Sensitivity analysis of minor actinides transmutation to physical and technological parameters

Buiron²,

Nuclear Science and Engineering

2017

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Introduction:Minor actinides transmutation is a potential solution which is currently investigated for long-term management of nuclear waste. In the case of a closed plutonium fuel cycle, minor actinides are the main responsible for long-term radiotoxicity and short-term decay heat of the nuclear waste package. In the transmutation process, neptunium, americium and eventually curium, which are the three main minor actinides produced in nuclear reactors, are submitted to a neutron flux in order to turn them into shorter-lived fission products by fission or successive captures followed by fissions. This way, radiotoxicity levels can be lowered up to a factor 200 in the best case [1] and a reduction of a factor 3 of the final repository footprint can be achieved [2].Various options have been proposed so far for minor actinides transmutation, including thermal reactors [3], ADS [4] and fast reactors [5]. We will focus here on the fast reactor option as targeted by French R&D programs. Two approaches have been discussed for transmutation in fast reactors, namely the homogeneous one and the heterogeneous one. A complete comparison of these two options can be found in [6] and a small breakdown of the most salient points for each case is done below.

Section: Characterization Of the Heterogeneous Approach For Minor Actmentioning

confidence: 99%

Section: B Technological Feasibility Assessmentmentioning

confidence: 99%

Optimization of Minor Actinide–Bearing Radial Blankets for Heterogeneous Transmutation in Fast Reactors

Buiron²,

Nuclear Science and Engineering

2017

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“…This conclusion may not stay true in the case of higher flux level or homogeneous transmutation due to the so-called 'curium peak' effect [9] in which the curium concentration (and the neutron source) increases to a maximum and then decreases after a given fluence.…”

Section: Resultsmentioning

confidence: 97%

“…This approach is based on the consideration that minor actinides transmutation can be characterized considering limited information on the neutron spectrum and the minor actinides loading, as discussed in [9].…”

Section: Outline Of the Optimization Approach Consideredmentioning

confidence: 99%

“…It has been shown that minor actinides transmutation performances and corresponding neutron source can be fully parametrized by the neutron spectrum and the amount of americium loaded in the blankets [9]. Considering the simple parametrization of the problem parameters and outputs, an optimization scheme under constraints was implemented in this work.…”

Section: Introductionmentioning

confidence: 99%

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Analysis and optimization of minor actinides transmutation blankets with regards to neutron and gamma sources

Buiron

EPJ Nuclear Sci. Technol.

2017

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Abstract. Heterogeneous loading of minor actinides in radial blankets is a potential solution to implement minor actinides transmutation in fast reactors. However, to compensate for the lower flux level experienced by the blankets, the fraction of minor actinides to be loaded in the blankets must be increased to maintain acceptable performances. This severely increases the decay heat and neutron source of the blanket assemblies, both before and after irradiation, by more than an order of magnitude in the case of neutron source for instance. We propose here to implement an optimization methodology of the blankets design with regards to various parameters such as the local spectrum or the mass to be loaded, with the objective of minimizing the final neutron source of the spent assembly while maximizing the transmutation performances of the blankets. In a first stage, an analysis of the various contributors to long-and short-term neutron and gamma source is carried out whereas in a second stage, relevant estimators are designed for use in the effective optimization process, which is done in the last step. A comparison with core calculations is finally done for completeness and validation purposes. It is found that the use of a moderated spectrum in the blankets can be beneficial in terms of final neutron and gamma source without impacting minor actinides transmutation performances compared to more energetic spectrum that could be achieved using metallic fuel for instance. It is also confirmed that, if possible, the use of hydrides as moderating material in the blankets is a promising option to limit the total minor actinides inventory in the fuel cycle. If not, it appears that focus should be put upon an increased residence time for the blankets rather than an increase in the acceptable neutron source for handling and reprocessing.

A comparison of curium, neptunium and americium transmutation feasibility

Buiron

Annals of Nuclear Energy

2018

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Minor actinides transmutation is the process of decreasing the long term radiotoxicity of the nuclear spent fuel by submitting it to a neutron flux so as to achieve fission of the heavy nuclides concerned. In the case of a closed fuel cycle, minor actinides are the main contributors to the spent fuel radiotoxicity after a few centuries. The isotopic vector of the minor actinides feed to be transmuted depends heavily on the fuel cycle considered: PWRs with UOX fuels will mainly lead to neptunium and americium production while MOX fueled reactors will produce mainly americium and curium. Americium is the main element currently considered for transmutation due to its relatively short half-life and important production. On the other hand, neptunium is seen as a secondary candidate for transmutation due to its very long half life and low activity while Curium has transmutation is generally ruled out due to the important activity of curium isotopes. Two modes of transmutation in fast reactors are generally opposed, namely the homogeneous approach in which minor actinides are directly mixed with the fuel while in the heterogeneous approach, the minor actinides are loaded in dedicated targets. It is shown in this paper that the impacts on the fuel cycle of heterogeneous americium transmutation are similar to the one of homogeneous curium transmutation. It is further shown that given the quantities of curium in the fuel cycle, only a limited number of reactors would be required to effectively transmute the curium production of fast reactors with americium bearing blankets. Curium transmutation thus appears a feasible option in a completely closed fuel cycle without significantly higher fuel cycle impacts than with only americium transmutation. It is finally verified that neptunium transmutation can be achieved regardless of the approach considered.