The Three Mile Island nuclear reactor partially melted down 40 years ago on March 28, 1979. See photos from the disaster.
The Three Mile Island nuclear reactor partially melted down 40 years ago.
The disaster near Harrisburg, Pennsylvania, occurred early on March 28, 1979, and mesmerized the nation and raised concerns about the release of radioactive material.
The U.S. Nuclear Regulatory Commission says it was the most serious in U.S. history at a commercial nuclear power plant.
Millions of people in the D.C.-Baltimore area closely watched what was happening after the reactor failed.
Today, the reactor remains permanently shut down.
Click through the gallery to see 1979 photos ranging from the reactor to the evacuations to the protests and congressional hearings.
Night crew at Three Mile Island nuclear power plant wear protective clothing as they sit in the back of a truck that transported them to the shut-down power plant in Harrisburg, Pa., March 29, 1979, at the beginning of their shift. (AP Photo/Gene Puskar)
AP Photo/Gene Puskar
A Pennsylvania state policeman and plant security guards stand outside the closed front gate to the Metropolitan Edison nuclear power plant on Three Mile Island near Harrisburg, Pa., after the plant was shut down following an accident. Some radiation escaped into the atmosphere Wednesday, March 28, 1979. In background are the plant's cooling towers. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
A safety official checks a worker from the Three Mile Island PWR for possible exposure to radioactivity, on March 28, 1979, in Middletown, Pa., shortly after an accident at the nuclear power plant led to the release of radioactive gas from the reactor into the atmosphere. (AP Photo)
AP Photo
Aerial view of Three Mile Island nuclear plant near Harrisburg, Pa., scene of a nuclear accident, Thursday, March 28, 1979. The plant started leaking radioactive steam contaminating the area. (AP Photo)
AP Photo
An undated file photo of the Three Mile Island nuclear power station near Harrisburg, Pennsylvania, USA, at dusk, circa 1979. An accident caused a radiation leak at the plant in March 1979. (AP Photo)
AP Photo
Residents of Goldsboro, Penn., go about their business even though the nuclear power plant across the Susquehanna River from their town was closed down following an accident at the plant, March 28, 1979. A plant cooling tower rises in the back ground. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
Harold Stoner carries boxes of provisions into the back of his van as his wife, Hazel, wears a towel over her head preparing to leave their home with grandson Joshua in Harrisburg, Pa., March 30, 1979. They are leaving after being warned of radiation leaking at Three Mile Island nuclear power plant. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
John Sweitzer helps his neighbor, Mrs. David Neel, daughter Danielle, 4, and pet dog leave the residential area next to the Three Mile Island nuclear power plant near Harrisburg, Pa., on March 30, 1979. Mrs. Neel became frightened when additional radiation escaped from the plant. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
One-year-old Elizabeth Cole sits on the lap of her mother, Karen, at an athletic arena at Hershey Park, Pa., Friday, March 30, 1979. The Coles live in an area near Three Mile Island nuclear generating plant. (AP Photo/Gene Puskar)
AP Photo/Gene Puskar
Unidentified mother and child at an athletic arena at Hershey Park, Pa., March 30, 1979. Mothers and children who live in an area near Three Mile Island nuclear generating plant were staying at the arena. (AP Photo/Gene Puskar)
AP Photo/Gene Puskar
Oran Henderson, director of the Pennsylvania Council of Civil Defense, answers a press question during a late news conference in Harrisburg, Pa., March 28, 1979. Henderson was speaking about the accident at the nuclear power plant near Harrisburg. At left is Lt. Gov. William Scranton III. (AP Photo/Fred Prouser)
AP Photo/Fred Prouser
Pennsylvania Gov. Dick Thornburgh, left, announces the closing of schools in the area around the Three Mile Island PWR, on March 30, 1979, in Harrisburg, Pa., after an accident at the nuclear power plant led to the release of radioactive gas from the reactor into the atmosphere. The governor advised the evacuation of small children and pregnant women. Standing at right is Lt. Gov. William Scranton. (AP Photo)
AP Photo
Walter Creitz, right, president of Metropolitan Edison Company, turns away as company Vice President John Herbein answers questions at a news conference in Hershey, Pa., on March 29, 1979. The conference was held because of an accident that occured at the company's Three Mile Island nuclear power plant near Harrisburg, Pa., that caused radiation leakage into the atmosphere. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
More radiation was vented from the Three Mile Island Nuclear power plant near Harrisburg, Penn., March 30, 1979, and some contaminated water was being pumped into the Susquehanna River, left. Area residents have been asked to stay inside and some children and pregnant women have been evacuated. (AP Photo/Barry Thumma)
AP Photo/Barry Thumma
Steam at left rises from the No. 2 containment building housing a nuclear reactor after it was closed down following an accident at the Metropolitan Edison Electric Company's Three Mile Island nuclear power plant, March 28, 1979. Some radiation escaped into the atmosphere near Harrisburg, Penn. (AP Photo)
AP Photo
A view of the nuclear power plants at Three Mile Island, near Harrisburg, Pa., USA. It was recently closed down after severe radiation leaks were discovered, Thursday, March 28, 1979. Causing the evacuation of some nearby residnets. (AP-Photo)
AP-Photo
An air view shows the Three Mile Island nuclear power plant near Harrisburg, Pa., March 30, 1979. The small dome at center is where the now-called "incident" occured Wednesday. (AP Photo/Barry Thumma)
AP Photo/Barry Thumma
A cooling tower of the Three Mile Island nuclear power plant near Harrisburg, Pa., looms behind an abandoned playground, March 30, 1979. (AP Photo/Barry Thumma)
AP Photo/Barry Thumma
A helicopter flies between two huge cooling towers at the Three Mile Island Nuclear Generation Plant in Harrisburg, Penn., March 30, 1979. The home in the foreground has been evacuated because of the radiation spill from the nuclear plant. (AP Photo/Jack Kanthal)
AP Photo/Jack Kanthal
Extra workers wait at the gate to enter Three Mile Island Nuclear Generating Plant near Harrisburg, March 30, 197 to help with cleanup following another radiation spill. (AP Photo/Jack Kanthal)
AP Photo/Jack Kanthal
Autos travel a road away from the Three Mile Island Nuclear Power Plant near Harrisburg, Penn., March 31, 1979, where a radioactive spill occurred on Friday. Many residents chose to evacuate the area. (AP Photo/Jack Kanthal)
AP Photo/Jack Kanthal
A night view shows two of the four cooling towers at the Three Mile Island Nuclear Generating Plant near Harrisburg, Penn., March 31, 1979. The plant has been leaking radiation for four days. The lines in the foreground are made by passing cars during the time exposure. (AP Photo/R.C. Greenawalt)
AP Photo/R.C. Greenawalt
A night view shows the Three Mile Island nuclear power plant near Harrisburg, Penn., March 30, 1979. Authorities said that radiation continues to leak from the plant since the accident. (AP Photo/R.C. Greenawalt)
AP Photo/R.C. Greenawalt
Workers from the Metropolitan Edison's Three Mile Island PWR check on radiation levels at the observation deck of the visitor's center just across the nuclear power plant, on March 30, 1979, in Middletown, Pennsylvania. The institution was shut down after an accident led to the release of radioactive gas from the reactor into the atmosphere. (AP Photo)
AP Photo
An unidentified man carries a Geiger counter in the vicinity of the Three Mile Island nuclear plant near Harrisburg, Penn., late March 1979, after an accident allowed radiation to leak out into the atmosphere. (AP Photo)
AP Photo
This is an aerial view of the Three Mile Island Nuclear power plant near Harrisburg, Penn., March 31, 1979. This is the site where the nuclear accident occurred Wednesday. (AP Photo/G. Paul Burnett)
AP Photo/G. Paul Burnett
Newsmen and spectators stand in front of the main gate of the Three Mile Island Nuclear Generating Station in Middletown, Penn., April 2, 1979. (AP Photo/Jack Kanthal)
AP Photo/Jack Kanthal
Steam flows from the cooling towers of the Three Mile Island Nuclear Plant, April 2, 1979, in the early morning. Officials of the plant say the dangerous gas bubble has all but disappeared from the nuclear reactor. And, according to the company officials, the reactor is being prepared for a final cool-down. (AP Photo/Gene Puskar)
AP Photo/Gene Puskar
This was the scene in Goldsboro, Penn., as most people in the area of the nuclear leak either evacuated or stayed indoors, March 31, 1979. In the background, above the end of the street, is one of the cooling towers of the Three Mile Island nuclear power plant. (AP Photo/R.C. Greenawalt)
AP Photo/R.C. Greenawalt
An undated photo of the Three Mile Island nuclear power station near Harrisburg, Pa., circa 1979. An accident caused a radiation leak at the plant in March 1979. (AP Photo)
AP Photo
Harold Denton, chief of operations for the Nuclear Regulatory Commission, describes the situation at the Three Mile Island Nuclear Power Generating Station in Middletown, Pa. on April 2, 1979. Denton's briefing takes place at the Middletown City Hall. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
Four anti-nuclear power protesters stand holding a banner reading 'nuclear waste' on Three Mile Island near Harrisburg, Pennsylvania, USA, 1979. 1979 saw a core meltdown at the Three Mile Island Nuclear Generating Station. (Photo by Keystone/Hulton Archive/Getty Images)
Photo by Keystone/Hulton Archive/Getty Images
Anti-nuclear power plant demonstrators mass on the front steps of the State Capitol in Harrisburg, Penn., April 8, 1979, urging a shut-down of Three Mile Island nuclear power plant. The plant had an accident, causing radiation to leak into the atmosphere. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
Two mothers along with their children carry signs in front of the State Capitol in Harrisburg, Penn., joining other anti-nuclear power plant demonstrators urging the shut-down of Three Mile Island (TMI) nuclear power plant near Harrisburg, April 8, 1979. The plant had an accident causing radiation to leak into the atmosphere. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
This is an aerial view of the Three Mile Island Nuclear power plant near Harrisburg, Penn., March 31 1979. This is the site where the nuclear accident occurred Wednesday. (AP Photo/G. Paul Burnett)
AP Photo/G. Paul Burnett
Three Mile Island nuclear power plant, south of Harrisburg, Pa., is shown on an unknown date before an accident that caused leakage of radioactive gases from one of the plant's reactors into the atmosphere in late March 1979. Pregnant women and pre-school age children were advised to leave the area within a 5-mile radius of the plant. (AP Photo)
AP Photo
Not caring for crytical radiation levels a farmer tends a field with his tractor, with the Three Mile Island nuclear plant near Harrisburg, Pa., USA, in the backgroung, April 4, 1979. The plant started leaking radioactive steam, Thursday, March 28, contaminating the area. (AP-Photo)
AP-Photo
Sen. Richard Schweiker, R-Pa., left, and Edward Kennedy, D-Mass., members of a Senate Health and Scientific Research subcommittee, confer during a meeting of the panel Wednesday, April 4, 1979 in Washington. The group is probing the nuclear accident at Three Mile Island nuclear power plant in Pennsylvania. (AP Photo/Charles Harrity)
AP Photo/Charles Harrity
Chairman Gary Hart (D-Colorado), right, of the Senate Nuclear Regulation Subcommittee, reaches to shake hands with Nuclear Regulatory Commission Chairman Joseph Hendrie in Washington, April 10, 1979, prior to the start of hearings to probe the NRC's role in the nuclear accident at Three Mile Island nuclear power plant. Commission member Victor Gilinsky is at right. (AP Photo/Charles Harrity)
AP Photo/Charles Harrity
Three Mile Island nuclear plant incident - President Jimmy Carter, second from left, visits the nuclear plant near Harrisburg, Pa., USA, April 4, 1979. The plant started leaking radioactive steam, Thursday, March 28, contaminating the area. (AP-Photo)
AP-Photo
An empty containment tank enters the Three Mile Island nuclear power plant at Middletown, Penn., March, 1979. (AP Photo/RIG)
AP Photo/RIG
U.S. President Jimmy Carter shown April 1, 1979 in the control room of the Three Mile Island nuclear power plant in Middletown, Pa. Standing with Carter from left: Harold Denton, director of the U.S. Nuclear Agency; PA. Gov. Dick Thornburgh; Rosalyn Carter; and an unidentified control room employee. (AP Photo)
AP Photo
U.S. President Jimmy Carter shown April 1, 1979 in control room of nuclear plant, of the Three Mile Island nuclear plant in Middletown, Pa. Standing with Carter from left: Harold Denton, Director of the U.S. Nuclear Agency; PA. Gov. Dick Thornburgh; an unidentified control room employee. (AP Photo)
AP Photo
Evacuated women and children sleep on army cots in a sports arena, Saturday, March 31, 1979, in Hershey, Pennsylvania. They left their homes near the Three Mile Island nuclear power plant. (AP Photo/Gene Puskar)
AP Photo/Gene Puskar
Kathy Moody, top right, uses a cardboard box for a playpen for 13-month-old Christina while they wait in evacuation center at Hershey sports arena for radiation from the Three Mile Island nuclear power plant to stop, March 31, 1979. The Pennsylvania governor has suggested that small children and pregnant women move away from the plant until the radiation spill is stopped. (AP Photo/Gene Puskar)
AP Photo/Gene Puskar
THREE MILE ISLAND Wearing protective boots, then President Carter, center right, accompanied by Dr. Harold Denton, then Director of the U.S. Nuclear Agency, left, and then Pennsylvania Gov. Dick Thornburg, left-rear, tour the control room of the Three Mile Island nuclear plant in Middletown, Pa. on April 1, 1979, four days after the nuclear accident. On March 28, 1999 will be the 20th anniversary of the nation's worst nuclear accident. Man at right is unidentified. (AP Photo/Rusty Kennedy)
AP Photo/Rusty Kennedy
Pennsylvania Governor Dick Thornburgh, left, and President Jimmy Carter inspect the control room of the crippled Three Mile Island Nuclear Generating Station in Middletown, Pa., on April 1, 1979. The president spent about two hours in the area. (AP Photo/Barry Thumma)
AP Photo/Barry Thumma
Sally Conover, 16, returns to her favorite sport of jogging after returning to her home near the nuclear power plant near Harrisburg, Pa., April 5, 1979. Sally left with her family following an accident at the Three Mile Island nuclear power plant causing leaking of radiation into the atmosphere. In the back is one of the plant's cooling towers. (AP Photo/Rusty Kennedy)
AP Photo/Rusty Kennedy
Elementary school school children prepare to board the school bus near their homes near the disabled Three Mile Island nuclear power plant after schools reopened in the Middletown, Pa., area, April 10, 1979. In the background are idle cooling towers of the plant that has been shut down following an accident causing radiation to leak into the atmosphere. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
Ronald Black stands behind his wife Yvonne holding their 18-month-old daughter Lisa Marie on her lap after they return to their home near the disabled Three Mile Island nuclear power plant near Middletown, Pa., April 10, 1979. The Black family returned home after officials announced it was safe after an accident at the plant caused many families to evacuate the area. (AP Photo/Prouser)
AP Photo/Prouser
Chris Becker, a dairy farmer who lives only a mile from the disabled Three Mile Island nuclear power plant, lies flat on his back as a machine moves over his body to scan for any possible radiation during a test in Middletown, Pennsylvania on April 10, 1979. Bill Gibson, a technician checks scanner. In background is a computer to read the results. (AP Photo/Vathis)
AP Photo/Vathis
Mrs. Ernestine Snyder, a Red Cross volunteer, lies flat on her back as a unit slowly moves over her body to scan for any possible radiation during a test in Middletown, Pennsylvania on Tuesday, April 11, 1979. Bill Gibson, a technician checks progress from a computer printout. Tests are being given following an accident at Three Mile Island nuclear power plant releasing radiation into atmosphere. (AP Photo/Vathis)
AP Photo/Vathis
Karen Ainsley, holding her daughetr Cherie, 3, opens the door to their car as her husband Timothy stands behind her with soin Timmy, 6, wait to enter car as they leave their home near Middletown near Three Mile Island nuclear power plant with cooling tower in background, April 15, 1979. (AP Photo/Fred Prouser)
AP Photo/Fred Prouser
A car passes through a security gate outside the Three Mile Island nuclear power station near Harrisburg, Pennsylvania, USA in this undated photo circa 1979. An accident caused a radiation leak at the plant in March 1979. (AP Photo)
AP Photo
Chris Becker, a dairy farmer who lives only a mile from the disabled Three Mile Island nuclear power plant, lies flat on his back as a machine moves over his body to scan for any possible radiation during a test in Middletown, Pennsylvania on April 10, 1979. Bill Gibson, a technician checks scanner. In background is a computer to read the results. (AP Photo/Vathis)
AP Photo/Vathis
An undated file photo inside the Three Mile Island nuclear power station near Harrisburg, Pa., circa 1979. An accident caused a radiation leak at the plant in March 1979. (AP Photo)
AP Photo
Workers from Metropolitan Edison's Three Mile Island nuclear plant stand outside visitors center early on March 30, 1979, as two cooling towers from the nuclear plant are visible in the background. Officials at the site declared an "on-site emergency" later Friday morning. (AP Photo/Rusty Kennedy)
AP Photo/Rusty Kennedy
This undated photo shows evidence of the clean-up operation at the Three Mile Island power plant near Harrisburg, Pa., following a radiation leak in March 1979. (AP Photo)
AP Photo
An undated file photo of the Three Mile Island nuclear power station near Harrisburg, Pennsylvania, USA, circa 1979. An accident caused a radiation leak at the plant in March 1979. (AP Photo)
AP Photo
An undated photo inside the Three Mile Island nuclear power station near Harrisburg, Pa., circa 1979. An accident caused a radiation leak at the plant in March 1979. (AP Photo)
AP Photo
A group of tourists have their photograph taken by a family member as they pose with cooling towers from Three Mile Island nuclear power plant near Middletown, Pa., May 11, 1979. (AP Photo/Fred Prouser)
AP Photo/Fred Prouser
Consumer advocate Ralph Nader faces reporters, Wednesday, April 18, 1979 in Washington where he called for a national march on Washington. Nader set the march for Sunday, May 6 in response to the Three Mile Island nuclear reactor accident. (AP Photo/Schwarz)
AP Photo/Schwarz
W. Wilson Goode, chairman of the Pennsylvania Public Utility Commission, called for a federal bailout of the utility that operates the Three Mile Island plant, April 30, 1979. Goode, appearing in Washington before the Senate nuclear regulation sub-committee, stated that it would be unfair to expect stockholders and consumers to shoulder the entire cost of the accident. (AP Photo/Harvey Georges)
AP Photo/Harvey Georges
Mrs. Joanne Noel, prepares her flower bed for planting in front of her Middletown, Pa., home as daughter Danielle, 4, watches as she sits on the ground, May 18, 1979. Noel evacuated her home with her children during the crisis at Three Mile Island, seen in the background. (AP Photo/Prouser)
AP Photo/Prouser
Actress-comedian Lily Tomlin, dressed as “The Bag Lady,” in Los Angeles, Calif., June 5, 1979, holds up her version of the “Presidential Booties” worn by President Carter when he visited the Three Mile Island Nuclear Power Plant. Tomlin, Peter Yarrow, Graham Nash and Jocko Marcellino along with the Alliance for Survival group, California’s largest anti-nuclear organization, held a news conference announcing plans to keep the Diablo Canyon Nuclear Power Plant from opening in California. (AP Photo/Lennox Mclendon)
AP Photo/Lennox Mclendon
Actress Jane Fonda and her husband Tom Hayden stand outside the front gates of the Three Mile Island nuclear power plant near Middletown, Pa., on Monday, Sept. 24, 1979 shortly before holding a news conference. The couple, both anti-nuclear, are on a 50-city national tour sponsored by the Campaign for Economic Democracy. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
Actress Jane Fonda and her husband Tom Hayden stand outside the front gates of the Three Mile Island nuclear power plant near Middletown, Pa., on Monday, Sept. 24, 1979 shortly before holding a news conference. The couple, both anti-nuclear are on a 50-city national tour sponsored by the Campaign for Economic Democracy. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
Three Mile Island engineers William Behrle, Michael Benson, Sam Griffith and Martin Cooper enter the containment building from the personal airlock in Middletown, Pa., on Aug. 15, 1980. The inner door seen through a porthole opens into the containment building. (AP Photo)
AP Photo
Photo taken by technicians on the second manned entry into the contaminated Unit Two reactor building at Three Mile Island, Middleton, Pa., Aug. 22, 1980, shows the reactor vessel head. No damage is visible in this exterior view, although technicians are unsure of possible damage to the reactors interior caused in the March 28, 1979 accident. (AP Photo)
AP Photo
George Kalman, right, a U.S. Nuclear Regulatory Commission engineer, has part of his breathing apparatus checked by a Three Mile Island PWR technician, on November 13, 1980, in Middletown, Pa., as he prepares to enter the containment building housing the damaged No. 2 nuclear reactor. This is the fourth manned entry into the building since March 28, 1979, when the reactor core was severely damaged in an accident, and radiocativity was released into the atmosphere. (AP Photo)
AP Photo
The last container of radioactive waste taken from the original accident water at Three Mile Island Unit 2 leaves the disabled nuclear power plant, destined for the U.S. Department of Energy laboratory at Richland, Wash., Aug. 30, 1983. The waste is from the Submerged Demineralizer System which processed highly radioactive water that has accumulated in the basement of the containment building at the time of the March, 1979 accident. Damaged fuel is still in No. 2 reactor. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
An employee of the Three Mile Island nuclear power plant checks a radiation monitor tape across the Suaguehanna River from the disabled Three Mile Island nuclear power plant testing for possible nuclear radiation leak on Monday, Feb. 11, 1980near Harrisburg, Pennsylvania. In background at right is disabled nuclear reactor no. 2 containment building and right of domed reactor is auxiliary building where cooling system leak spilled radioactive water for nearly two hours, leakage was contained inside building. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
The last container of radioactive waste taken from the original accident water at Three Mile Island Unit 2 leaves the disabled nuclear power plant in Middletown, Pennsylvania on Tuesday, Aug. 30, 1983, destined for the U.S. Department of Energy Laboratory in Richland, WA. The waste is from the Submerged Demineralizer System which processed highly radioactive water that was accumulated in the basement of the containment building at the time of the March 1979 accident. Damaged fuel is still in No. 2 reactor. (AP Photo/Paul Vathis)
AP Photo/Paul Vathis
Smoke billows from two active cooling towers of the Three Mile Island nuclear power plant in Middletown, Pa., Wednesday, Oct. 19, 2005. The power plant is nestled on an island in the middle of the Susquehanna River. (AP Photo/Carolyn Kaster)
AP Photo/Carolyn Kaster