According to the South China Morning Post (hattip Next Big Future),
The deadline to develop a new design of nuclear power plant has been brought forward by 15 years as the central government tries to reduce the nation’s reliance on smog-producing coal-fired power stations. A team of scientists in Shanghai had originally been given 25 years to try to develop the world’s first nuclear plant using the radioactive element thorium as fuel rather than uranium, but they have now been told they have 10, the researchers said.
I have to admit, I feel a little envious when I read things like that. The Chinese government is showing exactly the kind of leadership that’s necessary to guide the development of nuclear power along rational channels, and it’s a style of leadership of which our own government no longer seems capable.
What do I mean by “rational channels?” Among other things, I mean acting as a responsible steward of our nuclear resources, instead of blindly wasting them , as we are doing now. How are we wasting them? By simply throwing away the lion’s share of the energy content of every pound of uranium we mine.
Contrary to the Morning Post article, thorium is not a nuclear fuel. The only naturally occurring nuclear fuel is uranium 235 (U235). It is the only naturally occurring isotope that can be used directly to fuel a nuclear reactor. It makes up only a tiny share – about 0.7% – of mined uranium. The other 99.3% is mostly uranium 238 (U238). What’s the difference? When a neutron happens along and hits the nucleus of an atom of U235, it usually fissions. When a neutron happens along and hits the nucleus of an atom of U238, unless its going very fast, it commonly just gets absorbed. There’s more to the story than that, though. When it gets absorbed, the result is an atom of U239, which eventually decays to an isotope of plutonium – plutonium 239 (Pu239). Like U235, Pu239 actually is a nuclear fuel. When a neutron hits its nucleus, it too will usually fission. The term “fissile” is used to describe such isotopes.
In other words, while only 0.7% of naturally occurring uranium can be used directly to produce energy, the rest could potentially be transmuted into Pu239 and burned as well. All that’s necessary for this to happen is to supply enough extra neutrons to convert the U238. As it happens, that’s quite possible, using so-called breeder reactors. And that’s where thorium comes in. Like U238, the naturally occurring isotope thorium 232 (Th232) absorbs neutrons, yielding the isotope Th233, which eventually decays to U233, which is also fissile. In other words, useful fuel can be “bred” from Th232 just as it can from U238. Thorium is about three times as abundant as uranium, and China happens to have large reserves of the element. According to current estimates, reserves in the U.S. are much larger, and India’s are the biggest on earth.
What actually happens in almost all of our currently operational nuclear reactors is a bit different. They just burn up that 0.7% of U235 in naturally occurring uranium, and a fraction of the Pu239 that gets bred in the process, and then throw what’s left away. “What’s left” includes large amounts of U238 and various isotopes of plutonium as well as a brew of highly radioactive reaction products left over from the split atoms of uranium and plutonium. Perhaps worst of all, “what’s left” also includes transuranic actinides such as americium and curium as well as plutonium. These can remain highly radioactive and dangerous for thousands of years, and account for much of the long-term radioactive hazard of spent nuclear fuel. As it happens, these actinides, as well as some of the more dangerous and long lived fission products, could potentially be destroyed during the normal operation of just the sort of molten salt reactors the crash Chinese program seeks to develop. As a result, the residual radioactivity from operating such a plant for, say, 40 years, could potentially be less than that of the original uranium ore after a few hundreds of years instead of many thousands. The radioactive hazard of such plants would actually be much less than that of burning coal, because coal contains small amounts of both uranium and thorium. Coal plants spew tons of these radioactive elements, potentially deadly if inhaled, into the atmosphere every year.
Why on earth are we blindly wasting our potential nuclear energy resources in such a dangerous fashion? Because it’s profitable. For the time being, at least, uranium is still cheap. Breeder reactors would be more expensive to build than current generation light water reactors (LWRs). To even start one, you’d have to spend about a decade, give or take, negotiating the highly costly and byzantine Nuclear Regulatory Commission licensing process. You could count on years of even more costly litigation after that. No reprocessing is necessary in LWRs. Just quick and dirty storage of the highly radioactive leftovers, leaving them to future generations to deal with. You can’t blame the power companies. They’re in the business to make a profit, and can’t continue to operate otherwise. In other words, to develop nuclear power rationally, you need something else in the mix – government leadership.
We lack that leadership. Apparently the Chinese don’t.
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Thorium metal
