Features appear in each issue of Pennsylvania Heritage showcasing a variety of subjects from various periods and geographic locations in Pennsylvania.

Thursday, March 28, 1979, is a day forever etched in the memory of most Pennsylvanians and, indeed, many Americans. During the pre-dawn hours, events swiftly unfolded at a nuclear power plant on an island in the middle of the Susquehanna River near Harrisburg that would lead to the worst commercial nuclear accident in the nation’s history. In the days that followed, Three Mile Island (TMI) would become known across the world. As the nation was gripped by the unfolding drama, the dreaded “M” word – meltdown – was spoken by the news media as a possibility that could, according to a report read by CBS Evening News television anchor Dan Rather, render a large area of central Pennsylvania uninhabitable for one hundred thousand years.

The episode began with a malfunction in equipment designed to move water through TMI’s Unit Two reactor, licensed to produce electricity just three months earlier by the federal Nuclear Regulatory Commission (NRC). Steam and pressure began to build around the reactor prompting a relief valve to open. A few seconds later the valve was supposed to close but did not. Within minutes water was draining away from the reactor, unknown to the individuals assigned to operate Unit Two’s control room that morning.

Water is critical to most nuclear reactors. Deep within the core of TMI’s Unit Two, tremendous amounts of heat were generated by splitting atoms housed in uranium fuel. The heat produced steam that rotated a turbine which, in turn, produced electricity. The nuclear power plant’s sophisticated design included a system in which thousands of gallons of treated water flowed through the reactor to cool the core. A back-up cooling system – an essential element in this technological marvel – was supposed to ensure that water continued to flow in the event that the main cooling system failed. But on March 28, control room operators mistakenly interpreted that the reactor was being cooled when in fact water was draining away from the core. They turned off the backup cooling system.

The plant’s fate was sealed. The reactor began to cook. At times, the core reached a temperature, by one estimate, as high as four thousand degrees Fahrenheit. Radioactive water leaked onto the floor of the reactor’s concrete and steel containment building and into adjacent structures. Some radioactive elements were discharged into the air. Later that morning TMI’s owner, Metropolitan Edison, Inc., declared the first general emergency ever to occur in the nation’s short history of commercial nuclear power.

Since the end of the World War II, the United States embraced a policy to explore peaceful uses for the uranium atom. By the mid-1970s, as shortages in the nation’s energy supply concerned government policymakers and con­sumers alike, Congress dissolved the Atomic Energy Commission (AEC) and created the NRC to enhance the regulation of the nuclear industry. Dozens of utilities filed applications with the NRC to build atomic power plants. It appeared that nuclear power was here to stay. However, events in Pennsylvania in the spring of 1979 would dramatically alter the growth of this otherwise accepted means to meet the nation’s insatiable desire for energy.

The drama just south of Harrisburg contin­ued to unfold. The utility company lacked clear answers as to the extent of the problem. Reporters, many with sparse technical knowledge about nuclear power, inherited the Her­culean task of explaining the calamity to a skeptical public. Federal and state officials lacked accurate information; some even felt that they had been misled by the utility. By Friday, an unusually high radiation reading prompted Governor Dick Thornburgh to order the precau­tionary evacuation of pregnant women and preschool children living within a five-mile radius of TMI. People living within ten miles were advised to remain indoors with windows and doors closed. New concerns arose over the potential explosion of hydrogen gas that had accumulated around the reactor. Hydrogen was a by-product of melted metal tubes that housed uranium fuel. Large amounts could lead to a deadly detonation releasing extremely high amounts of radiation. Over one hundred thousand central Pennsylvanians fled the area.

Although tensions ran high until early April 1979, later studies revealed that the accident actually ended within a few hours after it began. Unknown at the time, most of the damage to the reactor – consisting mainly of melted uranium fuel and its housing – had occurred by late in the day on March 28 when plant operators restarted the emergency cooling system. In addition, Governor Thornburgh based a very difficult decision to order a limited evacuation on the best information he had available at the time, including the advice of some at the NRC. Although precaution was the mood of the day, it was later determined that the order was based on an inaccurate interpretation of the amount of radiation present in the air beyond the boundaries of the plant. Most experts later agreed that the concern over a hydrogen explosion was not warranted because oxygen and a spark – elements essential to any blast­ – were not present near the reactor. Further, the Report of the President’s Commission on the Accident at Three Mile Island later concluded that the operators, through a combination of confusion, distraction, and inadequate training, missed several key warnings that could have prevented the accident. In hind­sight, ambiguity about the extent of the accident and a crisis in communication between Metropolitan Edison, federal, state, and local government, and the
NRC proved to be among the most significant problems of all.

In view of the uncertainty and, at times, the outright public terror that accompanied the unfolding events at TMI, on Friday morning, March 30, Governor Thornburgh and President Jimmy Carter agreed that someone from the NRC had to be dispatched to Harrisburg to sort through the facts and advise local, state, and federal officials. At President Carter’s request, NRC Chairman Joseph Hendrie turned to Harold R. Denton, director of the agency’s Office of Nuclear Reactor Regulation. Denton and a small staff boarded a White House helicopter and were flown to Middletown.

Harold Denton had spent nearly two decades at the NRC in positions of increasing responsibility. He accepted the position as Nuclear Reactor Regula­tory director in 1978, never quite imagining that he would be thrust into the national spotlight. He came to TMI in March 1979 simply to do his job. Yet, individuals in the highest positions of responsibility, including the president and governor, came to rely upon his wisdom, knowledge, and advice. Denton’s composure and demeanor were credited by the public and media for calming the fear and anxiety that gripped the public. Indeed, in the twenty-one years that have passed since the nuclear accident at TMI, Harold Denton remains perhaps the one figure that most people remember, admire, and trust from a time when anxieties were running high.

According to Dr. Cynthia Bullock Flynn, in her 1979 telephone survey of residents in central Pennsylvania, submitted to the Nuclear Regulatory Commission, the NRC received the highest praise when comparing official and media sources regarding informa­tion they received during the TMI crisis. Twenty-seven percent of those surveyed found the information from the NRC “extremely useful” and thirty-six percent found it “useful.” The NRC representa­tive most frequently credited for providing public information during the crisis was Harold Denton. By contrast, only two percent of the respondents felt that Metropolitan Edison, the operator of TMI, provided “extremely useful” information and only nine percent more believed the operator issued “useful” information. Sixty percent found the utility company’s information “totally useless.” Only eleven percent of the respondents found the NRC information “totally useless.” Governor Thornburgh also faired relatively well with twenty­-one percent “extremely useful,” according to Dr. Flynn, and thirty-six percent found information from the governor’s office “useful.”

Now retired from the NRC and residing in Knoxville, Tennessee, with Lucinda, his wife of more than forty years, Harold Denton returned to central Pennsylvania in the spring of 1999 to commemorate the twentieth anniversary of the accident. He gave a talk at a public history symposium, dedicated a state historical marker documenting the accident, donated his personal papers on TMI to the Pennsylvania State Archives in Harrisburg, and graciously agreed to an oral history interview. This interview was excerpted from Denton’s commentary, which is safeguarded with his papers at the Pennsylvania State Archives.


Tell us about Harold Denton. Where were you born and raised?

I was born and raised in a town in eastern North Carolina called Rocky Mount, and went to grammar school just a block from my house. We went to high school in the same town. I have one brother who is about ten years younger. My parents were from the same area. My mother went to Trinity College, which was absorbed by Duke University. She taught school for a few years. My father dropped out of school at a fairly early age – seventh or eighth grade, because he was needed on the farm where his family raised tobacco. My mother died when I was quite young. I was in the fifth grade. She died of cancer. My father had his hands full with two boys. He was a salesman for the Merita Bread Company. He went to work at four in the morning and worked all day long. He remarried later, but for several years, we were motherless.

When did you first become interested in science and technology?

I had been fascinated by stories of atoms and electrons and protons even as a youngster. The nuclear world at the time was somewhat like the genetic engineering world today. It was brand new. I spent a lot of time in chemistry and physics lab in high school. One day the school got a call from the local newspaper wanting to know if anyone would be an apprentice photo-engraver and I volunteered to work part time for The Evening Telegram in Rocky Mount. In college, I wanted to be a civil engineer. North Carolina State had … the first privately owned nuclear reactor in the country. I went over and talked to the dean of the Nuclear Engineering Department. He said, yes, we can take you in this program, so I switched programs. I felt that was hot stuff at the time. It had a huge intellectual appeal.

How did you become involved in regulating nuclear power plants?

There weren’t that many jobs avail­able when I graduated in ’58. Lucinda and I were married in ’59 and I worked for DuPont at their Savannah River South Carolina facility that developed nuclear weapons material. My title was reactor physicist. Remember, we were in a big weapons race with the Soviet Union, so the more plutonium that could be produced for bombs, the better everyone liked it. They also had five large reactors on site. I stayed there for about five years. One of the bosses from DuPont joined the AEC [Atomic Energy Commission] and established a regulato­ry group for commercial power operations. I remember going to Wash­ington for a meeting of the American Nuclear Society and talking to this person in 1962. He made me an offer. I talked to my wife about moving to Washington – we had two children at the time, Elizabeth and Harold Jr. I held out for what I thought was a great salary improvement – twelve thousand dollars a year! I thought I was rich! I accepted it.

Tell us about your work at Atomic Energy Commission, then the Nuclear Regulatory Commission prior to Three Mile Island.

My first assignment was to inspect nuclear power plants. I traveled a lot. Then, in a short time, our third child, Spencer, was born, and I became chief of a regulatory program. The AEC was growing by leaps and bounds because more and more applications were coming in. At one time, there were over three hundred applications kicking around for nuclear power plants. I held increasingly responsible jobs. In 1978, the position of director of the Office in Nuclear Reactor Regulation was vacated. We all assumed that no one wanted that job! The chairman of the NRC, Joseph Hendrie, called me one day and offered me the job. I remember expressing some reservations. But Chairman Hendrie assured me that I would be the “inside” person and manage the program while he would be the “outside” person and manage the agency contacts, politicians, etc. So, in June or July of ’78 I became director of the Office of Nuclear Reactor Regulation. We had a staff of seven hundred people. Our job was to make sure that a plant met all of the NRC requirements before we issued a license.

When did you first learn of a problem at TMI?

I was in my office in Bethesda, Maryland, on March 28, 1979. At about 8 A.M. I heard that there had been an incident at TMI. We established an emergency communication center in Bethesda. To this point, most of the emergencies that had arisen weren’t really big ones. At first, it didn’t seem to anyone to be a big deal. It was another unusual event, but unusual events happen. I planned to leave town that day – had gone to work with my bags packed – to go out to inspect another reactor. As the day wore on, and I got briefed, it sounded more and more unusual. We couldn’t imagine that there’d be a serious accident. We have all these safety systems in the plant. It’s kind of like the mentality of the Titanic designers. This thing was designed with so much redundancy and diversity, you can’t possibly have a serious accident. By about four o’clock I had become suffi­ciently concerned by the turn of events. I canceled my plans to leave town. By that time the response center had a telephone line open to the control room and the NRC had sent people to the site from King of Prussia. We were beginning to get reports of very odd indicators – like very high core temperatures. I thought they must be erroneous. You can’t possibly have temperatures that high in the core. Vic Stello of my staff and I soon concluded that, whatever happened here, the water level dropped, and the core was uncovered. People in the control room had to wear protective masks at the time because of the radiation levels.

How did things evolve over the next few days?

On Thursday, we sent more NRC staff to TMI. It appeared as though we’d stabilized conditions but still weren’t completely sure what had happened. I went to bed Thursday night thinking that it was a bad accident, but not a serious challenge to public health and safety. On Friday, as soon as 1 got in the response center, all things were breaking loose. By that time, we had learned about an explosion of hydrogen in the containment. I took that as an indicator of severe core damage. By this time, it was an all-consuming issue. The NRC wanted answers from staff. The staff wanted answers from the utility. The Congress wanted answers from the NRC. Basically, nobody had any really good answers.

Then came the call for an evacuation. That was an event that cost Governor Thornburgh no end of grief. We were informed that morning about a reading that had been made by a helicopter in the vicinity of the plant. We’d been talking about what sort of levels might get produced off site if it were, heaven forbid, a serious release of radioactivity. Then a report came in that it was reading twelve hundred millirem – I think we all experienced cognitive dissonance! The federal guideline at the time was something like twenty-five! We thought that if we were going to assure the safety of the people downwind of the plant, we better get moving. I was on board with the evacuation recommendation because, while I couldn’t explain what had gone on, I saw the radiation reading as really bad news.

When did you become aware that both Governor Thornburgh and President Jimmy Carter were very concerned about events at TMI?

I had not talked to either Governor Thornburgh or President Carter before Friday. It was some time after the evacuation recommendation that the governor asked President Carter for someone to represent the federal government at the plant. So, I got a call from Chairman Hendrie. He told me that he’d had a conversation with the president and the president wants more of a federal presence up there. There was nothing in writing. It was just a telephone call. He said, “The White House will get you up there. Call this number for transportation.” So, the White House contact said, “Where do you want to be picked up by helicopter?” I said we we’re close to the Bethesda Naval Hospital. At eleven-thirty, the helicopter picked us up and away we go. There were twelve of us in all including Vic Stello and Joe Frouchard, the NRC public affairs person. On the way up, we decided who’s going to cover what aspect – to divide up the workload.

What did you find when you arrived?

Well, the utility was expected to run the plant. They knew all the details. We would oversee them. I had an order in my pocket that would have given the NRC authority to seize control of the plant. We had the authority in the Atomic Energy Act. I never wanted to do it unless the utility just completely abrogated their responsibilities. I asked the president of Met Ed to sign a blank check so that we could order whatever materials we needed to deal with the problem. He swallowed hard, but he signed it. Then we met with the presi­dent of GPU [General Public Utilities Corporation], Met Ed’s parent. He wanted to issue a joint press release with the NRC informing the public of the situation. To Joe Frouchard’s credit, he said we won’t have any joint press statements. Whatever the NRC puts out will be its own. In retrospect, that was a very wise decision. The NRC staff met in a small house across from the island. We had about twenty-five. people. I had to call the president every day at 7:45 A.M. and 3:45 PM. We organized ourselves into teams to work twelve-hour shifts. Once I got in the control room, I found that it wasn’t the absolute chaos that I thought.

Then I came into Harrisburg to brief Governor Thornburgh. He was highly skeptical when I walked in. I was grilled by him for about an hour. I told him what was going on and that there was no reason to panic and no reason for any further evacuation based on our knowl­edge. I felt that it had been a serious accident but that it was under control. The core wasn’t overheating any more than it had. We had monitors out in the field and there was no existing threat. I knew that in the worse case – if, for example, the reactor vessel failed on that day – it takes awhile before you can fail the containment structure. Remember that the containment building at TMI is stronger than most at nuclear power plants. Because of its proximity to the Harrisburg International Airport, it is built to withstand an airplane crash.

I never recommended an evacuation once I got here. Governor Thornburgh saw a lot of disadvantages with evacua­tion unless it was really necessary. I felt we could control things after I got here. Time was on our side. Then he asked me to go to a press conference with him. I had no real preparation. I didn’t have “spin doctors” as today. I don’t even
think I had any notes. We just got there and answered questions.

Through the weekend of March 30 how did you deal with the hydrogen bubble problem and the president’s visit?

Word began to come out of [NRC] Bethesda that there might be a core meltdown due to another potential hydrogen explosion. The question was whether enough oxygen was in the reactor that it can build up to a level [and combine with hydrogen] that it might explode. Vic Stello called a number of chemistry experts around the country. He had the view, by midday Saturday, that there’s no chance for an explosion. I had discounted the issue. By Saturday night, however, the story was breaking, and the fear, anxiety, and hysteria about the hydrogen bubble was as thick as pea soup. It was really an anxious time. Bethesda was putting out word in a way that differed from my opinion, I think, due to poor communication and the lack of chemistry experts in the NRC. I went to brief the governor about what we knew.

I’d been called Saturday night by the White House and questioned as to whether it was all right for the president to visit, in other words, is it safe? It was my view that it was. So Sunday morning there’s all of this turmoil about the bubble. The president is on his way. I’m standing at the airport waiting for him. A few minutes before the president’s helicopter landed, Chairman Hendrie arrived with a few NRC people. We had a chance to get together standing on the tarmac. Vic Stello explains that the hydrogen explosion can’t occur. It made sense to Hendrie. So the president’s party came in and we briefed him. I had flip charts and this sort of thing. He volunteered whatever help we needed. He was very helpful. Anything in the federal government we needed, we called this contact at the White House and it was done! It was a great feeling for several weeks.

You stayed about three weeks until things had calmed down?

Yes. After the first few anxious days up here, I began to feel that it was manageable, in spite of all the chaos that seemed to be going on. I talked to Lucinda every night. I had a lot of support from NRC staff. I went to church here on Easter Sunday. Then I felt that I could go home. By that time there were more problems at home. All the investigators were waiting! People wanted to interview me. There were so many different interests, from the criminal investigation side, the technical side, the political side. There were, I think, six major investigations that consumed my time for the next year.

It was a long time before the real extent of the accident was understood. In 1982, I went into the TMI Unit Two containment building for the first time to look around. We were fully suited in protective clothing. The only visible damage that I saw was a telephone that looked damaged and a fifty-five­ gallon drum that had the sides squeezed in. Yet, I realized that down in the basement of the building were three-quarters of a million gallons of highly contaminated water. But just from a casual look, you couldn’t see much damage.

Later the company removed the top off the core and lowered a camera in and found that the top quarter of the core was just a void. It was a molten mass in the entire core.

Can you comment on the public health risks caused by radiation releases from the accident?

They were minimal. At the time, we did our best to reconstruct what the doses were, and we concluded that the maximum dose – if someone had been standing there for the whole course of the accident – was at the north gate of the plant. Here the dose rate was about one hundred millirem, the amount of radiation that you normally receive in one year.

You visited Chernobyl in Ukraine following the nuclear accident there in 1986. How does Chernobyl compare with TMI?

I was one of the first Americans permitted to visit Chernobyl. I entered apartments in Chernobyl where people had just left everything – toys, dolls, clothing. They weren’t allowed back. I walked inside turbine hall at the power plant just briefly, just to get an idea of the damage. I took a few pictures and stepped out. The dose I received from thirty seconds in the turbine hall at Chernobyl was far, far greater than here at TMI. That really brought home to me the value of a strong reactor containment structure. To many people a containment building at a nuclear power plant is an ominous structure. It means bad news. However, if TMI wasn’t contained and had gone the wrong way, we could have had the same situation here. Chernobyl reinforced what TMI could have been, but fortunately wasn’t.

After Chernobyl, I became more involved in trying to work for nuclear safety worldwide. I took on the job of running the NRC’s international program and did more international work visiting essentially every country that had a Soviet designed reactor. We would swap inspectors and we’d put on training programs. I even had an opportunity to go to Cuba and look at the Cuban reactor and meet with Fidel Castro Jr.

What are some of the lessons of TMI?

I think the American nuclear industry went too big too fast. We went from little reactors to these thousand megawatt reactors all around the country, all different designs, without a more gradual growth period.

When I started in the industry, it was booming. There were a lot of technologi­cal advances. It was seen as a real cutting edge. As a nation we went through a period – forty to fifty years – when the smartest and brightest put a lot of effort in trying to make nuclear power peace­ful, reliable, and safe. We didn’t completely get there. Today we are dealing with nuclear waste issues and decontaminating power plants.

TMI really killed off the nuclear industry, at least in this country. I don’t see any rebirth of the industry in my lifetime. I do think that Mother Nature put so much energy in the uranium atom that we’re going to go back to it some day. My grandchildren or their grand­children might see its rebirth. We’re not going to find enough fossil fuels to keep this planet going forever. Nuclear is going to be there and maybe future designs will be safer since we have learned from TMI and Chernobyl. But at the moment, there’s very little money being spent on new designs or nuclear research. Yes, TMI changed things dramatically.


For Further Reading

Flynn, Dr. Cynthia Bullock. Three Mile Island Telephone Survey: Preliminary Report on Procedures and Fillings: A Report Submitted to the U.S. Nuclear Regulatory Commission. Tempe, Ariz.: Mountain West Research, Inc., 1979.

Goldsteen, Raymond L., and John K. Schorr. Demanding Democracy After Three Mile Island. Gainesville: University of Florida Press, 1991.

Gorinson, Stanley M., et al. Staff report to the President’s Commission on the Accident at Three Mile Island. Washington, D.C.: Nuclear Regulatory Commission, 1979.

Gray, Mike, and Ira Rosen. The Warning: Accident at Three Mile Island. Chicago: Contemporary Books, 1982.

Hassler, Peggy M. Three Mile Island: A Reader’s Guide to Selected Government Publications and Government-Sponsored Research Publications. Metuchen, N.J.: Scarecrow Press, 1988.

Houts, Peter S., et al. The Three Mile Island Crisis: Psychological, Social, and Economic Impacts on the Surrounding Population. University Park: The Pennsyl­vania State University Press, 1988.

Kemeny, John G., et al. Report of the President’s Commission on the Accident at Three Mile Island: The Need for Change: The Legacy of Three Mile Island. Washington, D.C.: President’s Commission, 1979.

Leppzer, Robert, ed. Voices from Three Mile Island: The People Speak Out. Trumans­burg, N.Y.: Crossing Press, 1980.


Kenneth C. Wolensky is a historian with PHMCs Division of History. The author wishes to thank Harold and Lucinda Denton for their participation in events to mark the twentieth anniversary of the nuclear accident at Three Mile Island, including the gracious donation of the Harold R. Denton papers and an oral history interview to the Pennsylvania State Archives.