Backfilling Measures

A multi-barrier system for a repository comprises #engineered, #geotechnical, and #geologic #barriers. They are to isolate the #radionuclides from the biosphere. The successful functioning of these systems requires that the barriers be permanently effective. However, their integrity can be compromised in many ways. To avoid damage to geologic barriers by rock pressure, cavities must be backfilled to stabilize the rock mass. In addition, construction materials are used to protect engineered barriers. Fluids can react with barriers and thus shorten their functional life, and they transport radionuclides. Consequently, their volume and flow in the repository must be minimized by backfilling measures. In addition, it may be necessary to create stable cavities as fluid reservoirs, which can delay and limit pressure build-up. Backfill materials can also actively contribute to the isolation of radionuclides by containing binding substances that damage the barriers. There are also many ways to reduce the solubility of radionuclides or fix the substances, which means there is a wide range of applications as a geochemical barrier.

Backfilled repository areas can also act as #geotechnicalbarriers to interrupt flow paths in the long term, and thus be an essential component of redundant and diverse sealing systems. Like geotechnical and #engineeredbarriers, backfilling measures must therefore be designed for specific sites and tasks and in the context of the multi-barrier system. This way, the individual elements, in combination and as part of an individually designed decommissioning concept, contribute optimally to the permanent protection of the biosphere.

The facts that solution is already intruding into the Asse II mine and that the radioactive waste has to be retrieved result in numerous specific backfilling measures, such as filling cavities with building material. The support effect of old crushed salt backfill is improved by employing injections that reduce the compactable pore space of the backfill. The work carried out by BGE TECHNOLOGY GmbH shows that backfill improved in this way can also act as a geotechnical barrier in the long term. Extensive work was carried out as part of the KOMPASS I and II research projects with the aim of being able to use the compaction of salt backfill when preparing safety demonstrations. They allow BGE TECHNOLOGY GmbH to reliably model and predict the behavior of salt backfill up to very low porosities and permeabilities. However, any application of backfill requires that the materials and the backfill structures meet a wide range of requirements. As the achievement of a defined installation condition is of particular relevance, the development of quality assurance programs has a long history at BGE TECHNOLOGY GmbH. In the future #Konrad repository, different backfill materials will have to be used, and several material streams and emplacement procedures will have to be considered. It was thus a great advantage to be able to use our wealth of experience. The examples illustrate how BGE TECHNOLOGY GmbH is creating an essential framework for the disposal of radioactive waste in deep geologic formations.