Passive long term safety of disposal system for low- and intermediate-level radioactive waste

About 100000 m(3) of solid conditioned low- and intermediate-level radioactive waste is to be disposed in a near-surface repository in Lithuania. In the previous studies in Lithuania quarried Triassic clay has been identified as the main candidate soil to seal radioactive waste disposal vaults. A large scale compaction test was performed in field similar conditions in order to investigate compactability of the Triassic clay and to confirm performance of the clay barriers as well as to select barriers emplacement methods. Two industrial compaction methods were applied and compared. The results of the test confirmed very good mechanical and isolating properties of the compacted Triassic clay and that the required characteristic of the clay layer can be reached using the both investigated compaction methods. This smectite rich Triassic clay can be applied in disposal facilities of radioactive as well as other dangerous wastes. Analysis of longevity and performance of the clay liners confirmed high safety level of the near-surface repository. Use of natural clay for engineered barriers yields a high performance. The proposed multiple barrier system provides adequate isolation of disposed waste within a required period of time. Safety of the repository is achieved by passive methods not requiring further supervision and maintenance.