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The consequences of hypothetical post-closure criticality

Published online by Cambridge University Press:  05 July 2018

R. M. Mason*
Affiliation:
AMEC, Kimmeridge House, Dorset Green Technology Park, Dorchester, Dorset DT2 8ZB, UK
P. N. Smith
Affiliation:
AMEC, Kimmeridge House, Dorset Green Technology Park, Dorchester, Dorset DT2 8ZB, UK
B. D. Turland
Affiliation:
AMEC, Kimmeridge House, Dorset Green Technology Park, Dorchester, Dorset DT2 8ZB, UK
C. P. Jackson
Affiliation:
AMEC, Building 150, Thomson Avenue, Harwell, Didcot, Oxfordshire OX11 0QB, UK
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Abstract

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The Environment Agency Guidance on Requirements for Authorisation (GRA) of a geological disposal facility (GDF) requires a demonstration that "the possibility of a local accumulation of fissile material such as to produce a neutron chain reaction is not a significant concern." A neutron chain reaction that is just self-sustaining is also known as critical.

Waste packages can be designed to ensure that criticality is impossible during the transport and operational phases of a GDF, and for a significant period post-closure. Over longer times, however, packages may degrade, and groundwater flows could lead to a localized accumulation of fissile material. Hence, even though the initial distribution of materials would need to change substantially, criticality cannot be ruled out completely.

This paper describes how an accumulation of fissile material could, hypothetically, lead to a critical configuration; how such a system could evolve; what the local consequences could be; and how the engineered and geological barriers could be affected. The conclusion from studies to date is that, even for large (and very unlikely) fissile accumulations, the consequences of a post-closure criticality event are not a significant concern.

Type
Research Article
Creative Commons
Creative Common License - CCCreative Common License - BY
© [2012] The Mineralogical Society of Great Britain and Ireland. This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY) licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2012

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