Transient Fission Matrix approach for assessing complex kinetics behavior in the ZEPHYR ZPR coupled core configurations

Abstract : The studies presented in this paper are performed in the general framework of future 3D kinetics capabilities of the ZEPHYR (Zero power Experimental PHYsics Reactor) ZPR currently being designed at the CEA's Cadarache Centre. Transient calculations with accurate neutron kinetics models are required to characterize spatial decoupling in the cores that are expected to be built for reactor physics purposes. An innovative fission matrix interpolation model has been implemented with a correlated sampling technique associated to the Transient Fission Matrix (TFM) approach and applied to the ZEPHYR reference fast/thermal coupled configuration. These studies are performed in the general framework of transient coupled calculations with accurate neutron kinetics models. Depending on the targeted accuracy, feedback can be limited to the reactivity for point kinetics (PK), or can take into account the redistribution of the power in the core for spatial kinetics (SK). The local correlated sampling technique for Monte Carlo calculation presented in this paper was developed for this purpose, i.e. estimating the coupling coefficients of influence on the neutron transport of a local variation of different parameters on integral quantities such as k-eff. A dedicated 1D benchmark demonstrates interesting features of this kind of coupled configurations for the validation of complex space-time kinetics transient experiments.