Design, synthesis and characterisation of ceramic wasteforms for radioactive waste immobilisation.

There is a significant amount radioactive waste, generated as a product of nuclear activities, both domestically here in the UK and internationally. The origins are many, ranging from the production and maintenance of nuclear armaments to the operation of commercial nuclear reactors, amongst others. This has created a large volume and variety of waste, which necessitate distinct methods of disposal and storage in order to ensure that the safety of the environment and public are upheld. One such method is to immobilise High Level Waste (HLW) in a ceramic wasteform. A chosen wasteform must be stable for many 10's of thousands of years, whilst likely being stored in an underground facility called a Geological Disposal Facility. To this end, ceramics are a promising candidate for HLW due to their desirable physical and chemical properties that are maintained over long period of times. However, an important consideration for the choice of ceramic is its potential to resist radiation induced damage. This predominantly comes in the form of alpha-recoil damage, which can eventually cause a crystalline to amorphous phase transition of the ceramic leading to many issues such as cracks and swelling, which consequently leads to the leaching of radionuclides by groundwater when stored underground.

Two important qualities that determine radiation damage resistance are the crystal structure and chemical composition of a material. To that end, this project will look to design, synthesise and characterise novel ceramic materials to address this issue. The A2BO5 family of ceramics allow for the incorporation of many actinide wastes and can take on a range of structures depending on the A and B-site cation sizes, fabrication methods, temperature and pressure. This is a promising wasteform that shows a good potential for resistance to radiation damage. To rapidly and systematically study the effects of radiation damage Heavy Ion Beam implantation will be used to accelerate the effects of radiation damage. This will allow for different qualities to be determined, such as the Critical Temperature of Amorphisation, the temperature at which the rate of radiation induced amorphisation is the same as the rate of recrystallisation. Characterisation of the these ceramics will be carried out through different methods, including Scanning Electron Microscopy and Transmission Electron Microscopy, X-Ray Diffraction and X-Ray Absorption Spectroscopy.