While the fresh fuel of a Pressurized Water Reactor (PWR) is purely composed of uranium dioxide – in some cases a mixture of uranium and plutonium oxides –, Spent Nuclear Fuel (SNF) features a way more complex isotopic composition. A comprehensive characterization of SNF assembly is essential for safe, secure, ecological and economical operations during transport, interim storage and final disposal. Apart from integral observables, such as decay heat, neutron and gamma-ray emission rate, the inventory of fissile nuclides and of strong neutron absorber nuclides is also required.
Some observables can be determined by Non-Destructive Analysis (NDA) methods. Howevere, since for instance a decay heat measurement of an assembly lasts at least one full day, it is often impractical to measure the entire SNF inventory produced over the lifetime of one or more Nuclear Power Plants (NPPs). Calculations are thus required for full characterization of SNF. The calculations involve a neutron transport code coupled with a depletion solver. The results depend on nuclear data and assay data. The latter consist of fuel fabrication data and information on irradiation conditions.
In this work the student is asked to identify and rank the major model parameters that affect the SNF-related observables in a fuel depletion/burnup calculation for a set of reference case studies. The sensitivity of the nuclide vector, as well as of integral values such as decay heat, neutron and gamma emission will be quantified with respect to model inputs, such as power history, boron concentration, fuel initial enrichment, etc. The student must develop a deep knowledge in burnup problems to identify possible uncertainties and correlations in the model inputs and implement them in their analysis.