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Conference Article: Coolant chemistry of the advanced carbon dioxide cooled reactor

Faircloth, R.L.; Norwood, K.S.; Prior, H.A. (UKAEA Atomic Energy Research Establishment, Harwell)

Abstract

The large scale production of electricity by uranium fission has been achieved in the United Kingdom exclusively by reactors which are gas cooled and moderated by graphite. In this way the use of uranium with close to the natural isotopic content was possible. Once the choice of graphite as moderator had been made then the selection of a suitable gas to transport heat from the core to the steam generating equipment was limited and, in fact, only two have been identified as having suitable chemical and nuclear properties, namely helium and carbon dioxide. The first of these has the disadvantage of being expensive but has a high heat transfer capability and is fundamentally inert, its reactivity being controlled entirely by the level of impurities such as hydrogen and water. With the closure of the OECD Dragon High Temperature Reactor Project interest in helium cooling for nuclear plant has faded in the UK. The alternative coolant, carbon dioxide, which is cheap but chemically reactive is used in the first generation Magnox power stations and in the Commercial Advanced Gas Cooled Reactor (CAGR) design. In the more highly rated CAGR design the fuel consists of enriched uranium in the form of dioxide encased in stainless steel. The gas outlet temperature of the core is increased to around 6000C. The purpose of this paper is to provide an insight into the current thinking about the nature of the complex chemistry associated with the CAGR coolant and how this chemistry influences the rate of deposition onto the fuel pin surfaces and the rate of graphite moderator oxidation. The application of these ideas to the prediction of the behaviour of a CAGR core with particular reference to the calculation of coolant composition within the porous moderator structure at points remote from the surface, is outlined and the use of all this information to define a satisfactory range of coolant composition is also described.

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key words: carbon dioxide cooled reactors; chemical reactions; chemistry; coolants; corrosion; diagrams; graphite; carbon; gas cooled reactors
Reference:
Specialists meeting on coolant chemistry, plate-out and decontamination in gas-cooled reactors Juelich, Federal Republic of Germany 2-4 December 1980
International Atomic Energy Agency, Vienna (Austria)
IWGGCR--2, pp:125-131