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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

References

Cummings, R., Smith, P.N. and Ghabaee, K. (2007) Understanding Criticality Under Repository Conditions: Results of Static Calculations. Serco Report to the Nuclear Decommissioning Authority, SA/ENV- 0770 Issue 3.Google Scholar
Cummings, R., Jackson, C.P. and Kelly, M. (2008) Repository Post-closure Criticality Consequences Assessment. Serco Report to the Nuclear Decommissioning Authority, SERCO/TAS-1017 Issue 1.1.Google Scholar
Environment Agency and Northern Ireland Environment Agency (2009) Geological Disposal Facilities on Land for Solid Radioactive Wastes: Guidance on Requirements for Authorisation. Environment Agency, Bristol, UK and the Northern Ireland Environment Agency, Belfast,UK.Google Scholar
Mason, R.M., Smith, P.N. and Cummings, R. (2007) Sensitivity Calculations Using the QSS Solver. Serco Report to the Nuclear Decommissioning Authority, SA/ENV-0830 Issue 2.Google Scholar
Mason, R.M., Cummings, R., Kudelin, Y., Martindill, J., Smith, P.J. and Smith, P.N. (2009a) A Suite of Calculations Using the QSS and RT Models. Serco Report to the Nuclear Decommissioning Authority, SA/ENV-0944 Issue 2.Google Scholar
Mason, R.M., Cummings, R., Hosking, J.G., Powney, D., Smith, P.J. and Smith, P.N. (2009b) Further Calculations Using the QSS and RT Models. Serco Report to the Nuclear Decommissioning Authority, SERCO/TAS-1004 Issue 4.Google Scholar
Mason, R.M., Smith, P.N., Sweet, D.W., Eaton, M.D., Goddard, A.J.H., Gomes, J.L.M.A. and Pain, C.C. (2009c) A Summary of Verification, Validation, Benchmarking, Uncertainty and Sensitivity for the FETCH, QSS and RTM Computer Models. Serco Report to the Nuclear Decommissioning Authority, SERCO/TAS/P3648/W001 Issue 2.Google Scholar
Mason, R.M., Turland, B.D. and Martin, J.K. (2011) Comparison of the QSS Model with the Oklo Natural Reactors. Serco Report to the Nuclear Decommissioning Authority, SERCO/TS/P6386/ W001 Issue 2.Google Scholar
Mason, R.M., Smith, P.N., Turland, B.D. and Jackson, C.P. (2012) The consequences of hypothetical postclosure criticality. Mineralogical Magazine, 76, 3155–3163.CrossRefGoogle Scholar
Naudet, R. (1991) Oklo: des Réacteurs Nucléaires Fossiles Etude Physique. Commissariat a` l’Energie Atomique, Paris.Google Scholar
Nuclear Decommissioning Authority (2010a) Geological Disposal : St e p s Towards Implementation. NDA Report no. NDA/RWMD/013. Nuclear Decommissioning Authority (2010b) Geological Disposal: An Introduction to the Generic Disposal System Safety Case. NDA Report No. NDA/RWMD/061.Google Scholar
Nuclear Decommissioning Authority (2010c) Geological Disposal: Criticality Safety Status Report. NDA Report No. NDA/RWMD/038.Google Scholar
Oversby, V.M. (1996) Criticality in a High Level Waste Repository: A Review of some Important Factors and an Assessment of the Lessons that can be Learned from the Oklo Reactors. SKB (Svensk Kärnbränslehantering) Technical Report 96–07.Google Scholar
Smellie, J. (2006) Analogue Evidence for Naturally Occurring Criticalities. John Smellie report to the Nuclear Decommissioning Authority.Google Scholar
Smith, P.N., Mason, R.M. and Cummings, R. (2007a) Understanding Criticality Under Repository Conditions: QSS - A Model for Quasi-Steady-State Criticalities. Serco Report to the Nuclear Decommissioning Authority, SA/ENV-0771 Issue 3.Google Scholar
Smith, P.N., Mason, R.M. and Cummings, R. (2007b) Understanding Criticality Under Repository Conditions: RTM - A Model for Rapid Transient Criticalities. Serco Report to the Nuclear Decommissioning Authority, SA/ENV-0772 Issue 3.Google Scholar
Zetterström, L. (2000) Oklo: A Review and Critical Evaluat ion of Li terature. SKB (Svensk Kärnbränslehantering) Technical Report TR-00-17.Google Scholar