Mechanisms and interaction phenomena influencing releases in low- and medium-level waste disposal systems

The report covers work done 1986-1990 at Risoe National Laboratory as part of the third EC Research Programme on Radioactive Waste Management. Waste product characterization: Leaching and volume stability of cemented ion-exchange resins. Wet/dry cycling was found to be an important degradation mechanism. Hygroscopic properties of cemented and bituminized radioactive waste. Water uptake from the air can be an important release mechanism when waste containing soluble salts are disposed of by shallow land burial. Water uptake and swelling of bituminized waste including studies on water migration in bitumen membranes and measurements of swelling pressures. Ageing of bituminized products was demonstrated to result in increasing stiffness of the materials. Nickel ferrocyanide in precipitation sludge was found to be unstable in contact with concrete. Barrier material properties: The influence of the pore structure in concrete on the hydraulic or diffusive transport of water and ions through concrete barriers was investigated. The main parameter is the water/cement ratio. A theoretical interpretation is given. Healing of cracks in concrete barriers by precipitation of calcium carbonate was demonstrated experimentally and described by a simplified model. Transport of components between two thin plates of cement paste with different composition stored together in water was found to take place at a low rate. The structure of degraded cement paste was studied using SANS (small angle neutron scattering). Interaction phenomena: - Integral experiments with migration of radioisotopes from cemented waste through barriers made from kaolin, chalk or concrete were made under different external conditions. The results can be used for model validation and some preliminary work was done. (author) 16 tabs., 51 ills., 25 refs