inFact with Brian Dunning inFact with Brian Dunning


Thorium Reactors: Fact and Fiction

Thorium reactors aren't the panacea some claim they are, but their benefits over light water reactors are many.

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The next-generation nuclear reactors on today's drawing boards are radically different from the ones you're familiar with, and they're absolutely essential if we want any hope of limiting global warming.

Thorium-powered nuclear reactors are all the rage, with a nearly cult-like following online. How much of that is justified? Turns out a lot of it, some of it, not so much.

The major difference is that thorium is typically used in a reactor with no solid core, called a Liquid Fluoride Thorium Reactor (LFTR for short). The fuel and the coolant are the same fluid, consisting of molten salts in which the fissile and fertile elements are dissolved. The reactors actually in use around the world are old designs that use uranium solid fuel rods cooled by water, called Light Water Reactors (LWR for short).

We did have prototype LFTRs working in the old days, but LWRs are what went into worldwide production, leaving us with clunky designs capable of meltdowns and that produce hazardous nuclear waste. The rage around LFTRs claims that they do neither, and rely on cheap, abundant thorium instead of rare and expensive uranium.

Claim #1: Thorium reactors cannot melt down.
This is absolutely fact! They have to already be molten to function. In fact, we have to work to keep the reaction going; if we stop adding thorium, they cool naturally; physics provides no way that their heat can get out of control in the way a LWR can.

Claim #2: All nuclear reactors produce dangerous waste.
This is a fact with LWRs; their fuel rods have to be discarded when 98% of their radioactivity still remains, requiring them to be stored for centuries as high-level radioactive waste. But the fuel in LFTRs is completely burned by the time it comes out. That waste is almost totally inert and almost all of it can be recycled into useful industrial materials.

Claim #3: Thorium is cheaper and more abundant than uranium and will last us nearly forever.
This is only a fact in some parts of the world. In other places like China, uranium is more abundant and easier to get.

Claim #4: LFTRs were suppressed by the government in favor of LWRs because they can't produce plutonium for nuclear weapons.
This mostly a false conspiracy theory; neither LFTRs nor LWRs are very good at producing plutonium. That's much more efficiently done in a special reactor designed for that purpose, older simpler machines called production reactors, of which only a few still exist.

The real reason LFTRs are not in widespread use is that in the early days of reactor development, they were more complicated and too expensive, and it was easier to put LWRs into production. Now after many decades, we have a solid infrastructure surrounding the LWR industry -- including major industrial and utility commitments, manufacturing and operating experience, and all the attending inertia.

Every credible plan to limit global warming to below about 2.5°C requires zero-carbon nuclear power to be a big part of the equation. If you want it safer and cleaner than ever, join the club of fanboys in support of thorium LFTR reactors.

— Brian Dunning

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References & Further Reading

Editors. "Breeder Reactor." RationalWiki. RationalMedia Foundation, 25 Apr. 2011. Web. 16 Jan. 2017. <>

Kasten, P., Bettis, E., Bauman, H., Carter, W., McDonald, W., Robertson, R., Westsik, J. Summary of Molten-Salt Breeder Reactor Design Studies. Oak Ridge: US Atomic Energy Commission, 1966.

Rosenthal, M. An Account of Oak Ridge National Laboratory's Thirteen Nuclear Reactors. Oak Ridge: US Atomic Energy Commission, 2009.

Touran, N. "Myths and Misconceptions about Thorium Nuclear Fuel.", 1 Feb. 2014. Web. 16 Jan. 2017. <>

USAEC. An Evaluation of the Molten Salt Breeder Reactor. Washington DC: US Atomic Energy Commission, 1972. 49.

WNA. "The Nuclear Fuel Cycle." Information Library. World Nuclear Association, 1 Jun. 2016. Web. 16 Jan. 2017. <>


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