Longer life and increased output may be both attractive objectives for HWR owner/operators. Both objectives could potentially be achieved, with a variety of measures. It is important to note that these changes must not degrade existing safety margins or result in unacceptable environmental impacts. Some of these measures impact the CANDU nuclear steam plant (NSP) that others that apply more to the balance of plant (BOP). The PLiM programme has an important role, both with the LTO and to power uprate, described below.

CANDU power uprates can involve fuel improvements (more heat generation), operational changes that mainly involve equipment improvements (for greater cycle efficiency) and operational changes that mainly involve improvements to plant maintenance, surveillance and inspection (for greater durations between outages). Usually combinations of these changes are considered. The technical and business case for implementing these changes must take an integrated approach and assess the impact of component life and performance, as well as the economic return-on-investment. It also involves the regulator if the changes impact on licensed conditions.

The assessment of changed conditions on component life is typically where the PLiM programme for these components is important and useful. Systematic ageing assessment processes in combination with any previous PLiM assessments are used to assess the revised operational conditions for the component of interest. The specific components that are assessed vary and depend upon the type of power uprate being considered. Typically it could involve the fuel channels, feeders, steam generators, turbine-generators, boiler feed pumps, moisture separator reheaters and the condensers as well as a variety of electrical equipment.

Some of the proposed changes could potentially impact system operating margins. These impacts must be assessed. Any ageing issues related to these systems (or important components within these systems) must also be considered. An example would be boiler feed pump vibration. If current performance (prior to power uprating) is marginal, then the proposed power uprated conditions must be carefully assessed. For example, one might first think that this would make the current situation worse but it might actually improve performance (for instance if the changed condition moved pump operation to a better point of the pump performance curve).

Assessing the power uprate changes is not just technical but also involves a detailed economic assessment. Usually the proposed changes are grouped into several packages. Then the net present value (NPV) of each package (say Option A, Option B, etc) is evaluated and compared to a base case. The economic calculations include parameters that affect the electricity generation value. Some of these are electricity price, fuel cost, Operations, Maintenance and Administration cost (OM&A) and capital cost. The recommended option is the one that provides the greatest improvement in net present value (NPV) over the remaining plant life, compared to the base case, provided the associated technical risks are acceptable.