Effective PLiM involves the integration of ageing management and economic planning. As plants age and as HWR owner/operators make decisions on age management programmes and on investments to enhance plant reliability and predictability, economic planning must consider the current and future condition of the plant with regard to ageing.

Most PLiM programmes that have been integrated with the economic planning decision making, utilize an economic model to evaluate operating alternatives for their HWR plants. For example, the following situations would typically be assessed with an economic model that includes the technical costs generated from the systematic ageing assessments:

• An evaluation of outage strategies — is it cost effective to add additional manpower (OM&A) to shorten the planned outage length (increase production)?

• An evaluation of the cost effectiveness of capital upgrades that can increase capacity or MCR (maximum continuous rating) and possibly increase the economic viability of a refurbishment.

• An assessment of when increasing operating and capital costs make a nuclear plant no longer financially viable.

• An evaluation of the additional value that can be realized by maintaining the option for continued operation.

• An assessment of the optimum economic strategy for a new plant design.

For HWRs, economic models specific to HWR technology, licensing practice and electricity pricing practice, have been developed and are being used to optimise decisions on plant projects that involve PLiM. For instance, economic models have been developed with capabilities to handle single unit or multi unit sites, the pressure tube style reactor, re-tubing, and outages not linked to refuelling.

Although repair/replacement for most SSCs is technically possible, ageing of most plant SSCs can indirectly impact on plant costs, because ageing-related behaviour can lead to forced outages, unplanned extensions to planned outages, reduced availability, and increased production costs. Measures to minimize ageing that involve system or component backfitting may be very expensive. For such measures, cost-benefit analysis will be necessary before making a decision. It must be noted that, when the plants get older, this type of cost-benefit analysis will require some assumptions about the planned plant service life.

An effective PLiM programme should ultimately improve capacity factors by reducing the number of unplanned shutdowns and assist in defining strategies to lengthen operating cycles. PLiM can also be a major force in optimizing and even reducing plant OM&A costs when applied properly and early in the life of a plant. An effective PLiM programme also provides rigorous end-of-life estimates and long life strategies needed for economic and risk evaluation of repair/refurbish/replace options.

PLiM is an important input into the long term strategic plan. This plan typically contains alternatives for long term operation, including shutdown at design life, or retube and extend life. Cost of other major component replacement and/or refurbishment is estimated and input to asset evaluation for each plant. Benchmarking (using experience from other plants) and/or system maintenance predictive models are used to estimate the change in maintenance costs with age. Alternative operating scenarios are analyzed, using discounted cash flow, to determine the alternative that creates the maximum value for the HWR owner/operator. Uncertainties (such as cost of licensing issues, major refurbishment, electricity pricing, future capacity factors) are addressed via an economic sensitivity analysis.

In summary, the PLiM programme should be linked to the station business plan. While the primary aim of most PLiM programmes is to improve the availability and assure safety throughout HWR NPP service life, PLiM can have a strong influence (and likely improve) NPP profitability.