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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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An EPR (European Pressurized water Reactor) unit is under construction at the Olkiluoto site in Finland. Living PSA is formally integrated in the regulatory process of NPPs already in the early design phase and it is to run through the construction and operation phases all through the plant service time.

A plant specific, design phase Level 1 and 2 PSA is required as a prerequisite for issuing the construction license for a new NPP unit and a complete Level 1 and 2 PSA for issuing the operating license as stated in the Regulatory Guide YVL 2.8. The plant specific Level 1 and 2 PSA should include internal initiators, fires, flooding, harsh weather conditions and seismic events for full power operation mode and for low power and shutdown mode. In practice the treatment of some parts was only qualitative. The following design objectives are set forth in the Regulatory Guide:

— The mean of the probability of core damage is less than 1E-5/a.

— The mean of the probability of a large release (more than 100 TBq Cs-137) must be smaller than 5E-7/a.

STUK reviewed the design phase Level 1 and 2 PSA and issued a safety assessment and positive statement about the application for the construction license in January 2005. The construction license was granted by the Government in February 2005.

The construction of OL3 and the respective licensing activities are in progress. In the course of the construction phase the applicant has to submit some specific PSA applications to STUK in support of drawing up Technical Specifications and inspection programs:

The testing program of safety significant systems and components, which is set forth in the context of Technical Specifications, shall be argued by the aid of PSA and the results of analysis have to be submitted to STUK. Accordingly, PSA is to be used to effectively optimize the test intervals and procedures of components and systems which contain the major risk reduction potential. The relevance of allowed outage times (AOT) of safety systems has to be evaluated with PSA as well.

The on-line maintenance of safety significant systems and components is allowed during operation in accordance with the restrictions set by Technical Specifications. If the licensee wants to perform preventive maintenance work during operation, an acceptable estimate of risk significance of preventive maintenance must be achieved.

The insights of PSA must be used in the drawing up and development of the inspection programs of piping (ISI). While drawing up the risk informed inspection program, the systems must be considered as a whole regardless of their safety class.

The safety classification document was reviewed already in conjunction with the application for a construction license. However, the safety classification has to be assessed with PSA also in the construction phase if substantial design modifications are performed.

The licensee shall submit a construction phase Level 1 and 2 PSA to STUK for review in context of the application for the operating license.

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