Our Documentary Heritage showcases holdings drawn from the vast collections of the Pennsylvania State Archives.

In late March 1979, south-central Pennsylvanians were startled to learn of an accident that had occurred at Three Mile Island (TMI) nuclear power plant in the Susquehanna River near Middletown, Dauphin County. In my own experience, the initial news came to me at Dallastown Elementary School in York County after a teacher shouted out to my fifth-grade class to come back inside the school building as we were crossing the playground to go to the cafeteria. At age 11, I was not yet aware of nuclear power and I certainly had no fear of it before that moment. One of my female classmates suddenly began to cry uncontrollably as we returned to our classroom; I found out she had a relative who was working at TMI.

As the national media picked up on the story and it was announced that a partial meltdown of the reactor core had occurred at Unit 2, we were sent home from school early. Tens of thousands of residents in a 20-mile radius would voluntarily evacuate their homes during the days following the accident. Although we lived 10 miles outside of the 20-mile radius, my mother, my oldest sister and I left our home on the night of Friday, March 30, for our cabin in Cowan’s Village in Fulton County.

The failure of a regulating valve to close after it relieved high pressure in Unit 2’s cooling system and the unfortunate human error of shutting down the emergency cooling system caused the partial melting of the core and contamination of the containment vessel on March 28. Restarting the emergency system later that same day solved the problem of the overheating core; however, a hydrogen bubble had formed in the containment vessel. The bubble had the potential to cause a significant explosion if oxygen reached the hydrogen. Fortunately, technicians were able to reduce the size of the bubble and its potential for destruction over the next several days.

The Nuclear Regulatory Commission sent representatives to TMI to advise Gov. Dick Thornburgh about the accident. One NRC official, Harold Denton (1936–2017), was the commission’s director of Nuclear Reactor Regulation and President Jimmy Carter’s personal representative at the TMI accident site. He became the face of calm to local residents, providing reassurance and technical expertise during the days immediately following the accident, and he helped both politicians and the public understand what was really happening at the site.

Many Pennsylvania schoolchildren were encouraged to write about their feelings concerning the TMI accident. The Harold and Lucinda Denton Papers (Manuscript Group 471) at the Pennsylvania State Archives contain some letters and cards written by children concerning their experiences, expressing fears and hopes regarding the TMI accident and its aftermath. Several of them thanked Denton specifically for his work at containing the emergency and saving their lives.

As cleanup of the TMI facility continued, it became apparent that the initial statements made by the operators of TMI understated the seriousness of the accident. It very easily could have become a major nuclear disaster that had the potential to damage or destroy thousands of human lives. The impact on the surrounding environment could have been catastrophic. As it was, TMI was the most serious nuclear power plant accident in U.S. history. Subsequently, public distrust of nuclear power plants increased, and applications to build new nuclear reactors around the country dropped significantly. Forty years after the accident, Exelon Corp., the current owner of the facility, has announced its intention to close TMI in 2019.


Richard C. Saylor is an archivist for the Pennsylvania State Archives and author of the award-winning book Soldiers to Governors and numerous articles on military, political and sports history.