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On March 28, 1979, as the sun rose over Harrisburg, Pennsylvania, a series of mechanical, electrical, and human failures led to what has been described as the worst nuclear power plant accident in the history of the United States. News of the accident rocked the nation, and its effects were keenly felt by those who lived in the shadow of the great concrete towers of Three Mile Island.

At 4:00 AM on March 28, 1979, a reactor at the Three Mile Island nuclear power facility near Middletown Borough, Pennsylvania suddenly overheated, releasing radioactive gases. During the ensuing tension-packed week, scientists scrambled to prevent the nightmare of a meltdown, officials rushed in to calm public fears, and thousands of residents fled to emergency shelters, others left the area. Equipment failure, human error, and bad luck would conspire to create America's worst nuclear accident.

This page contains information on what took place at Three Mile Island on March 28, 1979, The Nuclear Regulatory Commission's statement and testimonies of area citizens on their health issues.

It has been 35 years since the accident at Three Mile Island, many questions surrounding the accident remain unanswered. The truth is...we may never know the answers.


Three Mile Island Nuclear Generating Station

From Wikipedia

Three Mile Island Nuclear Generating Station (TMI) is a nuclear power plant (NPP) located on Three Mile Island in the Susquehanna River, south of Harrisburg, Pennsylvania in Londonderry Township. It has two separate units, known as TMI-1 and TMI-2. The plant is widely known for having been the site of the most significant accident in United States commercial nuclear energy, on March 28, 1979, when TMI-2 suffered a partial meltdown. According to the US Nuclear Regulatory Commission, the accident resulted in no deaths or injuries to plant workers or members of nearby communities. Follow up epidemiology studies have also not linked a single cancer with the accident. The reactor core of TMI-2 has since been removed from the site.

Three Mile Island is so named because it is located three miles downriver from Middletown, Pennsylvania. The plant was originally built by General Public Utilities Corporation, later renamed GPU Incorporated. The plant was operated by Metropolitan Edison Company (Met-Ed), a subsidiary of the GPU Energy division. During 2001 GPU Inc. merged with FirstEnergy Corporation, through the sale of its outstanding common stock.

Exelon owns and operates Unit 1 of the power plant. Three Mile Island Unit 1 is a pressurized water reactor designed by Babcock and Wilcox. The unit is capable of generating 852 net megawatts (MW), enough electricity to power over 800,000 average American homes. Three Mile Island Unit 2 is owned by First Energy Company of Akron which was damaged during an accident in 1979 and never reopened.

Accident Summary of Events

Before going on to the accident summary of events, let's take a look on how a nuclear reactor works.

How a Nuclear Reactor Works

At the heart of every nuclear power plant lies the radioactive core. The core is a nuclear furnace, generating heat as its atoms split during a controlled chain reaction. At Three Mile Island, the core stands 12 feet high and weighs 100 tons.

Control rods are lowered into or raised out of the core to control the rate at which the atoms split, and therefore the amount of heat generated by the core. Lowering the rods slows down the reaction; raising the rods increases the reaction.

Water in the primary loop flows around the core, absorbing the heat generated. Because it comes in contact with the core, the water in the primary loop is radioactive. Pumps move the water through the primary loop. The PORV is a pressure release valve. The EIW, or Emergency Injection Water, allows water to enter the system in the event of a "loss of coolant."

Heat transfers from the water in the primary loop to water in the secondary loop. The water in the secondary loop turns to steam. The steam powers a turbine, which is connected to a generator.The generator produces electricity. Pumps move the water through the secondary loop and back to where the heat is exchanged. Water in the secondary loop does not mingle with the water in the primary loop and therefore is not radioactive.

Surrounding the core and much of the primary loop is a four-foot-thick, concrete containment structure.

Countdown to Disaster

Wednesday, March 28, 1979. The time is just before 4am. The reactor is currently running smoothly.
0 sec    The pumps in the secondary loop shut down automatically, due to a slight malfunction.

1 sec     Alarms sound within the control room.

2 sec     Because heat is no longer being transferred to the secondary loop, water pressure and water temperature in the primary loop rise. This is normal and no cause for concern.

3 sec     The PORV (pressure relief valve) opens automatically, releasing steam into a holding tank.

4 sec     Backup pumps within the secondary loop automatically turn on. However, these pumps are disconnected from the system by cutoff valves. Operators assume that the pumps are doing what they're supposed to do.

9 sec     The control rods , made of boron and silver, are lowered, which slows down the nuclear chain reaction within the core. Heat is still generated, though. In this state, the core produces enough energy to light 18,000 homes.
  • The PORV light goes out, indicating that the valve is now closed. The valve is actually still open.
  • Steam and water continues to be released through the PORV, creating a LOCA (loss of coolant accident).

2 min     The EIW (emergency injection water) is activated, and water flows into the primary loop. This is a safety device, designed to keep the water at a safe level in the event of a LOCA. Operators are not too concerned when this happens, though -- the EIW has turned itself on many times in the past when there has been no leak.

4 min 30 sec    Operators observe that the water level in the primary system is rising and that the pressure is decreasing. They turn off the EIW . The water level still appears to be rising. The level is actually dropping. The water, along with the steam, is now released through the PORV.

8 min     An operator notices that the valves for the backup pumps in the secondary loop are off. He opens the valves. The secondary side now operating normally.

15 min     By this time approximately 3,000 gallons have escaped from the primary loop. The instrument that checks radioactivity levels does not trigger an alarm, so operators still have no reason to suspect a LOCA.

45 min     The water level in the primary loop continues to drop. Gauges in the control room erroneously indicate that the water level is up.

1 hr 20 min     The pumps that push water through the primary loop begin to shake violently. This is caused by the steam passing through the pumps. Two of the four pumps are turned off.

1 hr 40 min     The other two pumps turn off. Steam within the primary loop, now no longer circulating with the water, rises.
  • Also, because the water isn't circulating, the core heats up even more, converting more of the water into steam.
2 hr 15 min     Water no longer covers the top of the core. The heat from the exposed core soon turns the steam into superheated steam. The control rods, in turn, react to the superheated steam and begin to release hydrogen and radioactive gases. These are also released through the PORV.

2 hr 20 min     An operator from the next shift comes on duty and notices that the PORV discharge temperature is abnormally high. He stops the leak by shutting the PORV's backup valve. More than a quarter of a million gallons of radioactive cooling water has been discharged since the PORV first opened.
  • Operators still don't realize that the water level in the primary loop is low. The water within the loop continues to boil away, which causes more damage to the core, more heat, and more radioactivity.
2 hr 30 min     The operators receive the first indication that radiation levels are going up.

2:45     Radiation alarms sound. A site emergency is declared.
  • Half of the core is now uncovered, and the radioactivity of the water in the primary loop is 350 times its normal level.
3 hr     Even higher radiation levels prompt the declaration of a general emergency.
  • High temperatures in the core lead some to believe that the core is uncovered; others do not trust the temperature readings.
7 hr 30 min     Even after operators pump water into the primary loop, pressure is still high. The PORV' backup valve is opened to lower the pressure.

9 hr     Hydrogen explodes within the containment structure, causing a pressure spike on the control room guages and an audible thud. The spikes are believed to be caused by an electrical malfunction; the thud is thought, at least by some, to be just a ventilator damper.

15 hr 50 min     The primary loop's pumps are turned on, which circulate water around the core. The core's temperature is finally under control, although half of it is melted and part of it has disintegrated. Also, there's still hydrogen in the primary loop.
  • Now that the path toward meltdown has been averted, the significant problem of leaking radiation must be dealt with.

Details on What Happened

The accident began about 4 a.m. on Wednesday, March 28, 1979, when the plant experienced a failure in the secondary, non-nuclear section of the plant (one of two reactors on the site). Either a mechanical or electrical failure prevented the main feedwater pumps from sending water to the steam generators that remove heat from the reactor core. This caused the plant's turbine-generator and then the reactor itself to automatically shut down. Immediately, the pressure in the primary system (the nuclear portion of the plant) began to increase. In order to control that pressure, the pilot-operated relief valve (a valve located at the top of the pressurizer) opened. The valve should have closed when the pressure fell to proper levels, but it became stuck open. Instruments in the control room, however, indicated to the plant staff that the valve was closed. As a result, the plant staff was unaware that cooling water was pouring out of the stuck-open valve.

As coolant flowed from the primary system through the valve, other instruments available to reactor operators provided inadequate information. There was no instrument that showed how much water covered the core. As a result, plant staff assumed that as long as the pressurizer water level was high, the core was properly covered with water. As alarms rang and warning lights flashed, the operators did not realize that the plant was experiencing a loss-of-coolant accident. They took a series of actions that made conditions worse. The water escaping through the stuck valve reduced primary system pressure so much that the reactor coolant pumps had to be turned off to prevent dangerous vibrations. To prevent the pressurizer from filling up completely, the staff reduced how much emergency cooling water was being pumped in to the primary system. These actions starved the reactor core of coolant, causing it to overheat.

Without the proper water flow, the nuclear fuel overheated to the point at which the zirconium cladding (the long metal tubes that hold the nuclear fuel pellets) ruptured and the fuel pellets began to melt. It was later found that about half of the core melted during the early stages of the accident. Although TMI-2 suffered a severe core meltdown, the most dangerous kind of nuclear power accident, consequences outside the plant were minimal. Unlike the Chernobyl and Fukushima accidents, TMI-2's containment building remained intact and held almost all of the accident's radioactive material.

Federal and state authorities were initially concerned about the small releases of radioactive gases that were measured off-site by the late morning of March 28 and even more concerned about the potential threat that the reactor posed to the surrounding population. They did not know that the core had melted, but they immediately took steps to try to gain control of the reactor and ensure adequate cooling to the core. The NRC's regional office in King of Prussia, Pa., was notified at 7:45 a.m. on March 28. By 8 a.m., NRC Headquarters in Washington, D.C., was alerted and the NRC Operations Center in Bethesda, Md., was activated. The regional office promptly dispatched the first team of inspectors to the site and other agencies, such as the Department of Energy and the Environmental Protection Agency, also mobilized their response teams. Helicopters hired by TMI's owner, General Public Utilities Nuclear, and the Department of Energy were sampling radioactivity in the atmosphere above the plant by midday. A team from the Brookhaven National Laboratory was also sent to assist in radiation monitoring. At 9:15 a.m., the White House was notified and at 11 a.m., all non-essential personnel were ordered off the plant's premises.

By the evening of March 28, the core appeared to be adequately cooled and the reactor appeared to be stable. But new concerns arose by the morning of Friday, March 30. A significant release of radiation from the plant's auxiliary building, performed to relieve pressure on the primary system and avoid curtailing the flow of coolant to the core, caused a great deal of confusion and consternation. In an atmosphere of growing uncertainty about the condition of the plant, the governor of Pennsylvania, Richard L. Thornburgh, consulted with the NRC about evacuating the population near the plant. Eventually, he and NRC Chairman Joseph Hendrie agreed that it would be prudent for those members of society most vulnerable to radiation to evacuate the area. Thornburgh announced that he was advising pregnant women and pre-school-age children within a five-mile radius of the plant to leave the area.

Within a short time, chemical reactions in the melting fuel created a large hydrogen bubble in the dome of the pressure vessel, the container that holds the reactor core. NRC officials worried the hydrogen bubble might burn or even explode and rupture the pressure vessel. In that event, the core would fall into the containment building and perhaps cause a breach of containment. The hydrogen bubble was a source of intense scrutiny and great anxiety, both among government authorities and the population, throughout the day on Saturday, March 31. The crisis ended when experts determined on Sunday, April 1, that the bubble could not burn or explode because of the absence of oxygen in the pressure vessel. Further, by that time, the utility had succeeded in greatly reducing the size of the bubble.

Five hours in which the unthinkable happened

Wednesday, March 28, 1979, 4:00 a.m. to 9:00 a.m.
4:00 a.m. Operators trying to unclog some piping in the secondary (steam generating) water circulation system accidentally block the flow of water, stopping removal of heat from the reactor. Within ten seconds, all of the following events occur: The cooling water filling the reactor vessel, heated by the core, gets hotter and its pressure rises. A relief valve at the top of the pressurizer tank—the so-called pilot-operated relief valve (PORV)—opens automatically; steam escapes. But the temperature and pressure of the water in the primary system continue to rise because heat generated by uranium fission in the reactor’s core is no longer being removed from the reactor cooling water in the steam generator. Automatically, the control rods are thrust down into the reactor. The nuclear fission chain reaction in the uranium fuel is stopped, completely.

The PORV relief valve should now close automatically, and the indicator light in the control room says that it is closed. But in fact the valve is stuck open.

4:02 a.m. With the PORV relief valve stuck open, the pressure in the “head” of steam at the top of the pressurizer tank drops, allowing water in the pressurizer tank to boil violently and stream out through the open valve. The reactor is losing its cooling water.
Although this photo suggests the confusion and consternation that reigned in the TMI-2 control room early Wednesday morning, it was made later, probably on Friday or Saturday.
The fall in pressure says “leak” to the automatic controls, which turn on pumps to inject more water into the reactor. The operators, not knowing that the PORV relief valve is stuck open and that water is escaping through it from the reactor—and remembering earlier occasions when these emergency pumps had come on without reason—see no reason to add water. On the contrary, the violently boiling water creates the appearance of the pressurizer becoming filled with water, a condition that the operators have been trained to prevent. The operators therefore turn off the pumps.

This is a serious mistake. Although the production of heat by nuclear

Wednesday, March 28

Although a general emergency has been declared before breakfast, it will be days before any general emergency is felt. By evening the condition of the reactor seems to be improving and radiation levels in the TMI-2 buildings seem to be falling. Now begins the oddly long, slow process of accepting that major damage to the reactor’s core has in fact occurred in the early morning hours.

Thursday, March 29

A day of relative calm—until evening, by which time nuclear engineers and public health officials are beginning to confront the fact of major damage to the reactor. And major damage implies the possibility of large quantities of radioactivity escaping from TMI.

Friday, March 30

Nuclear Regulatory Commission (NRC) officials in Washington, after 48 hours of underestimating the seriousness of the accident, now overestimate the danger. Unsubstantiated reports of dangerous releases of radioactivity lead Pennsylvania Governor Richard Thornburgh, on the NRC’s advice, to recommended that pregnant women and young children leave the area.

Late that night Food and Drug Administration officials rouse chemical manufacturers from bed with urgent requests for a quarter-million bottles of potassium iodide solution. A few drops of this taken in time will block the uptake in the thyroid gland of cancer-causing radioactive iodine, perhaps the most immediately dangerous of the radioactive substances to which reactor fuel is converted by nuclear fission.

There are, in fact, no releases of radioactivity that constitute a danger to public health. Alarm about reported releases of radioactive gases soon after the accident arose from misunderstandings. And later concern about the possibility of dangerous releases arose from a mistaken conclusion that hydrogen gas accumulated in the reactor vessel could explode.

Saturday, March 31

It is accepted that early on Wednesday morning much of the reactor’s core had stood above the water level. Consequently, it was certain that the zirconium tubes forming the cladding around the intensely hot fuel pellets would react chemically with the hot steam, pulling the oxygen out of H2O molecules and releasing hydrogen. This scenario is supported by the fact, not at first explicable, that at midday on Wednesday there had been a sudden rise in the pressure in the containment building of almost two atmospheres. Almost certainly, this resulted from the rapid burning of hydrogen that had escaped through the PORV from the reactor vessel and cooling system into the reactor containment building. Moreover it is known that some oxygen (and some more hydrogen) is continually being produced in the once-again-water-covered reactor core by the action of radiation on water molecules, breaking them apart into hydrogen and oxygen.

Is there then, or will there soon be, enough oxygen inside the reactor vessel and cooling system for the large amount of hydrogen it holds to burn explosively? Again NRC officials—albeit supported by the opinions and calculations of many experts—unnecessarily heighten fears by telling reporters that an evacuation out to 10 or 20 miles (15 to 30 km) might become necessary.

Sunday, April 1

Assured that any explosion is at least a couple days away, President and Mrs. Jimmy Carter tour the TMI facility early in the afternoon. In the hours following their visit, the expert consensus swings around to the opposite view—that a hydrogen explosion is simply not possible. The crisis is over—although no one says that loud and clear.

fission is stopped completely by the insertion of the control rods, the radioactivity created in the fuel during months of operation of the reactor continues to generate lots of heat— 160 megawatts of heat immediately after the control rods go in, then falling over the first hour to 30 megawatts, and over the next three hours to 20 megawatts.

4:05 - 6:00 a.m. The water in the reactor boils away, leaving more and more of the reactor’s fuel “high and dry.” The operators disbelieve the various indications of serious trouble (including rising levels of radiation in the reactor buildings). Lacking any direct indicator of the water level in the reactor, they fail to grasp what is happening: the uranium fuel, intensely hot, is reacting chemically with the zirconium tubing from the inside, while superheated steam is reacting chemically with the zirconium from the outside. The fuel rods are rupturing.

6:18 a.m. Finally recognizing that the PORV relief valve could be open, the operators close a manual back-up valve. But it is another hour before it occurs to them that if the relief valve was open all this while, then the reactor could be running short of water.

7:20 a.m. Pumps are turned on to inject water into the reactor. The core is finally bathed again in cooling water, but the water cannot penetrate the mass of collapsed and melted fuel rods. This dense conglomerate continues to heat itself up.

7:45 a.m. By now there are at least 20, perhaps as many as 60, operators, supervisors, and other persons in the control room. Although none is yet ready to believe that the core had been uncovered, radiation levels in the power plant buildings are so high that Nuclear Regulatory Commission regulations require the declaration of a general emergency. While state and federal officials are being informed of elevated radiation levels, unbeknown to all, a molten mass of metal and fuel—some twenty tons in all—is spilling into the bottom of the reactor vessel. The bottom of the reactor vessel is steel, five inches (13 cm) thick. But even that thickness of steel would not be expected to hold up for more than a few hours against such heat.

9:00 a.m. The reactor vessel holds firm, and the molten uranium, immersed in water, now gradually begins to cool. The real danger is past without anyone knowing how great it had been.

If this meltdown were known, or even merely surmised, drastic emergency measures, including evacuation of the region for miles around, would certainly be ordered by the governor.


The NRC (Nuclear Regulatory Commission) conducted detailed studies of the accident's radiological consequences, as did the Environmental Protection Agency, the Department of Health, Education and Welfare (now Health and Human Services), the Department of Energy, and the Commonwealth of Pennsylvania. Several independent groups also conducted studies. The approximately 2 million people around TMI-2 during the accident are estimated to have received an average radiation dose of only about 1 millirem above the usual background dose. To put this into context, exposure from a chest X-ray is about 6 millirem and the area's natural radioactive background dose is about 100-125 millirem per year for the area. The accident's maximum dose to a person at the site boundary would have been less than 100 millirem above background.

In the months following the accident, although questions were raised about possible adverse effects from radiation on human, animal, and plant life in the TMI area, none could be directly correlated to the accident. Thousands of environmental samples of air, water, milk, vegetation, soil, and foodstuffs were collected by various government agencies monitoring the area. Very low levels of radionuclides could be attributed to releases from the accident. However, comprehensive investigations and assessments by several well respected organizations, such as Columbia University and the University of Pittsburgh, have concluded that in spite of serious damage to the reactor, the actual release had negligible effects on the physical health of individuals or the environment.


No Radiological Health Effects

The Three Mile Island accident caused concerns about the possibility of radiation-induced health effects, principally cancer, in the area surrounding the plant. Because of those concerns, the Pennsylvania Department of Health for 18 years maintained a registry of more than 30,000 people who lived within five miles of Three Mile Island at the time of the accident. The state's registry was discontinued in mid 1997, without any evidence of unusual health trends in the area.

Indeed, more than a dozen major, independent health studies of the accident showed no evidence of any abnormal number of cancers around TMI years after the accident. The only detectable effect was psychological stress during and shortly after the accident.

The studies found that the radiation releases during the accident were minimal, well below any levels that have been associated with health effects from radiation exposure. The average radiation dose to people living within 10 miles of the plant was 0.08 millisieverts, with no more than 1 millisievert to any single individual. The level of 0.08 mSv is about equal to a chest X-ray, and 1 mSv is about a third of the average background level of radiation received by U.S. residents in a year.

In June 1996, 17 years after the TMI-2 accident, Harrisburg U.S. District Court Judge Sylvia Rambo dismissed a class action lawsuit alleging that the accident caused health effects. The plaintiffs have appealed Judge Rambo's ruling. The appeal is before the U.S. Third Circuit Court of Appeals. However, in making her decision, Judge Rambo cited:

· Findings that exposure patterns projected by computer models of the releases compared so well with data from the TMI dosimeters (TLDs) available during the accident that the dosimeters probably were adequate to measure the releases.

· That the maximum offsite dose was, possibly, 100 millirem (1 mSv), and that projected fatal cancers were less than one.

· The plaintiffs' failure to prove their assertion that one or more unreported hydrogen "blowouts" in the reactor system caused one or more unreported radiation "spikes", producing a narrow yet highly concentrated plume of radioactive gases.

Judge Rambo concluded: "The parties to the instant action have had nearly two decades to muster evidence in support of their respective cases.... The paucity of proof alleged in support of Plaintiffs' case is manifest. The court has searched the record for any and all evidence which construed in a light most favourable to Plaintiffs creates a genuine issue of material fact warranting submission of their claims to a jury. This effort has been in vain."

More than a dozen major, independent studies have assessed the radiation releases and possible effects on the people and the environment around TMI since the 1979 accident at TMI-2. The most recent was a 13-year study on 32,000 people. None has found any adverse health effects such as cancers which might be linked to the accident.



The health of people in Middletown Borough, Pennsylvania, has been a major concern. A study done in 2002 by the University of Pittsburgh examined the dose of radiation to people near Three Mile Island at the time of the accident. The amount was one millirem, which is not harmful to humans (Powell). The average person receives 360 millirems a year, with one-tenth of a millirem from nuclear power (9). Another study conducted by the Radiation and Public Health Project states that the death of children, infants, and elderly dramatically increased two years after the meltdown. In 2004, yet another study was done to see if there was a rise of cancer-related deaths. Researchers found that there was no dramatic increase in the Pennsylvania region (Powell). The health of people in the region of Three Mile Island is important to how dangerous nuclear power appears to people around the world.

Powell, Albrecht. "Three Mile Island-25 Years Later."
The day of the accident, before the public was alerted, hundreds of residents living near Three Mile Island reported having had symptoms of radiation poisoning identical to those described by U.S. service members and down winders of atomic bomb blasts. These symptoms included a metallic taste in their mouths; skin rashes and instant sunburn of exposed skin; vomiting and/or diarrhea, which in some cases continued for months; hair loss; and intense weakness and flu-like symptoms.

Some also reported an eerie blue density in the air that lasted for days; a grayish-white ash that fell to the ground (also reported in the Marshall Islands immediately following atomic bomb tests in the Pacific, where the U.S. exploded 106 atomic bombs between 1946 and 1962); an unnatural orange glow above the reactor site; and rust-colored residue in their sinks and tubs, indicating radioactive contamination of the water supply. Several area residents reported the metallic taste and other physical symptoms over the next few years at times they later learned happened to coincide with the venting of radioactive krypton gas during the cleanup.

Over time, unusually high numbers of both strange and common cancers began showing up among residents, particularly those living in the path of the radiation plumes that crept over nearby communities during the first few days following the accident. Myriad other health problems appeared -- miscarriages, stillbirths, infant deaths, thyroid diseases, various autoimmune disorders, heart problems and the sudden onset of allergies.

Strange Diseases

Becky Mease, a nurse in her late twenties at the time, fled with her husband, eight-month-old daughter Pam, and two other adults two days after the accident, when then Pennsylvania Governor Dick Thornburgh suggested that pregnant women and preschool children within five miles of Three Mile Island evacuate. They drove more than 250 miles to Ocean City, Maryland, where they stayed for about three weeks. 

A significant rise in pregnancy complications, miscarriages, still births, birth defects

Recounting her experience to citizen researchers Katagiri Mitsuru and Aileen Smith in October 1982, Mease said Pam, who had been outside playing in the grass the day of the accident, had gotten violently ill with diarrhea and projectile vomiting about two days after they left. A full battery of tests at a local hospital failed to find any bacteria or foreign organism, which could cause such symptoms, so the hospital staff told them to go to a civil defense station. Mease knew radiation sickness can cause vomiting and diarrhea, so she asked the people at the civil defense office to check their car and belongings with a Geiger counter. “It just went completely crazy… It went like nuts when it went over my pocketbook, too," she said. “They told us to go wash everything down."

Pam's severe diarrhea lasted the entire three weeks they were away. “Her behind was so raw that we just left it lay on diapers. Didn't even put them on after a couple of days," said Mease.

In the summer of 1981, when Pam was two years old, she was diagnosed with severe cataracts in both of her eyes, which her doctor attributed to juvenile rheumatoid arthritis.

The Meases' ordeal was one of thousands area residents suffered in the aftermath of the accident. But the radiation effects weren't confined to humans. The evidence was visible across the landscape, too, with unprecedented numbers of sick and dying farm animals and strangely mutated plants.

Residents Struggle On Their Own

The residents were left to deal with these problems on their own. Nearly four years after the Three Mile Island disaster, citizens frustrated over the lack of help from public health authorities and other government officials went door-to-door to gather health data themselves. Mary Osborne, a longtime Harrisburg resident, was one of the survey takers. “Our door-to-door studies showed horrendous problems everywhere," she said. “At almost every household or every other household we found cancer or some kind of emergency problem, and in some cases, different family members had different cancers." Osborne also noted significant numbers of women who had pregnancy problems, babies with low birth weights, neonatal and newborn deaths, and Downs syndrome.

Despite the fact that the citizens had consulted Dr. Carl J. Johnson, an expert from Colorado, on the effects of radiation and public health, to help design their survey, the government and the nuclear industry dismissed their results as “unscientific." The government and the nuclear industry insisted then and now that nobody outside Three Mile Island was killed or injured as a result of the accident, because very little radiation escaped into the surrounding community, and therefore no injuries or deaths could have resulted from the accident.

But David Lochbaum, a nuclear engineer-turned-whistleblower who monitors the U.S. nuclear reactor fleet for the Union of Concerned Scientists, says radiation monitors on the vent stacks at Three Mile Island went off scale during the accident. The exact amount of radiation released will never be known, he says, because crucial records from the first two days following the accident somehow never surfaced, and not enough radiation dosimeters were deployed in surrounding communities to give a true reading. What is known is that the partial meltdown damaged at least 70 percent of the reactor core and caused more than one-third of its highly radioactive fuel to melt.

Three Mile Island plant owner Metropolitan Edison and the Nuclear Regulatory Commission (NRC) maintained that ten million curies of radioactive gases were released into the atmosphere from the accident, resulting in an average dose to area residents equal to a chest X-ray.

Lochbaum says that figure is grossly underestimated, because it is based on a measurement of radiation levels on the Three Mile Island site a year after the fact and does not account for shorter-lived radionuclides like iodine-131, which would not have been measurable by that time. Nor, he says, does the official figure include any leakage from the containment building, the concrete dome surrounding the core of the reactor, which is meant to prevent deadly radiation from escaping into the environment in the event of an accident. Lochbaum estimates that at least 40 million curies were released during the accident. Other more recent estimates by former nuclear industry executive Arnold Gundersen calculated the radiation releases at 100 to 1,000 times higher than NRC estimates.

Radiation and Women’s Health

He takes apart even the form of matter itself, he strips energy from mass, he splits what is whole, he takes this force for his own, he says. But what he has split does not stop coming apart. Fractures live in the air, invisible fractures come into his body, split his chromosomes, unravel the secrets in him. -- -- Susan Griffin

Health problems from radiation exposure reported from the Three Mile Island accident and specific to women include a significant rise in pregnancy complications, miscarriages, still births, birth defects, low birth weights of babies born after the accident, and cases of Downs syndrome. Though radioactive elements do have chemical components that determine what organ in the body they affect, it’s important to understand the danger of the radioactivity itself.

Radioactive elements, also known as radioisotopes or radionuclides, are unstable atoms that over time—sometimes as long as several billion years, depending on the radionuclide—become stable. Nuclear radiation expert Rosalie Bertell describes ionizing radiation, the release of energy that radionuclides give off, as “an explosion on the microscopic level."

The physics and chemistry of radiation is complicated and involves scores of different elements that behave in different ways depending on what they encounter in the outside environment or where they lodge inside our bodies. All of these “microscopic explosions" are able to break chemical bonds, which enables them to damage or destroy living cells.

The chemical properties of various radioactive elements determine where in the body they will concentrate. Below is a description of some of the organs and tissues most at risk from radioactivity.

Ovaries: Ionizing radiation damage to ovaries can cause birth defects, mutations, and miscarriages in the first and subsequent generations of women exposed. Some of the radionuclides involved are iodine-131, cobalt-60, krypton-85, ruthenuim-106, zinc-65, barium-140, potassium-42, cesium-137, and plutonium-239.
Thyroid: The thyroid, the master gland in metabolism, requires iodine in order to function. If the radionuclide iodine-131 is inhaled or ingested, the thyroid gland will take it up. Thyroid cancer is a particular risk for radiation exposure.
Bones: The bones are damaged by strontium-90, which mimics calcium, radium-226, zinc-65, yttrium-90, promethium-147, barium-140, thorium-234, phosphorus-32, and carbon-14.
Skin: sulfur-35.
Liver: cobalt-60.
Muscle: potassium-42 and cesium-137.
Lungs: radon-222, uranium 233, plutonium-239, and krypton-85.
Spleen: polonium-210.
Kidneys: ruthenium-106.

-Karen Charman

Health studies conducted by the Pennsylvania Department of Health, various federal government agencies, and Columbia University supported the nuclear industry claims. The affected citizens contend these studies were sloppy and included people who should not have been counted, excluded many who should have been, or the researchers did not do the necessary follow-up on people who left the area after the accident. The citizens also say study authors uncritically accepted the premise that not enough radiation was released to cause the illnesses people were experiencing, so that even when higher disease rates were found, they were attributed to other factors such as stress or “lifestyle factors" like smoking, drinking, poor diet, or taking too much anti-anxiety medication.

Nuclear Critics Drowned Out

Some scientists have attempted to find out what really happened to the community after the accident. Dr. Ernest J. Sternglass, a tenured professor of radiation physics at the University of Pittsburgh, immediately sought every relevant health statistic he could find. According to Sternglass, a student of Albert Einstein's who holds several patents on X-ray technology, the health impacts from the accident were unquestionable, significant, and included a sharp spike in infant deaths and hypothyroidism. Dr. Gordon MacLeod, Pennsylvania's Secretary of Health at the time, tried to ensure all health impacts from the accident were fully disclosed. He was fired by then Governor Dick Thornburgh for his efforts. More recently, University of North Carolina epidemiologist Steve Wing reanalyzed the data from the Columbia University study and concluded that people living closer to the path of the radiation cloud developed all types of cancers more frequently. In the areas of greatest fallout, lung cancer rates jumped 400 percent, and leukemia rates climbed 700 percent. These scientists -- and others who question the nuclear orthodoxy -- have all been either drowned out or viciously attacked as biased, unprofessional purveyors of panic with an anti-nuclear axe to grind.

More than 2,000 people participated in a class-action lawsuit claiming injuries against Three Mile Island. Although an unknown number of cases settled out of court with terms that must be kept confidential, in June 1996 the class-action lawsuit was dismissed on the grounds that the plaintiffs failed to prove that the Three Mile Island accident had caused their health problems.

Downwind Across the Nation

Mary Osborne is deeply disillusioned by what she characterizes as a gross miscarriage of justice. “Not a day goes by that I don't think about the accident."

35 years later, the Three Mile Island disaster and its aftermath continue to shape the lives of many who were exposed to the radioactive fallout. Three Mile Island serves as a model of what American citizens can expect if another nuclear disaster were to occur. With 104 mostly aging nuclear reactors not only still running but virtually all being granted 20-year license extensions, and, in some cases, permits to generate more power than they were designed to do, David Lochbaum believes that sheer luck rather than good management or serious concern for safety has so far prevented another nuclear disaster. Considering that approximately 190 million citizens live within 100 miles of at least one nuclear reactor, let's hope that luck holds.


Impact of the Accident

A combination of personnel error, design deficiencies, and component failures caused the Three Mile Island accident, which permanently changed both the nuclear industry and the NRC. Public fear and distrust increased, NRC's regulations and oversight became broader and more robust, and management of the plants was scrutinized more carefully. Careful analysis of the accident's events identified problems and led to permanent and sweeping changes in how NRC regulates its licensees – which, in turn, has reduced the risk to public health and safety.

Major changes that have occurred since the accident:

    Upgrading and strengthening of plant design and equipment requirements. This includes fire protection, piping systems, auxiliary feedwater systems, containment building isolation, reliability of individual components (pressure relief valves and electrical circuit breakers), and the ability of plants to shut down automatically;

    Identifying the critical role of human performance in plant safety led to revamping operator training and staffing requirements, followed by improved instrumentation and controls for operating the plant, and establishment of fitness-for-duty programs for plant workers to guard against alcohol or drug abuse;

    Enhancing emergency preparedness, including requirements for plants to immediately notify NRC of significant events and an NRC Operations Center staffed 24 hours a day. Drills and response plans are now tested by licensees several times a year, and state and local agencies participate in drills with the Federal Emergency Management Agency and NRC;

    Integrating NRC observations, findings, and conclusions about licensee performance and management effectiveness into a periodic, public report;

    Having senior NRC managers regularly analyze plant performance for those plants needing significant additional regulatory attention;

    Expanding NRC's resident inspector program – first authorized in 1977 – to have at least two inspectors live nearby and work exclusively at each plant in the U.S. to provide daily surveillance of licensee adherence to NRC regulations;

    Expanding performance-oriented as well as safety-oriented inspections, and the use of risk assessment to identify vulnerabilities of any plant to severe accidents;

    Strengthening and reorganizing enforcement staff in a separate office within the NRC;

    Establishing the Institute of Nuclear Power Operations, the industry's own "policing" group, and formation of what is now the Nuclear Energy Institute to provide a unified industry approach to generic nuclear regulatory issues, and interaction with NRC and other government agencies;

    Installing additional equipment by licensees to mitigate accident conditions, and monitor radiation levels and plant status;

    Enacting programs by licensees for early identification of important safety-related problems, and for collecting and assessing relevant data so operating experience can be shared and quickly acted upon; and

    Expanding NRC's international activities to share enhanced knowledge of nuclear safety with other countries in a number of important technical areas.


Current Status

Today, the TMI-2 reactor is permanently shut down and all its fuel had been removed. The reactor coolant system is fully drained and the radioactive water decontaminated and evaporated. The accident's radioactive waste was shipped off-site to an appropriate disposal area, and the reactor fuel and core debris was shipped to the Department of Energy's Idaho National Laboratory. In 2001, FirstEnergy acquired TMI-2 from GPU. FirstEnergy has contracted the monitoring of TMI-2 to Exelon, the current owner and operator of TMI-1. The companies plan to keep the TMI-2 facility in long-term, monitored storage until the operating license for the TMI-1 plant expires, at which time both plants will be decommissioned.  In 2009, the NRC granted a license extension which means the TMI-1 reactor may operate until April 19, 2034.

The Cleanup

Below is a chronology of highlights of the TMI‑2 cleanup from 1980 through 1993.

Date              Event
July 1980     Approximately 43,000 curies of krypton were vented            from  the reactor building.
July 1980    The first manned entry into the reactor building took place.

Nov. 1980     An Advisory Panel for the Decontamination of TMI-2, composed     of  citizens, scientists, and State and local officials, held its first meeting in Harrisburg, PA.
July 1984     The reactor vessel head (top) was removed.
Oct. 1985     Fuel removal began.
July 1986     The off-site shipment of reactor core debris began.
Aug. 1988     GPU submitted a request for a proposal to amend the TMI-2 license to a "possession-only" license and to allow the facility to enter long-term monitoring storage.
Jan. 1990     Fuel removal was completed.
July 1990     GPU submitted its funding plan for placing $229 million in escrow for radiological decommissioning of the plant.
Jan. 1991     The evaporation of accident-generated water began.
April 1991     NRC published a notice of opportunity for a hearing on GPU's request for a license amendment.
Feb. 1992     NRC issued a safety evaluation report and granted the license amendment.
Aug. 1993     The processing of accident-generated water was completed involving 2.23 million gallons.
Sept. 1993     NRC issued a possession-only license.
Sept. 1993     The Advisory Panel for Decontamination of TMI-2 held its last meeting.
Dec. 1993      Monitored storage began.


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Additional Sources for Information on Three Mile Island

Further information on the TMI-2 accident can be obtained from sources listed below. The NUREG documents, many of which are on microfiche, can be ordered for a fee from the NRC's Public Document Room at 301-415-4737 or 1-800-397-4209; Mailing address is: U.S. Nuclear Regulatory Commission, Public Document Room, Washington, D.C. 20555.

NRC Annual Report - 1979, NUREG-0690
"Population Dose and Health Impact of the Accident at the Three Mile Island Nuclear Station," NUREG-0558
"Environmental Assessment of Radiological Effluents from Data Gathering and Maintenance Operation on Three Mile Island Unit 2," NUREG-0681
"Report of The President's Commission on The Accident at Three Mile Island," October, 1979
"Investigation into the March 28, 1979 Three Mile Island Accident by the Office of Inspection and Enforcement," NUREG-0600
"Three Mile Island; A Report to the Commissioners and to the Public," by Mitchell Rogovin and George T. Frampton, NUREG/CR-1250, Vols. I-II, 1980
"Lessons learned From the Three Mile Island - Unit 2 Advisory Panel," NUREG/CR-6252
"The Status of Recommendations of the President's Commission on the Accident at Three Mile Island," (A ten-year review), NUREG-1355
"NRC Views and Analysis of the Recommendations of the President's Commission on the Accident at Three Mile Island," NUREG-0632
"Environmental Impact Statement related to decontamination and disposal of radioactive wastes resulting from March 28, 1979 accident Three Mile
     Island Nuclear Station, Unit 2," NUREG-0683
"Answers to Questions About Updated Estimates of Occupational Radiation Doses at Three Mile Island, Unit 2," NUREG-1060
"Answers to Frequently Asked Questions About Cleanup Activities at Three Mile Island, Unit 2," NUREG-0732
"Status of Safety Issues at Licensed Power Plants" (TMI Action Plan Reqmts.), NUREG-1435
Walker, J. Samuel, Three Mile Island: A Nuclear Crisis in Historical Perspective, Berkeley: University of California Press, 2004.