Amélioration de la précision du formulaire DARWIN2.3 pour le calcul du bilan matière en évolution

Abstract : The DARWIN2.3 calculation package, based on the use of the JEFF-3.1.1 nuclear data library, is devoted to nuclear fuel cycle studies. It is experimentally validated for fuel inventory calculation thanks to dedicated isotopic ratios measurements realized on irradiated fuel rod cuts. For some nuclides of interest for the fuel cycle, the experimental validation work points out that the concentration calculation could be improved. The PhD work was done in this framework: having verified that calculation-to-experiment (C/E) biases are mainly due to nuclear data, two ways of improving fuel inventory calculation are proposed and investigated. They consist on one hand in improving nuclear data using the integral data assimilation technique, and on the other hand in proposing new experiments to validate nuclear data involved in the buildup of nuclides for which there is no post-irradiation examination available to validate DARWIN2.3 fuel inventory calculation. At first, an integral assimilation of the data coming from the experimental validation of fuel inventory calculation with DARWIN2.3 was carried out using the CONRAD code dedicated to nuclear data evaluation. It relies on a Bayesian approach that allows fitting nuclear data involved in the buildup of nuclides of interest for the fuel cycle, and on an analytic marginalization technique that allows accounting for uncertainties on non-fitted nuclear data. The sources of uncertainties associated to the C/E values were combined beforehand in order to produce a correlation matrix between C/E values to be used during the adjustment procedure. This process leads to re-estimating some nuclear data. Based on the analysis of these trends, nuclear data evaluations can be recommended. They represent the fuel cycle studies feedback for nuclear data validation. These recommendations mainly concern capture cross-sections (U, Pu, Am, Cm, Rh, Eu), but also thermal cumulative fission yields (Ru, Cs, Ce) of major actinides. It was shown that these recommendations improve significantly the buildup of actinides and fission products of interest for the fuel cycle. Then, the design of an experiment dedicated to the validation of the cross-sections involved in 14C buildup, namely 14N(n,p) and 17O(n,α), was investigated. It consists in irradiating melamine (C3H6N6) and 17O-enriched water in order to produce 14C, to be measured thanks to a liquid scintillation process. Studies demonstrate the feasibility of such an experiment in the MINERVE reactor, the latter being permanently shut down today. The obtained results can still be reused for the design of a new experimental program that can be carried out in another experimental reactor.
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Axel Rizzo. Amélioration de la précision du formulaire DARWIN2.3 pour le calcul du bilan matière en évolution. Physique Nucléaire Expérimentale [nucl-ex]. Aix Marseille Université, 2018. Français. ⟨tel-02148659⟩

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