Identification of fission products affecting the criticality safety and fuel storage of reactor fuel
Introduction
Fast nuclear reactors are addressing key challenges of the nuclear energy sector such as waste management, resource sustainability, and safety. They make closing the nuclear fuel cycle feasible, which will reduce nuclear waste generation, and in general help to mitigate the climate change. Fast reactors are one of the key components of future nuclear energy development, and SCK CEN is hugely involved in the research for fast reactors, notably cooled by heavy liquid metals (lead or lead-bismuth eutectic).
Modelling fast reactor operation, as well as characterization of its used fuel and associated waste streams, relies on nuclear data, such as nuclear reaction cross sections, radioactive decay data and fission product yields. The latter ones determine the concentrations of fission products in the used nuclear fuels, and certain fission products determine safety characteristics of these fuels.
Traditionally, a safety concept of Burn-Up Credit (BUC) is introduced for spent nuclear fuels of thermal reactors, to account for the reduction in the reactivity of configurations with spent nuclear fuel due to the change in their composition after irradiation. In other words, the reactivity of spent nuclear fuel as function of residence time in the reactor must be accurately predicted for criticality safety. Another safety aspect is the decay heat of spent nuclear fuel, which directly affects the design of radioactive waste storage. Both BUC and decay heat of thermal reactors receive much attention nowadays. In contrast, used fast reactor fuels are not well characterized. In particular, the fission products are not ranked over their impact on BUC and decay heat.
Therefore, this thesis proposal aims at identifying a list of most important fission products which affect the BUC and decay heat of heavy liquid metal cooled fast systems.
Objectives
Taking a typical assembly model of heavy liquid metal cooled fast reactor and its estimated irradiation history, the candidate will perform depletion calculations and obtain the contributions of fission products into the reactivity of the fuel and its decay heat. Two Monte Carlo radiation transport and depletion codes will be used for this study: Serpent2 and ALEPH2, the latter one being the SCK CEN depletion tool which uses MCNP code for radiation transport calculations. Once the list of key fission products is identified, the sensitivities of observables to the neutron induced fast fission yields will be studied. This will help to understand the quality of fission yield nuclear data and the needs of its improvement.
Planning:
- get familiar with the fuel assembly model of heavy liquid metal cooled fast reactor and depletion codes;
- produce the ranking tables of fission products with respect to reactivity and decay heat as function of burnup;
- study the sensitivities of the observables to the yields of identified fission products;
- writing the thesis manuscript.