[en] This Report compares the costs of reprocessing spent fuels at the new THORP reprocessing plant at Sellafield with the alternative of storing them prior to final disposal. It finds that even when the cost of constructing THORP is treated as a sunk cost, reprocessing has no decisive economic advantage over spent fuel storage. The justifications put forward for THORP and two other reprocessing plants in France when they were designed in the 1970s are no longer valid. Natural and enriched uranium have become plentiful, and no-one expects plutonium-fuelled fast reactors to be constructed in any number before the middle decades of the next Century. The plutonium and uranium recovered from spent fuel is therefore no longer required for reasons of economy or supply security. In addition, it is now recognized that reprocessing complicates waste management by increasing the number and volume of waste streams. Electric utilities in Western Europe and Japan have already largely paid for the construction of the new British and French reprocessing plants. Today, their economic judgements therefore depend on the future costs of operating and eventually decommissioning the plants, and of dealing with the resulting wastes and separated products, the estimated cost of which has risen. Decisions on reprocessing and spent fuel management cannot be taken on economic grounds alone. Environmental, security and political considerations also have to be taken into account. On balance, these weigh heavily against reprocessing, not least due to the large amounts of plutonium that will be separated, posing a variety of security problems at home and abroad. (author)