Validation of a numerical release model (REPCOM) for the Finnish reactor waste disposal systems, part 2

The experimental modelling of the multibarrier system is conducted on laboratory scale by using the same principal materials as are employed in the Finnish reactor waste disposal concepts. Migration of radionuclides is then studied in two or more consecutive layers of these materials. The laboratory arrangements include the following test materials: bituminized resin and cemented ion-exchange resin, concrete, crushed rock, and water corresponding to the materials in the planned disposal systems. Cs-137, Co-60, Sr-85, and Sr-90 are used as tracers, with which the ion-exchange resin, water or crushed rock is labelled depending on the specimen type. The basic specimen geometries are cylindrical and cubic. In the cylindrical geometry the test materials are placed in sequence into PVC-tubes. The corresponding numerical model is one-dimensional. In the cubic geometry the materials are placed within each other forming cubic boundaries. The corresponding numerical model is three-dimensional. Altogether 13 different types of test system were produced. The gamme active nuclides in the cylindrical samples have been measured non-destructively with a scanner in order to determine the activity profiles in the samples. The gamma active nuclides in the cubic samples and the beta emitting Sr-90 in separate samples will be measured after splitting the samples. Three to seven activity profiles have been determined for each cylindrical gamma-active sample. So far clear diffusion is observed in the profiles for cesium and strontium in crushed rock. Diffusion of Cs-137 in concrete and Co-60 in crushed rock is evident, but not so clear. Some activity profiles have been measured for beta active Sr-90 samples, after splitting them. For the cubic samples no activity profiles have been measured yet