Sandia National Laboratories’ Kenneth Armijo, project lead, stands beside the Sandia Molten Salt Test Loop, reportedly the world’s largest lab-scale molten salt testing facility. (Photo by David Lienemann)
Sandia National Laboratories is thawing out what reportedly amounts to the world’s largest molten-salt test facility after a seven-year freeze, armed with a $2.5 million DOE grant that will let companies stress-test pumps, valves and heat-exchangers at 600°C.
Sandia intends to complete the restart next year. Once up and running, the revived 7,000-gal Molten Salt Test Loop (MSTL) is expected to speed the development of next-generation concentrating solar power and advanced nuclear reactor technologies, both of which rely on such high-temperature systems for efficient energy conversion and storage, as a Sandia announcement noted.
The initial outage of the molten-salt test facility traces back to problems with its dedicated electric heater. In 2017, a storm knocked out power, and the heat trace went cold. That led the nitrate salt to freeze solid in the pipes and storage tank. With the salt immobilized, technicians couldn’t drain or purge the system, so the facility sat on ice while Sandia completed a forensic assessment and cost estimate for repairs.
Private companies, including many small businesses and startups, have been working to commercialize molten salt systems for concentrating solar power, nuclear energy, fossil energy and other high-temperature industrial process heat applications. —Ken Armijo, Sandia solar researcher and the project lead
By providing an ndustrial-scale environment, the MSTL will allow researchers and commercial entities to validate novel components and integrated systems under the extreme conditions these energy applications demand. This capability is useful for de-risking new designs. It can also help researchers improve safety through scenarios like rapid shutdown tests, and ultimately helping to bring more resilient and efficient clean energy technologies.
According to a 2013 Sandia interface document (PDF), its Molten Salt Test Loop was originally built to circulate about 40,000 kg of “solar salt,” a 60/40 sodium-potassium nitrate blend. The system operated at temperatures from 300°C to 585°C (about 572 °F to 1,085 °F) and pressures up to 40 bar (580 psi). Three parallel test stands could push 44–50 kg/s (approximately 400–600 gal/min) of this salt past materials coupons, flex hoses, valves or even full-scale receiver panels. A 240 kW heater and a 1.4 MW air-salt cooler maintained the salt’s temperature. Engineers designed the loop for uninterrupted runs as long as 3,000 hours, with capabilities including dedicating up to 800 gallons of salt to a single test article and accepting up to 1.4 MW of experimental solar thermal input.
To keep that much molten nitrate in play, every pipe and valve was heat-traced to a nominal 300 °C. The system was also designed to gravity-drain back to the furnace if pump pressure vanished. These protective features were central to the aforementioned 2017 freeze incident.
