International Geologiical Congress - Oslo 2008

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NWG-02 Geology and disposal of nuclear waste: Nordic approach - special aspects of the disposal in crystalline bedrock

 

How to licence a disposal site for spent nuclear waste?

 

Kaisa-Leena Hutri, Radiation and Nuclear Safety Authority (STUK) (Finland)
Tero Varjoranta, Radiation and Nuclear Safety Authority (STUK) (Finland)
Risto Paltemaa, Radiation and Nuclear Safety Authority (STUK) (Finland)
 

 

Components of the regulatory process are: development of regulations and guides, review and assessment, authorization and inspection and enforcement. This approach is valid also to licensing a disposal facility for spent nuclear fuel.

Finland has the following regulation hierarchy: Nuclear Act, Government Decrees, YVL-Guides, STUK's decisions. The general safety regulations, issued by the Government, are not disposal technology specific, but the more detailed guidance is specifically targeted towards the suggested KBS-3 disposal system. The requirement development process is stepwise; requirements are developed in synchrony with developing safety relevant information. STUK follows the global trend in developing regulations; safety requirements are more performance based than prescriptive.

According to the Finnish regulations, a disposal facility, not a site as such is licensed. STUK's mandate covers both nuclear and radiation safety. STUK's regulatory control is safety based: structures, systems and components (SSC's) are classified based on their importance to safety. A SSC is defined safety significant if:
­its malfunction or breakage can significantly increase the radiation, exposure to people or the environment, it prevents the occurrence and propagation of transients and accidents, it mitigates the consequences of accidents and radiation releases.

A similar logic can be applied in the case of a disposal facility. The main safety driver and the most important safety function for STUK is "ensuring the integrity of the containment of the disposed waste", i.e. isolation. The secondary safety function is "effective limitation of release of radioactive materials", i.e. retardation.

At the Olkiluoto site, with respect to geosphere, STUK's focus is on important factors to the isolation and retardation properties of the site: stable chemical and mechanical conditions. Understanding how they are maintained or jeopardized, constitutes the basis for performance based safety requirements.
In setting requirements, STUK's main focus is on how the system behaves during an expected evolution, when the system experiences transients and disturbances, and in accident type of circumstances. Since detailed prescriptive requirements can not be given, importance of safety culture is emphasized. STUK reviews studies and technical plans for final disposal, with the aid of supporting experts. The most important documents to be reviewed is the Safety Case portfolio prepared by Posiva. In reviews and assessments, emphasis, again, is on the safety functions. One key issue is that is the current knowledge and understanding of the site and its forthcoming evolution sufficient.
Licensing of a nuclear facility in Finland is a step-by-step process. The first step is the Decision in Principle. Next steps are the Construction License, and Operation Licence. The fourth element of a licensing process is inspections and enforcement. Again, they are targeted to safety functions.

 

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