Leslie Dewan and Mark Massie who are nuclear engineering PhD students at MIT started working on their idea in 2010 and have formed Transatomic Power with an impressive team of scientists, investors, and entrepreneurs.
The product is an advanced molten salt reactor that consumes spent nuclear fuel cleanly and completely. Research on molten salt reactors goes back nearly to the beginning of the Nuclear Age, and Transatomic Power's designs use what was learned in that earlier research. "The main differences between Transatomic Power's molten salt reactor and previous molten salt reactors are our metal hydride moderator and LiF-(Heavy metal)F4 fuel salt. These features allow us to make the reactor more compact and generate electricity at lower cost than other designs." The Transatomic Power reactor can use "fresh fuel enriched to a minimum of 1.8% U-235, or light water reactor waste." An earlier design tested by Oak Ridge used uranium enriched to 33% U-235.
In addition to using a safer fuel, the reactor is far more efficient than reactors in use today. "Conventional nuclear reactors can utilize only about 3% - 5% of the potential fission energy in a given amount of uranium before it has to be removed from the reactor. Our design captures 96% of this remaining energy." As a result, the waste from a Transatomic reactor will be reactive for only a few centuries which is a solvable problem, as opposed to several millennia for waste from conventional reactors.
You can read their technical white paper here.
Transatomic Power's design also enables extremely high burnups – up to 96% – over long time periods. The reactor can therefore run for decades and slowly consume both the actinide waste in its initial fuel load and the actinides that are continuously generated from power operation. Furthermore, our neutron spectrum remains primarily in the thermal range used by existing commercial reactors. We therefore avoid the more severe radiation damage effects faced by fast reactors, as thermal neutrons do comparatively less damage to structural materials.
In a molten salt reactor, a radioactive fuel such as uranium or thorium is dissolved into fluoride or chloride salts to form a solution that we call a "fuel salt." The fuel salt is normally an immobile solid material, but when heated above approximately 500°C, it becomes a liquid that flows. Thus it is the liquid fuel salt, rather than water, that carries the heat out of the reactor. The plant can operate near atmospheric pressure with a coolant that returns to a solid form at ambient temperatures. This feature simplifies the plant and enables safety systems that do not require external electric power to safely shutdown, thereby assuring greater safety for the public.
Molten salt reactors are quite different from sodium fast reactors, even though many people think of sodium when they hear of salt. The sodium metals used by those reactors can release a hydrogen byproduct that is combustible in the presence of air or water. Our fluoride salts remove this fire risk, while further simplifying and increasing the safety of the plant design.
What about thorium? A version of our reactor can also operate using thorium fuel. Thorium has special merit as a nuclear fuel because of its generally shorter-lived waste and higher potential burn-up. The TAP reactor can also achieve the same benefits from uranium, which has an existing industrial base. Using uranium also lets us create a reactor that can slowly consume the world's existing stockpiles of spent nuclear fuel thereby providing a great benefit to society.
"When running on fresh fuel, the TAP reactor is able to generate up to about 75 times more electricity than a light water reactor per kilogram of natural uranium ore."
On their website they have a long list of news articles in various media
Here's a TEDx talk where the the young inventors explain the whole concept.
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