The three oldest Swiss nuclear power plants started operating in 1969 (Beznau-1), 1971 (Beznau-2) and 1972 (Mühleberg), respectively. This means that Beznau-1 will celebrate its 40th anniversary in 2009. Accordingly, long-term operation has been an issue in Switzerland for some years and, as long ago as 1991, the regulatory authority required all operators to have an ageing monitoring programme (AMP) in place.
The law does not specify any restriction on the period of operation; nuclear power plants can be operated as long as they are safe. For this reason, the assessment of safety is accorded high priority. There is a requirement for systematic annual safety assessments and a comprehensive Periodic Safety Review (PSR) every 10 years.
This review covers the presentation of the safety concepts, an assessment of operational management and operational behaviour, a deterministic safety status analysis including the assessment of all safety equipment and of any available incident analyses, together with probabilistic safety analyses at levels 1 and 2 taking account of all internal and external triggering events. The PSR must also include a predictive safety assessment for future operation, and must identify any back-fitting measures that are necessary.
One key element of a PSR is the evaluation and assessment of the AMP. According to this programme, the ageing mechanisms must be identified for all safety-relevant components or groups of components, and potential gaps in the monitoring concept must be recognised and eliminated. Moreover, experience gained from maintenance and operation must be evaluated and findings from research, technology and industry must be taken into account. All this information must be recorded in component-specific fact sheets.
This concept of continuous safety review and monitoring of ageing makes it possible to take responsibility for safe plant operation even beyond a period of 40 years.
This article was published in the July edition of “Contrôle”, the periodical of the French regulatory body, Autorité de sûreté nucléaire (ASN).