Fast-thermal coupled cores in zero power reactors: A demonstration of feasibility and pertinence for the ZEPHYR project

The development of GEN-IV fast reactor technology at an industrial scale will need significant improvement of nuclear data and related uncertainties to cope with awaited target uncertainties (Palmiotti and Salvatores, 2011). However, GEN-IV dedicated Zero Power Facilities are now sparse. In France, both the MASURCA Zero Power Reactor (ZPR) and the future ZEPHYR multipurpose ZPR to be built in Cadarache belong to this type of facilities. For this latest one, fast/thermal coupled configurations performed in MINERVE during the 1970's have been recently revisited using modern calculation tools. The principle of a fast zone fed by a thermal booster, known from decades as the concept of coupled cores regained interest in recent years. This paper describes the concept of fast/thermal coupled core, a deeper description of the physical characteristics of the adaptation zone, and its use in the improvement of fast-spectrum nuclear data thanks to integral experiments. An optimized configuration is then presented. The preliminary design phase is performed using deterministic tools, a posteriori validated against a full Monte Carlo calculation. Particular attention is paid on the impact of the buffer zone on the spectral characteristics in the oscillation channel, as well as the sample mass characteristics required to ensure a proper signal analysis. Moreover, preliminary studies dedicated to the experimental realization of such a configuration are described, including the reactivity stability in case of an accidental flooding of the fast central zone.