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Proceedings of the Eighth International Conference on Probabilistic Safety Assessment & Management (PSAM)

Michael G. Stamatelatos
Michael G. Stamatelatos
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Harold S. Blackman
Harold S. Blackman
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ASME Press
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A construction license was granted in early 2005 for a 1600 MWe European Pressurized Water Reactor to be built in Finland at the Olkiluoto site.

As required by the Finnish regulations, a preliminary Level 1 and 2 PSA (design phase PSA) was submitted with the construction licence application. During the detailed design and construction of the unit, the design phase PSA will completed into a construction phase PSA, which is appended to the operating licence application.

The core damage frequency of a new unit shall be less than 10−5/year and the frequency of exceeding the severe accident release limit (no early health effects and release of Cs-137 less than100 TBq) shall be less than 5·10−7/year.

The design phase PSA covers Level 1 and Level 2, full power states and low power and shut down states. In addition to internal initiating events (transients, LOCAs) also area events (internal fires, floods) and external events (seismic events harsh weather conditions and ocanographic phenomena) were considered. The scope and depth of the external events analysis are still quite limited. Internal fires and flood analyses cover only a few specific cases which have been quantified. A screening analysis has been performed for harsh weather but only three cases have been quantified: frazil ice in seawater, organic material in seawater and simultaneous strong wing and snow. No quantification was carried out for seismic events. Considering the low seismic activity in Finland, the seismic design requirements and past experience, it was argued that the seismic risk can be shown to be reasonable.

The incomplete quantification of area events and external events was explained, at least partly, by the fact that layout and systems design had not been completed and adequate input information had not been available for detailed analysis.

The regulatory review of the design phase PSA was focussed on establishing whether the quantitative risk limits can be fulfilled. The review of the area events and external events PSA was done jointly with the review of the PSAR related to internal and external hazards. This joint review will continue during the detailed design and construction phases, for example, regarding building and systems design and FMEA.

The conclusion of the review was that the detailed design of the plant can be carried out so that the risk limits can be fulfilled and that the risk due to area events and external events constitute only a moderate fraction of the risk limits. However, a number of remarks and requirements on further work were made in STUK's review reports.

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