Transient fission matrix approach for assessing complex kinetics behavior in the ZEPHYR ZPR coupled core configurations

Abstract CEA is currently working on a new ZPR called ZEPHYR (Zero power Experimental PHYsics Reactor), to be built on the Cadarache Center in the next decade. Its awaited experimental capacities should go well beyond traditional needs, and in particular extended possibilities to assess complex 3D kinetics. Transient calculations with accurate neutron kinetics models can be challenged by designing strongly spatially coupled to strongly spatially uncoupled cores with different kinetics constant. An innovative Monte Carlo Transient Fission Matrix (TFM) approach based on fission matrix interpolation model connected to correlated sampling technique has been implemented and applied to the ZEPHYR reference fast/thermal coupled configuration. The model takes into account the redistribution of the power in the core for spatial kinetics (SK) thanks to a local correlated sampling technique developed for this purpose. However, point Kinetics (PK) can be treated as well. The correlated model presented in this paper estimates the coupling coefficients or the 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. A further work will extend this preliminary results to a 2D study case.