CURRENT AND FUTURE RESEARCH ON PASSIVE SAFETY DEVICES AND ADVANCED FUELS FOR INNOVATIVE LWRS Part 2: Fuel Development for Advanced Light Water Reactors

摘要

Presently an enrichment limit of 5% ~(235)U is fixed in licenses all along the fuel cycle. Although working groups (e.g. DOE, WNA) are investigating incentives and prerequisites to increase the limit, it is widely expected that at least for the mid term (10-20 years) the limit will hold. For the EPR and SWR 1000 development the 5% enrichment limit was not a serious restriction, since for higher enrichment each fuel assembly has to be shimmed with fixed burnable absorbers anyway for criticality or reactivity reasons. Thus the fuel safety issues for these ALWR are the same as for currently operating LWR, essentially the influence of high burn-up on safety analyses (fuel response to transients e.g. RIA, LOCA). Operational behavior is of minor concern since the burn-up increase is slow enough to allow sufficient experience feedback. Worldwide the LWR fuel failure rates have not increased with burn-up. At present, and expected mid term, uranium prices are such that there is little incentive to look into other fissile materials like thorium. Nevertheless, on a small scale, R&D is ongoing to prepare a longer term alternative. Some R&D is also considered for the end of NPP lifetime fuel cycles, however there is little economic incentive for such (due to lifetime extension) rarely needed specific solutions. If nuclear fission energy is to be used in the real long term (beyond 50-100 years), then R&D on breeder reactor fuel will have to be resumed.