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Liquid-Flouride Thorium Reactor


by Joseph Dunlavey and Christopher Plummer




As of 2008, China became the single greatest contributor to Greenhouse Gas emissions accounting for 23% worldwide while still maintaining a low CO2/person/year quotient compared with the United States. Energy requirements in China [and India] will continue to skyrocket and “solar and wind energy is not stable enough and hydropower development is over the limit.” Simultaneously, China has been somewhat resolute to phase out the oldest coal plants “cutting annual coalconsumption by about 82 million tonnes [165 million tonnes of CO2]” since 2006. However, with about 1,000 billion tons still in reserve and a steady supply from Vietnam Coal will remain China's primary source of electricity generation amounting to 80%, followed by 15% from hydroelectric dams. This system remains admittedly inefficient due to “large-scale transportation over long distances of coal and oil from the north to the south, and transmission of natural gas and electricity from the west to the east.”

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Linfen City in Shanxi province (山西临汾市) is a seriously polluted area. Farmers after working in the cotton fields for 2 hours are covered with coal ashes. September 24 2007
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Breathing in large amounts of dust into the lungs, people get sick after working there for 1-2 years. Most of these migrant workers come from an area of poverty. April 10, 2005
Alarmingly, China's reliance on coal has lead to catastrophic levels of air pollution which choke out large cities “leading to the premature deaths of 350,000-400,000people each year.” On a daily basis, the environmental degradation of China is exchanged for economic gains that drive cheap production of plastics, chemicals, and alloys for consumption worldwide. Air pollution from Coal power plants is only one facet of the poisons such as sulfur dioxide, lead, and arsenic that pollute the air and fresh water supplies.

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Linfen, the most polluted city in China and probably the world.

For these reasons, Nuclear Power has been the backbone of "clean"-energy initiatives leading to 2020. In this regard, "clean" energy must be defined in terms of greenhouse gas production and not in terms of radioactive waste. As of July 2011, “China has 14 nuclear power reactors in operation, more than 25 under construction,” and at least another 35 in planning and licensing stages. Following the example of most countries, most of these power plants follow the Pressurized Light-Water Reactor (PWR) design and construction. “China is rapidly becoming self-sufficient" in developing nuclear power having achieved critical mass recently at China's first Sodium-Cooled Fast Reactor (SFR) near Beijing.

On January 26th, 2011, the Chinese Academy of Sciences unveiled a program that would hopefully become “the future of advanced nuclear fission energy.” With this announcement, China will officially finance research of Thorium-Fueled Molten Salt Reactors. Dr. Jiang Mianheng the son of former President Jiang Zemin, will head the engineering initiative to create a functioning thorium molten reactor system in 20 years in order to earn “all intellectual property rights."




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“The political and technical support for the program in the United States was too thin geographically...only in Oak Ridge...was the technology really understood and appreciated.” H.G. MacPherson in The Molten Salt Adventure
Thorium-fueled Molten Salt Reactors (TFMSR) have the potential to create huge quantities of electricity. A similar design concept, coined the Liquid Flouride Thorium Reactor (LFTR) by Kirk Sorensen claims that 1,000 kg of Thorium-232could produce 9,900GWe*hr(Gigawatt-hours electrical) through fission of Uranium-233 and daughters. Such an achievement would change the world and could be the "silver bullet" for the Energy Crises. The history of the LFTR goes way back to the post-WW2 nuclear era and the birth of the Atomic Energy Commission.

From 1950 until 1976, Oak Ridge National Laboratory researched designs incorporating liquid flouride salts as a means of powering a nuclear powered aircraft. "In 1956, the objective shifted to civilian nuclear power, and reactor concepts were developed using a circulating UF4- ThF4 fuel, graphite moderator, and Hastelloy N pressure boundary. The program culminated in the successful operation of the Molten Salt Reactor Experiment (MSRE) in 1965 to 1969." While promising, the Molten Salt Breeder proposal ultimately faltered in the political climate of the Cold War. Liquid Metal Cooled Fast Breeder Reactors (LMFBR) not only eased fears of uranium scarcity but also produced weapons grade plutonium.

The US did experiment with the Thorium Fuel Cycle in a number of ventures including Shippingport from 1977 to 1982. Originally designed in 1957 by Dr. Alvin Radkowsky of Navy Propulsion (during the tenure of Admiral Hyman Rickover) Shippingport was devoted to peacetime nuclear nonproliferation. A faithful advocate of thorium energy, Dr. Radkowsky's legacy continues through Lightbridge's "thorium-based seed and blanket fuel with significant back-end advantages and enhanced proliferation resistance of used fuel." The five year experiment at Shippingport hinted at the potential of the Thorium Fuel cycle as "the core contained approximately 1.3% more fissile materialafter producing heat for five years than it did before initial operation." On the downside, this experiment also suggests the necessity of patience for a thorium fuel cycle that "can only breed thorium into about 109% of the uranium-233 fuel it consumes. This means that obtaining enough uranium-233 for a new reactor can take eight years or more." Likewise, evidence "indicates an [LFTR] fissile material loss of 0.1 percent or less per pass through the processing plant." Such issues require a keen eye and loads of R&D funding to work out in practice.
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The miniFuji MSR designed in 2007

One of the greatest single advantages of a LFTR would come with meltdown safety. In the wake of Chernobyl, resurgent interest grew throughout the world to find safe alternatives for nuclear reactors. Recently, the Fukushima Daiichi Nuclear Disaster has made reactor safety a clear priority. Many people are excited about the potential benefits thorium has because in a Liquid-Fluoride Thorium Reactor (LFTR), the chemicals used are much more stable and therefore safer than a typical nuclear power plant. Also, nuclear waste may be a thing of the past as LFTR's could arguably breed fissile fuel with efficient burns and less waste. Unlike PWRs that use enriched uranium, LFTRs could contain the most dangerous actinides within the fuel loop. Many advantages are inherent to LFTRs such as there is no pressure inside the reactor which removes the concern of explosions. Also, waste removal from the reactor can be done through chemical processing of the molten salts which could also lead to the capture of valuable rare earths elements such as xenon, molybdenum, and neodymium. Moreover, LFTRs could provide nuclear fission power without encouraging nuclear proliferation.

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LFTRs Would Not Directly Produce Carbon Dioxide

With the amount of fossil fuels diminishing more and more every year, the need for a new way to generate electricity is evident. Equally as important to finding a new way to create electricity is doing it in a way that has the smallest impact on the earth. Nuclear power has the potential to be not only a very clean source for electricity but also a relatively safer option. Some of the issues that exist with the typical nuclear power plant are that the reactors are under a lot of pressure which requires very stringent construction of reinforced concrete pressure vessels. Similarly, Nuclear Waste from PWRs can have half-lives of 24,000 years (Pu239)and also includes transuranics as "fission products." Liquid-Fluoride Thorium Reactors run even cleaner than the typical nuclear power plant and does so in a much more stable way. Since a LFTR burns at a slower ratio, the fuel is thoroughly consumed. Accordingly, 1 Ton of Thorium in a LFTR = 200 Tons of Enriched Uranium in a PWR = 3,500,000 Tons of Coal. Using the conversion factor 2.93 kgCO2/kgCoal a LFTR could potentially remove 10,255,000 Tons of CO2 PER Ton of Thorium from the atmosphere.


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The LFTR design within the context of the Gen IV MSR

1. The molten fuel salt in a LFTR would be of the
composition 7LiF + BeF2 + ThF4 + UF4 for a
self sustaining Th232–U233 fuel cycle at thermal breed temperature 700°C, 1292°F. The Coolant Salt consists of NaBr4 + NaF. Since the salts are stable, the reactor structure remains sound.
2. In a two-fluid LFTR approach, the graphite moderator plumbing is bombarded with neutrons causing stress and warp and potential leaks. In a single-fluid design graphite moderators also stress allowing Kr and Xe to penetrate which throws off the neutron balance of the cycle. Replacement of graphite must occur in as little as 4 years. Simpler single fluids like David LeBlanc's DMSR make gains on the graphite issue, but single-fluid LFTRs make Chemical Reprocessing particularly challenging.
3. LFTRs are virtually proliferation proof, and anyone trying to remove nuclear bomb material would be bombarded by gamma rays from decay of Uranium-233 daughters Thallium-208 (2.6 MeV) and Bismuth-212 (0.4 to 2.1 MeV)! Also, if fissile fuel is removed, the loss in breed ratio would halt reactions.
4. A freeze plug melts instead of a meltdown.
5. Chemical Processing allows for the harvest of valuable rare earths such as xenon and neodymium. Also excess heat may be used for desalination or hydrogen separation.

Fertile Thorium-233 Must Decay to Fissile Uranium-233 in a Viable Thorium Fuel Cycle
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In a single fluid LFTR, Pa-233 must be balanced through processing in order to maintain proper neutron flux for fissile U-233




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Yucca Mountain Nuclear Waste Repository, NV
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Paduca, KY

LFTRs & Nuclear WasteLFTRs would produce 10,000 times less nuclear waste than an PWR. Compared with Uranium mining operations, thorium extraction would result in 4,000 times less mining waste. Thorough burn ratios in the thorium fuel chain would be the greatest contributors to waste reduction in LFTRs. After processing "the majority of the waste products (83%) are safe within 10 years, and the remaining waste products (17%) need to be stored in geological isolation for only about 300 years (compared to 10,000 years or more for [PWR] waste)." Finally, hopes persist that LFTRs could be used to burn waste from other PWRs. Kirk Sorensen believes that "nearly the entiretyof the United States' nuclear waste stockpile" could be converted "into the standard waste products of an LFTR, avoiding the need for long-term storage of nuclear waste." Such projections rely on keeping harmful transuranics within the fuel loop, which places large amounts of faith in the theoretical functions of the Chemical Processing Plant. As of April 2011, the United States does not have a "long term storage site for high level radioactive waste" after Yucca Mountain was closed due to congressional Federal Budget Cuts. Stuck in a dilemma, the Department of Energy's "failure to perform to contractual requirements will cost the taxpayer $11 billion by 2020."


Why India Pursues a Different Direction with Thorium
While natural deposits of uranium are limited, thorium ore is prevalent in the monazite sand beaches of the Indian coast. For this reason, India favored the use of thorium cycles early in their nuclear history and planned ahead to make that decision viable.

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The Father of Indian Atomic Energy

In 1957, Homi Jehangir Bhabha envisioned a thorium/plutonium future stating, “it is necessary for us to start producing this fuel now by converting natural uranium into plutonium, and thorium into uranium-233 in atomic reactors. If we are therefore, not to lose further ground in the modern world, it is necessary for us to set up some atomic power stations within the coming five years, which will produce plutonium for our future power reactors, in addition to producing electricity now.”
At this same time, India's CIRUS Heavy Water Reactor was being constructed and fitted. Canada designed the reactor and the US supplied the heavy water deuterium moderator for the venture. All three countries had formally agreed that India would use the reactor for peaceful purposes. Such trust by Canada and the US was clearly short-sighted in light of Bhabha's views. Shortly after criticality in 1960, Indian physicists added a plutonium separation plant to CIRUS effectively giving India weapons grade fuel by 1964. This decision to proliferate led the international community to officially limit uranium trade to India for decades, which hampered Indian development of civil nuclear energy until 2009.
Following through on the thorium vision has continued to be a priority for India. Although uranium deposits in India have been discovered recently thorium could fuel India's burgeoning electricity needs indefinitely.
Building on experience with Pressurized Heavy-Water Reactors (PHWR), India's approach to achieve Bhabha's thorium/plutonium vision is three-pronged:
  • PHWR fueled by natural uranium to produce plutonium.
  • Fast breeder reactors (FBRs) using plutonium-based fuel to breed U-233 from thorium will be blanketed by uranium as well as thorium, so that further plutonium (particularly Pu-239) is produced as well as the U-233.
  • Advanced Heavy Water Reactors burn the U-233 and Pu-239 with thorium, getting about 75% of their power from thorium. The used fuel will then be reprocessed to recover fissile materials for recycling.
Presently, India has incorporated thorium dioxide (ThO2) pellets for neutron flux flattening during initial start-ups of cores. India's experimental Fast Breeder Test Reactor incorporates a ThO2 blanket. While thorium remains an integral part of India's future, most of this momentum will be targeted away from Molten Salt Reactors (MSR).


Conclusion
The LFTR promises a lot, but we believe that it will be hard to deliver on these wishful promises. Many years of research are required to drive this program forward in order to answer these questions. While LFTRs could arguably be cheaper to build in the long-run, the grass roots research to develop them safely within the context of the international regulatory climate will require a massive investment by governments. For this reason, China's move toward unlocking the potential of TFMSR is an exciting thought. We are eager to see whether the Chemical Processing will be all that it is cracked up to be. Also, the dissolution of the graphite moderator seems to be a precursor of problems with the design that need improvement.
TerraPower research into Travelling Wave Reactors (TWR) is equally interesting and viable in our opinion. The TWR represents a variation of a Sodium Cooled Fast Breeder Reactor but the Fuel would be Depleted Uranium. What a great idea! Basically, the goal is to create a reactor that behaves like an underground firelog, slowly and thoroughly burning up the recycled uranium fuel for a period of 40 years. In this case, timing is everything. In an interesting twist, the uranium waste in this reaction could be burned up in a LFTR further reducing nuclear waste. At this point in the game, free flow of ideas in a rational manner is accepted by any and all who want to fix the Energy Crises.


Thorium and LFTR Propaganda
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