## 6 Conclusions and Policy Implications  
Based on the results obtained from the comparison of the different scenarios, several basic conclusions can be drawn. Due to the reduced storage costs in the CISFs, the construction of them is cost efficient in almost every scenario. This reduction in costs can be explained by economies of scale in the CISFs and the decreased penalty fees the DOE has to pay to the NPP operators. These results are congruent to the DOE study (2016) concluding that there is a total cost avoidance in total system lifecycle costs, especially post-shutdown at-reactor storage costs for any opening date of a final repository. In addition, the storage at an CISF is also safer than at an independent storage facility in terms of protecting the HLW against any natural or human impact. More capacity for interim storage is needed than the DOE has planned to provide by 2025. Depending on the scenario, CISFs with overall capacities between 20,000 and 120,000 MTU have been built in the model. Since the opening of a final repository in 2030 is rather unlikely this indicates that the capacity of 20,000 MTU the DOE has planned to provide by 2025 is not sufficient to save more costs and follow the best economic strategy. Furthermore, all CISFs are built in the first year of the model, which shows that the construction of those facilities would have to start immediately in order to reduce cost. From the point of logistics, locating the CISFs strategically close to the NPPs at the East coast and close to a final repository would be best. In half of the scenarios the location near Yucca Mountain has been chosen to build a CISF. In addition, further CISFs have been built at different locations near the East cost, where the majority of all NPPs is located. Therefore, it can be concluded that the location closest to the final repository (Yucca Mountain) as well as any location nearby the NPPs are preferable, due to decreased transportation cost. Any delay in finding and opening a final repository increases total cost, as seen by the cost differences between the 2030 and 2060 scenarios. The difference lies in the range of 15-30% for every ten years of delay. If CISFs are built and a final repository is operational by 2060, all independent spent fuel storage installations by reactor sites could be closed by 2080. Independent from the exact opening date and the number of final repositories, all scenarios including a final repository have in common that all HLW currently stored by the reactor sites in ISFSIs is transported to CISFs or the final repository at the latest by 2050. Therefore this seems to be a realistic time frame for shutting down ISFSIs, given that the mentioned conditions are fulfilled. Reprocessing is not efficient due to very high costs. Only by reducing them by 90%, reprocessing becomes more cost efficient than to leave all the waste in ISFSIs and CISFs. The evaluation of an even longer time frame seems not useful, considering technological development and the change of costs coming along with new innovations in the field of nuclear waste processing. Furthermore, the reduction of volume of HLW does not seem like a good-enough reason to produce plutonium, a bomb material and therefore proliferation risk, through the irradiation of uranium fuel. A simple yet relevant addition to the work presented would be the inclusion of further scenarios addressing the date of opening of Yucca Mountain as well as other final repository options. Also, the perspective of having to store the HLW for many more years without having a final repository could be examined which seems plausible regarding the political development during the past years. Even though it might make economic sense and be safer to have a final repository, the public acceptance in the affected region is a key problem. Similar issues with public acceptance that have to be taken into consideration can be seen in many large infrastructure problems regarding e.g., electricity lines, airports or highways.