You’ve likely heard of the 1979 Three Mile Island nuclear accident. It’s often cited as an example of the dangers of nuclear power. It’s usually mentioned in the same breath as Chernobyl and Fukushima.
But what exactly happened there? Was it truly an exemplar of the grave dangers posed by nuclear power?
The answer is no. No one died. No one was injured. The other reactor on the site was still in operation until September 20 (yes, September 20 of last year). The Three Mile Island incident is an example of both the recallability trap and the sometimes negative results of being too yielding to the demands of the precautionary principle.
The Psychological Impacts
The main impact of the Three Mile Island accident has been psychological rather than physical. Big events like this one shape public attitudes for decades. People don’t remember the real impact of the event; they remember the feelings of uncertainty and fear that came with it. Those feelings now taint the public image of nuclear power in the United States.
The accident at Three Mile Island Unit 2 occurred at 4 a.m. on March 28, 1979. There was a malfunction in the reactor’s secondary cooling circuit, and the temperature of the reactor’s primary coolant rose, causing an automatic shutdown of the reactor. Control room instruments didn’t alert operators that a relief valve failed to close. Because of this, the reactor did not cool as it should have, and the core was damaged. Later that day, a small amount of gas was released accidentally, but the released gas traveled through air filters, which removed all of the radionuclides save the relatively harmless and short half-lived noble gases.
The event caused no physical harm, but the public perception of the risks of nuclear energy was heightened dramatically.
The accident created public fear but posed no real threat to the public. According to the Nuclear Regulatory Commission (NRC), the two million people in the area around TMI-2 at the time of the accident received an estimated dose of only 1 millirem above the usual background dose of radiation, less exposure than they would receive from a chest x-ray and a tiny fraction of the 100-125 millirem normal yearly background dose in the area. This is a minuscule amount of radiation compared to what all of us encounter in the normal course of everyday life.
Because of cancer concerns following the accident, the Pennsylvania Department of Health maintained a registry of people living within five miles of Three Mile Island when the accident occurred. The 30,000 person list was kept up until mid-1997 when it was determined that there had been no unusual health trends or increased cancer cases in the area immediately surrounding the accident.
People were frightened by the event, but there was no physical harm. Only the public perception of the risks of nuclear energy was heightened dramatically. The greatest effects were on the future permitting and construction of reactors and on NRC rules and procedures.
Changes in Nuclear Regulation and Construction
Following this accident, it became far more difficult to construct a reactor in the United States, in part because the politics and economics both shifted. Heightened fear makes approval more difficult and causes people to be less supportive of new construction, and changes on the regulatory side of things increase costs, shifting the economics of bringing new plants online. A 1984 New York Times article on the abandonment of construction of the Marble Hill plant in Indiana cites more than 100 plant cancellations following the Three Mile Island Accident.
Significant changes came to the NRC following Three Mile Island. It expanded its resident inspector program in which two NRC inspectors live near each of the plants and provide oversight of adherence to the agencies’ regulations.Safety became a more essential element of the system, but regulatory costs also rose. It also expanded both safety and performance-oriented inspections and established an operations center staffed 24 hours a day to provide assistance in plant emergencies. The Institute of Nuclear Power Operations, which is now the Nuclear Energy Institute, was also established to be an internal policing mechanism for the industry, providing a single point of interaction with NRC and other agencies on many issues and allowing them to share a framework for approaching generic issues they all experience.
Plants were also required to install additional equipment to monitor certain conditions in order to mitigate future accidents. These and other changes created a far more safety-oriented regulatory environment than previously existed. Safety became a more essential element of the system, but regulatory costs also rose.
The Role of Precautionary Thinking and the Recallability Trap
This is certainly a case where the downside of the precautionary principle has negative effects. Decisions that account more for the damage caused by rare accidents than by the constant benefits produced operate under an inaccurate cost-benefit analysis. This is even more true in this case, where there was widespread fear but no real off-site damage.
The Mercatus Center’s Adam Thierer made a similar point about the aftermath of Japan’s Fukushima disaster in an October 31 piece titled “How Many Lives are Lost Due to the Precautionary Principle?” wherein he pointed out the hidden costs of overly precautionary thinking. Following Fukushima, Japan stopped using nuclear power, which had previously been 30 percent of its energy. Energy prices rose, and in the subsequent four years, there were 1,280 cold-related deaths. Precautionary thinking can lead to costly unforeseen outcomes.
Reliable and affordable energy is essential—a fact no more apparent than when it becomes less affordable and less reliable. Although the Three Mile Island aftermath isn’t quite so dramatic, it’s a similar concept. Fears of worst-case scenarios prevent the development of important resources.
Overprecaution fueled by outlier events means that less nuclear power is constructed, plants are shut down before they need to be, and the public is misinformed about the safety of this technology.
The public is strongly influenced by accidents in this space, and public perception is quickly changed when they occur.
When major events occur, we often fall into the recallability trap, wherein more dramatic events are remembered more sharply and seen as more likely to occur than less dramatic ones. We might be more afraid of a nuclear disaster or a lightning strike than we are of a car crash or heart attack even though we’re far more likely to be done in by the latter than the former.
Rare but dramatic events tend to feel far more likely than statistics indicate. We misestimate the chances of these things happening. The recallability trap is especially relevant to nuclear power. Although there have only been three major commercial nuclear accidents—Three Mile Island, Chernobyl, and Fukushima—and only one of those was in the United States, the general public views these events as far more likely.
According to a CBS News survey, in 1977, 69 percent of Americans favored building new nuclear power plants, but by 1979, after Three Mile Island, support fell to 46 percent. Following Chernobyl in 1986, support had fallen to just 34 percent. By 2008, it had risen to 57 percent, but in 2011, after Fukushima, it fell back down to 43 percent. The public is strongly influenced by accidents in this space, and public perception is quickly changed when they occur.
Shifting Public Support
Following the Three Mile Island incident, attitudes toward nuclear power in the United States shifted.
The impetus to license new plants was all but gone. Public fear was overwhelming enough to discourage new development. From 1978 to 2012, the NRC didn’t approve the construction of any new commercial reactors. As the chart below shows, new reactors were still constructed following the incident, but new permitting did not occur, although various projects were attempted throughout the period. Much of this gap can be attributed to the Three Mile Island accident. Indeed, in 2019, Exelon, the owner of the Three Mile Island plant, announced it would be closing down its final remaining reactor after years of losing money. Following an incident like this one, people become overcautious.
Nonetheless, in the early 2000s, this finally started to change as the “nuclear renaissance” began. Following a few decades of no development, nuclear power was planning a big comeback. But because of a combination of the fears created by Fukushima and economic realities at home thanks to the financial crisis, the renaissance never materialized.
So, even though no one died or was even harmed in the Three Mile Accident, its impact is still clearly seen today. The accident seemed major and ominous, and because it was seen that way, public pressure made new construction far more difficult than it otherwise would have been.