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Unclear On Nuclear? Try Thorium – Nuclear Energy Without The Side Effects

HomeInventor  Inventor Spot   23 March 2011

If the current events in Japan have demonstrated one thing, it’s that nuclear energy in its current form is not safe. Put simply, if the Japanese can’t do it right with their impeccable approach to workmanship, then heaven help the rest of us.

But nuclear energy produces about 13,000 times the amount of energy per pound of fuel than coal, and considerably less waste. The only problem with the waste, of course, is that uranium and plutonium produce immeasurably more dangerous waste than coal, or oil, or natural gas, or any other energy source currently in widespread use: not only does it need to be stored safely for thousands of years (like that’s going to happen), but if it gets in the wrong hands, well, use your imagination.

With so many unknowns surrounding nuclear power – the impossibility of 100% safe operation; the unlikeliness of ensuring safe storage of nuclear waste across millennia; the probability of some of that waste ending up in the hands of terrorists or rogue states – you could justifiably be wondering why there are nearly 450 nuclear power stations operating around the world, with a further 65 under construction.

You could especially be wondering why, if you knew that a way to process a much safer form of nuclear energy has been available for nearly the last half a century. And then if you discovered that the source of this energy was four times more abundant than uranium (which contains all the plutonium), you could well be vigorously shaking and slapping your head simultaneously.

Don’t do it to yourself! Even if it is true that thorium possesses all these properties.

The primary advantage of thorium is probably safety. As reported recently in The Telegraph, thorium expert Kirk Sorensen claims that, “If it begins to overheat, a little plug melts and the salts drain into a pan. There is no need for computers, or the sort of electrical pumps that were crippled by the tsunami. The reactor saves itself. They operate at atmospheric pressure so you don’t have the sort of hydrogen explosions we’ve seen in Japan. One of these reactors would have come through the tsunami just fine. There would have been no radiation release.” This is largely because thorium is not fissile: it cannot sustain a nuclear chain reaction without a catalyst.

But that’s not all. Because thorium is lighter than uranium (which is lighter than plutonium), it doesn’t produce as many heavy, radioactive byproducts. It produces considerably less waste than its heavier cousins, and that is waste that only needs to be managed for 500 years – still a long time, but nowhere near the 10,000 years that some existing nuclear waste requires. That’s if you want to store it. Alternatively, you could add a bit of plutonium to the mix, and you’d burn it all up as part of the energy creation process. That’s right: handled properly, a thorium reactor produces no radioactive waste.

Oh, and thorium comes out of the ground as 100% thorium. It doesn’t need to be enriched, like uranium, which contains less than 1% fissionable material. So, while there is around four times as much thorium in the ground as uranium, there is closer to 6,000 times more usable thorium than usable uranium.

In the USA, which possesses the world’s largest thorium reserves, an experimental thorium reactor was built at the Oak Ridge National Laboratory in Tennessee back in the ’60s, operating for around five years before its funding was cut. Today, there is an operating thorium reactor in India, and plans for them in China, Russia and Norway.

Liquid Fluoride Thorium Reactor

A quite different concept is the Liquid Fluoride Thorium Reactor (LFTR), utilizing U-233 which has been bred in a liquid thorium salt blanket.

The core consists of fissile U-233 tetrafluoride in molten fluoride salts of lithium and beryllium at some 700°C and at low pressure within a graphite structure that serves as a moderator and neutron reflector. Fission products dissolve in the salt and are removed progressively – xenon bubbles out, others are captured chemically. Actinides are less-readily formed than in fuel with atomic mass >235, and those that do form stay in the fuel until they are transmuted and eventually fissioned.

The blanket contains a mixture of thorium tetrafluoride in a fluoride salt containing lithium and beryllium, made molten by the heat of the core. Newly-formed U-233 forms soluble uranium tetrafluoride (UF4), which is converted to gaseous uranium hexafluoride (UF6) by bubbling fluorine gas through the blanket solution (which does not chemically affect the less-reactive thorium tetrafluoride). Uranium hexafluoride comes out of solution, is captured, then is reduced back to soluble UF4 by hydrogen gas in a reduction column, and finally is directed to the core to serve as fissile fuel.

The LFTR is not a fast reactor, but with some moderation by the graphite is epithermal (intermediate neutron speed). Safety is achieved with a freeze plug which if power is cut allows the fuel to drain into subcritical geometry in a catch basin. There is also a negative temperature coefficient of reactivity due to expansion of the fuel.

The China Academy of Sciences in January 2011 launched an R&D program on LFTR, known there as the thorium-breeding molten-salt reactor (Th-MSR or TMSR), and claimed to have the world’s largest national effort on it, hoping to obtain full intellectual property rights on the technology.

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