TVA and Kairos Announce Plans to Develop Low-Power Nuclear Pebble-Bed Reactor

Jun, 2021 - By WMR

Hermes reactor makes use of fluoride salts as coolant instead of water and fuel of pebble-bed.

Kairos Power and the US Tennessee Valley Authority (TVA) in a latest agreement announced plans to build Kairos' Hermes, a low-power demonstration pebble-bed reactor, which is molten-salt cooled, in East Tennessee Technology Park (ETTP) in Oak Ridge, Tennessee.

With the increasing pressure of policies for climate change and opposition to use of fossil fuels officially in the U.S, industries are finding nuclear power increasingly attractive. Currently, organizations such as the TVA, which accounts for generating 40% of nuclear power in the US, are increasingly looking for unorthodox and advanced plant designs, including pebble-bed reactors such as Hermes and small modular reactors. Although the pebble-bed reactor concept is known since 1947, and consists of self-regulating and simple principle, a number of technical hurdles were present to overcome, hence all the reactors that were built are all prototype or research designs, but no construction of fully operating plants was done.

As per Kairos, Hermes is a demonstrator reactor to develop the technologies which will evolve into advanced reactors used for actual service in the future. Melted fluoride salts have replaced gas in the Hermes. Water has a 100 °C (180 °F) temperature range, from melting point to boiling point, and is able to suddenly flash in vapor under the appropriate conditions, whereas fluoride salts comes with above 1,000 °C (1.800 °F) range, which gives permits for transferring heat in huge amounts at normal pressures. Along with this, they're stable chemically, are able to operate in absence of expensive and bulky structures of high-pressure containment, and, in case of reactor failure, they are able to keep temperature of the core low through natural circulation.

The Hermes is able to put out 140 MWE while up and running, at 585 °C (1,085 °F) operating temperature with the use of fuel containing pebbles enriched upto 19.75%.