Managing the risks of the backfill production line from material acquisition to installation

Document available in extended abstract form only. The tunnel backfill of Finnish KBS-3V type repository for spent nuclear fuel consists of foundation layer that is installed at site, pre-compacted backfill blocks that fill most of the tunnel and bentonite pellets to fill the gap between blocks and tunnel wall. In order to ensure the quality, availability, and timely delivery of backfill materials and components, and further to ensure the fulfillment of the requirements and specifications set for backfilling of deposition tunnels, the backfill production line was explored step-by-step, and risks related were defined and analyzed. The work described in this paper was initiated by Posiva Oy and is reported in Keto et al. (2012). The first part of the backfill production line is described in Figure 1 for Friedland clay that is designed to be used for the backfill blocks. It consists of excavation, processing and delivery of materials to backfill production facility. Second part of the production line consists of manufacturing of the backfill components, and the third part is the installation. A preliminary risk assessment was done in 2011 for the acquisition of Friedland clay and manufacturing and installation of foundation layer, blocks and pellets. The critical points of the production line were determined using a material flow description where risk is defined as a probability of something unwanted to happen times the severity of the consequences. Risk analysis was performed by going through the whole backfill production line step by step and analyzing all the incidents, which have occurred (or might occur) during the backfilling operations. A risk number from 1 to 25 was given to each step of the chain depending on how long delay the problem causes and how often it occurs. Low risk was the target for each step of the chain, medium risk was considered tolerable, for high risks management actions to decrease the risk number were considered and extremely high risks were not tolerated at all, i.e., the chain was changed in a way, that the risk decreases to risk numbers below 21. Based on the given risk numbers, the need for quality assurance testing, monitoring or other risk decreasing actions were assessed for each step of the chain or at least for risk numbers above 13. Highest risks for the production line of blocks were discovered to be related to material availability. Hence, the main conclusion was that in order to decrease the risks there needs to be more than one material supplier available. In 2012, the material acquisition and quality work is continued by optimizing the chain for block material iteratively, by defining the acquisition part of the chain also for other backfill components (pellets, foundation layer material), and by performing a preliminary risk assessments for these materials correspondingly