The Effects of Uncertainty of Input Parameters on Nuclear Fuel Cycle Scenario Studies

Abstract

International audienceNuclear systems, composed of reactors and fuel cycle facilities, are complex and in constant evolution. Fuel cycle scenario studies aim at evaluating the consequences of decisions taken in the near term on the eventual outcomes of a chosen fuel cycle.Scenario studies require a large amount of data and hypotheses, such as the energy demand and its evolution or the performances and characteristics of existing and future technologies. Each hypothesis, represented by a parameter, is a potential source of uncertainty that can impact the scenario outcomes. The Nuclear Energy Agency's Expert Group on Advanced Fuel Cycle Scenarios (NEA/AFCS) recently completed an activity that used sensitivity studies to evaluate the impact of uncertainty of the primary scenario input parameters on scenario results.At the beginning of the study, a base case scenario was specified and evaluated. It considers a PWR UOX reactor fleet using low enriched uranium oxide fuel and its gradual replacement by a sodium fast reactor (SFR) fleet using uranium/plutonium mixed oxide fuel. Each member of the group evaluated this scenario with its own scenario code (COSI, COSAC, FAMILY, SITON, TR_EVOL or VISION). It is noteworthy that the different codes show a good consistency in the results and that the differences have been investigated and documented in order to ensure a strong basis for comparison in the sensitivity study.Then, 17 key input parameters and their range of variation as well as 22 scenario outputs were identified and sensitivity analyses were conducted. The key parameters were chosen amongst the general assumptions on the scenario (energy demand, introduction date of fast reactor), reactors and facilities characteristics (burn-ups, losses at reprocessing) and some minor actinides recycling parameters. As far as possible, each parameter was varied independently from the others. This sensitivity study shows the relative impact of each parameter on each output metric. In order to compare the large amount of results, two methods of summarization were adopted, as described in the paper. These comparisons have shown that some parameters, such as the energetic production or the introduction date of fast reactors, have a strong impact on the results whereas others, like the UOX fabrication time, have almost no impact on the studied scenario