Evaluation of actual/aged condition in safety-critical SCs is the basic method for identifying the ageing mechanisms and their effects on the intended functions. Plant condition has to be reviewed for the feasibility study of LTO. Review and evaluation of plant condition is an obligatory part of both the periodic safety review (Safety Factor 2 in the PSR, see IAEA, 2003) and the justification of safe operation in the licence renewal process.

The scope of review and evaluation of actual plant condition covers the safety — and seismic-classified SSCs and non-safety SSCs, failure of which may in turn jeopardize the safety functions. The review of plant condition is based on the information related to the health of components from the following sources:

• Results of operational information, records of the operational events.

• Failure data, root-cause analysis, failure statistics.

• Outage and maintenance records.

The inspection programme for safety Class 1 SCs is the most rigorous. It includes the following:

• Data of the non-destructive testing of the SCs.

• Evaluation of the results of the in-service inspections.

• Evaluation of the results/findings of the maintenances.

• Evaluation of the results of the ageing management programmes.

• Evaluation of failure data and other lifetime information.

• Evaluation of operational information.

Non-destructive testing is a regular activity at nuclear power plants. However, in the context of the plant review for the justification of LTO, some additional tests might be necessary. Individual programmes can be useful and developed for the Class 1 SCs, the reactor, main isolation valves (if such exist), main pipelines of the primary loops, steam generators and pressurizer.

In the case of SSCs in safety Classes 2 and 3, the most practical review method is visual on-site inspection. Application of the graded approach is useful, so that, in the case of higher importance or safety relevance, the inspection has to be performed for each particular item, whereas the review can be limited to the inspection of a representative sample of the commod­ity. The selection of the representative sample has to be made taking into account its type, the material, dominating degradation mechanism, environ­mental stressors, etc.

There are minor aspects to be checked during the inspections, for example: [10]

After performing all of the on-site inspections, the findings have to be eval­uated and any corrective measures identified. The final result of their eval­uation can result in:

• modification of the maintenance procedures

• modification of the periods of maintenance

• introducing new diagnostic/monitoring measures in order to determine the necessary additional actions

• performing additional evaluation of the situation

• modifications such as implementing new sealing

• replacement of the component for a different type.

The information obtained has to be taken into account while reviewing and developing the ageing management programmes. Review and revali­dation of the time-limited ageing analyses can also be considered as part of the evaluation of the part conditions. Feedback from experience of other VVER plants and the research results provide some guidance and back­ground information for the review and evaluation of plant condition.