Summer II 2012: Group 4: Thorium Reactors

Abstract

Nuclear energy has been shown to be a powerful and efficient energy source while maintaining the health of the environment. Previously, uranium was the primary source of nuclear energy. Using uranium as a leading energy source produces nuclear waste, and can also use excess energy on unnecessary steps. To overcome these limitations thorium has recently been explored as a bright and promising alternative to uranium. This popular and capable element reduces nuclear waste and produces more tuned energy with fewer steps. This energy alternative source has the potential to release us of our fossil fuel dependence while promoting a healthy living environment.


Background

Nuclear power has been under intense theoretical and experimental investigation since the 1950’s. [7] Its use as an energy source has proven to be very attractive, as it is extremely high yielding, has a low environmental impact, and can provide energy for remote areas of the world. [7] Today, more than 15% of the world’s electricity comes from nuclear power plants, and over 150 naval vessels are nuclear-powered. [8] Even a few vehicles in space rely on nuclear energy. [8] However, an energy source this powerful inevitably comes with its risks.

Due to major nuclear power plant accidents in the late 70’s and 80’s, the public soon became afraid of nuclear technology, and plants were quickly pulled off the power grid. [7] It was several years before concerns regarding global warming and energy costs started to arise, and it was only then that people decided that it was time to look back into nuclear technology as an energy source. [7] Nuclear power has been revitalized and, consequently, so has the nuclear debate.

The Nuclear Debate

The reawakening of the nuclear debate is a result of the increase in global energy demands, global warming, and new technologies introduced to nuclear energy production. We want to find out whether or not nuclear power has the ability to reduce the cost of energy and greenhouse gas emissions. Also, does new technology in the field reduce safety concerns? [9]

Typical questions asked in the nuclear debate include:[9]

  • Is nuclear power helpful in reducing greenhouse gas emissions?
  • Can nuclear power become a serious energy replacement of coal electric power?
  • Does any part of the nuclear energy production process contribute to global warming?
  • What are the current concerns with nuclear waste?
  • How long can we expect nuclear fuel supplies to last?
  • Do nuclear plants pose a risk of "melt-downs", or have modern designs eliminated this risk?
  • Are there any radiation risks to workers and/or to local communities nearby nuclear plants?
  • What about the threat of terrorist attacks on nuclear plants?
  • What weapons proliferation risks surround nuclear energy?

Today, we find that new questions have been added, specifically to the debate concerning thorium based nuclear energy.
Thorium reactors have been around since the 1960’s but were never used as a main stream energy source.[10] However, we find a lot more modern nuclear energy advocates pushing for this technology as a safer, cleaner, and more efficient source of power, especially over the current fuel choice, uranium.[11]

Notable and Famous Disasters

What most people find most intimidating about nuclear power is its risks of malfunction or potential accidents. Radiation is sometimes released into the environment and causes significant damage to surrounding communities. There have been about 33 notable nuclear power plant accidents since 1952; about 11 of which were major accidents and 2 which are famous within the nuclear power debate.

Fukushima disaster

Severe damage was done to Japan and surrounding areas on March 11, 2011, after the Great East Japan Earthquake hit. The region was inflicted with further damage upon the subsequent tsunami strike. All of the nuclear reactors operating within the area responded accordingly and were immediately shut down by automated systems at the first signs of threat. The safety systems in place all worked without a hitch. It wasn’t until the 15 meter tsunami hit that everything started going wrong.[35]

Three cores largely melted within three days of the natural disaster. The accident was rated a 7 on the INES scale, the worst accident possible. It took three weeks to stabilize the reactors and it wasn’t until mid-December that the reactor reached official cold shutdown status. Even so, there have been no deaths or cases of radiation sickness from the accident.[35]

Chernobyl disaster

The April 1986 accident at the Chernobyl nuclear power plant in Ukraine was due to a defective Soviet nuclear reactor design and serious mistakes made by the plant operators. As well, the Cold War and a lack of safety culture played into the causes of the accident.[36]

On the 25 of April, the operators were setting up for a test, to see how long the turbines could continue producing electricity if the system had a full shutdown. To do this, they decided to turn off all emergency systems. As they inserted the control rods to shutdown, due to design flaws, there was a surge of energy. With no emergency system, and operators not understanding what was going on, there was a spike in pressure and explosion. There was a 5% release of radioactive core into the atmosphere. Two plant workers died the night of the accident and a further 28 people within a few weeks due to radiation poisoning. Today the surrounding areas are said to have little public health impact, and resettlement is ongoing.[36]


Uranium Reactors

A.Uranium

Uranium is the most important fissile isotopes in current world. In nature, uranium is found as uranium-238, uranium-235 and a very small amount of uranium-234. Many contemporary uses of uranium exploit its unique nuclear properties. Uranium-235 has the distinction of being the only naturally occurring fissile isotope. Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor[37]

Present nuclear reactors generally use uranium as nuclear fuel. Usually pellets of uranium oxide (UO2) are arranged in tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core. [38] There are two main types of nuclear reactors, the Thermal reactors, which depend on U-235 and Fast neutron reactors, which use mainly U-238. For Thermal reactors, this type having been used most widely, its power is from the fission of U-235. After U-235 absorbs a neutron, it splits into many lighter nuclei, releasing kinetic energy, gamma radiation and free neutrons. Those neutrons continue to be absorbed by other U-235 and a nuclear chain reaction occurs[39].

B.Safety Concerns

Uranium is an excellent energy source. Besides it is a kind of clean energy, not producing any CO2 or smokes, Uranium also has an amazing efficiency. A kilogram of uranium-235 (U-235) converted via nuclear processes releases approximately three million times more energy than a kilogram of coal burned conventionally. However, Uranium still has some serious danger.
Plutonium
First danger is from Plutonium, the product of the fission of Uranium. Neutrons from the fission of uranium-235 are captured by uranium-238 nuclei to form uranium-239; a beta decay converts a neutron into a proton to form Np-239 (half-life 2.36 days) and another beta decay forms plutonium-239. [40] Plutonium is a very terrible element because of its some features. The half life of U-239 is 24,000 years! This means the waste of fission of Uranium will keep radioactivity, becoming a horrible threat to human beings, for a very long time. Moreover, the toxicity of Plutonium is very big. According to a 1995 report from the Lawrence Livermore National Laboratory, you would have to ingest about .5 grams of plutonium to die immediately, compared to about .1 grams of cyanide[41] In the perspective of Physiology, Plutonium emits alpha radiation, a highly ionizing form of radiation, rather than beta or gamma radiation. When alpha-emitters get inside cells, on the other hand, they are extremely hazardous. Alpha rays sent out from within cells cause somewhere between 10 and 1,000 times more chromosomal damage than beta or gamma rays, greatly increasing the risk of cancer, especially lung cancer, liver cancer and bone sarcoma[42].
Other defects
Except Plutonium, the current nuclear reactor for Uranium reaction is also very risk. Actually, the environment where Uranium reaction occurs is very harsh. The temperature and pressure are both high. Therefore, some measurements should be taken to ensure the reactor is under control. However, those special measurements always not perfect.
Right now, the method of controlling the reaction of Uranium is mainly by varying absorbers, which are commonly in the form of movable elements—control rods—or sometimes by changing the concentration of the absorber in a reactor coolant[43].However, the control rods are not safe enough. For many years, the Chernobyl disaster stood as a prime worst-case example of nuclear malfunction. On 26 April 1986 in Ukraine, The Chernobyl disaster happens and the main reason is related to the control rods. Another weakness of Uranium reactor is its cooling system. To remain the reactor working in a stable temperature requires an efficient cooling system. Current design also has many serious defects. On Friday, March 11, 2011, Japan suffered the largest earthquake in modern history. It destroyed Fukushima-Daiichi nuclear facility’s backup diesel generators that powered the water coolant pumps which circulate water through the reactor to remove decay heat. Furthermore, the reactor radiation began to split the water into oxygen and volatile hydrogen. The resulting hydrogen explosions breached the reactor building's steel containment panels [43].In sum, the harsh working environment increases the risk of nuclear facility and make nuclear reactor brittle.


Thorium Reactors

About Thorium:

Thorium is a radioactive element that might change the way we look at nuclear energy. In nature, this material is always found as Thorium 232 [3]. It is not a fissile material, however, which means that it is not susceptible to the process of fission, which is required in nuclear reactions to produce energy. Thorium's half-life is 14 billion years, which means that this material is not highly radioactive. Shorter half-lives mean more radiation [3]. 

The Thorium Nuclear Reaction (Liquid Fluoride Thorium Reactor):

When Thorium is hit with a neutron, it becomes Uranium 233, which is a fissile material that is incredibly efficient and useful in a nuclear reaction [2]. The Uranium 233 then waits until another neutron hits it. Once this happens, the element will undergo fission, which produces energy (in the form of heat), and 2 to 3 more neutrons. The heat is then transferred through a system of heat exchanging to power turbines to produce electricity. Small amounts of wastes are generated in this process[4].

Safety:

Proliferation Resistance: One of the most notable advantages to a Thorium reactor is that weapons-grade material becomes very inaccessible. In order to retrieve the fissionable material (Uranium 233) from the reactor, one would risk heavy exposure to the wastes generated from the nuclear reactions. One of the notable wastes is Uranium 232 that eventually decays into Thallium, which in itself is highly radioactive and death is highly probable [4]. Also, this high gamma radiation can be highly damaging to electronics and  other materials of a nuclear weapon – therefore, no country has ever attempted to weaponize with this material [5]. 

Waste:

Another advantage to Thorium is that the waste remains radioactive for a much shorter time than wastes generated from Uranium <INSERT CHART (Adapted from Sylvan David et al, Revisiting the thorium-uranium nuclear fuel cycle, Europhysics news, 38(2), p 25.)>. As you can see, the life-span of radioactive materials is reduced from hundreds of thousands of years to mere hundreds of years. 

To produce one gigawatt of electricity, it takes 800kg of thorium. 83% of the fission byproducts are safe in ten years, 17% are safe within 350 years. No Uranium or Plutonium are left over as a waste [6]. 

Chain Reaction:

Because Thorium is not a fissile material, it cannot, by itself, sustain a nuclear reaction. During the nuclear reaction process, only a few neutrons are released, which are not enough to keep the entire reaction going by itself. This requires outside sources to maintain the reaction. As a result, whenever the nuclear reaction is supposed to stop, all that must happen is the neutron source be severed [1]. 

No Meltdowns:

Most reactor designs involve a plug at the bottom of the main reactor chamber. The plug is essentially frozen salts, and this drain leads to a cold containment tank. Should the reactor get too hot, the plug melts and everything in the reactor drains safely away [4]. These Thorium reactor designs also include the ability for the reactor to cool down without water and electricity, so given a catastrophic event of severe weather, odds of anything going wrong are very slim [6]. 

No Explosions:

One of the more common things that come to mind in a nuclear reactor meltdown is an explosion. In Uranium reactors that we have today, the reactors get incredibly hot. The way we cool these reactors is to pump cool water through tubes around the core of the reactor and the hot water out. The problem is that the water gets so hot, it's hard to keep it in liquid form. In order to keep it in liquid form, the pressure in the tubes is increased. By increasing the pressure, the evaporating point of the water is increased so it can remain in liquid form at temperatures much greater than 212F. As a result, if anything goes wrong with the reactor, there is a high risk of an explosion from this superheated, pressurized water. [6]

Thorium reactors are not cooled by pressurized water. Instead, the reactors can be cooled by liquid salts that can remain at atmospheric pressure, eliminating the possibility of an explosion. [6]

Efficiency:

Energy Production:

Because nearly all of the thorium is used up in the energy reaction (compared to a mere 0.7% of Uranium Light-Water Reactors), we are capable of achieving an energy efficiency nearly 300 times more efficient than a Uranium reactor. The designs of the thorium reactor also allow for much higher temperatures which leads to the possibility of converting 50% of heat energy to electricity (compared to 33% of the Uranium reactors). Experts estimate that the cost of electricity from a Thorium reactor to be 25-50% less than from a Uranium reactor. [5]

Reactor Costs:

Liquid Fluoride Thorium Reactors lack the necessity for pressurized cooling structures and blast chambers. With less complicated systems comes less cost with regards to inspecting, repairing, and otherwise maintaining these complex systems [5][6]. Likewise the overall size of these reactor structures goes down dramatically [6]. 

Fuel Costs:

Thorium preparation does not require isotopic separation, which is an expensive and complicated process. This is the process that Uranium undergoes in order to gain Enriched Uranium from natural Uranium. [1]

Existing World Thorium Reserves

The use of thorium is occurring across many different countries worldwide. The World Thorium Reserves [30]
were calculated in the years 1996-2010 based on the amount of tonnes the countries had access to.

The amount of which each country holds of the total World Thorium Reserves is calculated by two types of factors. The first being the US Geological Survey (USGS) and the second being accumulated by the Organization for Economic Co-Operation and Development (OECD) and the International Atomic Energy Agency (IAEA).

The OECD [31] is made up of the involvement of 34 countries to try and create economic progress.

The USGS predicts that Australia and India are two countries that have sufficient thorium reserves. It has been noted that each country has about 25% of the world’s existing thorium reserves. However, both factor types differ in some of the countries predicted calculations.

Thorium has been found in many countries. India and Turkey have been estimated to hold the most of the World’s Thorium Resources [32]. The United States holds about 915,000 tons of thorium reserves. States from Idaho and Montana [33] have been reported to been home bases for these reserves. Other countries that have reserves include: Australia, Brazil, Canada, India, Malaysia, Norway, Turkey, and South Africa.

The Nuclear Energy Agency (NEA) [34] has predicted that the World’s supply of Thorium Reserves have the potential to last for several hundred years.


Existing Thorium Projects

Thorium is becoming the more popular choice very quickly in surrounding countries. This rare-earth mineral is available about four times [12] the amount of its competitor uranium.

The first profitable power station powered mostly by thorium was invented in Germany. The creation was named the THTR-300 [13]. This High Temperature Reactor has only been activated by Germany starting in 1985. The effectiveness of this project [14] has been reported to be about 40.5%.

It has been recorded that India has one of the world’s biggest thorium reserves [14]. It has been estimated that they hold about 200 tonnes. They have been running their own nuclear power projects for the last five decades [15]. India has a major interest in using thorium because they have a large natural supply [16] of the rare-earth mineral [17].

In 1958, India declared that they were taking on a three-stage plan [15] to put their thorium reserves to full use. They designed pressurized heavy-water reactors [18] which would generate pure uranium [18]. The byproducts of these reactors would produce plutonium [19]. The second stage of India’s plan involves using the produced plutonium to then create future fuel for the reactors. Finally, the third part included Advanced Heavy Water Reactors [20] which would create byproducts, thorium and uranium-233 [21]. Other countries such as the United States and Russia have reviewed this three stage plan but have decided that it is not the best way to make electricity. It has been reported that currently twelve reactors are in full operation. In 2011, India announced that they began construction on their 300 MWe AHWR [22]. India is able to use 4.7 tonnes to generate fuel per year. Since this amount is relatively small in comparison; India will be able to have this production [23] for voluminous years to come.

One drawback of the AHWR is that the reactor needs to be started by another source. Their solution to this problem is to use low-enriched uranium [24] (LEU). However, this design is only in its beginning stages. Although, in the future India plans to have the AHWR be a successful, cheaper alternative fuel resource.

In the years of 1980, the United States decided to develop its own uranium plutonium cycle [17]. The United States new project is the Liquid Fluoride Thorium Reactor [25] (LFTR). The LFTR is a type of thorium molten salt reactor (TMSR) [26]. Molted salt [27] has been noted to be more of a user friendly form of liquid fuel.

The United States Department of Energy has been working with China [28]. They have been formulating a new plan together in order to create a successful thorium reactor project. The USDE has customized a plan known as Title X [29] which is used to pay back the rare-earth minerals processing sites.


Conclusion

Research proves that Thorium is an upcoming better alternative to nuclear energy. This rare-earth mineral serves many advantages to the leading mineral uranium. Nuclear energy is becoming an important choice today worldwide. Additionally, thorium has been proven by research to be a safer and a more environmental friendly energy source. When thorium is used as a nuclear energy source; it is more efficient than the leading brand as well as more cost effective. Projects for this new nuclear energy source currently exist in many countries; due to the fact, that these countries have their own source of this rare-earth mineral available to them.


See also


References

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