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Conference Article: Graphite core stability during 'care and maintenance' and 'safe storage'

Wickham, A.J.; Marsden, B.J. (AEA Technology plc, Warrington, Cheshire (United Kingdom)); Sellers, R.M. (Liabilities and Decommissioning Div., Magnox Electric plc, Berkeley Centre, Berkeley, Gloucestershire (United Kingdom)); Pilkington, N.J. (AEA Technology plc, Harwell, Didcot, Oxfordshire (United Kingdom))

Abstract

The current decommissioning strategy for the graphite-moderated reactors operated by Magnox Electric plc, Nuclear Electric Ltd and Scottish Nuclear Ltd is to delay dismantling and to initiate a monitored period of care and maintenance followed by a period of safe storage totaling up to 135 years. This philosophy has the considerable advantage of permitting the majority of radionuclides to decay, thereby minimising personnel dose during dismantling which itself will require far less complex remote-handling equipment. It also defers the disposal of the graphite and other components so that the provision of a deep land-based repository can be achieved. A comprehensive review of all relevant data on the chemical, physical and mechanical properties of the graphite and its potential reactions, including radioactivity transport, has been undertaken in order to demonstrate that there are no potential mechanisms which might lead to degradation of the core during the storage period. It is concluded that no significant experimental work is necessary to support the safe storage philosophy although, since the ingress of rainwater over long periods of time cannot be assumed incredible, a number of anomalies in chemical leaching rates may be worthy of re-examination. No other potential chemical reactions, such as the radiolytic formation of nitric acid leading to corrosion problems, are considered significant.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
Technical committee meeting on technologies for gas cooled reactor decommissioning, fuel storage and waste disposal. Juelich (Germany) 8-10 Sep 1997
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--1043, pp:225-232