Correlated sampling in Monte Carlo calculations has been developed previously and shows a limitation due to the poor convergence if the perturbation of the source neutron distribution is too large. Instead of estimating the influence of a macroscopic cross-section variation with two independent Monte Carlo calculations, this effect is evaluated using the same neutron histories, leading to a great improvement of the statistical convergence. The feedback effects considered are the sodium density and the Doppler effects. Another element developed here is the point kinetics local feedback parameter estimation. Our main focus is on the description of a correlated sampling technique associated to Monte Carlo calculations for the interpolation model used in the spatial TFM approach. In this paper, we use a sodium fast reactor as an example, in which the low void effect requires a highly discretized geometry with a large sodium plenum and an axial blanket between two fissile zones. They are not appropriate for fast reactors with a heterogeneous core and specific developments are required to improve the interpolation. These models are restricted to thermal reactors with a small neutron migration area, or fast reactors without fuel heterogeneities. Previous developments provided interpolation models for PWRs and MSFRs (Molten Salt Fast Reactors), allowing 3D calculations coupled to Computational Fluid Dynamics to be performed. The TFM approach requires the development of specific interpolation models to perform coupled calculations in order to take into account the evolution of the system's cross-sections during the transient. This approach is based on a conversion to discretized Green functions of the Monte Carlo response in order to perform kinetic calculations without new reference calculation during the transient and thus with a reduced computation time. In this frame, the Transient Fission Matrix (called TFM) approach developed in and presented in Section 2 is used here. Hybrid approaches may be used, like improved quasistatic methods, but they require regular updates of the power shape and of the reactivity using precise core calculations.
#Transformice codes 2017 full
In this frame, some simplifying assumptions in neutron kinetics modeling have to be made since the increase of computation capabilities is not yet sufficient for direct time-dependent Monte Carlo calculations at the full reactor core scale. Each component of these interactions implies complex feedback effects resulting in a strong coupling that requires dedicated appropriate physical models and numerical resolution to balance precision and reasonable computation time. This kind of application may require multi-physics tools able to take into account the interaction between the neutronics that provides the fission power source and other physics such as the thermal hydraulics that models the cooling aspects, or mechanics to take into account the core deformation or the pellet-cladding interaction. The study of power reactor behavior during normal and abnormal operation raises the incentive of modeling the transient phases.
#Transformice codes 2017 license
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Laureau et al., published by EDP Sciences, 2017 This approach is also used to estimate local feedback effects for point kinetics resolution. Finally, an accurate estimation of the feedback effects on these Green functions provides an on-the-fly prediction of the flux redistribution in the core, whatever the actual perturbation shape is during the transient. This method is associated to an innovative spatial kinetics model named Transient Fission Matrix, which condenses the time-dependent Monte Carlo neutronic response in Green functions. estimating the influence on the neutron transport of a local variation of different parameters such as sodium density or fuel Doppler effect. The local correlated sampling technique for Monte Carlo calculation presented in this paper has been developed for this purpose, i.e. Depending on the targeted accuracy, this feedback can be limited to the reactivity for point kinetics, or can take into account the redistribution of the power in the core for spatial kinetics. This kind of application requires a modeling of the influence on the neutronics of the macroscopic cross-section evolution. These studies are performed in the general framework of transient coupled calculations with accurate neutron kinetics models. Axel Laureau *, Laurent Buiron and Bruno Fontaine
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