Thorium

Thorium
Thorium is 3-4 times more abundant than Uranium, cannot sustain a nuclear chain reaction (and thus is incapable of exploding), is only mildly radioactive, can produce a significant amount of power (it can theoretically produce 200 times more power than uranium, per kilogram), produces little to no greenhouse emissions from energy production, produces short lived and difficult to weaponize nuclear waste, and because of these features and more would make an ideal fuel source. [1][2][3] Fissionable Thorium releases approximately the same amount of energy as Uranium per kilogram, but as nearly 100% of Thorium found in nature is fissionable (99.98% being Thorium 232) in comparison to only .7% of Uranium (U-235), and more usable thorium can be extracted from the source material than from Uranium, Thorium possesses approximately 140-200 times the power of uranium for each kilogram of the fuel found in nature. As Thorium is approximately 3-4 times more abundant than Uranium, it provides the potential for energy for thousands of years, securing sufficient power production until fusion energy can be perfected. The primary issue of Thorium rests in creating reactors which can reliably produce the energy, which while a small handful exist, is a less developed technology than Uranium-based reactors. Particularly, Thorium requires an external high energy neutron source, such as from an accelerator to accelerate the particles, other nuclear reactions including uranium, plutonium or fusion, or a neutron reflector, making it's inherent safety and stability it's key detriment for easy power generation. As it is difficult for Thorium atoms to be split on their own, it requires constant external output to produce power, which while guaranteeing high stability, makes it difficult to use as a power source.

Thorium is an abundant element, roughly 3 times more abundant than tin and uranium, and approximately as abundant as lead.[1][2][3][4] Found in nature in almost 100%  pure concentrations of Thorium-232, or the stable fissionable type of Thorium, there is a higher quantity of usable Thorium available, and no required breeding process, allowing for 140-200 times more usable Thorium than Uranium. Thorium is present in ordinary soil, on average, at about 6 parts per million, or about 1 in 166,000, making it's presence on earth widespread. [1][2][3] Thorium is only mildly radioactive, so it doesn't present a significant radiological threat despite it's naturally wide spread abundance. There is an estimated 1.6-2.8 million tonnes of Thorium in the world, with approximately 400-440,000 in the United States alone. [1] This is in theory sufficient to power the world's energy needs, at it's current rate of consumption (which is subject to change), for several thousand years, presuming most of the energy from the Thorium could be extracted.

The key component to Thorium's safety, and difficulty for use, is in low reactivity and high stability. With a half-life of approximately 14 billion years, or roughly the life of the universe, and difficulty in creating a self sustaining reaction, it cannot be used in a weapon or go critical accidentally, however given it's stability it is difficult to use for power generation, as it is difficult to extract power from as it will not start a self sustainable chain reaction. Thorium requires an external neutron source to be powered, as it is fertile, but not fissile.[1][2][3] It can be used as fuel, under the right conditions, but it does not support a self sustaining reaction (like uranium-235 or plutonium-239) and cannot be used in an atom bomb or similar weapon, or result in a catastrophic melt down. In order for Thorium to operate it must be continually fed high velocity, high energy neutrons from an outside source, to break down the bonds of the atom and subsequently cause fission, which is the splitting of the atom to produce energy. The fission of U-235 for example, a fuel source commonly used in atom bombs and light water reactors (common in the U.S.), releases 2-3 neutrons capable of causing fission, meaning that each U-235 atom concurrently releases 2-3 more neutrons, and each of those neutrons release 2-3 more until an exponentially accelerating chain reaction occurs. Unlike uranium or plutonium, Thorium does not release neutrons during fission, nor do the majority of it's by products (U-233), disallowing the fission of Thorium to initiate the fission of another Thorium atom.[1][2][3] Thorium is therefore functionally incapable of supporting a nuclear chain reaction, and so energy cannot be released exponentially in an uncontrolled manner, or go critical, and thus cause a melt down or be weaponized. With a subcritical reactor, the reaction will cease unless continually fed neutrons from an outside source.[1][2][3] This means that if the mechanism shuts down or fails, it will not be able to release energy, making the design inherently safe, but also difficult to maintain. The crux of current Thorium power generation is this key issue, which can be resolved potentially in a number of ways, of which no large scale power plants exist, with only small, experimental reactors being used.

In addition to this, Thorium is only mildly radioactive and thus generally safe to humans[1][2][3], as it produces alpha particles, which are incapable of getting through human skin.[1][2][3] With a half life of roughly 14.05 billion years, or over the estimated length of the life of the universe, thorium is unlikely to produce significant amounts of radiation or by products when compared to other comparable fission fuel sources such as uranium.[1][2][3][4] Thorium was used frequently, and still is used commonly in gas mantles or lanterns, giving the lanterns a distinctive appearance, and was also used in the production of crucibles and various kinds of clay. [1][2][3] Despite recent concerns of potential health risks, even in relatively high concentrations Thorium poses little if any major health risk unless inhaled or consumed in abundant quantities. As it has low biological toxicity in addition to it's low radiotoxicity, it would take extremely high concentrations to make Thorium dangerous. [1][2][3][4] However when powered Thorium metal is pyrophoric, which means it can spontaneously combust in mid-air, making it a fire hazard risk.



Potential Reactor Designs and Costs
There are many potential reactor designs for Thorium, ranging from plutonium initiated designs, to fusion initiated, to accelerator driven "sub-critical" designs, and heavy water reactors. Thorium offers promising features over uranium reactors, as it would be able to produce over 200 times the power of Uranium, per kilogram, has short lived weakly radioactive waste, and wouldn't require the proliferation of dangerous or hazardous materials such as P-239. In all systems, regardless, they have the potential to produce cheap, clean power for many hundreds to thousands of years. These systems do not require a breeding process like with uranium, nor expensive safety restrictions and protections due to their inherent safety. The cost of the fuel, reactor, power plant, are all that are required to determine the cost of Thorium, which removes much of the insurance and interest costs of uranium, which are also likely excessive for Uranium. With a higher degree of inherent safety and a greater abundance of fuel, Thorium offers the potential for cheaper power, in addition to a long term solution for global energy needs.

Since the energy levels of Thorium are comparable to Uranium, and the primary costs from uranium come from the breeding process and safety issues, it's conceivable Thorium could be substantially cheaper for the same power output. Uranium powers roughly 20.9% of the nation's energy[1][2][3], with approximately 104 reactors[1][2][3]. Annually, roughly 6,000 tonnes of uranium are consumed [1][2][3]; the U.S. peaked mining at roughly 16,000 tonnes in X year.[1][2] Uranium costs roughly 125 dollars per kilogram[1][2][3][4]; this means that for annual consumption, the fuel costs are only roughly 750 million to 2 billion dollars. Yet annually, from this uranium, the costs for uranium power were around 80 billion dollars. [1][2][3] The rest of the cost for uranium rests in processing, safety protocols, the breeding process, safe transportation, waste disposal, and various other issues.[1][2] Since much of this could be eliminated with Thorium, it is conceivable that Thorium could be significantly cheaper based on these features alone.

This means that Thorium is not only safe, clean, and abundant, but potentially an incredibly cheap power source as well, like Uranium. The primary issue is that Thorium depends on high energy neutrons in order to operate. In theory this can come from another fission process, such as with plutonium or uranium, however this will have the side effect of decreased safety and higher levels of radioactive waste, negating much of the advantage of Thorium, and be more difficult to produce. Hybrid fusion reactors hold a considerable amount of promise, as fusion produces very little waste but is not economically viable on it's own, producing less energy than is put in to it, and thorium being added to the fuel cycle could increase efficiency and total energy output than fusion alone. As modern fusion reactors waste most of the energy on the reactor walls, creating a modern fusion reactor with it's walls made out of Thorium may alleave this issue to some extent, capturing the stray neutrons and producing energy instead. However, fusion reactors also are an underdeveloped technology, hindering this process somewhat. Accelerator driven reactors hold a large amount of promise in that they simply accelerate particles to the velocity needed to cause sub-critical Thorium fission, however the spallation material makes the neutron bombardment inconsistent as particle accelerators can generally not accelerate neutrons, but only charged particles such as protons, making the proccess inefficient.





In Short

In short, Thorium, even with the most promising, and most ambitious accelerator driven designs, could reduce energy costs substantially, potentially 10's of  times that below current energy costs, which could help out the U.S. in a variety of ways. With it's short lived waste, no emissions, and potential for thousands of years worth of electricity, it is a suitable replacement for energy levels of the U.S. and potentially the rest of the world.