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Criticality in a Repository for Spent Fuel: Lessons From Oklo

Published online by Cambridge University Press:  10 February 2011

V. M. Oversby
V. M. Oversby*
Affiliation:
VMO Konsult, Karlavägen 70, S-1 14 59 Stockholm, Sweden
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Abstract

The conditions that are needed to achieve criticality in a high level waste repository for spent nuclear reactor fuel are reviewed. The effect of initial enrichment of the fuel, burnup, and of mixed oxide fuels on the conditions for criticality are discussed. The situations that produced criticality at Oklo, Gabon, 2000 million years ago are summarized. A model based on the Oklo conditions is presented for estimating the amount of fissile material that must be assembled to create a critical mass in typical granitic rocks. Mechanisms for movement of uranium and plutonium to achieve a critical configuration are discussed and compared to the conditions that are likely to occur in a repository in granite. The sequences of events needed to produce a critical assemblage are shown to be in conflict with the conditions expected in the repository and, in some cases, to require internally inconsistent assumptions to produce the postulated sequence of events. No credible scenario for achieving criticality in a high level waste repository has been found.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 506: Symposium – Scientific Basis for Nuclear Waste Management XXI , 1997 , 781
Copyright
Copyright © Materials Research Society 1998

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References

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