10.1. INTRODUCTION/OBJECTIVES

The purpose of this chapter is to describe briefly the evolutionary water reactor designs that have evolved from current generation commercial reactors. These evolutionary designs have been developed during the 1990s, taking advantage of lessons learned from existing plant. The chapter focuses on water reactor systems because these occupy the dominant position among the evolutionary reactor designs that are currently under consideration for building in the short term. Other types of advanced reactors are considered later in the book. There is no attempt to describe all possible designs in detail. Rather the approach is to categorise the various designs into different types and then describe the representative features of the reactors within a given type. This enables the reader to understand the general design features that are currently being put forward. References are given for the comprehensive range of reactor types.

Various evolutionary improvements have been proposed for all the major water reactor types currently in operation, i. e. PWRs, BWRs, and HWRs. Common general features are simplification in design to reduce cost, coupled with increased safety features. Many of the designs are available at different power capacity ratings, from medium size, e. g. ~ 500-600 MWe range, through to 1000-1300 MWe range. These have been put forward to provide more flexibility to meet the current market demand but also have evolved to meet perceived changes in demand. There was a trend in the mid-1990s to produce medium-range designs to take advantage of increased passivity in design. However, the economics of larger plants are now thought to be more favourable, and present trends are more towards the larger plant scale. Further it has been shown that the medium-sized passive designs can be scaled up.