CONCLUSIONS OF WORKING GROUP 4

摘要

Immobilisation processes, by which solutes are retained in the geological environment for long periods of time (relative to the timescales of interest for radioactive waste disposal), are commonly observed in nature but mostly represent near-surface phenomena at suitable redox/chemical interfaces. There is a general lack of documented evidence from deeper, strongly reducing bedrock conditions that are more representative of a repository environment. Furthermore, the available data from all natural observations are difficult to characterise and quantify and are not incorporated into performance assessment (PA) models at present. Working Group 4 examined the main immobilisation processes that are familiar to geologists and explored the possibilities for making them more accessible to PA. Discussions focused mainly on fractured crystalline rocks as these were of greatest interest to the Working Group members.