The project will firstly be of use for the development of Gen IV reactors. In particular, we will investigate small modular reactors of molten salt or lead type. The results will allow for a better burnup of nuclear fuel and optimized reactor operation since a well-founded uncertainty propagation will allow for less conservative assumptions when calculating safety margins. Experimental data and models have associated uncertainties. Consequently, nuclear data libraries also contain uncertainties. At Uppsala University, we specialize in calculating uncertainties and covariances of nuclear data libraries and in propagating these uncertainties in applications. We have strong international collaborations and plan to hire a Ph.D. candidate who will work with us and be partially stationed at a partner institution. This will help strengthen our collaborations with other research groups in the future.