For the development high-density, low-enriched research reactor (RR) fuels, uranium alloys (eg. U-Mo) or intermetallics (eg. U3Si2) are used. These are most often dispersed in an Al based matrix and sandwiched as a thin layer in an Al alloy cladding to form a fuel plate by hot rolling. These fuels are used up to very high burnups (>75% or fission densities >5E21 f/cc) and operated at fairly low temperatures (<250°C fuel temperature). Since each fission causes 2 ions (the fission products) to be propelled at high energy (~80-100 MeV each) through the fuel and eventually become implanted in the fuel, a lot of damage cascades are created in the lattice, causing it to accumulate important amounts of deformation energy (high defect concentration) over time.

Description

Within this PhD project, the goal is to separate out the phenomenon of recrystallisation and provide a scientific description. All efforts to ‘simulate’ the effect of fission on the fuel matrix have important limitations, so to achieve a representative study, it is necessary to use irradiation. Within this PhD, the ultimate goal is to irradiate small disks of U7Mo in the BR2 reactor at representative temperatures and up to appropriate fission densities. Possibilities for such an irradiation have been verified, but the candidate will need to work out the details of the experiment. Collaborations with PNNL, INL and ANL in the USA are possible for this. By such an experiment, a systematic matrix of materials irradiated at different temperatures and up to different fission densities will be generated and the irradiated disks can be examined with a variety of techniques, particularly microhardness measurements, SEM-TEM for microstructure work, laser flash (collaboration with ITU) for thermal conductivity, X-ray diffraction for lattice parameter, etc. This will allow a deeper understanding of the mechanisms underlying the recrystallisation, help in defining thresholds for recrystallisation in terms of fission density, temperature and the influence of the microstructure on the recrystallisation effect. In the end, this data will provide input for mechanistic modeling (not within the scope of this work) of fuel behaviour.

Nr of positions available : 1

Research Fields

Engineering

Career Stage

Early stage researcher or 0-4 yrs (Post graduate)

Research Profiles

First Stage Researcher (R1)