Science

Thorium: A safer alternative for nuclear power generation?

Thorium: A safer alternative f...
Thorium could provide a cleaner and more abundant alternative to uranium (Photo: Three Mile Island Nuclear Power Plant/ Lyndi & Jason via Flickr)
Thorium could provide a cleaner and more abundant alternative to uranium (Photo: Three Mile Island Nuclear Power Plant/ Lyndi & Jason via Flickr)
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Thorium could provide a cleaner and more abundant alternative to uranium (Photo: Three Mile Island Nuclear Power Plant/ Lyndi & Jason via Flickr)
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Thorium could provide a cleaner and more abundant alternative to uranium (Photo: Three Mile Island Nuclear Power Plant/ Lyndi & Jason via Flickr)

The world's growing need for energy, the limits of our supply of fossil fuels and concern about the effects of carbon emissions on the environment have all prompted interest in the increased use of nuclear power. Yet the very word "nuclear" carries with it an association of fear. People are concerned about the waste produced by reactors, the possibility of catastrophic accidents as highlighted by recent events in Japan and the link between nuclear power and nuclear weapons. Yet what if there existed a means of nuclear power generation with which these risks were drastically reduced?

The answer could be thorium - an element occurring as a silvery metal that's more abundant, cleaner and can produce more bang-per-buck in energy terms than uranium. So how does thorium differ from uranium and plutonium, and why isn't it being used? First, a quick run-down on how nuclear energy works.

What is nuclear power?

The word "nuclear" refers to the nucleus, or dense center of the atom. In a nuclear power reactor, these nuclei are split into smaller parts through a process known as fission. A sub-atomic particle known as a neutron strikes the nucleus of an atom of suitable fuel (particular isotopes of the heavy elements uranium and plutonium) breaking it into its component parts. Each fission results in the release of energy in the form of electromagnetic radiation and kinetic energy in the fragments of the split nucleus. This effect is twofold; the release of energy will produce heat, and the release of neutrons, which can in turn fission other atoms.

In material that has typically been employed as nuclear fuel, this reaction occurs in a "chain reaction" and is self-sustaining. When this is occurring, the reactor can be said to be"'critical". In a fission weapon, a mass of plutonium or uranium in excess of critical is assembled very quickly, with a flood of neutrons from a device known as an "initiator". The release of energy is extremely rapid and results in a massive explosion.

In a nuclear power reactor, the reaction is far slower and more controlled - the heat produced can be harnessed to boil water to spin turbines for the generation of electricity and this has been in practice for decades. The use of nuclear reactors for power generation began on 27 June 1954 at the Obninsk power plant in the former Soviet Union and has continued in numerous countries to this day.

There are of course, some significant problems with nuclear power. Fission reactions will always result in the production of radioactive waste products which require secure storage and pose a health risk to humans and the environment. There is the possibility that the operators may lose control of the fission chain reaction resulting in an accidental release of this material (often referred to as a "meltdown"). There's also the concern that reactors may also be used for the production of material suitable for nuclear weapons.

Modern nuclear reactors

The two main types of reactors used for commercial power generation are the pressurized water reactor (PBR) and the boiling water reactor (BWR), which both typically make use of uranium in the form of uranium oxide fuel rods. The criticality of the reactor is managed by control rods, which when inserted absorb neutrons that would otherwise cause the chain reaction to continue. The reactor can be shut down, or "scrammed", by the rapid insertion of these control rods. However, this is a manual process and there is a possibility of an error occurring.

Criticality, fertility and the potential of thorium

The element thorium, named after the Norse god of thunder, may provide a safer alternative as a fuel. The key difference between thorium and other nuclear fuels is that it cannot sustain a chain reaction on its own. Fissile fuels like uranium and plutonium are able to sustain a chain-reaction, yet fission can also be achieved in material like thorium that is not fissile but fertile - i.e. it can produce fissile material, if neutrons are provided from an outside source.

Thorium is estimated to be three to four times more plentiful than uranium in the Earth's crust and has the advantage of being found in nature in the one isotope, which makes it suitable as a nuclear fuel as it need not be enriched to separate the right isotope. For convenience, thorium fuel can be used in the form of a liquid molten salt mixture.

Accelerator Driven System

Fission occurs in thorium when atoms absorb a neutron to become a heavier isotope and quickly decay into an isotope of the element protactinium and then an isotope of uranium, which is fissioned when struck by an additional neutron. The number of neutrons produced is not sufficient for a self-sustained chain reaction.

A particle accelerator could be used to provide the necessary neutrons for fission to occur in thorium and a nuclear reactor making use of such an outside neutron source would be known as an 'accelerator driven system' (ADS).

The notion of the ADS is credited to Carlo Rubbia of the European Organisation for Nuclear Research (CERN) joint winner of the 1984 Nobel Prize for Physics. The ADS would likely be far smaller than other reactors and if the accelerator were to be turned off, the nuclear reaction would cease, although it should be noted that even in a reactor which is not critical, the heat from the decay of materials can be significant and cooling is required.

In a thorium reactor, quantities of other fuels could be included, without the fuel being capable of sustaining a chain reaction, and thus the reactor could be used to provide energy from disposing of material such as plutonium from disassembled nuclear weapons. It's also possible to ensure that the reactors are designed in such a way that it is not possible to extract fissile material, which can be used to manufacture nuclear weapons.

Though all nuclear reactors will produce waste products, a reactor fulled by thorium will produce far less long-lived waste products than one fueled by uranium or plutonium, with waste decaying to the same level of radioactivity as coal ashes after 500 years.

Thorium also produces more energy from the same amount of material compared to uranium.

"Two hundred tonnes of uranium can give you the same amount of energy you can get from one tonne of thorium," Rubbia told the BBC News in a recent interview.

Towards a thorium reactor

Though several reactors have made use of thorium for experimental purposes, a thorium power reactor is not as yet a reality. Countries like Russia, India and China are looking at the use of thorium and such a reactor may one day soon be a viable energy source.

So why has it taken so long for thorium to hit the nuclear power agenda? The key reason seems to be that because it can't be used to make a nuclear bomb, it was largely ignored during the Manhattan project and in the development of nuclear power stations that followed.

34 comments
dwreid
Google sponsored some lectures on LIFTR (LIquid Fluoride Thorium Reactor) technology a few years back. You can find them on YouTube if you do a search. Some very good (and technical) information there. Almost all upside. Almost no downside. (Nothing is perfect) Significantly greener than oil, gas or the current state of nuclear. If you take into account the massive amount of pollution created by the production of photo-voltaic it\'s even greener than that and doesn\'t consume thousands of acres of delicate desert land. Have a look.
Windmaster Hiroaki
This ain\'t new, the idea has been around for some time... but it\'s time someone build one using Thorium rather than Uranium...
Earl Leonard
What\'s the environmental impact of the mining process like compared to uranium? And where are the main deposits of the stuff located, internationally speaking? (as in, what countries would stand to gain/lose from a Thorium reactor revolution mining wise).
Patrick McGean
A nuke dummy I almost fell for the hook. The grid is the issue. Individual power no grid no stock holders, no officers to drive the cost of energy up so the sale of planes, boats and fast cars can continue unabated. The Grid comes down, get ready with individual power sources, Red Dawn is the model, and the Grid makes us vulnerable to Canadians looking for a beach. The fossil fuel revolution comes to an end before we all suffocate. Nuke ends before we cook ourselves to death, Fukushima is a four letter for GE. The Agents of the Crystalline Matrix
Dawg
Get a grip guys. This is just old hogwash: In 2008 a report from the Norwegian Radiation Protection Authority (NRPA) revealed that thorium-based nuclear energy plants - once vaunted as a clean alternative type of nuclear energy - have the same negative environmental consequences as their uranium-based cousins do. The NRPA report dealt with the environmental consequences of potential thorium related industry in Norway. The report takes on various aspects of the thorium fuel cycle from mining and extraction, fuel production, reactor operation and waste handling. The report concludes that the environmental consequences of using thorium-based nuclear power will result in the same problems the world faces today with uranium bases reactors. "The NRPA invalidated that thorium is kind nuclear power, as many have earlier asserted," said Nils Bohmer, nuclear physicist with Bellona, a Norwegian based environmental organization. "Using thorium leads to highly radioactive nuclear waste and the risk of accidents will always be present." According to the NRPA, thorium-based nuclear energy, uncontrolled chain reactions and, in the worst case, meltdowns can occur. The NRPA also asserts that thorium-based nuclear energy will produce long-lasting radioactive waste that will demand the same handling as highly radioactive waste from current nuclear reactors. The NRPA report also points out that it is impossible to give a full value oversight of all potential environenmental consequences of thorium-based nuclear energy. The report shows that each form of thorium extraction, whether by open-pit mining or underground mining, will lead to negative burdens on the environment. Extraction will produce radioactive waste in the form of slag heaps that can lead to an escalation of radiation for humans and the environment, and the spread of radioactivity. Earlier, many had asserted that thorium technology cannot be used for weapons purposes. Even though this would be more difficult than with current technology, the NRPA report shows that this will continue to be possible. In the 1950s, the United States accomplished its first test explosion with uranium 233, which is the material thorium-based energy production produces. Additionally, highly enriched or plutonium is required as an additive to thorium to produce a chain reaction. These are materials that can be abused for weapons grade purposes.
Griffin
Go,Thor! HAMMER DOWN! {^,^}
Fabrizio Pilato
Thorium is highly abundant and easily attainable. It runs on a low pressure system, so much safer than present day high pressure Nuclear reactors. It\'s also nearly 100% efficient. Here are some figures from Kirk Sorenson\'s Google presentation: 6600 tonnes of thorium (500 quads) is equal to one of the following in the list below: - 5.3 billion tonnes of coal (128 quads) - 31.1 billion barrels of oil (180 quads) - 2.92 trillion m3 of natural gas (105 quads) - 65,000 tonnes of uranium ore (24 quads) more figures. 6 kg of thorium metal in a liquid-fluoride reactor has the energy equivalent (66,000 MW*hr electrical*) of: - 230 train cars (25,000 MT) of bituminous coal or, - 600 train cars (66,000 MT) of brown coal or, - 440 million cubic feet of natural gas (15% of a 125,000 cubic meter LNG tanker), - or, 300 kg of enriched (3%) uranium in a pressurized water reactor. Kirk Sorenson is an expert on the matter, check his site for how things are developing: http://energyfromthorium.com/about/
Michael Mantion
Um the grid does need a serious upgrade. but the grid is good silly rabbit. If you live on a farm and don\'t have a family sure you can have some wind mills, most people live in burbs or cities.. What then? No one wants solar panels even with subsidies they are 30-40 cents per kwh, and then you have to charge something to get through the night.. then it gets to a $1 per kwh. No thanks I think we will keep the grid and just build more nuclear plants.
Michael Mantion
Thorium is very abundant. but then again so is uranium, especially all the spent fuel that could be reprocessed.
Eletruk
One of the promising things about Thorium reactors is that they can be built significantly smaller than current Uranium based reactors. It\'s possible that a town could purchase and install their own reactor rather than relying on grid power. There even is a proposal for a portable reactor designed for remote site power and heat generation. http://nextbigfuture.com/2011/05/thorenco-llc-presents-little-40-mw.html