Concept of innovative water reactor for flexible fuel cycle (FLWR)

In order to ensure sustainable energy supply in the future based on the matured light water reactor (LWR) and coming mixed oxide (MOX)-LWR technologies, a concept of innovative water reactor for flexible fuel cycle (FLWR) has been investigated in Japan Atomic Energy Research Agency (JAEA). The concept consists of two parts in the chronological sequence. The first part realizes a high conversion type core concept, which is basically intended to keep the smooth technical continuity from current LWR and coming MOX-LWR technologies without significant technical gaps. The second part represents the reduced-moderation water reactor (RMWR) core concept, which realizes a high conversion ratio over 1.0 being useful for the long-term sustainable energy supply through plutonium multiple recycling based on the well-developed LWR technologies. The key point is that the two core concepts utilize the compatible and the same size fuel assemblies, and hence, the former concept can proceed to the latter in the same reactor system, based flexibly on the future fuel cycle circumstances during the reactor operation period around 60 years.At present, reprocessed plutonium from the LWR spent fuel is to be utilized in MOX-LWR. After this stage, the first part of FLWR, i.e. the high conversion type, can be introduced as a replacement of LWR or MOX-LWR. Since the plutonium inventory of FLWR is much larger, the number of the reactor with MOX fuel will be significantly reduced compared to the MOX-LWR utilization. When the fuel cycle for plutonium multiple recycling with MOX fuel reprocessing is realized, the fuel assembly will be replaced with another type of the tight-lattice one for RMWR with different rod diameter, rod gap width and so forth even in the same reactor system, being flexibly corresponding to the fuel cycle circumstances.Investigation on the core for both the parts of the FLWR concepts has been performed, including the core conceptual design, the core characteristics under Pu multiple recycling, the thermal hydraulic investigation in the tight-lattice core, and so forth. Up to the present, promising results have been obtained.