THE DRY -CAP* SPENT FUEL STORAGE/TRANSPORT CASK

Increasing inventories of spent fuel and decreasing storage capacities at reactors are prompting development of alternative storage technologies. In the United States of America, the Department of Energy is engaged in the development of a geological repository and is committed to begin accepting fuel for permanent storage by 31 January 1998. Until this time, US utilities have assumed the responsibility for handling this material. The storage situation is also recognized in Japan and several utilities are now engaged in the development of alternative storage options. In recognition of these situations, Combustion Engineering, Inc. and Sumitomo Heavy Industries Ltd are engaged in a programme to develop and manufacture a cask capable of safely storing and transporting spent nuclear fuel. The cask is designed in accordance with US I 0CFR71 and I OCFR 72 criteria lll}d has one of the largest capacities of spent fuel casks, with the ability to hold 24 PWR or 60 BWR spent fuel bundles and remain under the 125 t crane capacity of most power plants. The Dry-Cap spent fuel storage cask consists of a 16! ft (5 m) long by 7! ft (2.27 m) diameter thick-walled steel cylinder surrounded by shielding material. Dry-Cap is a relatively simple design, easily manufactured and, unlike other cask designs, requires no external fms for cooling. Dissipation of decay heat is accomplished by natural convection between the fuel and its helium environment and the cask and its surrounding environment. One of the most important features of the Dry-Cap design is that it does not require poison material for criticality control, since the basket design utilizes credit for burnup. Taking credit for the known irradiation heating of discharged fuel, and the fact that it has a low residual reactivity, can simplify and minimize the maintenance and monitoring requirements for long term storage. The Dry-Cap cask is desianed to fulfli the long and short term storage needs for utilities.