Introduction: Coal mining accidents have killed 10s of thousands, and in China coal pollution kills 100s of thousands per year. The world is almost out of hydro power and that too has done a lot of damage. Like it or not, nuclear power has killed very few people, and emits almost no carbon.
Thorium reactors are vastly safer but were apparently rejected because they were of no use to for making nuclear weapons. This needs more documentation, but you must admit, it’s plausible. Given that global warming may well prove serious, we should take another look at what Dr. Strangelove rejected.
A Thorium Reactor Lesson by: Karl Denninger, Friday, April 01, 2011. (edited by Steven Stoft)
Consider this: There is 13 times as much energy in coal in the form of Thorium as there is in the form of Carbon!
What is Thorium? It’s a an element like Uranium, but it’s not capable of fission. Instead, it can be turned into to fissile Uranium (U-233) by the neutrons that come from nuclear fission. So once you get that started, it can self perpetuate.
Unlike traditional nuclear reactors which uses water a moderator and coolant Thorium reactors use a liquid salt, and they need some help getting started.
The US ran one for nearly four years in the 1960s at the Oak Ridge National Laboratory. It was scrapped in favor of the traditional uranium fuel cycle we use today because the fuel it produces is very difficult to exploit for nuclear weapons, and it breeds fuel at a slow rate. The natural process of the nuclear reactions in the core of such a unit produces a byproduct that is a very strong gamma emitter that is difficult to separate from the other reaction products. For this reason – and because we wanted both nuclear power and nuclear weapons – we built the infrastructure for uranium and plutonium rather than thorium.
Thorium-based reactors have several significant advantages and a few disadvantages. We have much less experience with them, simply because we stopped working with them for political and war-fighting reasons. They use a fluoride salt which is quite reactive when in contact with water, but the reactivity is a bonus in all other respects, because it tends to encapsulate the reaction products (the nasty fission products that you don’t want in the environment) through that same chemical process. It runs at a much higher temperature (typically 650C) than a traditional reactor and unlike a traditional reactor the fuel and the working fluid is the same – there are no fuel rods that can melt and release their nasty fission product elements, as the fuel is dispersed in the coolant.
Finally, the unit is intrinsically safe. It does not require high pressure; the working fluid and coolant is a liquid at ordinary atmospheric pressure. This gets rid of the need for high-pressure pumps, pipes and similar materials. Without the moderator the reactivity is insufficient to sustain a chain reaction, and the moderator is in the reactor vessel itself through which the fuel/coolant is pumped, so criticality is impossible outside of the reactor vessel and inside the vessel the fuel and coolant are the same, and a liquid. The working fluid is contained in the reactor loop by an actively-cooled plug. If power is lost cooling ceases and the plug melts; then the working fluid drains into tanks by gravity under the reactor and cools into a solid, as it cannot maintain criticality outside of the reactor itself (there’s no moderator in the tank or the plumbing.) As the fuel is in the fluid, there is no core to melt as occurred in Japan and being dispersed over a much larger area the working fluid naturally cools from liquid to solid without forced pumping and cooling. This safety feature was regularly tested in the unit at Oak Ridge – they literally turned off the power on the weekends and simply went home!
There are some downsides. The working fluid requires special metals made out of Hastelloy. But these are no longer particularly-special materials, being used in other chemical plants where highly-corrosive material is commonly handled. They are expensive, but then again so are traditional reactor pressure vessels which require high-pressure integrity and thus special welding and inspection techniques. [End of Denninger excerpt.]
Some notes from Wikipedia
Some benefits of thorium fuel when compared with uranium were summarized as follows:
- Weapons-grade fissionable material (233U) is harder to retrieve safely and clandestinely from a thorium reactor;
- Thorium produces 10 to 10,000 times less long-lived radioactive waste;
- Thorium comes out of the ground as a 100% pure, usable isotope, which does not require enrichment, whereas natural uranium contains only 0.7% fissionable U-235;
- Thorium cannot sustain a nuclear chain reaction without priming, so fission stops by default.
However, unlike uranium-based breeder reactors, thorium requires irradiation and reprocessing before the above-noted advantages of thorium-232 can be realized, which makes thorium fuels initially more expensive than uranium fuels. But experts note that “the second thorium reactor may activate a third thorium reactor. This could continue in a chain of reactors for a millennium if we so choose.” They add that because of thorium’s abundance, it will not be exhausted in 1,000 years.
The Thorium Energy Alliance (TEA), an educational advocacy organization, emphasizes that “there is enough thorium in the United States alone to power the country at its current energy level for over 1,000 years.
The German THTR-300 was the first commercial power station powered almost entirely with Thorium. India’s 300 MWe AHWR CANDU type reactor will begin construction in 2011. The design envisages a start up with reactor grade plutonium which will breed U-233 from Th-232.After that the input will only be thorium for the rest of the reactor’s design life.
