As coal is burned, thorium-232 (232Th) and uranium-238 (238U) are released as exhaust products in coal ash. What could be done with these isotopes if they were recovered? At least one scenario is readily apparent.

Because atoms of 232Th and 238U do not split, or "fission," when bombarded with slow (thermal) neutrons, they are referred to as "fertile," rather than fissionable, materials_materials that can be used to "breed" nuclear fuel by the addition of a neutron to each atomic nucleus. For example, when the nucleus of a thorium atom absorbs a neutron, it becomes 233Th, which decays in relatively short order to 233U, a nuclear fission fuel. Similarly, plutonium-239 (239Pu), an efficient fuel for both reactors and nuclear weapons, can be bred by the capture of neutrons from fissioning Uranium-235 (235U) in a blanket of 238U.

A potential source of the neutrons required to breed nuclear fuels from these isotopes is the fission of 235U--the reaction that powers nuclear power plants. The fission of each 235U nucleus releases 2 or 3 neutrons that either produce more fissions, breed new fuel through capture in fertile materials, or decay into a proton, an electron, and an anti-neutrino. In a "breeder" reactor environment 238U or 232Th can capture enough of these neutrons to breed more fissionable material than is consumed during fission of the original 235U fuel in the reactor.

Typical nuclear power plants rely on the heat produced from the splitting of 235U and heat from its "daughters," radioactive elements formed in the process. This heat converts the water circulating through the reactor to steam, which drives turbines for generating electricity. The same process could be fueled by the fission of 233U or 239Pu, isotopes that could be bred from the discarded leftovers of coal combustion.

At least 73 elements found in coal-fired plant emissions are distributed in millions of pounds of stack emissions each year. They include: aluminium, antimony, arsenic, barium, beryllium, boron, cadmium, calcium, chlorine, chromium, cobalt, copper, fluorine, iron, lead, magnesium, manganese, mercury, molybdenum, nickel, selenium, silver, sulfur, titanium, uranium, vanadium, and zinc.


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