Approval of nuclear pilot plant that uses molten salt coolant instead of water a step towards safer reactors

Kairos Power, a Californian startup, has received approval for the construction in Tennessee of its Hermes demonstration reactor, which uses molten fluoride salt – rather than water – as a coolant. Molten salt-cooled reactors are considered inherently safer, more flexible and more efficient than their water-cooled equivalents as they operate at much lower pressures. The startup has received authorisation from the Nuclear Regulatory Commission (NRC) for the pilot plant, the first time in 50 years that a non-water-cooled reactor has successfully gone through the testing process, which took nearly two years to complete. ‘Kairos Power is thrilled to have achieved this major regulatory milestone as we make final preparations to start construction at the Hermes site next year,’ said Mark Laufer, Kairos Power’s chief executive.

Kairos’s fluoride salt-cooled, high temperature reactor uses an efficient and flexible steam cycle to convert heat from fission into electricity. The molten salt differs from a water coolant in that it remains liquid at high temperatures (~600°C) at atmospheric pressure. These molten coolants are considered safer than their water counterparts because the salt remains liquid without pressurisation up to nearly 1400°C, compared with water-cooled systems which only operate at about 300°C at 1.5MPa. A pressurised water reactor (PWR) circulates water around the reactor core under high pressure to prevent boiling, both cooling the nuclear fuel and acting as moderator that absorbs neutrons to help regulate the reaction. The water in the core is heated by nuclear fission and then pumped into a heat exchanger where a separate source of water is boiled to produce the steam that powers the turbines that generate electricity.