Waste Forms–French Leaching Test Compared with Lysimeter Tests

Abstract

Leaching tests are a means to determine if a radioactive waste package is acceptable for final disposal in accordance with the requirements of the regulation authorities. The relation between the leaching behavior of solidified waste with hydraulic binders or polymer matrices in the following different testing conditions has been examined: (1) French standard leaching tests (immersion in a specific volume of shallow land-disposal groundwater); (2) lysimeter experiments in various hydraulic environments with lower water contents. Real lysimeter experiments are complex, and their relations with a standard test are even more so; therefore, after a brief survey of the generally published works confirming this complexity, the choice of an approach starting from a step-by-step simulation is defined, and the experiments are presented in order of development. The results generated for cemented wastes provide the following conclusions: (1) Activity fractions released are little different (maximum difference is 25%) between the two following types of tests: (a) the type of test where waste forms are placed in contact with an inert simulated backfill material with different moisture contents (from a 35% volumetric water content in saturated state to {approximately}2% in unsaturated equilibrium) and with sequential renewal of the leachant; and (b) the referencemore » case derived from the French standard leaching test. (2) A rough preliminary trial of waste forms in a silica sand backfill led to the same conclusion as the results of waste forms release in a backfill material simulated by glass beads. (3) Moreover, with a high steady flow rate of water directly around the waste form sample and then 10 to 100 times the standard test water volume, the differences in leaching prove to be relatively slight and principally affected by the carbonate contents in the leachant synthetic groundwater. (4) Typical experiments with nearly dry waste environments are also in progress.« less