System understanding as a scientific foundation in radioactive waste disposal, legacy site and decommissioning programmes.

Ongoing national programmes and International forums have in recent decades developed and enhanced methods and strategies in how to address the characterisation of potentially suitable sites for radioactive waste repositories. Siting processes, site selection and site investigation programmes have been conducted for near surface and geological repositories and plans for construction are in progress or have already been implemented. Lessons learned from these national and international programmes are available and results are published. In this paper we synthesize the methods and our lessons learned in how to plan, conduct, and achieve site understanding. Effective site understanding should incorporate a multi-disciplinary and integrated view of geosphere and biosphere information for a site, together with the designed parts of a repository or installation that constitute the total system. We argue that this integrated approach, following a staged program of repository development and adopting a graded approach to assessment at each stage, is to be recommended. The recommendation is supported by the results of international cooperation and progress with national programmes (e.g., the Swedish SKB). Further, we argue that this strategy is valid as a foundation for planning and execution of other types of radioactive waste management programmes such as decommissioning, legacy site management and remediation projects.