Radioactive waste handling and storage poses challenges due to the inherent chemical and physical hazards of the waste. The wastes from decommissioning range from wet, mobile slurries and sludges to large heavy pieces of plant and building structures.
Individually these wastes may be problematic due to radiological and chemotoxic hazards that may preclude direct man access to facilities in order to deploy equipment. The facilities containing waste do not have man-access. Further waste arising from decommissioning may be mixed and potentially need further segregation, for example pieces of plant such as tanks and vessels may still contain residual liquors, slurries or deposits.
Innovative tools and techniques for the remote handling of waste are required to work alongside or replace baseline technologies so that waste handling is more efficient.
Cryoroc have been making freeze cast ceramics for many years, using their expertise to produce products including lightweight glass-ceramic armoured shielding for the US Air Force Hercules C130 aircraft and ceramic mould used to make the bumper for the Bugatti Veyron.
Freeze Casting is a process which uses a novel ceramic manufacturing route to immobilise radionuclides. The equivalent current process is cementitious grout but the ceramic route introduces a bonding material called a glass-ceramic which crystallizes to form a durable material capable of trapping the nuclides by reacting with them.
The freeze casting process is simple to operate and has low capital cost.
Using a liquid nitrogen tunnel freezer to form the ceramic/waste slurry it would be possible to design a continuous process. The ceramic/waste can be cast into almost any size and shape.
- Ceramic powders (e.g. Molochite & Waste Material) mixed with a colloidal ceramic sol (e.g. Silica) containing ceramic nanoparticles
- Transferred to a mould (any volume) and freeze rapidly to –50ºC (using liquid nitrogen)
- The water in the slurry keeps the sol stable but on freezing the nanoparticles bond strongly together and form a solid which is irreversible
- The frozen casting is brought back to room temperature and dried at 30ºC
- This has high strength even in the green state but can be sintered at elevated temperature
The process is fast and inexpensive since the equipment needed has a low capital cost and the materials used are all commercially available