§ Mr. Hooleyasked the Secretary of State for the Environment (1) what is the maximum temperature to which vitrified nuclear waste is likely to be subjected if deposited below 5,000 ft in impermeable clay strata; and what studies on this have been made at Harwell;
- (2) what is the maximum temperature to which vitrified nuclear waste is likely to be subjected if deposited below 5,000 ft in salt domes; and what studies on this have been made at Harwell.
- (3) what is the maximum temperature to which vitrified nuclear waste is likely to be subjected if deposited below 5,000 ft in granite geological formations; and what studies on this have been made at Harwell.
§ Mr. Denis Howell:No decisions have yet been taken about whether vitrified radioactive waste should be disposed of in geological formations on land. But if such waste were emplaced below 5,000 ft in granite, clay, or salt domes, it is likely that a maximum temperature of around 100°C would be specified for the repository. This can be ensured by appropriately controlling the age and concentration of the waste in the vitrified blocks.
At the Atomic Energy Research Establishment, Harwell, vitrified radioactive waste has been subjected to the action of water at temperatures between 20°C and 100°C. But in a repository the glass would be contained in a corrosion resistant canister which would protect it from contact with water until such 796W time as the temperature had fallen to around 50°C. At 50°C the leach rate of the glass by water would be between 0.4 and 4 mm per century. This work is relevant to emplacement in granite and in clay. Research on leaching by salt solution is in progress in West Germany and Holland, and the United Kingdom has full access to the results.
§ Mr. Hooleyasked the Secretary of State for the Environment what is the maximum pressure to which vitrified nuclear waste is likely to be subjected if deposited below 5,000 feet in (a) granite, (b) impermeable clay and (c) salt domes; what effect such pressures will have on the leaching or physical disintegration of the vitrified radioactive material; and what studies of these effects have been made at Harwell.
§ Mr. Denis Howell:If vitrified radioactive waste were to be emplaced at levels below 5,000 ft. in granite, clay or salt domes it would be subjected fairly quickly to the natural ambient pressure once the excavation had been backfilled and sealed. The pressure in granite would be about 410 atmospheres and in clay and salt about 330 atmospheres. At these pressures it is calculated that there would be only a very small effect on the chemical reactions between vitrified waste and water. The vitrified waste could not disintegrate because its comprehensive strength is well able to withstand such pressures.