Advanced plant designs are being developed to meet the requirements of utilities and regulators discussed above. They aim to provide significant improvements in performance and safety over current generation plants.

As stated earlier, advanced power plant designs are often separated into two categories, evolutionary and innovative, see for example (Juhn, 1999). Evolutionary plants are based on an evolution from an existing design through relatively small changes. The aim is to remain with design features that are proven and hence to reduce technological and other risks. Evolutionary reactors have been developed through the 1990s taking advantage of lessons learned from existing plants. These designs are, therefore, at an advanced stage of development. A number of designs have already received design certification.

Innovative designs incorporate much more radical changes in design compared with existing plants. They may include features that need verification and hence give rise to

less quantifiable risk. By definition these designs are not likely to be available for at least several decades. Table 7.6 gives some indication of the relative investment that is needed between the two categories of plant, before reaching commercial operation.