Long-term behaviour of nuclear wasteforms under geological disposal conditions

Geological disposal of nuclear waste is an internationally accepted methodology for nuclear waste management and pursued by the United Kingdom. However, self-irradiation damage due to the decay of the confined radioisotopes and corrosion under disposal conditions are two major concerns that need to be addressed to demonstrate the safety of geological disposal. By using the MIAMI TEM (transmission electron microscopy) with in-situ ion irradiation facility to simulate the self-irradiation damage and leaching tests to simulate the corrosion under disposal conditions, this research will help identify and design durable nuclear wasteforms for safe disposal of nuclear waste in the UK.

Electricity generation from nuclear fission reactors mainly involves the fission of U-235 atoms (nuclear fuel) into smaller atoms called fission products and emission of neutrons and gamma rays. The emitted neutrons help sustain the nuclear fission but they also lead to the formation of highly radioactive elements such as minor actinides. A majority of the fission products and minor actinides are radioactive elements that will undergo alpha and beta decays for hundreds of thousands to millions of years. The nuclear fuel, when taken out of the reactor (called as spent fuel) is highly radioactive and needs to be isolated from the biosphere.

One of the methods that has been internationally accepted involves isolating the radioactive elements from the spent fuel (through various chemical processes) and confining them in materials such as glasses, ceramics and glass-ceramic composites (called as waste matrices). These waste matrices are then intended to be disposed into a deep geological repository (called as geological disposal). The waste matrices will be subjected to radiation damage due to the decay of the confined radioisotopes (called self-irradiation damage) and they will be corroded when in contact with the surrounding geology and water. As a result of the corrosion and self-irradiation damage, the waste matrices may lose their confining properties releasing the radioactive elements into the biosphere (at a certain rate). To demonstrate the long-term safety of geological disposal it is essential to design radiation and corrosion-resistant materials and develop a fundamental understanding of the effects of self-irradiation damage and corrosion under disposal conditions.

To develop this fundamental understanding, the candidate will work in collaboration with the nuclear research centres in the UK, France, Australia and the USA undertaking various experiments to simulate the self-irradiation damage and corrosion. The candidate will use the world-class MIAMI Transmission Electron Microscope (TEM) with in-situ ion irradiation facility at the University of Huddersfield to simulate the self-irradiation damage. The candidate will be trained in the use of TEM, ion accelerators, Focussed Ion Beam (FIB) and other specimen preparation techniques. To study the corrosion, in lab leaching tests will be undertaken and the candidate will use mass spectroscopy techniques (ICP-OES/MS), Nuclear Magnetic Resonance (NMR) and TEM/SEM/EDX to evaluate the effects of corrosion. This will also involve characterising glass specimens supplied by the collaborating partners that have undergone corrosion under controlled conditions for decades and other glass and mineral specimens, either already collected or to be collected by the candidate from nature during field trips, that have undergone corrosion for hundreds to thousands of years. The global aim is to develop a holistic picture of the corrosion and self-irradiation damage.