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Conference Article: Behaviour of particles in a commercial advanced gas-cooled reactor

Garland, J.A.; Wells, A.C.; Hedgecock, J.B. (AERE Harwell (United Kingdom))

Abstract

Certain hypothetical fault conditions cause fission products to escape from a fraction of the fuel to an intact coolant circuit. A significant fraction of the activity, including iodine isotopes, is expected to attach to small particles suspended in the gas coolant, and the fate of the particles may influence the fraction of the activity available to escape to the environment with the small amount of gas that leaks continuously from the coolant circuit. A series of experiments has provided an understanding of the behaviour of such particles. Tracer particles of 0.6, 2, 5 and 17 mum diameter, labelled with 59Fe, were dispersed as aerosols in the reactor coolant, and the subsequent variation of concentration was observed by measurement of a sequence of filter samples of the coolant gas. The changes in concentration were influenced by mixing processes, but showed clearly that loss processes reduced the burden in the coolant by two or three orders of magnitude within 3 h. The concentration did not follow a simple exponential decrease. Small particles deposited more rapidly than the largest size studied. These observations imply that particles both impact onto, and also bounce and resuspend from, the internal surfaces of the coolant circuit. Although the physical mechanisms of the particle-surface interaction cannot be described in detail, the results clearly demonstrate a large benefit due to deposition reducing the amount of circulating activity. The quantity of particle-borne activity available for escape with leaking coolant during 24 h following a release from fuel is reduced by a factor ranging from several hundred to a few thousand.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
Specialists' meeting on fission product release and transport in gas-cooled reactors Berkeley (United Kingdom) 22-25 Oct 1985
International Atomic Energy Agency, International Working Group on Gas-Cooled Reactors, Vienna (Austria)
IWGGCR--13, pp:250-261