PROGRESS IN DESIGNING THE INTERNAL ARRANGEMENTS OF PACKAGINGS FOR LWR SPENT FUEL

The internal arrangements (baskets) of casks for L WR spent fuel must provide subcriticality control, decay heat transfer, additional shielding, resistance to mechanical strain and case of operation for a number of spent fuel assembly specifications (i.e. up to 3.7% initial enrichment, down to 8 months cooling time). The Transnuclear group of companies has developed, over three generations and according to such design criteria as structure, subcriticality control and heat transfer, large-capacity baskets for uanspon casks. Thus, the trend has been to simplify from 'one specific material for a specific task' to 'one material for all purposes'. Transnucltaire is now engaged in the next step, which bas resulted in a new high performance cast basket for highly enriched fu.el. In order to further increase the payload for transport/storage casks, Transnucltaire bas also developed a new basket concept in which water gaps have been replaced by 'poisoning' the fuel medium itself. This is accomplished by inserting poison rods in the spent fuel assembly guide thimbles and by building a basket with thin partitions made of interlocking Al-B plates. This basket is designed to deform under heavy accidental loads, while continuing to perform all its functions, especially subcriticality control. An active test of such a basket at the Idaho National Engineering Laboratory is under way to verify the predicted behaviour under normal conditions. This concept provides an approximately 20% increase in the payload of a given cask and decreases the manufacturing cost by almost 50%.