A stochastic method to propagate uncertainties along large cores deterministic calculations

Abstract : Several evolutionary advanced nuclear reactors, whose operational life is intended to be 60 years, are currently being built throughout the world. Deterministic uncertainty propagation methods are certainly powerful and time-sparing but their access to uncertainties related to the power map stays difficult due to a lack numerical convergence. On the contrary, stochastic methods facilitate the propagation of uncertainties related to the core power map and they enable a more rigorous access to those concerning the prompt fission neutron spectrum. In this sense, they supplement previous studies. Our method combines an innovative calculation chain and a stochastic way of propagating uncertainties on nuclear data : first, our calculation scheme consists in the calculation of assembly self-shielded cross sections and a flux calculation on the whole core. Bias is quantified and the CPU time needed is suitable to lead numerous calculations. Then, we sample nuclear cross sections with consistent probability distribution functions with a correlated sampling. Finally, we deduce the power map uncertainties from the study of the output response functions. We performed our study on the system described in the framework of the OECD/NEA Expert Group in Uncertainty Analysis in Modelling (UAM). Results show $^{238}U$ inelastic scattering, the $^{235}U$ PFNS and the $_{26}Fe$ cross sections as major contributors of the total uncertainty on the power map whose value is 3% (1σ) with the COMAC covariance library.
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European Journal of Physics, European Physical Society, In press
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Ludovic Volat, Bernard Gastaldi, Alain Santamarina. A stochastic method to propagate uncertainties along large cores deterministic calculations. European Journal of Physics, European Physical Society, In press. 〈cea-01597850〉

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