In underground repositories for radioactive waste, significant quantities of gases may be generated as a result of several processes. The potential impact of gas generation, accumulation and migration on the performances of the various barriers and, ultimately, on the long-term safety of a repository, should therefore be assessed in the development of safety cases for underground repositories. It was in this context that the EC and the NEA organised a workshop on "Gas Generation, Accumulation and Migration in Underground Repository Systems for Radioactive Waste: Safety-relevant Issues" in Reims, France on 26-28 June 2000. This book includes the texts of the invited presentations, the reports of the deliberations held in the five working groups, as well as the main conclusions of the workshop.

PART A. SYNTHESIS OF THE WORKSHOP
-Executive Summary
PART B. WORKSHOP PROCEEDINGS
Session I. Presentation of the EC/NEA Gas Status Report
-Introduction to the EC/NEA Status Report: "Gas Migration and Two-Phase Flow through Engineered and Geological Barriers for a Deep Repository for Radioactive Waste" by William R. Rodwell
-Gas Generation by Wolfgang Muller
-Gas Migration through Bentonitic Engineered Barrier Systems and through Non-Indurated Clays by Lorenzo Ortiz Amaya and Steve Horseman
-Gas Migration through Indurated Clays (Mudrocks) by Steve Horseman
-Gas Migration through Crystalline Rocks by William R.Rodwell
-Gas Migration through Salt Rocks by Wolfgang Muller
-The EC/NEA Status Report: Conclusions and Outstanding Issues by William R. Rodwell
Session II. Present Approaches to Dealing with Gas-Related Issues in Performance Assessment Exercises
-The Gas Pathway in a Site-Specific Performance Assessment: Nirex 97 by Alan Hooper
-The Treatment of Gas in the SR97 Performance Assessment for a Spent-Fuel Repository in the Swedish Crystalline Basement by Patrick Sellin
-The Treatment of Gas in the H12 Peformance Assessment for HLW Disposal in Japan by Kenji Tanai,Mikazu Yui, Hiroyuki Umeki and Mikihiko Yamamoto
-Treatment of Two-Phase Flow in Repository Performance Assessment at Yucca Mountain by Karsten Pruess
-The Treatment of Gas in the Performance Assessment for the Disposal of HLW and MLW in Boom Clay by Geert Volckaert and D. Mallants
Session III. Regulatory Point of View and Expectations
-Gas Generation in High Level Waste Geological Disposal: Elements for Integration in a Safety Strategy by Francois Besnus
-Licensing Oriented Scoping Analysis of Gas and Nuclide Transport in Underground Repositories by Vijen Javeri and Bruno Baltes
Session IV. Planned Strategies for Dealing with Gas-Related Issues
-ANDRA's Strategy for the Treatment of Gas-Related Issues by Gauthier Vercoutere
-NAGRA Strategy for the Treatment of Gas-Related Issues for Disposal of Long-Lived Waste and Low and Intermediate Level Waste in Sedimentary Host Rocks by Paul Marschall and Piet Zuidema
-GRS/ISTec Strategy for the Treatment of Gas-Related Issues for Repositories Located in Rock Salt by Ingo MUller-Lyda, Vijen Javeri, and Wolfgang Muller
-ENRESA Strategy for the Treatment of Gas-Related Issues for HLW Repositories Sited in Graniteic and Argillaceous Settings by Juan Luis Stntiago and Miguel A. Cunado
Session V. In-Depth Discussion by Working Groups
-Gas Flow Anomalies in Natural and Engineered Barriers by Gunter Pusch, H. Alkan, Y Cinar, R. Meyn and V. Reitenbach
Participants List