2002:22 Review of data types for the SKB site investigation programme

SKB is currently undertaking a detailed site investigation programme (SIP) to characterise the geology and surface ecosystems in areas around potential sites for a planned repository for spent nuclear fuel. This report reviews site specific and generic data types needed to characterise biosphere processes relevant to the evaluation of long-term radiological safety in the context of assessments of future impacts arising from the deep geologic disposal of spent nuclear fuel. Focus is on the types of data that make up the different elements of radiological assessment models and how the data used relate to site-specific characteristics. The relevance of the SIP to the development of assessment models for long-term assessment is addressed, including the representation of the geospherebiosphere interface.

Reference to SKB’s programme is made in order to determine how well the current programme will meet the needs of assessment models that will be developed and used in the assessment of long-term safety. The review also provides SSI with a basis for the planning of further SSI R&D work. The process, by which site-specific information is converted into a form suitable for use in numerical assessment models, can be quite complex. An overview of assessment model concepts is provided and the links between these and real-word site information considered. Focusing on the needs of assessment models, the review provides a summary of the main types of analyses and site-specific models that are needed for safety evaluations. Review of the SIP indicates that information from the programme feeds into a set of detailed site description models. However there is a gap between the descriptive components and the detailed model descriptions needed to configure numerical assessment models. Details of system evolution are not clearly dealt with in the programme.

The SIP focuses on a detailed description of the site the present day. However, radiological impacts are not expected to reach their peak until far into the future. It is not yet apparent how SKB will use SIP information in the representation of the biosphere system at future times. It is concluded that the SIP addresses the right kind of entities to allow radiological assessment models to be defined. However it is suggested that a change of emphasis be introduced, so as to focus more on the driving forces for contaminant bearing material fluxes rather than on turnover times. This means that more attention should be paid to the physical transport processes, integrating existing details of the different ecosystems relevant to Swedish conditions. Developments of assessment modelling capability should consider the need to include a more spatially extended assessment model representation than has been the case so far in radiological assessments.