Thorium nuclear reactors – less safe than they thought

Is the “Superfuel” Thorium Riskier Than We Thought? A new study in Nature says that using thorium as a nuclear fuel has a higher risk for proliferation into weapons than scientists had believed. Popular Mechanics 16 May 14, By Phil McKenna   Imagine a cheap, plentiful source of energy that could provide safe, emissions-free power for hundreds of years without refueling and without any risk of nuclear proliferation. The fuel is thorium, and it has been trumpeted by proponents as a “superfuel” that eludes many of the pitfalls of today’s nuclear energy. But now, as a number of countries including China, India, and the United States explore the potential use of thorium for nuclear power, researchers say one of the biggest claims made about the fuel—its proliferation resistance—doesn’t add up.

“It may not be as resistant as touted and in some cases the risk of proliferation may be worse than other fuels,” says Stephen Ashley of the University of Cambridge. In an article published in the journal Nature online today, Ashley and his colleagueshighlight the potential dangers of thorium fuel. When thorium is irradiated, or exposed to radiation to prepare it for use as a fuel in nuclear reactions, the process forms small amounts of uranium-232. That highly radioactive isotope makes any handling of the fuel outside of a large reactor or reprocessing facility incredibly dangerous. The lethal gamma rays uranium-232 emits make any would-be bomb-maker think twice before trying to steal thorium.

But Ashley and his co-authors say a simple tweak in the thorium irradiation recipe can sidestep the radioactive isotope’s formation. If an element known as protactinium-233 is extracted from thorium early in the irradiation process, no uranium-232 will form. Instead, the separated protactinium-233 will decay into high purity uranium-233, which can be used in nuclear weapons.

“Eight kilograms of uranium-233 can be used for a nuclear weapon,” Ashley says. “The International Atomic Energy Agency views it the same as plutonium in terms of proliferation risk.” Creating weapons-grade uranium in this way would require someone to have access to a nuclear reactor during the irradiation of thorium fuel, so it’s not likely a terrorist group would be able to carry out the conversion. The bigger threat is that a country pursuing nuclear energy and nuclear weapons (say, Iran) could make both from thorium. “This technology could have a dual civilian and military use,” Ashley says.  …..

Thierry Dujardin, deputy director for science and development of the Organisation for Economic Co-operation and Development’sNuclear Energy Agency takes a middle of the road approach to concerns over proliferation with thorium. “It’s probably as wrong to claim there is no proliferation concern as to say it’s worse than other fuels,” Dujardin says. ……. for cost reasons alone, Dujardin says it may be better to continue developing next-generation reactor designs using existing uranium fuel technology. ….”The difference in the state of development of thorium versus other sources of fuel is so vast and the cost of developing the technology is so high, it’s really questionable today whether it’s worthwhile to spend a lot of money on the development of thorium.”
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