Use of reference biospheres to prove long-term safety of repositories for radioactive waste Workshop, Berlin, August 2008

Topics of Discussion: Session 1: Climate impact on biosphere modelling Chair: Dr. G. Kirchner, BfS Conclusions: Focus should be on environmental impact instead of climate impact only. There is no climate that establishes a “worst case”, but at some latitudes there seems to be a trend that a warmer and thus dryer climate leads to higher doses (irrigation). Transition phases are of high importance, as they might result in higher releases. Geosphere/ biosphere interface processes are of high importance. BIOCLIM may be a valuable methodology but downscaling needs much effort.

Topics of Discussion: Session 1: Climate impact on biosphere modelling Chair: Dr. G. Kirchner, BfS Conclusions: One key aspect is the influence of the climate on the hydrological cycle. Site specific scenarios differ drastically depending on whether glaciation has to be assumed.

Topics of Discussion: Session 2: Radionuclide transition processes between biosphere models and/or from geosphere to biosphere Chair: Dr. J. Wollrath, BfS Conclusions: There should be a detailed understanding of the groundwater flow system to define radionuclide outlets. Influence of environmental changes on groundwater flow and RN transport should be assessed in more detail; emphasis should be on the dynamics of changes and related accumulation processes. Processes at the biosphere and geosphere transition zone are of major importance. Cooperation of experts is needed. Site specific assessment is essential to model the transition processes.

Topics of Discussion: Session 3: Radiation protection criteria (specific reference biosphere models, dose/risk constraint, size of critical group, etc.) Chair: Dr. K. Gehrcke, BfS Conclusions: Wells show high variabilities with regard to the capacity etc -> no standard well can be defined -> well scenarios are not always conservative Simulations should be performed for various age groups. Informations on the influence of climate change on mobility and biotic accumulation of radionuclides in various ecosystems are available from the literature, whereas influence of rising CO 2 levels on these processes is still a growing scientific domain.

Topics of Discussion: Session 3: Radiation protection criteria (specific reference biosphere models, dose/risk constraint, size of critical group, etc.) Chair: Dr. K. Gehrcke, BfS Conclusions: Biosphere models should be based on a site-specific prediction of potential future developments. For each of these, the specific biosphere models should balance the generic nature of any long- term prediction with the complexity needed for including all major pathways to man. Selection of the parameters for the critical group should account for the distribution of behaviours, consistent with viable existence (at least at some level of sustainability) in the biosphere system assumed.

Topics of Discussion: Priorities of future work Chair: Dr. G. Kirchner, BfS Evaluation of radionuclide accumulation and release during climate transition phases. Processes in the geosphere/biosphere transition zone should be modelled in more detail with special regard to long term erosion of soil/ rock climate induced changes to hydrology. It should be reconsidered whether well scenarios are a conservative approach for estimating doses to humans. Information on uncertainties of dose coefficients should be estimated for the radionuclides of primary interest for waste disposal.