13.18. An evolutionary reactor design is one that draws heavily upon a successful previous design but incorporates many improvements that are desirable as a result of technological development, experience, and possibly new requirements. The basic features are retained so that there would be a high level of confidence that a new plant would operate reliably without the need to first build a demonstration plant.

13.19. An example of this approach for a PWR that is to be available whenever orders for new reactors are forthcoming is the Combustion En­gineering System 80 Plus™ reactor model [4]. Several general needs were addressed in developing this design for a so-called “next-generation plant” which provide some background for new reactor trends. A European PWR design meets similar needs.

13.20. The opinion of utilities regarding desirable characteristics of fu­ture plant designs was determined by EPRI. Of major importance was the need to satisfy public acceptance with regard to safety, economics, and reliability. Design simplification, standardization, increased safety margins, and various technical improvements were felt to help satisfy public con­cerns. However, other issues also affect the attractiveness of utility in­vestment in new plants. Predictable licensing and a stable regulation climate were considered necessary to avoid nontechnical and expensive delays that have plagued the industry in the past. Also recognized was the need to have fair treatment by state regulatory agencies on financial and planning matters.

13.21. Design simplification is accomplished by eliminating unnecessary duplication of functions performed by separate systems or in some cases combining component functions. Both simplification and improved plan­ning should lead to shorter construction schedules, which are essential for improved economics. It is also desirable to include in a new plant features that will mitigate the effects of a severe accident. For example, changing the reactor vessel geometry to deal with molten core material can be ac­complished in a new design at relatively little cost.