Logistics optimization code for spent fuel assembly loading into final disposal canisters

The loading of the nuclear Spent Fuel Assemblies (SFAs) produced in Switzerland into disposal canisters for their final emplacement into a deep geological repository has to be planned in advance. To limit the associated cost and the operational time of the corresponding surface facility, an optimization should be applied to the aforementioned problem, since its solution cannot be found analytically. To that end, the National Cooperative for the Disposal of Radioactive Waste (Nagra) developed the logistics optimization code “SIMAN”, using the so called Simulated Annealing (SA) method. The objective is to find the best possible loading configuration to minimize the total number of canisters needed. The aims of this study were to finish and analyze the performance of the previous code system and to provide features for extended analysis on the resulting canister loading configurations. Two code revisions were used to simulate different boundary conditions regarding the disposal procedure. Realistic boundary conditions confirmed to add a 10% increase (conservatively) to the total number of disposal canisters needed, compared to the solution for the simplified boundary conditions. In addition, the various reasons and their relative contributions to this increase have been determined and quantified. Finally, an extension to the reference disposal concept has been investigated (so-called “mixed canister”) indicating significant potentials for further decrease of the total number of canisters.