ABSTRACT
This chapter discusses the major points of an analysis of the accident at Three Mile Island. A normal accident occurs in a complex and tightly coupled system when there are unanticipated multiple failures in the equipment, design, or operator actions. The accident at Three Mile Island displayed the four characteristics of normal accidents: warning signals, equipment and design failures, operator errors, and unanticipated events. The major operator "error" was throttling back on two high-pressure injection pumps to decrease water pressure, thus allowing the core to become uncovered and to overheat. Failures in the design of the plant and in the equipment were manifold. Key valves failed and had failed before; equipment was out of service, which violated federal rules; leaks abounded; and indicators malfunctioned. Most of the commissioners were critical of the performance of the utility and the Nuclear Regulatory Commission.
