American Scientist

Three Mile Island: A Nuclear Crisis in Historical Perspective. J. Samuel Walker. xii + 303 pp. University of California Press, 2004. $24.95.

The accident at Three Mile Island Nuclear Generating Station in Pennsylvania on March 28, 1979, was "the single most important event in the fifty-year history of nuclear power regulation in the United States," says J. Samuel Walker. Many critics of nuclear power point to the accident as a turning point for the industry, noting that no new plants have since been ordered in the United States and that many planned in prior years were subsequently canceled.

Walker provides a gripping, detailed account of the accident and an analysis of its impact and significance in Three Mile Island: A Nuclear Crisis in Historical Perspective. It is his fourth book as the official historian of the U.S. Nuclear Regulatory Commission (NRC). In the preface Walker assures readers that he had complete independence as the author and that the NRC placed no restrictions on what he could say. However, Walker provides an historical account of the events; he does not evaluate the performance of the NRC during those events.

The first two chapters effectively fill readers in on the historical context for the accident, giving a brief overview of the government-supported growth of commercial nuclear power in the 1960s and 1970s, and describing the emerging controversy during that period over the safety of nuclear power. The public worried both about the risk of accidents and about routine low-level releases of radioactive material. (The latter concern was inspired in large part by fears of cancers caused by exposure to radioactive fallout from nuclear-weapons testing.)

Many people contended that the Atomic Energy Commission (AEC) could not acceptably regulate nuclear power at the same time that it was engaged in promoting it. So as Walker recounts, Congress passed the Energy Reorganization Act of 1974, dividing the AEC into two entities: the NRC, which was charged with regulating commercial nuclear technology, and the Energy Research and Development Administration, which assumed all of the other roles of the AEC and later evolved into the U.S. Department of Energy. Walker provides some interesting descriptions of the last days of the AEC and the selection of members of the new commission.

Reacting to the OPEC oil crisis of 1973, the Nixon and Ford administrations launched Project Independence, an effort to meet our energy needs without depending on foreign sources. President Ford, in his 1975 State of the Union address, set a goal of having "200 major nuclear power plants" in operation within 10 years. Nevertheless, a "nuclear power slump" ensued. Walker attributes the failure to follow Ford's plan to rising costs—the energy crisis drove up the fuel prices for electric utilities, and the then-rampant inflation in interest rates made it hard to raise capital for new plants—and to a decline in the demand for electricity that occurred because the country was in a recession. Very high interest rates persisted through the end of the 1970s. By late 1975, 122 out of 191 nuclear power projects had been deferred and 9 had been canceled.

In chapter 3, Walker gives a simplified explanation of the principal safety issues with reactors of the same type as Three Mile Island Unit 2, where the accident took place. Even though he uses fairly plain language, readers who are not already familiar with the technology involved may find this material tough going. Nevertheless, this chapter is a useful technical preamble to the account of the accident itself.

The core of the book consists of six chapters, one covering each of the 5 days (Wednesday, March 28, through Sunday, April 1, 1979) of the crisis phase of the accident and another covering its immediate aftermath. Walker draws on the full panoply of sources for his presentation of events, but principally on the report of the Kemeny Commission, which President Carter appointed immediately after the disaster to investigate its causes and make safety recommendations, and the Rogovin Report, which was the product of the NRC's own inquiry into the matter. These chapters are well annotated: ­References include the full set of specific sources for a passage, not just citations for quotations.

Walker describes events and actions in language that any reader can easily understand. His account is quite accurate. I was a member of the NRC staff assigned to prepare the Rogovin Report, and I feel that Walker has caught the essential character of the remarkable degree of confusion that prevailed throughout the course of the emergency. That confusion was caused by the inadequate flow of information between all of the responsible parties: the plant operators (Metropolitan Edison Co.) and their own management, Governor Richard L. Thornburgh and other Pennsylvania authorities, the NRC headquarters staff and the Commission, and the NRC regional staff and headquarters staff who went to the site early in the accident. Walker includes short background descriptions of key participants to enhance understanding of their actions.

The chain of events that precipitated the crisis at the plant included a number of minor equipment failures, but operator errors (to which design flaws contributed) converted those malfunctions into a major accident. The first problem occurred at about 4:00 a.m. on Wednesday in the turbine building, in the condensate cleanup system, while the plant was operating at about 97 percent power. The pumps in the condensate system turned off for unknown reasons, leading to a trip, or shutoff, of the turbine and the pumps that fed water back into the steam generator. This in turn caused the nuclear reactor to automatically shut down—a response the operators were trained to expect. They were also trained to expect that an energy surge into the steam-generating system would follow, because even after a reactor trips from full power and nuclear fission stops, immediate radioactive decay of isotopes in the core continues to generate about 5 percent as much heat as is produced when the plant is operating at full power.

The energy surge into the steam-generating system increased pressure in the reactor coolant system and in a device called the pressurizer, causing the pilot-operated relief valve (PORV) to open to relieve that pressure. This too the operators were trained to expect, but they were not trained to recognize the symptoms that would ensue if the valve stuck open, as it did. They had no way of directly ascertaining the water level in the pressurizer. When the valve stuck open, venting steam and reactor coolant into the containment building, water was being lost from the pressurizer, but operators didn't realize it; instead they got the false impression from the high pressure readings that the reactor cooling system was overfilling, and they worried that the pressurizer was "going solid"—reaching a state of being entirely filled with water (rather than water plus a cushion of steam)—a condition they were trained to avert. For hours the operators acted on the misperception that the cooling system was overfilling (taking such ill-advised steps as turning off the water pumps in the emergency core cooling system) and ignored all other contrary signals, including high temperatures in the core, instability in the flow of reactor coolant, high radiation in the containment building and so forth. It was not until 6:22 a.m. that a shift supervisor who had just arrived on the scene figured out that the PORV must be stuck open, and closed its backup, a block valve.

Therein lies the confusion that characterized the accident: The operators did not really understand what had happened and were unable to explain it to their own management, to the NRC, to the State of Pennsylvania or to the public.

The devastation of the reactor core—about half of which melted, releasing great amounts of hydrogen gas into the reactor coolant system and into the containment building—was essentially over by the evening of the first day, Wednesday. Thursday, Friday, Saturday and Sunday were occupied by slowly cooling down the reactor and venting the hydrogen from the reactor coolant system. An understanding of what had happened was slow to penetrate the fog of confusion that prevailed at all levels. So there was an evacuation crisis on Friday morning, and fears that the hydrogen bubble might catch fire or explode extended even into Sunday, when President Carter visited the site. Fortunately, the grievous damage to the reactor did not result in any injuries or deaths, in large part because of the robust design of all of the plant's systems.

The book describes all this and concludes with an interesting discussion of the long-term effects of the crisis at Three Mile Island. This last chapter covers the extensive investigations that followed the accident, and the analyses, recommendations and reforms that resulted from them. The incident was "a major embarrassment and a severe setback" to the fortunes of the nuclear industry; however, it was not really a singular turning point, since—as noted above—many nuclear power projects had already been deferred or canceled years earlier. After the accident, another 19 planned nuclear plants were canceled, including some that were nearly completed.

The TMI-2 cleanup took 11 years and cost about $1 billion. Although at the time of the accident, damage to the core was believed not to be extensive, continuing investigations ultimately revealed that about 70 percent of the core had been damaged and 50 percent of it had melted. Some nuclear critics had asserted that a core meltdown would inevitably breach containment. In the 1960s, nuclear critics had coined the term "the China syndrome" to describe an accident in which a core would overheat and melt through the bottom of a plant and down through the Earth's core toward China, and two weeks before the accident at Three Mile Island, a movie called The China Syndrome was released, a thriller about the dangers of nuclear power. But at Three Mile Island, the pressure vessel did not fail (which would have allowed the core to fall into the containment structure), even though it was not designed to withstand the heat the accident generated. Researchers concluded that when a portion of the molten core first reached the bottom of the vessel, it was cooled by the small amount of water that was still there and solidified into a crust that helped protect the vessel floor from the heat.

Walker reports that studies looking for long-term health effects from radiation released during the accident have reached conflicting conclusions. But it appears any increase in cancers is slight enough that it may have occurred by chance.

This is a comprehensive historical account, with 42 pages of notes, an essay on sources and a 13-page index. But despite these scholarly trappings and the complexity of the events described, the book is eminently readable.