (HTGRs)) and a liquid salt coolant. It delivers heat to industry or the power cycle at temperatures between 600 and 700°C with higher average heat delivery temperatures than other reactors. There are several candidate liquid salt coolants—all with melting points above 450°C. The high melting points of salt coolants require special features to control temperatures—avoiding excessively high temperatures, and freezing of the coolant that could impact decay heat cooling systems. Decay heat removal systems must shut down as decay heat decreases to avoid freezing of the coolant salt that could limit heat removal and overheat the reactor core. We describe herein requirements and options for temperature control. The paper describes many options but only a few options have been investigated in sufficient detail to provide a quantitative understanding of the advantages and benefits of the specific options. Leading candidates include heat pipes, systems with selective freezing of salts and systems that use radiation cooling. Each of these systems have some physical characteristic where heat removal is a very strong function of temperature resulting in high decay heat removal rates at high temperatures and shutdown of cooling below some temperature. Based on simplicity, successful development for other applications and expected performance (decay heat removal without overcooling and freezing salt), it is recommended that a serious examination of heat pipes for FHR decay heat removal be undertaken.

Program:     ANP : Advanced Nuclear Power Program

Type:     TR 

RPT. No.: 183