Abstract
These studies are performed in the general framework of transient coupled calculations with accurate neutron kinetics models. This kind of application requires a modeling of the influence on the neutronics of the macroscopic cross-section evolution. 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. The local correlated sampling technique for Monte Carlo calculation presented in this paper has been developed for this purpose, i.e. estimating the influence on the neutron transport of a local variation of different parameters such as sodium density or fuel Doppler effect. 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. 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 approach is also used to estimate local feedback effects for point kinetics resolution.
Highlights
IntroductionThe study of power reactor behavior during normal and abnormal operation raises the incentive of modeling the transient phases
The study of power reactor behavior during normal and abnormal operation raises the incentive of modeling the transient phases. This kind of application may require multiphysics 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
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
Summary
The study of power reactor behavior during normal and abnormal operation raises the incentive of modeling the transient phases This kind of application may require multiphysics 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. 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 In this frame, the Transient Fission Matrix (called TFM) approach developed in [1,2,3] and presented in Section 2 is used here. The calculation of the Green function’s perturbation on a simple test case is detailed in Section 4 to illustrate the approach
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