Since the early days of nuclear power, a large number of different design concepts have been considered. These have now been licensed, built and operated successfully but not without significant effort and investment. Now that these systems are proven, the tendency has been to focus on evolutionary designs (IAEA-TECDOC-1117, 1999; Juhn, 1999), largely arising from the need to move forward cautiously. Regulators tend to adopt a conservative line in licensing new developments. Utilities seek to reduce risk by staying close to proven technologies. De-regulation of the industry and reducing investment from governments have resulted in the reluctance of building and financing new prototypes.

Evolutionary water-cooled reactors benefit from the wide range of experience that has been accumulated from operation of present generation plant. This experience has been embodied into the Electric Power Research Institute (EPRI) User Requirements Documents (URDs) and the European Utility Requirements (EURs) and other utility design guidelines. Such international experience has been disseminated through the activities of WANO and the IAEA.

Examples of improved performance that can be established during the design phase include IAEA-TECDOC-1117 (1999), some particular goals, e. g. short outages, overall simplicity of design and on-line maintenance. These can be achieved by improved man — machine interfaces, better computers and IT, more plant and component standardisation and better operator qualification and training. Better availability can be achieved by increased design margins, enabling greater robustness against reactor trip. This can also help in extending plant lifetimes, which are often limited by eroding margins in present day plant.

It should be possible to meet increasingly stringent safety objectives by incorporating new design features. The readiness of these features to improve accident prevention and mitigation has been tested.

Economic competitiveness is important for advanced plants in the same way as for present generation plants. Simplicity of design is a key factor. Further, designs must be substantially completed prior to start of production. This helps to avoid hold-ups in regulatory requirements, long construction delays and facilitates the operations’ manage­ment. The increasing de-regulation of the electricity markets is a continuing drive to ensure designers strive for simpler designs, without compromising safety.

The financing of new plants is likely to require special conditions to minimise risk and, therefore, keep financing rates to a minimum. Conditions to be considered are a favourable national policy regarding nuclear power, economic competitiveness, feasibility of the project, adequate revenues, e. g. from long-term purchase agreements and no open-ended liabilities.

Finally public acceptance of new designs will need to be gained. This may be achieved by education and demonstration that severe accidents of the past would be eliminated through new design technologies.

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