thorium fuel cycle

thorium fuel cycle. The thorium fuel cycle is a potential nuclear fuel cycle that uses the fertile isotope thorium-232 to breed the fissile material uranium-233. Unlike the dominant uranium fuel cycle, which relies on uranium-235 and bred plutonium-239, this cycle offers the possibility of enhanced fuel utilization and reduced long-lived actinide waste. Research into the cycle has been pursued in several countries, including India, the United States, and Germany, often in conjunction with advanced reactor designs like the molten salt reactor.

Overview

The fundamental process involves irradiating thorium-232 in a nuclear reactor, where it captures a neutron to become thorium-233. This isotope undergoes beta decay to protactinium-233, which further decays to fissile uranium-233. This newly created fuel can then sustain a nuclear chain reaction. The cycle can be implemented in various reactor types, including thermal reactors and fast neutron reactors, though it is particularly suited to designs with a high thermal neutron economy. Key facilities for studying aspects of the cycle have included the Oak Ridge National Laboratory and the Kurchatov Institute.

Fuel and reactor types

Thorium-based fuels can be utilized in several reactor architectures. Solid fuel forms include thorium dioxide mixed with plutonium dioxide or uranium-233 dioxide, as tested in the Light Water Breeder Reactor at the Shippingport Atomic Power Station. The Advanced Heavy Water Reactor design, developed by the Bhabha Atomic Research Centre, is a prominent Indian project aimed at utilizing thorium in a heavy water moderated system. Alternatively, fluid fuel designs, exemplified by the Molten-Salt Reactor Experiment at Oak Ridge National Laboratory, dissolve thorium and fissile material in a fluoride salt, allowing for continuous online reprocessing and fission product removal.

Advantages and challenges

Proponents highlight several potential benefits, including the greater natural abundance of thorium compared to uranium, superior material properties of thorium dioxide, and reduced production of long-lived transuranic waste like plutonium. The cycle also offers inherent proliferation resistance due to the high gamma radioactivity of uranium-232 that is co-produced with uranium-233. Significant technical challenges remain, however, such as the handling of radioactive protactinium-233 during fuel reprocessing, the need for extensive neutron irradiation to breed sufficient fuel, and the current lack of a commercial uranium-233 fuel infrastructure. Organizations like the International Atomic Energy Agency continue to assess these factors.

History and development

Early investigation began during the Manhattan Project, with research by Glenn T. Seaborg and others. The Aircraft Reactor Experiment in 1954 was an early foray into molten salt systems. Major development occurred from the 1960s to 1970s, notably with the Molten-Salt Reactor Experiment and the Light Water Breeder Reactor. The Thorium High-Temperature Reactor in Germany also provided data. While interest waned after the 1970s due to the prevalence of uranium and the closure of programs like the Clinch River Breeder Reactor Project, recent decades have seen renewed research in countries like India, China, and Norway, often through collaborations with the European Organization for Nuclear Research or the Department of Energy.

Comparison with uranium fuel cycle

The traditional uranium fuel cycle is established globally, with fuel fabrication, reactor operation, and reprocessing centered on isotopes like uranium-235 and plutonium-239, as seen in facilities such as the La Hague site and the Mayak Production Association. In contrast, the thorium cycle requires initial fissile material from the uranium cycle, such as plutonium or highly enriched uranium, to start the breeding process. While the uranium cycle produces significant quantities of plutonium-239, the thorium cycle generates less long-lived minor actinide waste. The energy yield from thorium is potentially higher, but the technological maturity and industrial scale of the uranium fuel cycle, supported by entities like the World Nuclear Association, remain far greater.

Category:Nuclear technology Category:Nuclear fuel cycle