Thorium Nuclear Reactors

[Orca]

Heya folks,

I was listening to the Skeptic's Guide podcast this week and they were talking about the viability of generating nuclear power using thorium instead of uranium. You can read the brief article they referenced here.

Apparently there are some glaringly huge advantages to using thorium instead of uranium as fuel for fission reactors. Thorium would be a far more efficient fuel than uranium; you can get a lot more power out of a much smaller amount of thorium vs uranium. From the article:

Dr Rubbia says a tonne of the silvery metal – named after the Norse god of thunder, who also gave us Thor’s day or Thursday - produces as much energy as 200 tonnes of uranium, or 3,500,000 tonnes of coal. A mere fistful would light London for a week.

Thorium is more common than uranium; apparently miners have to just throw the stuff aside as they work.

Thorium reactions would produce less toxic waste. Also, thorium reactors would be much smaller and safer because the reactions can happen at ambient temperatures; no need for pressurized cooling and such.

Thorium is much harder to make into weapons. This is perhaps the reason we built uranium reactors in the 60's...we wanted a supply of plutonium (a byproduct of uranium reactors) for making weapons.

When I think about all this, I can't help but ask "what's the catch?" This all seems too good to be true. I suppose the biggest hurdle is the funding required for R&D and to get the first large-scale reactor up and running. However, if the benefits of thorium reactors are not overstated here, this might be the ticket until we can improve even greener technology.

Anyway, I am curious to see what you guys think about this.

[Beyond]

Orca, if what is said in your post is true -- i would not be able to print here what i though of the situation!!

[Beyond]

Orca, how come your Avatar is a bird of prey and the name below it is an ocean mammal of prey? Do you do a lot of preying
It is a nice looking bird of prey. You can fly through my Redwood forest anytime.

[neufer]

<<Thorium is a chemical element with the symbol Th and atomic number 90. Thorium is a naturally occurring, slightly radioactive metal. It is estimated to be about three to four times more abundant than uranium in the Earth's crust. It has been considered a waste product in mining rare earths, so its abundance is high and cost low.

Pure thorium is a silvery-white metal which is air-stable and retains its luster for several months. When contaminated with the oxide, thorium slowly tarnishes in air, becoming gray and finally black. The physical properties of thorium are greatly influenced by the degree of contamination with the oxide. The purest specimens often contain several tenths of a percent of the oxide. Thorium is slowly attacked by water, but does not dissolve readily in most common acids, except hydrochloric acid. Pure thorium is soft, very ductile, and can be cold-rolled, swaged, and drawn. Powdered thorium metal is often pyrophoric and requires careful handling. When heated in air, thorium metal turnings ignite and burn brilliantly with a white light. Thorium has the largest liquid range of any element: 2946 °C between the melting point (1842 °C),  and boiling point (4788 °C).

M. T. Esmark found a black mineral on Løvøy Island, Norway. The Swedish chemist Jöns Jakob Berzelius analyzed it and named it after Thor, the Norse god of thunder. The metal had virtually no uses until the invention of the gas mantle in 1885.

Thorium dioxide has the highest melting point (3300 °C) of all oxides. Thorium dioxide is a material for heat-resistant ceramics, e.g., for high-temperature laboratory crucibles. When added to glass, it helps increase refractive index and decrease dispersion. Such glass finds application in high-quality lenses for cameras and scientific instruments. Thorium dioxide and thorium nitrate were used in mantles of portable gas lights, including natural gas lamps, oil lamps and camping lights. These mantles glow with an intense white light (unrelated to radioactivity) when heated in a gas flame, and its color could be shifted to yellow by addition of cerium. Thoriated tungsten elements are found in the filaments of magnetron tubes. Thorium is added because of its ability to emit electrons at relatively low temperatures when heated in vacuum. Those tubes generate microwave frequencies and are applied in microwave ovens and radars.

Thorium dioxide has been used as a catalyst in the conversion of ammonia to nitric acid, in petroleum cracking and in producing sulfuric acid.

Despite its radioactivity, thorium fluoride (ThF₄) is used as an antireflection material in multilayered optical coatings. It has excellent optical transparency in the range 0.35–12 µm, and its radiation is primarily due to alpha particles, which can be easily stopped by a thin cover layer of another material. Thorium fluoride was also used in manufacturing carbon arc lamps, which provided high-intensity illumination for movie projectors and search lights.>>

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<<Thorium was first observed to be radioactive in 1898. Between 1900 and 1903, Ernest Rutherford and Frederick Soddy showed how thorium decayed at a fixed rate over time into a series of other elements. This observation led to the identification of half life as one of the outcomes of the alpha particle experiments that led to their disintegration theory of radioactivity.

The name ionium was given early in the study of radioactive elements to the ²³⁰Th isotope produced in the decay chain of ²³⁸U before it was realized that ionium and thorium were chemically identical. The symbol Io was used for this supposed element.

Naturally occurring thorium is composed mainly of one isotope: ²³²Th.
²³⁰Th occurs as the daughter product of ²³⁸U decay.

Twenty-seven radioisotopes have been characterized, with the most stable being:

• ²³²Th with a half-life of 14.05 billion years,
  ²³⁰Th with a half-life of 75,380 years,
  ²²⁹Th with a half-life of 7340 years, and
  ²²⁸Th with a half-life of 1.92 years.

All of the remaining radioactive isotopes have half-lives that are less than thirty days and the majority of these have half-lives that are less than ten minutes. One isotope, ²²⁹Th, has a nuclear isomer (or metastable state) with a remarkably low excitation energy of 7.6 eV.>>

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<<Thorium was successfully used as a breeding (fertile) source for nuclear fuel – uranium (233) in the molten-salt reactor experiment from 1964 to 1969, as well as in several light water reactors using solid fuel composed of a mixture of ²³²Th and ²³³U, including the Shippingport Atomic Power Station, but a thorium-uranium mix was only used at end of life to demonstrate Th-to-U breeding.

Advocates of the use of thorium as the fuel source for nuclear reactors, such as Nobel laureate Carlo Rubbia, state that they can be built to operate significantly cleaner than uranium-based power plants as the waste products are much easier to handle. According to Rubbia, a ton of thorium produces the same energy as 200 tons of uranium, or 3.5 million tons of coal. Edward Teller, co-founder and director of Lawrence Livermore National Laboratory, promoted thorium energy until his death, and scientists in France, Japan, India, and Russia are now creating their own thorium-based power plants. One leading commentator is calling for the creation of a new Manhattan Project, stating that the use of thorium fuel for energy would "reinvent the global energy landscape . . . and an end to our dependence on fossil fuels within three to five years."

When used in molten-salt reactors, thorium bred to ²³³U removes weaponization dangers, because no uranium exists in solid form and the reactor runs continuously, with no shutdown for refuelling—all thorium and fissile uranium is consumed and any undesired gases and uranium/plutonium isotopes are flushed out as gases (e.g., as uranium hexafluoride) as the hot, liquid salt is pumped around the reactor/exchanger system.>>

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<<Thorium, as well as uranium and plutonium, can be used as fuel in a nuclear reactor. A thorium fuel cycle offers several potential advantages over a uranium fuel cycle, however, including much greater abundance on Earth, superior physical and nuclear properties of the fuel, enhanced proliferation resistance, and reduced nuclear waste production. Nobel laureate Carlo Rubbia at CERN (European Organization for Nuclear Research), has worked on developing the use of thorium as a cheap, clean and safe alternative to uranium in reactors. Rubbia states that a ton of thorium can produce as much energy as 200 tons of uranium, or 3,500,000 tonnes of coal.

One of the early pioneers of the technology was U.S. physicist Alvin Weinberg at Oak Ridge National Laboratory in Tennessee, who helped develop a working nuclear plant using liquid fuel in the 1960s. Thorium-fluoride reactors can operate at atmospheric temperature, and plants would be much smaller and less expensive. In addition, not requiring pressurized water in the reactor, there is no need for huge containment domes.

According to Australian science writer Tim Dean, "thorium promises what uranium never delivered: abundant, safe and clean energy - and a way to burn up old radioactive waste." With a thorium nuclear reactor, Dean stresses a number of added benefits: there is no possibility of a meltdown, it generates power inexpensively, it does not produce weapons-grade by-products, and will burn up existing high-level waste as well as nuclear weapon stockpiles. Ambrose Evans-Pritchard, of the British Telegraph daily, suggests that "Obama could kill fossil fuels overnight with a nuclear dash for thorium." He advocates setting up a new Manhattan Project, as the U.S. did to rapidly develop nuclear weapons during World War II, in order to "marshal America’s vast scientific and strategic resources" in developing thorium reactors. It could put "an end to our dependence on fossil fuels within three to five years," he stresses.

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." They also note that a thorium power plant can be "designed to tap right in at the source of a current coal or uranium plant," without the need for laying a new grid. In addition, reducing coal as an energy source, according to science expert Lester R. Brown, of The Earth Policy Institute in Washington DC, would reduce deaths, certain diseases, and medical costs. He estimates that air pollution from coal-fired power plants causes 23,600 U.S. deaths per year.

Although not fissile itself, ²³²Th will absorb slow neutrons to produce ²³³U, which is fissile. Hence, like ²³⁸U, it is fertile. It is at least 4-5 times more abundant in Earth's crust than all isotopes of uranium combined and is fairly evenly spread around Earth, with many countries having large supplies of it. Also, preparation of thorium fuel does not require isotopic separation.

The thorium fuel cycle creates ²³³U, which, if separated from the reactor's fuel, can be used for making nuclear weapons. This is why a liquid-fuel cycle (e.g., MSR) is preferred — only a limited amount of ²³³U ever exists in the reactor and its heat-transfer systems, preventing any access to weapons material; however the neutrons produced by the reactor can be absorbed by a thorium or uranium blanket and fissile ²³³U or ²³⁹Pu produced. Also, the ²³³U could be continuously extracted from the molten fuel as the reactor is running. Since there are no neutrons from spontaneous fission of U-233, solid U-233 can be used easily in a simple gun-type nuclear bomb design. In 1977, a light-water reactor at the Shippingport Atomic Power Station was used to establish a Th232-U233 fuel cycle. The reactor worked until its decommissioning in 1982. Thorium can be and has been used to power nuclear energy plants using both the modified traditional Generation III reactor design and prototype Generation IV reactor designs.

A seed-and-blanket fuel using a core of plutonium surrounded by a blanket of thorium/uranium has been undergoing testing at Moscow's Kurchatov Institute, under a 1994 agreement between the institute and McLean, Virginia-based Thorium Power Ltd. Russian government-owned nuclear design firm Red Star formed an agreement with Thorium Power in 2007 to continue work on scaling up the test fuel rods to commercial use and licensing in VVER-1000 reactors. This assembly could achieve a more efficient disposal method of weapons-grade plutonium than the mixed-oxide disposal method, especially with the 2009 decision by the US to shelve the Yucca Mountain nuclear waste repository highlighting the issue of what to do with all the plutonium left over from decommissioned nuclear weapons. Thorium Power, with offices in London, Dubai, and Moscow and with Dr. Hans Blix serving as an advisor, also advises the United Arab Emirates on their fledgling nuclear program. They are awaiting the finalization of the US-India nuclear 1-2-3 Agreement to complete a joint-venture with Punj Lloyd, an Indian engineering firm with nuclear reactor construction ambitions.

Unlike its use in MSRs, when using solid thorium in modified light water reactor (LWR) problems include: the undeveloped technology for fuel fabrication; in traditional, once-through LWR designs potential problems in recycling thorium due to highly radioactive ²²⁸Th; some weapons proliferation risk due to production of ²³³U; and the technical problems (not yet satisfactorily solved) in reprocessing. Much development work is still required before the thorium fuel cycle can be commercialized for use in LWR. The effort required has not seemed worth it while abundant uranium is available, but geopolitical forces (e.g. India looking for indigenous fuel) as well as uranium production issues, proliferation concerns, and concerns about the disposal/storage of radioactive waste are starting to work in its favor. In 2008, Senator Harry Reid (D-Nevada) and Senator Orrin Hatch (R-Utah) introduced the Thorium Energy Independence and Security Act of 2008, which would mandate a US Department of Energy initiative to examine the commercial use of thorium in US reactors. The bill, however, did not reach a full Senate vote.

The thorium fuel cycle, with its potential for breeding fuel without fast neutron reactors, holds considerable potential long-term benefits. Thorium is significantly more abundant than uranium, and is a key factor in sustainable nuclear energy. Perhaps more importantly, thorium produces one to two orders of magnitude less long-lived transuranics than uranium fuel cycles, though the long-lived actinide protactinium-231 is produced, and the amount of fission products is similar.

An early effort to use a thorium fuel cycle took place at Oak Ridge National Laboratory in the 1960s. An experimental reactor was built based on MSR technology to study the feasibility of such an approach, using thorium-fluoride salt kept hot enough to be liquid, thus eliminating the need for fabricating fuel elements. This effort culminated in the Molten-Salt Reactor Experiment that used ²³²Th as the fertile material and ²³³U as the fissile fuel. This reactor was operated successfully for about five years. However, due to a lack of funding, the MSR program was discontinued in 1976.

India's Kakrapar-1 reactor is the world's first reactor which uses thorium rather than depleted uranium to achieve power flattening across the reactor core. India, which has about 25% of the world's thorium reserves, is developing a 300 MW prototype of a thorium-based Advanced Heavy Water Reactor (AHWR). The prototype is expected to be fully operational by 2011, following which five more reactors will be constructed. Considered to be a global leader in thorium-based fuel, India's new thorium reactor is a fast-breeder reactor and uses a plutonium core rather than an accelerator to produce neutrons. India currently envisages meeting 30% of its electricity demand through thorium-based reactors by 2050.

In 2007, Norway was debating whether or not to focus on thorium plants because of the large deposits of thorium ores in the country, particularly at Fensfeltet near Ulefoss in Telemark county.

The primary fuel of the HT3R Project near Odessa, Texas, USA will be ceramic-coated thorium beads.

However, the best results occur with molten-salt reactors (MSRs), such as ORNL's LFTR, which have built-in negative-feedback reaction rates, due to salt expansion and thus reactor throttling via load. This is a great safety advantage, since no emergency cooling system is needed, which is both expensive and adds thermal inefficiency. In fact, an MSR was chosen as the base design for the 1960s DoD Atomic Plane largely because of its great safety advantages, even under aircraft maneuvering. In the basic design, an MSR generates heat at higher temperatures, continuously, and without refuelling shutdowns, so it can provide hot air to a more efficient (Brayton Cycle) turbine. An MSR run this way is about 30% better in thermal efficiency than common thermal plants, whether combustive or traditional solid-fuelled nuclear.

In 2010, Congressman Joe Sestak added funding for research and development of a destroyer-sized reactor using thorium.>>

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Thorium offers several potential advantages:

<<Thorium is estimated to be about three to four times more abundant than uranium in the Earth's crust, although present knowledge of reserves is limited. Current demand for thorium has been satisfied as a by-product of rare-earth extraction from monazite sands. Also, unlike uranium, mined thorium consists of a single isotope (²³²Th) in significant quantities. Consequently, it is useful in thermal reactors without the need for isotope separation.

Thorium-based fuels exhibit several attractive nuclear properties relative to uranium-based fuels. The thermal neutron absorption cross section (σ_a) and resonance integral (average of neutron cross sections over intermediate neutron energies) for ²³²Th are about three times and one third of the respective values for ²³⁸U; consequently, fertile conversion of thorium is more efficient in a thermal reactor. Also, although the thermal neutron fission cross section (σ_f) of the resulting ²³³U is comparable to ²³⁵U and ²³⁹Pu, it has a much lower capture cross section (σ_γ) than the latter two fissile isotopes, providing fewer non-fissile neutron absorptions and improved neutron economy. Finally, the ratio of neutrons released per neutron absorbed (η) in ²³³U is greater than two over a wide range of energies, including the thermal spectrum; as a result, thorium-based fuels can be the basis for a thermal breeder reactor.

Thorium-based fuels also display favorable physical and chemical properties which improve reactor and repository performance. Compared to the predominant reactor fuel, uranium dioxide, thorium dioxide has a higher melting point, higher thermal conductivity, and lower coefficient of thermal expansion. Thorium dioxide also exhibits greater chemical stability and, unlike uranium dioxide, does not further oxidize.

Because the ²³³U produced in thorium fuels is inevitably contaminated with ²³²U, thorium-based used nuclear fuel possesses inherent proliferation resistance. ²³²U can not be chemically separated from ²³³U and has several decay products which emit high energy gamma radiation. These high energy photons are a radiological hazard that necessitate the use of remote handling of separated uranium and aid in the passive detection of such materials.

The long term (on the order of roughly 10³ to 10⁶ years) radiological hazard of conventional uranium-based used nuclear fuel is dominated by plutonium and other minor actinides, after which long-lived fission products become significant contributors again. A single neutron capture in ²³⁸U is sufficient to produce transuranic elements, whereas six captures are generally necessary to do so from ²³²Th. 98–99% of thorium-cycle fuel nuclei would fission at either ²³³U or ²³⁵U, so fewer long-lived transuranics are produced. Because of this, thorium is a potentially attractive alternative to uranium in mixed oxide (MOX) fuels to minimize the generation of transuranics and maximize the destruction of plutonium.>>

[Beyond]

Hey neufer, aren't you a little thor from all that posting on Thorium I got pooped from perusing

[Orca]

Orca, how come your Avatar is a bird of prey and the name below it is an ocean mammal of prey? Do you do a lot of preying
It is a nice looking bird of prey. You can fly through my Redwood forest anytime.

You know I hadn't thought of that. The avatar is a picture of an osprey. I didn't intend to have a "carnivorous" tone; I just happen to find them both to be very fascinating animals. They were fresh in my mind as I was fortunate to see several pairs cruising around when I went camping a few months ago. I've always found whales and dolphins very interesting as well, hence the handle. It's a very old and well-used handle of mine.

Orca, if what is said in your post is true -- i would not be able to print here what i though of the situation!!

You mean you'd say something like, "why the %#*@ haven't we been doing this all along?" That's sort of what I thought. But again, when it comes to energy production I am highly skeptical when a new power source comes along and says, "use me, I will solve the lion's share of your problems."

I am also nervous about nuclear power in general. It has a lot of stigma and, I think, rightfully so. Others disagree; supposedly, modern reactors are far safer and more efficient than they were in the past. At any rate I feel like the current push toward traditional nuclear energy solves current problems at the cost of future generations. The problem of radioactive waste will grow exponentially if countries around the world keep moving that direction.

Unfortunately "green" technology is just not going to fill the gaps as soon as we'd hoped. Solar moves forward in tiny steps but isn't really viable for large-scale energy production yet. Wind is unpredictable and has plenty of draw backs in and of itself (like giant, expensive, loud towers in your back yard). Bio fuel energy output doesn't seem to be great enough to balance the energy cost to produce it. And of course the Holy Grail of energy production -controlled fusion - seems as far out of reach as it ever was.

Anyway, perhaps thorium may be an intermediate step.

[neufer]

Hey neufer, aren't you a little thor from all that posting on Thorium I got pooped from perusing

I'm a strong believer in science & technology.

Thorium seems like the best option for a new green nuclear energy option.

[Beyond]

Hey neufer, aren't you a little thor from all that posting on Thorium I got pooped from perusing

I'm a strong believer in science & technology.

Thorium seems like the best option for a new green nuclear energy option.

Yes, it does! But like all Great discoveries that "Buck" The System, they have a way of being swept under the rug and disappearing, if they are too big a threat to the establishment.

[BMAONE23]

Looks to me like it could be a viable alternate energy source for longer term space travel.