Molten salt reactors appear to be the new big thing in civilian nuclear power. The hype over reactors that feature combining the coolant and the neutron moderator in one salty liquid to produce very high temperatures, and also lend itself to small packages, is everywhere. They will be cheap. They can run on nuclear waste. They will be safe. They have no emissions. They can be modular.
Governments are getting involved: Canada, the U.S. Department of Energy, China, Indonesia. The International Atomic Energy Agency ran a webinar in 2020 titled “Molten Salt Reactors: A Game Changer in the Nuclear Industry” without even a question mark.
A Norwegian ship building company, Ulstein Group, is trumpeting a concept for a 500-foot-long ship powered by a molten salt reactor, using thorium as a fuel, aimed at servicing companion expedition cruising ships running on batteries. The nuclear craft would be named “Thor,” both for its fuel, and for the Norse god of thunder. Thor would provide electricity for a fleet of cruise ships. In essence, Thor would be a floating nuclear power plant in the form of a modern ship.
All the hullabaloo about molten salt sounds great, but to crib from a popular ad of times past, where’s the beef?
Paper reactor designs always work perfectly, as former Union of Concerned Scientists’ nuclear safety engineer Bob Pollard was wont to say. The problems come when it’s time to turn plans into reality.
That’s the case for molten salt reactors, argues University of British Columbia scholar and physicist M. V. Ramana in a new article in the Bulletin of the Atomic Scientists, “Molten salt reactors were trouble in the 1960s—and they remain trouble today.” Ramana has a long history of puncturing nuclear technology balloons.
Ramana makes the case that molten salt reactor technology has little real history, and that history is problematic. Molten salt technology has its roots in the U.S. military’s 1950s attempt to develop nuclear-powered strategic bombers that could stay aloft for long periods without a need for refueling. Oak Ridge National Laboratory got the task of developing the reactor.
What Oak Ridge came up with didn’t quite meet the paper promise. Ramana writes, “The 2.5 megawatt [thermal—Ed.] reactor operated for a mere nine days in November 1954. Some Oak Ridge officials considered running the reactor longer, but others grew concerned about overheating of one of the reactor components. That concern was legitimate; five days later, this component failed and “released radioactive gas into the reactor compartment.”
But that experience didn’t dampen the enthusiasm of the Atomic Energy Commission, and Oak Ridge director Alvin Weinberg, who remained enthralled by molten salt for the rest of his life. In 1958, the AEC kicked off the Molten Salt Reactor Experiment (MSRE) with “an air of urgency.” The Oak Ridge reactor went critical in June 1968, by which time the atomic bomber program had long been cancelled with no flights and at a cost of more than $1 billion at a time when that was a lot of government money.
After fiddling with the fuel, which switched from a mixture of depleted uranium and highly enriched (93%) U-235 to thorium-derived U-233, the machine entered it real testing phase in 1968. Despite claims by molten salt devotees, the technology had basic problems, says Ramana. The prototype was designed to produce 10 MW, but was never able to achieve that output, only reaching 8 MW.
Even for this lower power output, operations were anything but smooth. “At the most general level, the fact that the reactor operated for just 13,172 hours over those four years,” he writes,
“or only around 40 percent of the time.” The plant shut down in 1969, and cleanup cost about $130 million.
Ramana adds, “During its operational lifetime, the Molten Salt Reactor Experiment was shut down 225 times. Of these 225 interruptions, only 58 were planned. The remaining interruptions were due to various technical problems, including: ‘chronic plugging’ of the pipes that led into charcoal beds intended to capture and remove radioactive materials so the reactor could operate; failures of the blowers that removed the heat produced in the reactor; and fuel draining through the so-called freeze valve safety system intended to prevent an accident.”
That’s it. That’s the sole experience base for the hyperbole about molten salt reactors.
Ramana argues that the fundamental problem of the reactors is a lack of materials that can withstand the “high-radiation, high-temperature, and corrosive environment inside a molten salt reactor. In 2018, scientists at the Idaho National Laboratory conducted an extensive review of different materials and, in the end, could only recommend that ‘a systematic development program be initiated.’ In other words, fifty years after the molten salt reactor was shut down, technical experts still have questions about materials development for a new molten salt reactor design.”
–Kennedy Maize
Twitter (@kennedymaize)