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Comparison of a post-closure transient criticality model with the Oklo natural reactors

Published online by Cambridge University Press:  05 July 2018

R. M. Mason ,
J. K. Martin ,
P. N. Smith  and
B. D. Turland
R. M. Mason*
Affiliation:
AMEC, Kimmeridge House, Dorset Green Technology Park, Dorchester, Dorset DT2 8ZB, UK
J. K. Martin
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
*
*E-mail: robert.mason@amec.com
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Abstract

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In support of the disposal system safety case for a geological disposal facility (GDF) there is a requirement to consider 'what-if' hypothetical scenarios for post-closure nuclear criticality. Although all such scenarios are considered very unlikely, one 'what-if' scenario is the mobilization of fissile material from a number of waste packages and its slow accumulation within the GDF or the immediate surroundings. Should sufficient fissile material accumulate a quasi-steady-state (QSS) transient criticality event could result. A computer model has been developed to understand the evolution and consequences of such an event.

Since a postulated QSS criticality could persist for many millennia, building confidence in the modelling approach is difficult. However, the Oklo natural reactors in Africa operated for similar durations around two billion years ago, providing a natural analogue for comparison. This paper describes the modelling approach, its application to hypothetical criticality events for a GDF, and how the model can be compared to Oklo. The model results are found to be in agreement with the observational evidence from Oklo, building confidence in the use of the QSS model to simulate postulated post-closure criticality events in GDFs.

Keywords

disposalpost-closurecriticality
Type
Research Article
Information
Mineralogical Magazine , Volume 76 , Issue 8 , December 2012 , pp. 3145 - 3153
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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