Natural analogues for predicting the reliability of the engineered barrier system for high-level waste

Abstract

The application of natural analogues in predicting the long-term reliability of engineered barrier materials is reviewed. Excellent natural and archaeological analogues exist for predicting the stability conditions for several metals as container materials. Analogues for corrosion-resistant and corrosion-allowance materials are problematical; they are non-existent for the former and restricted to modes of failure (i.e., uniform corrosion) for the latter materials that are irrelevant to their expected failure at weldments, for which there are no suitable analogues. Abundant natural analogues indicate that at temperatures below 100°C, smectitic clay will remain unaltered for more than 106 years. Natural analogues also confirm the expected dissolution behavior and alteration sequence for metastable alteration products of nuclear waste forms under repository conditions. Numerous natural analogues also confirm the applicability of thermodynamic equilibrium and mass-transfer models in predicting the migration of radionuclides through the near field. The role of natural analogues in guiding experimental work and evaluating the adequacy of experimental apparatus is often overlooked and should be extended in this direction. In particular, “acceleration” of short-term laboratory tests to collect data under repository-relevant conditions that are representative of much longer durations should be based on correlations developed from natural sytems. Analogues composed of two or more components of the engineered barrier system (EBS) should be sought to evaluate the potential for synergistic reactions. Co-precipitation of trace-element concentrations of radioelements under low-temperature conditions is a complex, yet vital, issue that should be resolved by natural analogue studies in conjunction with laboratory tests.