Thermal optimization of the final disposal of spent nuclear fuel

The thermal optimisation for the Teollisuuden Voima Oy's (TVO) and Imatran Voima Oy's (IVO) nuclear fuel waste disposal from the current 4 nuclear power units has been studied in this calculation report. A procedure for loading different aged nuclear fuel in canisters in such way, that the decay power per canister is minimized at the stage when the canister is disposed. The length of the disposing period is assumed to be 20 - 25 years starting immediately after the planned usage period of the current plants in 2020. The disposal of the canisters has been optimised in such way, that the maximum temperature in the interface of the canister mantle and the bentonite buffer keeps always below the set limit, +100 deg C. In this optimisation the minimum distance between the two neighbouring canisters is calculated. In the assessment the TVO's BWR-fuel, the IVO's VVER 440 fuel, the three repository site candidates (Olkiluoto, Kivetty and Romuvaara), and two different size copper/steel canisters containing 9 or 11 bundles of fuel waste have been separately investigated and assessed. (orig.) (11 refs.)