Circumstances of Creation
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The original Liquid-Fueled Thorium Reactor (LFTR) was designed in 1965 during the height of the cold war, and while nuclear technology was still fairly novel. Called the Molten Salt Reactor Experiment (MSRE) it was headed in development by Alvin Weinberg, the Director of the Oak Ridge National Laboratory from 1955 to 1973 (Zucker, n.d.). Whereas traditional nuclear reactors use small Uranium-235 (U-235) pellets of Uranium Oxide, Weinberg’s Molten Salt Reactor uses Thorium-232 dissolved into a solution of Fluoride. Thorium is about four times as abundant as Uranium, and is most often found in rare earth mineral mines where it is easily separated from other elements. In contrast, U-235 makes up less than 1% of naturally occurring Uranium, so it must first go through a purification cycle before it is fit for reactor use. Once the U-235 has been obtained, there are other problems to be overcome, mainly in the products of this fission reaction. Uranium fission produces some very toxic products which “include long-lived transuranic materials (elements above uranium in the periodic table), such as plutonium, americium, neptunium and curium” (Moir and Hargraves, 2010, 305-306). These elements give off extreme amounts of radiation and have half-lives of many centuries, meaning they must be kept in complete isolation. Back when our nuclear infrastructure was beginning to take shape and the main fuel source was still in question, using U-235 as our nuclear fuel made the most sense because we were most familiar with it, but more likely because one of the aforementioned by products, Plutonium, was critical to our development of thermonuclear warheads. Plutonium is extremely rare within the crust of the Earth, and so this “bonus” was very attractive to our government, who were looking for any possible advantage over the Soviets in the Cold War.
Other Advantages of the LFTR
Using U-235 fuel rods, only about 5% of the available energy in the Uranium is actually used up, as products which endanger the reactor begin to build up. One of these is a form of Xenon gas, which becomes locked in the solid structure of the fuel pellets and could potentially cause a catastrophic meltdown if left unchecked. Using a liquid fuel allows the gas to form bubbles which are dispersed as the fuel is cycled out of the main sequence. This would allow a Thorium reactor to utilize all stored energy of the original fuel, as any harmful build-ups are processed out as the U-233 is captured (Moir & Hargraves, 2010, 308).