by Mike Weaver
July 2, 2013
An important step forward in energy technology has quietly occurred recently in Norway. Thor Energy have fired up their thorium test reactor for a five year trial run. Thorium has long been offered as a superior alternative to uranium for nuclear power generation. This test reactor is an important first step in validating thorium as a fuel source.Many people feel that nuclear power is vital to the success of our species, at least in the near term. Properly implemented, nuclear power can provide a bridge power source to take us from fossil fuels to greener options, while those options are still being developed. Uranium is the fuel of choice for all commercial power reactors, however, the use of uranium as a fuel brings a number of legitimate concerns to the table which have hampered the use of nuclear power as an alternative to oil, gas, or coal.
The primary concerns with uranium fuel are safety, weapons proliferation, and waste management. Uranium fuel requires enrichment (concentration), produces highly radioactive waste (plutonium and other products), and the reactors can be used to create weapons-grade fissile materials.
This article by Sebastian Anthony, in ExtremeTech, digs into the recent efforts of Thor Energy in developing and testing a thorium reactor.
In a conventional nuclear reactor, enriched uranium fuel is converted into plutonium and small amounts of other transuranic compounds. There are ways to recycle plutonium, but for many countries, such as the USA, it is simply a waste product of nuclear power — a waste product that will be dangerously radioactive for thousands of years. While the safety of nuclear power plants is hotly contested, no one is arguing the nastiness of plutonium. What Thor Energy have done is blend thorium oxide with 10% plutonium oxide to create a mix which will, more easily, hit the critical mass necessary to have a chain reaction. From the article:
Natural thorium, which is fairly cheap and abundant (more so than uranium), doesn't contain enough fissile material (thorium-231) to sustain a nuclear chain reaction. By mixing thorium oxide with 10% plutonium oxide, however, criticality is achieved. This fuel, which is called thorium-MOX (mixed-oxide), can then be formed into rods and used in conventional nuclear reactors. This fuel design, thorium-MOX, is claimed to offer a number of benefits. Firstly, the fuel rods made from thorium-MOX can be used with conventional reactor designs. Secondly, waste plutonium can be recycled safely into this fuel, which does not produce plutonium as a waste product. It does solve one the problems mentioned above, the lack of fissile material. Here is an article on thorium from the web site of the World Nuclear Association.
Thorium (Th-232) is not itself fissile and so is not directly usable in a thermal neutron reactor — in this regard it is very similar to uranium-238. However, it is 'fertile' and upon absorbing a neutron will transmute to uranium-233 (U-233), which is an excellent fissile fuel material. Thorium fuel concepts therefore require that Th-232 is first irradiated in a reactor to provide the necessary neutron dosing. The U-233 that is produced can either be chemically separated from the parent thorium fuel and recycled into new fuel, or the U-233 may be usable 'in-situ' in the same fuel form.Thorium reactors, as it is understood, require more active radionuclides to 'activate' it into uranium for actual fission. This is a good use for waste materials and shows, in my opinion, good thinking on the part of Thor Energy (love that name). The linked article from the WNA above is well worth a read if you're interested in thorium-based power. They also had some thoughts on the non-proliferation (of nuclear weapons) aspect of thorium power:
The thorium fuel cycle is sometimes promoted as having excellent non-proliferation credentials. This is true, but some history and physics bears noting. The USA produced about 2 tonnes of U-233 from thorium during the 'Cold War', at various levels of chemical and isotopic purity, in plutonium production reactors. It is possible to use U-233 in a nuclear weapon, and in 1955 the USA detonated a device with a plutonium-U-233 composite pit, in Operation Teapot. Yield was less than anticipated, at 22 kilotons. In 1998 India detonated a very small device based on U-233 called Shakti V. However, the production of U-233 inevitably also yields U-232 which is a strong gamma-emitter, as are some decay products, making the material extremely difficult to handle and also easy to detect.
While thorium itself isn't suitable for nuclear weapons, the driver fuel can be used to make weapons and, possibly, used to create more weapons-grade fissile materials. However, it is challenging to do so and, as noted, easier to detect (for compliance monitoring). Again, thorium seems to be a reasonable choice for civilian, commercial power generation.I'm excited to see that a thorium reactor is actually running now to gather useful data. I look forward to the results and, hopefully, the replacement of harmful power generation systems with thorium reactors to buy us time until fusion or other, better, technology is viable.
Be well. http://www.extremetech.com/extreme/160131-thorium-nuclear-reactor-trial-begins-could-provide-cleaner-safer-almost-waste-free-energy
by Mike Weaver
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