At ISOLDE and MEDICIS facilities at CERN, radioactive isotopes are produced by irradiating materials such as uranium carbide with high energy protons. The so-called “target material” is brought to high temperature (>2000°C) under vacuum to promote isotope release. However, the release process is highly dependent on the microstructural properties of the target material (e.g. porosity and grain size) which degrade over time due to sintering.
New nanostructured uranium carbide target materials were developed over the last decade to improve isotope release while keeping a stable microstructure at high temperature. However, the new materials were found highly pyrophoric (self-ignition at room temperature) and require extreme care in all handling procedures. Since uranium carbide materials are not compatible with long-term storage requirements, a safe process for their conversion into stable oxides is investigated.
In this thesis, the oxidation of five different uranium carbide and carbon composite materials was investigated. A combination of material characterization and thermal analysis techniques were used to study the chemical reaction mechanism and its kinetics (i.e. reaction rate). It was found that, despite their different characteristics, materials generally followed a similar reaction pathway. However, oxidation temperatures and kinetics were strongly affected by sample form, grain size and carbon content.
The study provided valuable inputs for the design of safe oxidation and disposal procedures for current and future uranium carbide targets waste, such as microporous, high density or nanostructured targets.
This research project has been supported by a Marie Skłodowska-Curie Innovative Training Network Fellowship of the European Commission's Horizon 2020 Programme under contract number 642889 MEDICIS-PROMED.