Testing complete at molten salt demo

02 July 2024

The first iteration of an engineering test system for Kairos Power's Hermes low-power reactor, is now being decommissioned after more than 2,000 hours of pumped salt operations. Construction of the next iteration - which will demonstrate the modular design of the reactor - is already under way.

ETU 1.0 is, to date, the largest FLiBe molten salt system ever built (Image: Kairos Power)

Engineering Test Unit (ETU 1.0) is the first of three systems that are being built to inform the design, construction, and operation of Hermes, which will advance the development of Kairos's fluoride salt-cooled high-temperature reactor (KP-FHR) technology. Hermes, which is being supported by the US Department of Energy's Advanced Reactor Demonstration Program (ARDP), will use a TRISO fuel pebble bed design with a molten fluoride salt coolant to achieve a thermal power level of 35 megawatts.

ETU 1.0 is the first in a series of multiple prototypes that are being designed and built as part of Kairos' "rapid iterative development". A full-scale, electrically heated prototype of Hermes, ETU 1.0 served as a vehicle for Kairos Power to exercise the supply chain and establish new capabilities, including the production of high-purity fluoride-lithium-beryllium salt coolant known as FLiBe, and specialised reactor components.

ETU 1.0, at Albuquerque, New Mexico, started operations in December 2023. Using 12 tonnes of FLiBe produced by Kairos in partnership with Materion Corporation at its Molten Salt Purification Plant in Elmore, Ohio, the system was filled with 30,000 surrogate fuel pebbles and more than 300 graphite reflector blocks to replicate conditions inside the Hermes reactor core. Over six months, it carried out more than 2000 hours of pumped salt operations including regular operation and tests designed to simulate failure scenarios. At its peak, the system reached 675°C and a salt flow rate of 3000 gallons (more than 11,300 litres) per minute.

The test unit was monitored around the clock, providing more than 10 terabytes of performance data in addition to information from the analysis of salt samples and inspections of 1673 surrogate fuel pebbles.

"With our iterative approach, Kairos Power aims to learn by building, and we’ve learned a tremendous amount from building and operating ETU," said Edward Blandford, Kairos Power Chief Technology Officer and co-founder.

The next iteration - ETU 2.0 - is being built in Albuquerque. ETU 3.0 will be built in Oak Ridge, Tennessee, adjacent to the site where the Hermes reactor will eventually be built. Kairos Power plans to have the reactor, which will lay the groundwork for commercialising the 140 MWe KP-FHR, operational as early as 2026.

Researched and written by World Nuclear News