12.3. The prevention of the release of harmful amounts of radioactivity beyond the site boundaries has become the most important objective in the design and operation of nuclear power plants. Although our indus­trialized society has become accustomed to other types of hazards, a public sensitivity to the effects of radiation has played a strong role in the ac­ceptability of nuclear power plants. This has been so although the actual risks to public health have been substantially less than those from the burning of fossil fuels [1].

12.4. The present generation of nuclear power plants in the United States and many other countries now have numerous design features that make the risk of harmful accidental release of radioactivity to the public extraordinarily low. These features have evolved not only through con­servative design, but also by continued analysis and research on the nature of postulated accidents. The design and operation of nuclear power plants are also strictly regulated to assure public safety. In fact, regulatory re­quirements have an important role in establishing the level of safety or risk that is acceptable. Therefore, throughout this chapter, we will mention relevant regulatory considerations, as appropriate.

12.5. In the United States during the 1970s, the ordering of new nuclear power plants ceased, primarily because of economic factors and uncertainty regarding long-time regulatory requirements. A contributing economic fac­tor was the added cost of many new safety-related features. In addition, public acceptance was eroded by the Three-Mile Island accident in 1979, and further reduced by the Chernobyl accident in 1986. Since there will be a need to construct new plants to meet energy requirements, substantial efforts have been made during recent years to develop advanced “next — generation” designs that will have passive safety features and be economical to construct. Improvements in regulatory procedures have likewise re­ceived attention.

12.6. Our purpose in this chapter is to describe the many aspects of reactor safety, including accident analysis. Design features can best be understood in light of postulated accident scenarios. Also, with this back­ground, the advantage of future plant passive features can be examined.