An overall approach to PLiM is to consider all the issues relating to plant ageing in a fully integrated programme. Figure 6 shows an overview of a high level comprehensive approach, which determines whether the plant will continue to perform in accordance with the specified expectation or be forced to shut down, depending on several factors influencing the cost — benefit equation to restore the performance capabilities of the asset.

The physical plant assessment focuses on the continuing ability of the structure or system, component to meet the specified performance criteria over its design life. If, in spite of maintenance and or refurbishment, a critical structure or component is deemed not likely to be able to meet its performance requirements, then a timely replacement must be undertaken with due consideration to the associated cost-benefits justification. Otherwise the plant is forced to shut down by default until the issue can be resolved satisfactorily.

Similarly, if the institutional infrastructure is allowed to degrade beyond HWR owner/operator management criteria, then the plant will be forced to shutdown until the underlying issues can be resolved in a satisfactory manner. The issues related with institutional ageing are not discussed further in this report as they are primarily related to performance of the utility management.

The various key elements of a life management programme for physical plant are shown in Figure 7 as follows:

• Screening: Screening/prioritization of systems and components to understand their importance. This will allow for the application of the appropriate ageing assessment procedures.

• Ageing assessment: Ageing assessments are methodologies used to assess the effect of degradation on SCCs and determine the appropriate inspection and mitigation techniques. They include:

• Condition assessment (CA): Typically for less critical systems, structures and components. The CA process may place related components in commodity groups such as instruments, and valves, where they are evaluated together. The methodology entails a general review of plant data in order to establish current condition and to evaluate ageing degradation at a component level. The CA report provides a prognosis for attainment of design life and/or long term operation with associated recommendations. Recommendations provide the technical basis for on­going ageing management of the subject structure, component or commodity and may identify a need for further assessment.

• Life assessment (LA): Performed typically for most critical structures and components that are generally passive in nature and typically designed not to be replaced as part of normal maintenance programme. This involves a rigorous assessment of all plausible ageing related degradation mechanisms. The methodology entails a detailed review of plant data in order to establish current condition and to evaluate ageing degradation at a sub-component level. Similar to a CA, the LA report provides a prognosis for attainment of design life and/or long term operation with associated recommendations. Recommendations provide the technical basis for on-going ageing management of the subject structure or component and may be used for economic planning.

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Systematic assessment of maintenance (SAM): This form of assessment makes use of Failure Mode Effect Analysis (FMEA) methodologies and information from internal and external feedback and R&D findings. It utililizes streamlined Reliability Centred Maintenance techniques, as modified for nuclear plant applications. It is performed for critical systems with emphasis on active components (that are generally designed to be replaced as part of the normal maintenance programme), in order to preserve the defined systems functions [29].

• Integrated safety and performance assessment is an on-going activity primarily managed by the utilities with designer support in order to demonstrate continued compliance with the safety and licensing basis requirements as the plant ages.

• Technology watch programme addresses key emerging issues that may adversely impact on plant safety and reliability and may not be addressed by the assessment process described above. This programme relies on monitoring of the operating experience feedback, recent R&D activities, and new developments in regulatory requirements and industry practices. Utilities should search better methodologies to improve chemical treatment, inspection, maintenance, etc. by actively exchanging information with other plants either directly or through international organizations like IAEA, COG, WANO, INPO, or other organizations (eg. AECL).

• Obsolescence studies are performed on generic plant components that cannot be maintained or refurbished in a cost effective manner due to several factors (such as availability of spares and new developments in technology that make replacement a viable option). Obsolescence relates primarily to instrumentation and control component and computer systems.

• Feedback/Continuous Improvement: Following appropriate disposition of the

recommendations, the PLiM should remain an active programme. The technology watch programme described above provides updates to the information used during the ageing assessment process. The assumptions made and conclusions reached during the initial assessment process should be periodically reassessed to incorporate new understanding of known ageing degradation mechanisms obtained, for example, through R&D programmes and/or operational events. In addition, through surveillance programmes and, occasionally through operational events, previously unconsidered degradation mechanisms may be discovered. The SSC ageing assessments should be reviewed and revised if necessary, to ensure their continued validity.

Establishing a database of all plant information (design, manufacturing, operation, inspection, maintenance) and maintaining it throughout plant life (high degree of utilization by all plant engineers, constant updating) is one of the key factors to achieving a successful ageing management programme.