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

Mason, R. M.; Martin, J.; Smith, Paul N.; Turland, B. D.

doi:10.1180/minmag.2012.076.8.28

Cited by 8 publications

(8 citation statements)

References 2 publications

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“…compared with the current 0.7%) in what is now a region of Gabon in Africa (Mason et al, 2012b). In overview, once it has been established that an initially critical system would have a negative temperature feedback, the QSS model requires user input to inform how k effective would vary with changes in temperature and the composition of the fissile material, including fission of isotopes such as 235 U and 239 Pu, capture of neutrons in isotopes and radioactive decay.…”

Section: Analysis: Criticality Transients and The Local Consequencesmentioning

confidence: 99%

Consequence modelling of hypothetical post-closure criticality events for spent fuel disposal

et al. 2015

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In support of the Radioactive Waste Management (RWM) safety case for a geological disposal facility (GDF) in the UK, there is a regulatory requirement to consider the likelihood and consequences of nuclear criticality. Waste packages are designed to ensure that criticality is not possible during the transport and operational phases of a GDF and for a significant period post-closure. However, over longer post-closure timescales, conditions in the GDF will evolve.For waste packages containing spent fuel, it can be shown that, under certain conditions, package flooding could result in a type of criticality event referred to as 'quasi-steady-state' (QSS). Although unlikely, this defines a 'what-if' scenario for understanding the potential consequences of post-closure criticality. This paper provides an overview of a methodology to understand QSS criticality and its application to a spent fuel waste package.The power of such a hypothetical criticality event is typically estimated to be a few kilowatts: comparable with international studies of similar systems and the decay heat for which waste packages are designed. This work has built confidence in the methodology and supports RWM's demonstration that post-closure criticality is not a significant concern.

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Section: Analysis: Criticality Transients and The Local Consequencesmentioning

confidence: 99%

Consequence modelling of hypothetical post-closure criticality events for spent fuel disposal

et al. 2015

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“…Interest in radioactive waste storage lead to the development of sophisticated deterministic codes for modeling criticality and these have also been applied to Oklo [37,38].…”

Section: Monte-carlo Simulations Of Oklo Reactorsmentioning

confidence: 99%

“…Modeling the potential for criticality in geological storage is an important issue and continues to be studied intensively. Here again the Oklo reactor zones have served as a testing ground for new approaches and new computation codes [37,38,62,63].…”

Section: Geological Repository Of Nuclear Wastesmentioning

confidence: 99%

Oklo reactors and implications for nuclear science

Davis

Gould

Sharapov

2014

Int. J. Mod. Phys. E

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We summarize the nuclear physics interests in the Oklo natural nuclear reactors, focusing particularly on developments over the past two decades. Modeling of the reactors has become increasingly sophisticated, employing Monte Carlo simulations with realistic geometries and materials that can generate both the thermal and epithermal fractions. The water content and the temperatures of the reactors have been uncertain parameters. We discuss recent work pointing to lower temperatures than earlier assumed. Nuclear cross sections are input to all Oklo modeling and we discuss a parameter, the $^{175}$Lu ground state cross section for thermal neutron capture leading to the isomer $^{176\mathrm{m}}$ Lu, that warrants further investigation. Studies of the time dependence of dimensionless fundamental constants have been a driver for much of the recent work on Oklo. We critically review neutron resonance energy shifts and their dependence on the fine structure constant $\alpha$ and the ratio $X_q=m_q/\Lambda$ (where $m_q$ is the average of the $u$ and $d$ current quark masses and $\Lambda$ is the mass scale of quantum chromodynamics). We suggest a formula for the combined sensitivity to $\alpha$ and $X_q$ that exhibits the dependence on proton number $Z$ and mass number $A$, potentially allowing quantum electrodynamic and quantum chromodynamic effects to be disentangled if a broader range of isotopic abundance data becomes available.Comment: 40 pages, 7 figures. Review pape

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“…This work (Nuclear Decommissioning Authority, 2010b), has been designed to explore the processes that would control the nature and magnitude of a hypothetical criticality under the particular post-closure conditions arising in a GDF containing ILW. Models of transient criticality have been developed (Mason et al, 2009); as part of their verification and validation, one model has been compared with some of the behaviour of the Oklo natural reactors (Mason et al, 2012). Further work is underway to apply models and approaches to scope the consequences of criticality transients in other materials and concepts and to recommend how the associated models and understanding should be developed and applied in future, beyond the preparatory studies phase.…”

Section: Criticality Safetymentioning

confidence: 99%

An introduction to package evolution and criticality research studies relevant to the UK disposal programme

2012

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In the UK, radioactive wastes currently planned for disposal in a geological disposal facility (GDF) include intermediate level waste, some low level waste and high level waste. Disposal of other materials, including spent fuel, uranium and plutonium is also being evaluated to inform the safety case for a GDF, if such materials were to be classified as wastes in the future. This paper describes the generic safety functions through which waste packages can contribute to the safety case of a GDF in the UK. It describes the engineering approach used or envisaged, in the UK and internationally, to ensure that waste packages retain their safety functions for the required periods of time and summarizes the scientific basis underpinning the current understanding of relevant evolution processes. Where gaps in the knowledge exist, the Nuclear Decommissioning Authority Radioactive Waste Management Directorate has identified specific research activities needed to close out such gaps to a level of maturity sufficient for this stage of the disposal programme (generic). This paper describes the latest results from their R&D programme and presents a summary of the research activities planned to meet the current needs of the disposal programme with specific reference to the topics of package evolution and criticality safety.

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

Cited by 8 publications

References 2 publications

Consequence modelling of hypothetical post-closure criticality events for spent fuel disposal

Consequence modelling of hypothetical post-closure criticality events for spent fuel disposal

Oklo reactors and implications for nuclear science

An introduction to package evolution and criticality research studies relevant to the UK disposal programme

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