Thorium-based Nuclear Power

Thorium-based nuclear power generation is fueled primarily by the nuclear fission of the isotope uranium-233 produced from the fertile element thorium. According to proponents, a thorium fuel cycle offers several potential advantages over a uranium fuel cycle—including much greater abundance of thorium on Earth, superior physical and nuclear fuel properties, and reduced nuclear waste production. However, development of thorium power has significant start-up costs. Proponents also cite the lack of easy weaponization potential as an advantage of thorium, while critics say that development of breeder reactors in general (including thorium reactors, which are breeders by nature) increases proliferation concerns. As of 2019, there are no operational thorium reactors in the world.

A nuclear reactor consumes certain specific fissile isotopes to produce energy. The three most common types of nuclear reactor fuel are: 

• Uranium-235, purified (i.e. "enriched") by reducing the amount of uranium-238 in natural mined uranium. Most nuclear power has been generated using low-enriched uranium (LEU), whereas high-enriched uranium (HEU) is necessary for weapons.
• Plutonium-239, transmuted from uranium-238 obtained from natural mined uranium.
• Uranium-233, transmuted from thorium-232, derived from natural mined thorium, which is the subject of this article.

The concept of using thorium as a nuclear fuel in place of Uranium was put forward by an Indian physicist Homi Bhabha in 1950.

Some believe thorium is key to developing a new generation of cleaner, safer nuclear power. According to a 2011 opinion piece by a group of scientists at the Georgia Institute of Technology, considering its overall potential, thorium-based power "can mean a 1000+ year solution or a quality low-carbon bridge to truly sustainable energy sources solving a huge portion of mankind’s negative environmental impact."

After studying the feasibility of using thorium, nuclear scientists Ralph W. Moir and Edward Teller suggested that thorium nuclear research should be restarted after a three-decade shutdown and that a small prototype plant should be built.

Background and Brief History

After World War II, uranium-based nuclear reactors were built to produce electricity. These were similar to the reactor designs that produced material for nuclear weapons. During that period, the government of the United States also built an experimental molten salt reactor using U-233 fuel, the fissile material created by bombarding thorium with neutrons. The MSRE reactor, built at Oak Ridge National Laboratory, operated critical for roughly 15,000 hours from 1965 to 1969. In 1968, Nobel laureate and discoverer of plutonium, Glenn Seaborg, publicly announced to the Atomic Energy Commission, of which he was chairman, that the thorium-based reactor had been successfully developed and tested.

In 1973, however, the US government settled on uranium technology and largely discontinued thorium-related nuclear research. The reasons were that uranium-fueled reactors were more efficient, the research was proven, and thorium's breeding ratio was thought insufficient to produce enough fuel to support development of a commercial nuclear industry. As Moir and Teller later wrote, "The competition came down to a liquid metal fast breeder reactor (LMFBR) on the uranium-plutonium cycle and a thermal reactor on the thorium-233U cycle, the molten salt breeder reactor. The LMFBR had a larger breeding rate ... and won the competition." In their opinion, the decision to stop development of thorium reactors, at least as a backup option, “was an excusable mistake.”

Science writer Richard Martin states that nuclear physicist Alvin Weinberg, who was director at Oak Ridge and primarily responsible for the new reactor, lost his job as director because he championed development of the safer thorium reactors. Weinberg himself recalls this period:

[Congressman] Chet Holifield was clearly exasperated with me, and he finally blurted out, "Alvin, if you are concerned about the safety of reactors, then I think it may be time for you to leave nuclear energy." I was speechless. But it was apparent to me that my style, my attitude, and my perception of the future were no longer in tune with the powers within the AEC.

Martin explains that Weinberg's unwillingness to sacrifice potentially safe nuclear power for the benefit of military uses forced him to retire: 

Weinberg realized that you could use thorium in an entirely new kind of reactor, one that would have zero risk of meltdown. ... his team built a working reactor .... and he spent the rest of his 18-year tenure trying to make thorium the heart of the nation’s atomic power effort. He failed. Uranium reactors had already been established, and Hyman Rickover, de facto head of the US nuclear program, wanted the plutonium from uranium-powered nuclear plants to make bombs. Increasingly shunted aside, Weinberg was finally forced out in 1973.

Despite the documented history of thorium nuclear power, many of today’s nuclear experts were nonetheless unaware of it. According to Chemical & Engineering News, "most people—including scientists—have hardly heard of the heavy-metal element and know little about it...," noting a comment by a conference attendee that "it's possible to have a Ph.D. in nuclear reactor technology and not know about thorium energy." Nuclear physicist Victor J. Stenger, for one, first learned of it in 2012: 

It came as a surprise to me to learn recently that such an alternative has been available to us since World War II, but not pursued because it lacked weapons applications.

Others, including former NASA scientist and thorium expert Kirk Sorensen, agree that "thorium was the alternative path that was not taken … " According to Sorensen, during a documentary interview, he states that if the US had not discontinued its research in 1974 it could have "probably achieved energy independence by around 2000."

Possible Benefits of Thorium Power

The World Nuclear Association explains some of the possible benefits

The thorium fuel cycle offers enormous energy security benefits in the long-term – due to its potential for being a self-sustaining fuel without the need for fast neutron reactors. It is therefore an important and potentially viable technology that seems able to contribute to building credible, long-term nuclear energy scenarios.

Moir and Teller agree, noting that the possible advantages of thorium include "utilization of an abundant fuel, inaccessibility of that fuel to terrorists or for diversion to weapons use, together with good economics and safety features … "Thorium is considered the "most abundant, most readily available, cleanest, and safest energy source on Earth," adds science writer Richard Martin. 

• Thorium is three times as abundant as uranium and nearly as abundant as lead and gallium in the Earth's crust. The Thorium Energy Alliance estimates "there is enough thorium in the United States alone to power the country at its current energy level for over 1,000 years." "America has buried tons as a by-product of rare earth metals mining," notes Evans-Pritchard. Almost all thorium is fertile Th-232, compared to uranium that is composed of 99.3% fertile U-238 and 0.7% more valuable fissile U-235.
• It is difficult to make a practical nuclear bomb from a thorium reactor's byproducts. According to Alvin Radkowsky, designer of the world's first full-scale atomic electric power plant, "a thorium reactor's plutonium production rate would be less than 2 percent of that of a standard reactor, and the plutonium's isotopic content would make it unsuitable for a nuclear detonation." Several uranium-233 bombs have been tested, but the presence of uranium-232 tended to "poison" the uranium-233 in two ways: intense radiation from the uranium-232 made the material difficult to handle, and the uranium-232 led to possible pre-detonation. Separating the uranium-232 from the uranium-233 proved very difficult, although newer laser techniques could facilitate that process.
• There is much less nuclear waste—up to two orders of magnitude less, state Moir and Teller, eliminating the need for large-scale or long-term storage; "Chinese scientists claim that hazardous waste will be a thousand times less than with uranium." The radioactivity of the resulting waste also drops down to safe levels after just a one or a few hundred years, compared to tens of thousands of years needed for current nuclear waste to cool off.
• According to Moir and Teller, "once started up [it] needs no other fuel except thorium because it makes most or all of its own fuel." This only applies to breeding reactors, that produce at least as much fissile material as they consume. Other reactors require additional fissile material, such as uranium-235 or plutonium.
• Thorium fuel cycle is a potential way to produce long term nuclear energy with low radio-toxicity waste. In addition, the transition to thorium could be done through the incineration of weapons grade plutonium (WPu) or civilian plutonium.
• Since all natural thorium can be used as fuel no expensive fuel enrichment is needed. However the same is true for U-238 as fertile fuel in the uranium-plutonium cycle.
• Comparing the amount of thorium needed with coal, Nobel laureate Carlo Rubbia of CERN, (European Organization for Nuclear Research), estimates that one ton of thorium can produce as much energy as 200 tons of uranium, or 3,500,000 tons of coal.
• Liquid fluoride thorium reactors are designed to be meltdown proof. A plug at the bottom of the reactor melts in the event of a power failure or if temperatures exceed a set limit, draining the fuel into an underground tank for safe storage.
• Mining thorium is safer and more efficient than mining uranium. Thorium's ore monazite generally contains higher concentrations of thorium than the percentage of uranium found in its respective ore. This makes thorium a more cost efficient and less environmentally damaging fuel source. Thorium mining is also easier and less dangerous than uranium mining, as the mine is an open pit—which requires no ventilation, unlike underground uranium mines, where radon levels can be potentially harmful.

Summarizing some of the potential benefits, Martin offers his general opinion: "Thorium could provide a clean and effectively limitless source of power while allaying all public concern—weapons proliferation, radioactive pollution, toxic waste, and fuel that is both costly and complicated to process.  Moir and Teller estimated in 2004 that the cost for their recommended prototype would be "well under $1 billion with operation costs likely on the order of $100 million per year," and as a result a "large-scale nuclear power plan" usable by many countries could be set up within a decade.

A report by the Bellona Foundation in 2013 concluded that the economics are quite speculative. 

Thorium nuclear reactors are unlikely to produce cheaper energy, but the management of spent fuel is likely to be cheaper than for uranium nuclear reactors.

Possible Disadvantages of Thorium Power

Some experts note possible specific disadvantages of thorium nuclear power: 

• Breeding in a thermal neutron spectrum is slow and requires extensive reprocessing. The feasibility of reprocessing is still open.
• Significant and expensive testing, analysis and licensing work is first required, requiring business and government support. In a 2012 report on the use of thorium fuel with existing water-cooled reactors, the Bulletin of the Atomic Scientists suggested that it would "require too great an investment and provide no clear payoff", and that "from the utilities’ point of view, the only legitimate driver capable of motivating pursuit of thorium is economics".
• There is a higher cost of fuel fabrication and reprocessing than in plants using traditional solid fuel rods.
• Thorium, when being irradiated for use in reactors, makes uranium-232, which emits dangerous gamma rays. This irradiation process may be altered slightly by removing protactinium-233. The irradiation would then make uranium-233 in lieu of uranium-232 for use in nuclear weapons—making thorium into a dual purpose fuel.

Thorium-Based Nuclear Power Projects

Research and development of thorium-based nuclear reactors, primarily the Liquid fluoride thorium reactor (LFTR), MSR design, has been or is now being done in the United States, United Kingdom, Germany, Brazil, India, China, France, the Czech Republic, Japan, Russia, Canada, Israel, and the Netherlands.  Conferences with experts from as many as 32 countries are held, including one by the European Organization for Nuclear Research (CERN) in 2013, which focuses on thorium as an alternative nuclear technology without requiring production of nuclear waste. Recognized experts, such as Hans Blix, former head of the International Atomic Energy Agency, calls for expanded support of new nuclear power technology, and states, "the thorium option offers the world not only a new sustainable supply of fuel for nuclear power but also one that makes better use of the fuel's energy content."

World Sources of Thorium

Thorium is mostly found with the rare earth phosphate mineral, monazite, which contains up to about 12% thorium phosphate, but 6–7% on average. World monazite resources are estimated to be about 12 million tons, two-thirds of which are in heavy mineral sands deposits on the south and east coasts of India. There are substantial deposits in several other countries.

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 Monazite is a good source of REEs (Rare Earth Element), but monazites are currently not economical to produce because the radioactive thorium that is produced as a byproduct would have to be stored indefinitely. However, if thorium-based power plants were adopted on a large-scale, virtually all the world's thorium requirements could be supplied simply by refining monazites for their more valuable REEs.

Another estimate of reasonably assured reserves (RAR) and estimated additional reserves (EAR) of thorium comes from OECD/NEA, Nuclear Energy, "Trends in Nuclear Fuel Cycle", Paris, France (2001). (see table "IAEA Estimates in tons") 

IAEA Estimates in tons (2005)
Country	RAR Th	EAR Th
India	519,000	21%
Australia	489,000	19%
US	400,000	13%
Turkey	344,000	11%
Venezuela	302,000	10%
Brazil	302,000	10%
Norway	132,000	4%
Egypt	100,000	3%
Russia	75,000	2%
Greenland	54,000	2%
Canada	44,000	2%
South Africa	18,000	1%
Other countries	33,000	2%
World Total	2,810,000	100%

The preceding figures are reserves and as such refer to the amount of thorium in high-concentration deposits inventoried so far and estimated to be extractable at current market prices; millions of times more total exist in Earth's 3×10¹⁹ tonne crust, around 120 trillion tons of thorium, and lesser but vast quantities of thorium exist at intermediate concentrations.  Proved reserves are a good indicator of the total future supply of a mineral resource. 

Types of Thorium-based Reactors

According to the World Nuclear Association, there are seven types of reactors that can be designed to use thorium as a nuclear fuel. Six of these have all entered into operational service at some point. The seventh is still conceptual, although currently in development by many countries: 

• Heavy water reactors (PHWRs)
• High-temperature gas-cooled reactors (HTRs)
• Boiling (light) water reactors (BWRs)
• Pressurized (light) water reactors (PWRs)
• Fast neutron reactors (FNRs)
• Molten salt reactors (MSRs), including Liquid fluoride thorium reactors (LFTRs). Instead of using fuel rods, molten salt reactors use compounds of fissile materials, in the form of molten salts that cycle through the core to undergo fission. The molten salt then carries the heat produced by the reactions away from the core, and exchanges it with a secondary medium. Molten salt breeder reactors, or MSBRs, are another type of molten salt reactor that use thorium to breed more fissile material. Currently, India's nuclear program is looking into using MSBRs to take advantage of their efficiency and India's own available thorium reserves.
• The Oak Ridge National Laboratory designed and built a demonstration MSR that operated from 1965 to 1969. It used U-233 (originally bred from Th-232) for fuel in its final year.
• Aqueous Homogeneous Reactors (AHRs) have been proposed as a fluid fueled design that could accept naturally occurring uranium and thorium suspended in a heavy water solution. AHRs have been built and according to the IAEA reactor database, 7 are currently in operation as research reactors.
• Accelerator driven reactors (ADS)

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