There are many reactors in operation over the age of 25 years, relative to typical licensed operation of 30-40 years (IAEA-TECDOC-1084, 1999; Figure 2.6). Without extension of life there would need to be significant investment to replacing generating capacity by new plant (nuclear or non-nuclear). This is the situation in many countries in Western and Eastern Europe, in the Russian Federation and in the US.

There are obvious incentives in extending the life of a plant. The capital costs of building new plant (even non-nuclear plant) are likely to be high compared with a plant that is continuing to operate well. Decommissioning activities will be delayed and thus present day decommissioning costs are avoided. In decision-making for lifetime extension, there are various factors that need to be considered.

Firstly, the technical feasibility must be considered. The performance of major plant components for an extended period must be guaranteed. Integrity of structures such as the reactor pressure vessel, steam generators, pressurisers, primary and secondary circuit pipe­work and the containment structures must be assessed against any deleterious effects of ageing. In general, ageing processes reduce margins for operation and it may be difficult to substantiate the performance of these components for long lifetime extensions since the original lifetime of the plant will have been set at the operational limits of these key components in the first place.