Very High Temperature Gas Cooled Reactors

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In 2007, approximately 40% of the energy consumption in the U.S. was in the form of electrical energy. About 39% of the electrical energy generated is used in the commercial sector, 35% for residential sector, and 26% for industry. The energy for electrical production and comes from a variety of fuels including petroleum, coal, nuclear, natural gas, and renewables. If one looks at the overall energy generation picture, petroleum accounts for 39% of the energy consumed in the U.S. the majority of it being used for transportation. Natural gas generated about 23% of the energy consumed with natural gas being used in roughly equal amounts for industry, electric power generation and for the commercial and residential sector. Coal generated about 22% of the energy used in the U.S. with the majority of the coal consumed being used for electricity generation. Nuclear accounts for about 8% of the energy used with all of it being in the form of electricity. Renewables currently account for about 7% of the energy used in the U.S.

It is difficult to see how nuclear energy in its present form can be used in the industrial sector to replace carbon-based fuels since much of the energy is used in the form of process heat. Process heat applications typically require temperatures well in excess of those that can be achieved with the current generation of light water reactors. Because of physical limitations inherent in light water reactors, it is unlikely that current light water reactor technology can be used to replace fossil fuels in these applications. However, very high temperature gas cooled reactors have the potential to replace carbon based fuels in some applications as these reactors are thought capable of producing temperatures of 900°C and above, sufficient for many industrial processes. A gas cooled reactor, unlike a water-cooled reactor, uses helium as a coolant. Under high pressure the helium is circulated through the reactor core where it removes the heat generated by the fission process. The helium gas can then be used either directly as a source of heat or can be used to generate very high temperature steam that can then be used as a source of heat in an industrial process.

The core of a gas-cooled reactor, like that of a light water reactor, uses enriched uranium. Unlike a light water reactor the uranium is typically enriched to a higher value, typically from 10% to about 19%. Graphite is used extensively in gas-cooled reactors for structural material and also as a means of slowing the fission neutrons down to enhance the likelihood of inducing another fission.

A number of such reactors have operated successfully, including Peach Bottom One in the U.S., a 40 MWe reactor that began commercial operation in 1967 and operated until 1974, the Fort St. Vrain reactor also in the U.S., a 330 MWe reactor that began operation in 1976 and operated until 1989, and the German AVR reactor that operated successfully for over 20. China recently placed a 10 MWt prototype gas cooled reactor into operation and South Africa has embarked on the development of a commercial scale gas cooled reactor based on the German AVR.

Such technology has the potential to efficiently and economically generate hydrogen from water through thermochemical water splitting for use as a replacement for petroleum or for the liquefaction of coal. Such a process involves a set of chemical processes that use heat to decompose water into hydrogen and oxygen at efficiencies of up to 50%. Currently, China, South Africa, and France are actively pursuing the development of these reactors. Unfortunately, the U.S. program is fraught with uncertainty due to political considerations. It is likely that China, and possibly South Africa, will have gas-cooled reactors in operation on a large scale within the next 8-10 years. These will be used for both electricity generation and for process heat.

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