Safety assessment for a geological disposal facility in domal salt: The Dutch case

In the Netherlands, all radioactive waste is currently collected and stored above ground for at least 100 years by COVRA. After 100 years, all radioactive waste must be permanently disposed of. One option for permanent disposal currently considered is a purpose-built geological disposal facility in rock salt, where a combination of natural and engineered barriers is expected to provide the necessary safety. Rock salt, as a natural barrier, is considered impermeable when undisturbed. Therefore, radionuclides can only reach the surface via the mined openings of the geological disposal facility. Here, multiple engineered barriers provide the necessary safety. In the short term, these include concrete seals, HLW packages, and waste forms. In the long term, moisturized granular salt backfill provides containment. Here, we present the safety assessment of a geological disposal facility in rock salt, using the updated Dutch disposal concept and waste inventory. In total, seven different scenarios are modelled: the (1) normal evolution scenario in which the geological disposal facility evolves as expected, and six alternative scenarios: failure of (2) the high level waste packages, (3) failure of the tunnel seals, (4) failure of the spiral ramp seal, (5) flow path between a brine pocket and mine excavations, (6) less probable characteristics of radionuclide mobilization and transport, (7) and reduced long-term sealing by backfill. Model results show that when the geological disposal facility evolves as expected, no release of radionuclides is expected. Likewise, no release is expected in the six alternative scenarios, although differences exist in the extent to which radionuclides are able to travel within the geological disposal facility. These results indicate that the engineered barriers, combined with the natural barrier of the rock salt, are effective in isolating and providing containment during at the least the first million years after closure.