In many countries, the safety performance of the NPPs is periodically followed and characterized via the periodic safety review (PSR) approach [24]. The regulatory review and acceptance of the PSR gives the licensee the permission to operate the plant for up to the end of the next PSR cycle (usually 10 years). The regulatory system does not limit the number of PSR cycles, even if the new cycle is going beyond the original design lifetime of the plant. The only condition is to demonstrate the safety of the plant operation for the next PSR cycle while maintaining safety and operational margins.

The PSR is a tool that may be used by regulators for the identification and resolution of safety issues in NPPs. In this framework, continued operation may be strived for by applying the results of the PSR, by identification and resolution of the safety issues as a condition of operation for the new PSR cycle. The PSR is not an adequate tool to control changes and tendencies with an evolution time shorter than 10 years. It is also not a suitable system in case the licensee needs a technological guarantee for a long term operation longer than 10 years; in many cases economical considerations suggest an extension of 20 years, or more, of the original design life. Figure 4 shows the flowchart of an overall process for periodic safety review of NPP.

However, it must be noted here that the concept of PSR was developed to be part of the normal regulatory or safety monitoring process, and not specifically to justify beyond design life operation of a plant. The PSR was originally used primarily to assess the safety status of the plants designed to early standards. In these cases, the PSR gives an overall review of all aspects of plant operation that may be relevant to safety. This review includes subjects such as emergency arrangements, organization and administration, procedures, research findings and feedback of experience. All of them are mainly relevant to current operation, and not directly related to the justification for continued operation.

A PSR implemented beyond the original NPP’s design life may require a deeper safety review, addressing the following:

• Evaluation of the plant safety against current standards;

• A new evaluation and/or qualification for items affected by time-dependent phenomena;

• The AMP, which has to be extended over the extended operating life; and

• A new safety assessment, to show that the as-designed conservatism (not the safety margin) may be reduced, based on improved plant operation practices and better understanding of the degradation mechanisms. The overall safety margin must be kept consistent with current safety requirements.

In conclusion, a full scope PSR applied with a view beyond design life operation is fully not different in principle than a usual PSR applied during the design life at ten-yearly intervals, but the emphasis has to be oriented to the ageing of SSCs limiting the total plant operational life and always on the related safety issues. Table 2 shows the list of PSR implementation in Member States.

Starting point
of
PSR

Steps

of

review

procedure

End point
of
PSR