At most multi-unit CANDU NPPs, the PLiM programme is implemented as part of the annual business planning, work management and asset management processes. There is a yearly review of condition assessments to identify actions for the work plan (maintenance and inspection, 1 year time-frame), business plan (1 to 5 year time-frame), and the strategic plan (> 5 year time­frame). Fuel channel, feeder and steam generator life cycle plans are reviewed annually to identify required inspections and input to the generation plan.

III.1. PLANNING FOR LONG TERM OPERATION

The philosophy at the multi-unit CANDU NPPs has been to preserve the option for LTO, through ageing management of major components. The LTO decision will be made as required, given the lead-time for procurement of major equipment, and potential overlap of units in refurbishment.

Design life for the plant and major components was 30 years. Service life, during which components operate safety and reliably, may exceed the design life. Alternatively components may be replaced at 30 years to provide a longer service life for the plant as a whole. Therefore, unless there are critical components that cannot be physically replaced or refurbished at their end of life, the optimum life for the plant may be based on economics rather than technical issues.

The most expensive component that requires replacement in order to extend plant life is the pressure tubes. Pressure tube replacement or large scale fuel channel replacement (LSFCR) is required at about 30 years, due to ageing degradation similar to what was described in Section 3 for single unit HWRs. LSFCR was accomplished successfully at Pickering A in the 1990s, and there have been developments since then in reducing the cost and time required.

The second most expensive component to replace for LTO of the multi-unit CANDUs is the steam generators. The current target life for steam generators at the older sites (Pickering, Bruce) is to reach pressure tube end of life, so that replacement of steam generators and pressure tubes could be accomplished in the same outage. These two plants have Inconel 600 as the steam generator tube material. Worldwide experience with Inconel 600 steam generator tubes has been that a high percentage of them were subject to stress corrosion cracking so severe that replacement around 20 years service life was required.

The multi-unit CANDU plants have all implemented steam generator life cycle management plans to inspect, monitor and mitigate steam generator degradation to achieve the design life. However, steam generator replacement will be required for life extension, except at Darlington. Darlington is the newest multi-unit CANDU, and has Inconel 800 SG tubes that are not expected to require replacement for LTO.

Bulk feeder replacement is another significant activity that may be required for life extension, depending on the effectiveness of current and planned activities to mitigate feeder wall thinning due to Flow Accelerated Corrosion. Replacing feeders during the LSFCR may actually reduce the duration of the LSFCR by improving access to the fuel channels.

Annual PLiM plans are produced as part of overall utility long term strategic planning (OPG, input from Bruce Power is needed). These life cycle plans contain alternatives for long term operation, including shutdown at design life, or retube and extend life. The main elements of the LCPs are listed below:

• Extended life is to the end-of-life of the replacement pressure tubes (additional 30 years);

• Cost of retube, replacement of SG, feeder replacement and other refurbishment is estimated and input to asset evaluation for each plant;

• Benchmarks are used for change in maintenance costs with age; and

• Environmental, safety and emerging regulatory and licensing issues will need to be considered in any life extension decision.

Alternative operating scenarios are analyzed, using discounted cash flow, to determine the alternative that creates the maximum value for the corporation. Uncertainties in the cost of licensing issues, refurbishment (balance of plant, retube costs), electricity cost, capacity factor, etc. are captured through a sensitivity analysis.

Equipment lifetime estimates and repair/replacement costs are required as input to the life extension decision. Equipment obsolescence is to be addressed by re-engineering and spare parts strategies (control, instrumentation equipment obsolescence and computer system upgrades). The cost of other balance of plant refurbishment activities as described below also needs to be factored into the LTO decision.