SKB has been conducting an appropriate scientific and technical programme of research and development work to investigate the many processes that may affect the choice of backfill materials, the practicali- ties of backfill emplacement, and the properties of the emplaced backfill that may affect long-term radiological safety. On the basis of this re- search and development work SKB has outlined a process for backfilling the repository deposition tunnels.
SKB’s research and development programme has identified and addres- sed, but not yet resolved various potential practical hindrances that may affect the backfilling process. Principal amongst these potential practi- cal hindrances are the effects of water inflow to the repository tunnels on the backfill materials during the backfilling operations (e.g. piping and erosion, wetting of the backfill bottom bed). The magnitude and significance of these hindrances will depend very much on the condi- tions (e.g. of water inflow) encountered underground in the repository.
The rate of backfilling that can be achieved is another key factor that will require further consideration. Further work would also be needed to develop and/or obtain and test presses for the production of the largest backfill blocks in the reference design, which lie above the range of current experience. It may be beneficial to continue investigating improved methods for backfill block emplacement.