NEACRP-A- SBS Recycle of Uranium-236 J R Askew The Chairman of the Working Party on Nuclear Fuel Cycle Requirements has sought the advice of this Committee on the problems associated with the possible future recycle of U236 in thermal reactors. Some of these, for example whether the used uranium would be recycled through the enrichment process or have highly enriched material added, will be for the Working Party to decide before calculations are performed. There remained the question of the methods and data which should be used in such studies, and whether these would lead to differences of view between NEA member countries. It appeared to me that a simple benchmark calculational exercise might best provide the answer to this auestion and I agreed- to raise the matter before the NEACRP. As only the calculational capabilities, and not the actual cycle details, are at issue it might be adequate to use a greatly simplified problem on the following lines: 1. Specify a typical PWR pin-cell or assembly designed for approximately 35,000 MWdIte. Possibly include a fixed buckling. 2. Burnup for designed life and determine U236 and other actinide content at 35,000 MWdIte. Determine lifetime average multiplication. 3. Run a second case with specified U236lU235 ratio. Determine enrichment needed to give same lifetime average multiplication as in the base case, and discharge isotopics. This should suffice to identify any significant differences of view on the behaviour of U236 in the fuel cycle. As the Working Party next meets in April 1984it would be desirable to have the preliminary review of results before that date. The UK is prepared to undertake the specification of the problems and collection of results if the NEACRP so desires. AEE Winfrith 12 October 1983 .