Loading optimization algorithm for solving assembly assignment problem in the final disposal of spent nuclear fuel in Finland

Abstract

In Finland, the final disposal of spent nuclear fuel assemblies includes inserting them into disposal canisters being disposed of in bedrock. This final disposal will be a century long process. The choice of which fuel assemblies are assigned to which canisters determines the decay heat powers of canisters. A loading optimization algorithm to make these choices is developed. The assembly assignment problem is formulated as a multiobjective mixed-integer nonlinear programming problem, but the loading optimization algorithm will solve the problem heuristically. The developed algorithm can be seen as a new version of the algorithm to solve the minimax canister formation problem, where canisters disposed of in the near future are considered more carefully than the rest of the canisters being more exposed to uncertainties related to schedule and predicted decay heat powers of future fuel assemblies. Furthermore, new constraints and objectives have been taken into account. The developed loading optimization algorithm facilitates the safe and cost-efficient assignments of fuel assemblies to canisters in Finland.