Atomic Insights looks at Alvin Weinbergs Liquid Fuel Reactors Physicist Alvin Weinberg worked on the Manhattan Project and later co-invented the pressurized water nuclear reactor. As Director of Oak Ridge National Laboratory he led development of liquid fuel reactors, including walk-away-safe liquid fluoride thorium reactors with inexhaustible fuel. Today such cheap, safe, clean energy has the potential to economically displace worldwide coal burning, inspiring many efforts to implement Weinberg’s achievements. This was a guest article by Robert Hargraves.
In 1944 Hyman Rickover’s team came to Oak Ridge to learn of the potential of nuclear power for the US Navy. Rickover favored sodium-cooled reactors, but Weinberg convinced the Navy that the simpler, more compact pressurized water reactor (PWR) would fit better in a submarine. In 1955 Rickover’s atomic-powered Nautilus was launched.
“Thus was born the pressurized-water reactor—not as a commercial power plant, and not because it was cheap or inherently safer than other reactors, but rather because it was compact and simple and lent itself to naval propulsion.” Weinberg went on, “It was chosen for Shippingport after President Eisenhower had vetoed the Navy’s proposal to build a nuclear aircraft carrier powered by a larger version of the Nautilus power plant. A demonstration of a power plant that would operate as part of an electrical utility was being urged by the Atomic Energy Commission. The only reactor that was on hand was the one designed for the canceled aircraft carrier.” A hundred commercial PWR-style electric power plants were consequently built by US utilities and staffed largely by veterans of the Navy’s nuclear submarine corps. Weinberg was long astonished at the resulting 100% US market dominance.
Although “Rickover’s thorium-based U-233 seed-blanket light water breeder” at Shippingport also demonstrated a 1.01 breeding ratio, producing more fissile fuel than it consumed, Weinberg was disappointed that the public hardly noticed this proof that the world had an inexhaustible energy source – thorium.
Weinberg continued pursuit of the thorium-uranium breeder goal. ORNL designed a 10 MW molten salt reactor with uranium fluoride dissolved in molten fluoride salts of lithium and beryllium. By 1966 the 7.5 MW Molten Salt Reactor Experiment (MSRE) began operation, continuing until 1969. This prototype did not include thorium-uranium breeding. It was tested with uranium-235 and then uranium-233 bred from thorium in other reactors. No turbine generator was attached; the fission energy heat was dissipated with a salt-to-air radiator.
MSRE was a success. Fission product xenon gas was continually removed to prevent unwanted neutron absorptions. Online fuel addition was demonstrated. Minor inter-grain boundary corrosion of the Hastelloy vessel, piping, and heat exchanger was later addressed. Oak Ridge also developed chemistry for separation of thorium, uranium, and fission products in the fluid fluoride salts. Fluorination and distillation processes could separate fission products from the salt.
Weinberg was thrilled with the success that would lead to inexhaustible energy. ORNL then developed a conceptual design for the Molten Salt Breeder Reactor for sustainable commercial power generation.
But Weinberg’s dream was not to be achieved in his lifetime. The Oak Ridge work was stopped when President Nixon decided instead to fund work on the solid-fuel liquid-metal fast breeder reactor in California. Weinberg wrote to NRC Commissioner Glenn Seaborg, “Our problem is not that our idea is a poor one, rather it is different from the main line and has too chemical a flavor to be fully appreciated by non-chemists.” Later Weinberg said “It was a successful technology that was dropped because it was too different from the main lines of reactor development.” Colleague Herbert MacPherson explained, “Political and technical support is too thin geographically. Oak Ridge is the only stakeholder.”
Molten Salt Related Work Today
Weinberg’s work on a totally different sort of safer, cheaper nuclear reactor continues to inspire many people to pursue this alternative to the PWR.
Ralph Moir continues studies of these fluid fuel reactors, advising three start-up ventures who seek to bring the technology to commercial success.
Kirk Sorensen was formerly a NASA employee researching nuclear power plant designs for a moon base. He discovered molten salt reactor R&D document dormant in ORNL’s records, published them on the Internet, and later founded Flibe Energy to commercialize the technology here on earth.
Robert Hargraves and Ralph Moir published Liquid Fluoride Thorium Reactors in American Scientist in 2012, sparking China’s Academy of Science to undertake a $350 million development project.
Canadian David Leblanc writes and presents articles as well as starting up Terrestrial Energy, which may first harness process heat from a commercial MSR.
Recent MIT PhD Leslie Dewan and student Mark Massie founded Transatomic Power to promote an MSR design moderated with zirconium hydride.
Other, quiet private ventures continue in Florida, New York, and South Africa.