Radiation-stimulated drift and escape of radionuclides from glassy matrices

In evaluating the effectiveness of materials for solidifying radioactive wastes the most important indicator is the rate at which radionuclides escape from the matrix by ground water and leaching is taken into account. The normalized rate of escape from modern matrices (borosilicates, phosphate glasses, the material SYNROC, etc.), measured under laboratory conditions, equals 10-7-10-5 g·cm-2·days-1. Storage locations and methods that would reduce to a minimum the possibility of contact between the matrix and groundwater are being sought. There arises the question of the rate of escape of radionuclides from the matrix under conditions of dry storage. The paper describes a phenomenon that can lead to the accumulation of radionuclides at the interface between the matrix and the metal casing. When the matrix breaks down owing to corrosion or for some other reason the radionuclides accumulated on the surface will enter the environment directly from the interface. The value determined by an equation derived here establishes some lower limit for the rate of escape of radionuclides from the matrix under any storage conditions. This limit cannot be lowered merely by increasing the chemical stability of the matrix with respect to water