The possible role of reduced-moderation water reactors and its sensitivity to fuel recycling conditions

In this study, many scenarios were defined for future development of nuclear power generation and fuel cycle systems in Japan. These scenarios were quantitatively analyzed from the viewpoint of plutonium recycling, natural uranium consumption, stock of spent fuel, etc. Following findings were obtained from the analysis. Reduced Moderation Water Reactors (RMWRs) will contribute to control the uranium consumption at certain finite levels if net conversion ratio (CR) is kept higher than 1.0. However, since RMWRs do not have an excellent breeding performance in comparison with sodium-cooled fast breeder reactors, their effect is very sensitive to the conditions on fuel recycling processes. Judging from the results of analysis using a RMWR design with gross CR 1.06, it would be necessary for RMWRs to have net CR 1.04 in order to replace enriched uranium fuelled LWRs by around the year 2200, and thereby to keep ultimate natural uranium consumption at rather low levels. This can be achieved by controlling fuel duration time outside reactors to shorter than 4 years or 6 years, when total loss of plutonium during the processes of recycling is 1.0% or 0.2%, respectively. (author)