The notion of a “meltdown” leading to reactor failure becomes irrelevant in a reactor designed around the use of liquid fuels. The fluid salt in the core is not pressurized, thus eliminating the fundamental driving force present in the core of legacy water-cooled reactors (like those at Fukushima-Daiichi). The properties of fluoride salts offer LFTR enhanced safety characteristics over existing reactor technologies. The fuel salt, blanket salt and clean coolant salt circuits are each maintained at near atmospheric pressure. The heat generated from nuclear fission in LFTR is transferred via heat exchangers to a clean coolant salt loop that exits the containment boundary and is then transferred to supercritical carbon dioxide, the working fluid of a gas turbine engine, to generate power. Once a LFTR is operational, thorium is the only input required to perpetuate the thorium-to-uranium fuel cycle. Uranium-233 is extracted from the blanket salts and is then fed back into the reactor core where fission of the uranium-233 produces high heat for power generation and more neutrons to convert thorium-232 into uranium-233, perpetuating the fuel production cycle. Thorium-232 in the blanket salt absorbs neutrons released by fission in the core and is ultimately converted into uranium-233.
Into this liquid salt are mixed salts of uranium for the core salt and of thorium for the blanket salt. Furthermore, the salts’ ionic bonds are unaffected by neutrons or radiation, making them a nearly ideal medium for sustaining a nuclear reaction. These salts have exceptional chemical stability, which gives them a remarkable heat storage capacity over a thousand-degree liquid range. Liquid-fluoride reactors use a chemically stable fuel form based on fluoride salts of lithium and beryllium. Several countries are researching the thorium fuel cycle for use in solid-fueled, water-cooled reactors. For example, LWRs can use thorium in solid fuel form to produce U233, however, they cannot provide the various advantages of the combination of the thorium cycle in liquid-fueled reactors that LFTR technology achieves. Use of thorium in a liquid fuel form is LFTR’s key differentiator from other efforts to employ thorium as a nuclear fuel. Liquid versus Solid Fueled Thorium Reactors LFTRs can be produced as modules in a factory and can be made to be air-cooled or water-cooled, land-based or submersible, fixed or mobile, offering more flexible siting, installation and deployment options and with much less visual intrusion. Waste products from a LFTR are predominantly fission products rather than actinides, and decay much more rapidly. LFTRs can consume the unused fissile material available in existing spent nuclear fuel waste and weapons stockpiles. The liquid fuel form allows fuel to be added and byproducts to be removed even while the reactor remains online. Thorium is abundant and inexpensive and LFTR’s liquid thorium fuel is easily produced, compared to costly, complex fabrication of solid fuel rods used in legacy water-cooled reactors. Use of thorium fuel in a LFTR generates orders-of-magnitude less mining waste and long-lived transuranic waste than existing light-water reactor (LWR) technology. LFTRs high temperatures (650 C) enable greater thermal-to-electric conversion efficiencies and use of more compact power conversion systems. In particular, ambient or low reactor operating pressures means no risk of high-pressure atmospheric releases and no need for massive containment structures that can withstand high pressure. LFTRs operate at near atmospheric pressure offering unmatched safety and greatly simplified reactor designs. LFTRs use liquid-fluoride salts as both a coolant and as a carrier for the thorium and thorium-derived fuels. Among possible reactor coolants (water, gas, metal and salt), only liquid salts offer the desirable combination of low pressure operation at high temperatures.
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