Development of On-site Spent Fuel Transfer System Designs

Since the passage of the Nuclear Waste Policy Act (NWPA), nuclear utilities have recognized that spent fuel storage was to be a growing concern that would have major operational and economic impact on their nuclear plants. R&D was initiated some ten years ago to develop safe, economical and licensable dry storage technologies that would meet the growing on-site storage requirements. As development work progressed, it became clear that utilities favored storage that could be added in modular fashion in order to avoid large up-front capital costs. On the other hand, it also became clear that in order to reduce unit costs and minimize the plant operational impact, the modules should be relatively large. Based on the limiting size of cranes and plant facilities, the optimum module size was found to be packages that held about 21 to 24 PWR fuel assemblies. This resulted in shielded packages, either concrete or metal, that ranged from 100 to 150 tons in weight. In the case of concrete, it also required a large diameter package that challenged many plants' handling systems. The result was that many utilities with smaller cranes or other plant restrictions could not take advantage of the larger module storage designs. Given this incentive, EPRI began to explore the possibility of using the concept of a small-cask-to-large-cask transfer as a way to allow all utilities to make use of the larger storage modules and their favorable economics. It was soon apparent that such a transfer technology could have other NWPA applications. For instance, it may be possible to ship a greater proportion of fuel in more efficient large rail casks by using a small-cask transfer system at the restricted plants. Also in the scenario of early receipt at a Monitored Retrievable Storage (MRS), before all the facilities are fully in place, it looked promising to make a small-cask transfer from a transport cask into a large storage system using similar transfer technology.