Three Mile Island accident

Three Mile Island accident

Overview
The Three Mile Island accident was a core
Nuclear reactor core
A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place.- Description :...

 meltdown
Nuclear meltdown
Nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. The term is not officially defined by the International Atomic Energy Agency or by the U.S. Nuclear Regulatory Commission...

 in Unit 2 (a pressurized water reactor
Pressurized water reactor
Pressurized water reactors constitute a large majority of all western nuclear power plants and are one of three types of light water reactor , the other types being boiling water reactors and supercritical water reactors...

 manufactured by Babcock & Wilcox
Babcock and Wilcox
The Babcock & Wilcox Company is a U.S.-based company that provides design, engineering, manufacturing, construction and facilities management services to nuclear, renewable, fossil power, industrial and government customers worldwide. B&W's boilers supply more than 300,000 megawatts of installed...

) of the Three Mile Island Nuclear Generating Station
Three Mile Island Nuclear Generating Station
Three Mile Island Nuclear Generating Station is a civilian nuclear power plant located on Three Mile Island in the Susquehanna River, south of Harrisburg, Pennsylvania. It has two separate units, known as TMI-1 and TMI-2...

 in Dauphin County, Pennsylvania
Dauphin County, Pennsylvania
Dauphin County is a county in the U.S. state of Pennsylvania and is one of the three counties comprising the Harrisburg–Carlisle Metropolitan Statistical Area. As of 2010 census, the population was 268,100. The county includes the city of Harrisburg, which has served as the state capital...

 near Harrisburg
Harrisburg, Pennsylvania
Harrisburg is the capital of Pennsylvania. As of the 2010 census, the city had a population of 49,528, making it the ninth largest city in Pennsylvania...

, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 in 1979.

The power plant was owned and operated by General Public Utilities and Metropolitan Edison (Met Ed). It resulted in the release of approximately 2.5 million curie
Curie
The curie is a unit of radioactivity, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit,...

s of radioactive gases, and approximately 15 curies of iodine-131
Iodine-131
Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical...

.

The accident began at 4 a.m.
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Encyclopedia
The Three Mile Island accident was a core
Nuclear reactor core
A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place.- Description :...

 meltdown
Nuclear meltdown
Nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. The term is not officially defined by the International Atomic Energy Agency or by the U.S. Nuclear Regulatory Commission...

 in Unit 2 (a pressurized water reactor
Pressurized water reactor
Pressurized water reactors constitute a large majority of all western nuclear power plants and are one of three types of light water reactor , the other types being boiling water reactors and supercritical water reactors...

 manufactured by Babcock & Wilcox
Babcock and Wilcox
The Babcock & Wilcox Company is a U.S.-based company that provides design, engineering, manufacturing, construction and facilities management services to nuclear, renewable, fossil power, industrial and government customers worldwide. B&W's boilers supply more than 300,000 megawatts of installed...

) of the Three Mile Island Nuclear Generating Station
Three Mile Island Nuclear Generating Station
Three Mile Island Nuclear Generating Station is a civilian nuclear power plant located on Three Mile Island in the Susquehanna River, south of Harrisburg, Pennsylvania. It has two separate units, known as TMI-1 and TMI-2...

 in Dauphin County, Pennsylvania
Dauphin County, Pennsylvania
Dauphin County is a county in the U.S. state of Pennsylvania and is one of the three counties comprising the Harrisburg–Carlisle Metropolitan Statistical Area. As of 2010 census, the population was 268,100. The county includes the city of Harrisburg, which has served as the state capital...

 near Harrisburg
Harrisburg, Pennsylvania
Harrisburg is the capital of Pennsylvania. As of the 2010 census, the city had a population of 49,528, making it the ninth largest city in Pennsylvania...

, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 in 1979.

The power plant was owned and operated by General Public Utilities and Metropolitan Edison (Met Ed). It resulted in the release of approximately 2.5 million curie
Curie
The curie is a unit of radioactivity, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit,...

s of radioactive gases, and approximately 15 curies of iodine-131
Iodine-131
Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical...

.

The accident began at 4 a.m. on Wednesday, March 28, 1979, with failures in the non-nuclear secondary system, followed by a stuck-open pilot-operated relief valve
Pilot-operated relief valve
Like other pressure relief valves , pilot operated relief valves are used for emergency relief during overpressure events . The distinction between PORV and conventional PRV is that pilot valves use system pressure to seal the valve...

 (PORV) in the primary system, which allowed large amounts of nuclear reactor coolant
Nuclear reactor coolant
A nuclear reactor coolant is a coolant in a nuclear reactor used to remove heat from the nuclear reactor core and transfer it to electrical generators and the environment....

 to escape. The mechanical failures were compounded by the initial failure of plant operators to recognize the situation as a loss-of-coolant accident due to inadequate training and human factors
Human factors
Human factors science or human factors technologies is a multidisciplinary field incorporating contributions from psychology, engineering, industrial design, statistics, operations research and anthropometry...

, such as human-computer interaction design oversights relating to ambiguous control room indicators in the power plant's user interface
User interface
The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...

. In particular, a hidden indicator light led to an operator manually overriding the automatic emergency cooling system of the reactor because the operator mistakenly believed that there was too much coolant water present in the reactor and causing the steam pressure release. The scope and complexity of the accident became clear over the course of five days, as employees of Met Ed, Pennsylvania state officials, and members of the U.S. Nuclear Regulatory Commission
Nuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...

 (NRC) tried to understand the problem, communicate the situation to the press and local community, decide whether the accident required an emergency evacuation, and ultimately end the crisis. The NRC's authorization of the release of 40,000 gallons of radioactive waste water directly in the Susquehanna River led to a loss of credibility with the press and community.

In the end, the reactor was brought under control, although full details of the accident were not discovered until much later, following extensive investigations by both a presidential commission and the NRC
Nuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...

. The Kemeny Commission Report concluded that "there will either be no case of cancer or the number of cases will be so small that it will never be possible to detect them. The same conclusion applies to the other possible health effects". Several epidemiological studies in the years since the accident have supported the conclusion that radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...

 released from the accident had no perceptible effect on cancer incidence in residents near the plant, though these findings are contested by one team of researchers. Cleanup started in August 1979 and officially ended in December 1993, with a total cleanup cost of about $1 billion. The incident was rated a five on the seven-point International Nuclear Event Scale
International Nuclear Event Scale
The International Nuclear and Radiological Event Scale was introduced in 1990 by the International Atomic Energy Agency in order to enable prompt communication of safety significance information in case of nuclear accidents....

: Accident With Wider Consequences.

Communications from officials during the initial phases of the accident were confusing. There was an evacuation of 140,000 pregnant women and pre-school age children from the area. The accident crystallized anti-nuclear
Anti-nuclear
The anti-nuclear movement is a social movement that opposes the use of nuclear technologies. Many direct action groups, environmental groups, and professional organisations have identified themselves with the movement at the local, national, and international level...

 safety concerns among activists and the general public, resulted in new regulations for the nuclear industry, and has been cited as a contributor to the decline of new reactor construction that was already underway in the 1970s. Public reaction to the event was probably influenced by The China Syndrome
The China Syndrome
The China Syndrome is a 1979 American thriller film that tells the story of a reporter and cameraman who discover safety coverups at a nuclear power plant. It stars Jane Fonda, Jack Lemmon, Michael Douglas, Scott Brady, James Hampton, Peter Donat, Richard Herd, and Wilford Brimley.The film was...

, a movie which had recently been released and which depicts an accident at a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

.

Stuck valve


In the nighttime hours preceding the incident, the TMI-2 reactor was running at 97% of full power, while the companion TMI-1 reactor was shut down for refueling. The chain of events leading to the partial core meltdown began at 4 am EST on March 28, 1979, in TMI-2's secondary loop, one of the three main water/steam loops in a pressurized water reactor
Pressurized water reactor
Pressurized water reactors constitute a large majority of all western nuclear power plants and are one of three types of light water reactor , the other types being boiling water reactors and supercritical water reactors...

.

Workers were cleaning a blockage in one of the eight condensate polisher
Condensate polisher
A condensate polisher is a device used to filter water condensed from steam as part of the steam cycle, for example in a conventional or nuclear power plant...

s (sophisticated filters cleaning the secondary loop water), when, for reasons still unknown, the pumps feeding the polishers stopped. When a bypass valve did not open, water stopped flowing to the secondary's main feedwater pumps, which also shut down. With the steam generators
Steam generator (nuclear power)
Steam generators are heat exchangers used to convert water into steam from heat produced in a nuclear reactor core. They are used in pressurized water reactors between the primary and secondary coolant loops....

 no longer receiving water, they stopped and the reactor performed an emergency shutdown
Scram
A scram or SCRAM is an emergency shutdown of a nuclear reactor – though the term has been extended to cover shutdowns of other complex operations, such as server farms and even large model railroads...

 (SCRAM). Within eight seconds, control rod
Control rod
A control rod is a rod made of chemical elements capable of absorbing many neutrons without fissioning themselves. They are used in nuclear reactors to control the rate of fission of uranium and plutonium...

s were inserted into the core to halt the nuclear chain reaction
Nuclear chain reaction
A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes or the fusion of light isotopes...

 but the reactor continued to generate decay heat
Decay heat
Decay heat is the heat released as a result of radioactive decay. This is when the radiation interacts with materials: the energy of the alpha, beta or gamma radiation is converted into the thermal movement of atoms.-Natural occurrence:...

 and, because steam was no longer being used by the turbine, heat was no longer being removed from the reactor's primary water loop.

Once the secondary feedwater pumps stopped, three auxiliary pumps activated automatically. However, because the valves had been closed for routine maintenance, the system was unable to pump any water. The closure of these valves was a violation of a key NRC rule, according to which the reactor must be shut down if all auxiliary feed pumps are closed for maintenance. This failure was later singled out by NRC officials as a key one, without which the course of events would have been very different.

Due to the loss of heat removal from the primary loop and the failure of the auxiliary system to activate, the primary loop pressure began to increase, triggering the pilot-operated relief valve
Pilot-operated relief valve
Like other pressure relief valves , pilot operated relief valves are used for emergency relief during overpressure events . The distinction between PORV and conventional PRV is that pilot valves use system pressure to seal the valve...

 (PORV) at the top of the pressurizer
Pressurizer
The basic design of the pressurized water reactor includes a requirement that the water in the reactor coolant system not boil. Another way to put this is that the coolant must remain in the liquid state at all times, especially in the reactor vessel...

—a pressure active-regulator tank—to open automatically. The relief valve should have closed again when the excess pressure had been released, and electric power to the solenoid
Solenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...

 of the pilot was automatically cut, but the relief valve stuck open due to a mechanical fault. The open valve permitted coolant water to escape from the primary system, and was the principal mechanical cause of the true coolant-loss meltdown crisis that followed.

Human factors – confusion over valve status


Critical human factors and user interface engineering problems were revealed in the investigation of the reactor control
Process control
Process control is a statistics and engineering discipline that deals with architectures, mechanisms and algorithms for maintaining the output of a specific process within a desired range...

 system's user interface
User interface
The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...

. Despite the valve being stuck open, a light on the control panel indicated that the valve was closed. In fact the light did not indicate the position of the valve, only the status of the solenoid, thus giving false evidence of a closed valve. As a result the operators did not correctly diagnose the problem for several hours.
The design of the PORV indicator light was fundamentally flawed, because it implied that the PORV was shut when it went dark. When everything was operating correctly this was true, and the operators became habituated to rely on it. However, when things went wrong and the main relief valve stuck open, the unlighted lamp was actually misleading the operators by implying that the valve was shut. This caused the operators considerable confusion, because the pressure, temperature and levels in the primary circuit, so far as they could observe them via their instruments, were not behaving as they would have done if the PORV was shut; they were convinced it was. This confusion contributed to the severity of the accident because the operators were unable to break out of a cycle of assumptions that conflicted with what their instruments were telling them. It was not until a fresh shift came in who did not have the mind-set of the first set of operators that the problem was correctly diagnosed. But by then, major damage had occurred.

The operators had not been trained to understand the ambiguous nature of the PORV indicator and look for alternative confirmation that the main relief valve was closed. There was a temperature indicator downstream of the PORV in the tail pipe between the PORV and the pressurizer that could have told them the valve was stuck open, by showing that the temperature in the tail pipe remained higher than it should have had the PORV shut. But, this temperature indicator was not part of the "safety grade" suite of indicators designed to be used after an incident, and the operators had not been trained to use it. Its location on the back of the desk also meant that it was effectively out of sight of the operators.

Consequences of stuck valve


As the pressure in the primary system continued to decrease, reactor coolant continued to flow, but it was boiling inside the core. First, small bubbles of steam formed and immediately collapsed, known as nucleate boiling
Nucleate boiling
Nucleate boiling is a type of boiling that takes place when the surface temperature is hotter than the saturated fluid temperature by a certain amount but where the heat flux is below the critical heat flux. For water, as shown in the graph below, nucleate boiling occurs when the surface...

. As the system pressure decreased further, steam pockets began to form in the reactor coolant. This departure from nucleate boiling caused steam voids in coolant channels, blocking the flow of liquid coolant and greatly increasing the fuel plate temperature. The steam voids also took up more volume than liquid water, causing the pressurizer water level to rise even though coolant was being lost through the open PORV. Because of the lack of a dedicated instrument to measure the level of water in the core, operators judged the level of water in the core solely by the level in the pressurizer. Since it was high, they assumed that the core was properly covered with coolant, unaware that because of steam forming in the reactor vessel, the indicator provided misleading readings. This was a key contributor to the initial failure to recognize the accident as a loss-of-coolant accident, and led operators to turn off the emergency core cooling pumps, which had automatically started after the PORV stuck and core coolant loss began, due to fears the system was being overfilled.

With the PORV still open, the quench tank that collected the discharge from the PORV overfilled, causing the containment building sump
Sump
A sump is a low space that collects any often-undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers....

 to fill and sound an alarm at 4:11 am. This alarm, along with higher than normal temperatures on the PORV discharge line and unusually high containment building temperatures and pressures, were clear indications that there was an ongoing loss-of-coolant accident, but these indications were initially ignored by operators. At 4:15, the quench tank relief diaphragm ruptured, and radioactive coolant began to leak out into the general containment building
Containment building
A containment building, in its most common usage, is a steel or reinforced concrete structure enclosing a nuclear reactor. It is designed, in any emergency, to contain the escape of radiation to a maximum pressure in the range of 60 to 200 psi...

. This radioactive coolant was pumped from the containment building
Containment building
A containment building, in its most common usage, is a steel or reinforced concrete structure enclosing a nuclear reactor. It is designed, in any emergency, to contain the escape of radiation to a maximum pressure in the range of 60 to 200 psi...

 sump to an auxiliary building, outside the main containment, until the sump pump
Sump pump
A sump pump is a pump used to remove water that has accumulated in a water collecting sump basin, commonly found in the basement of homes. The water may enter via the perimeter drains of a basement waterproofing system, funneling into the basin or because of rain or natural ground water, if the...

s were stopped at 4:39 am

After almost 80 minutes of slow temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 rise, the primary loop's four main pumps began to cavitate
Cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...

 as a steam bubble/water mixture, rather than water, passed through them. The pumps were shut down, and it was believed that natural circulation would continue the water movement. Steam in the system prevented flow through the core, and as the water stopped circulating it was converted to steam in increasing amounts. About 130 minutes after the first malfunction, the top of the reactor core was exposed and the intense heat caused a reaction to occur between the steam forming in the reactor core and the Zircaloy
Zircaloy
Zirconium alloys are solid solutions of zirconium or other metals, a common subgroup having the trade mark Zircaloy. Zirconium has very low absorption cross-section of thermal neutrons, high hardness, ductility and corrosion resistance...

 nuclear fuel rod cladding, yielding zirconium dioxide
Zirconium dioxide
Zirconium dioxide , sometimes known as zirconia , is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the rare mineral baddeleyite. The high temperature cubic crystalline form is rarely found in nature as mineral tazheranite O2...

, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, and additional heat. This fiery reaction burned off the nuclear fuel rod cladding, the hot plume of reacting steam and zirconium damaged the fuel pellets which released more radioactivity to the reactor coolant and produced hydrogen gas that is believed to have caused a small explosion in the containment building later that afternoon.
At 6 am, there was a shift change in the control room. A new arrival noticed that the temperature in the PORV tail pipe and the holding tanks was excessive and used a backup valve—called a block valve—to shut off the coolant venting via the PORV, but around 32000 US gal (121,133.2 l) of coolant had already leaked from the primary loop. It was not until 165 minutes after the start of the problem that radiation alarms activated as contaminated water reached detectors; by that time, the radiation levels in the primary coolant water were around 300 times expected levels, and the plant was seriously contaminated.

Emergency declared


At 6:56 am, a plant supervisor declared a site emergency, and less than 30 minutes later station manager Gary Miller announced a general emergency, defined as having the "potential for serious radiological consequences" to the general public. Metropolitan Edison
FirstEnergy
FirstEnergy Corp. , is a diversified energy company headquartered in Akron, Ohio. Its subsidiaries and affiliates are involved in the generation, transmission, and distribution of electricity, as well as energy management and other energy-related services...

 notified the Pennsylvania Emergency Management Agency
Pennsylvania Emergency Management Agency
Pennsylvania Emergency Management Agency is a cabinet-level agency in Pennsylvania.-External links:*...

 (PEMA), which in turn contacted state and local agencies, Governor Richard L. Thornburgh and lieutenant governor
Lieutenant Governor of Pennsylvania
The Lieutenant Governor is a constitutional officer of the Commonwealth of Pennsylvania. The Lieutenant Governor is elected every four years along with the Governor. Jim Cawley of Bucks County is the incumbent Lieutenant Governor...

 William Scranton III, to whom Thornburgh assigned responsibility for collecting and reporting on information about the accident. The uncertainty of operators at the plant was reflected in fragmentary, ambiguous, or contradictory statements made by Met Ed to government agencies and to the press, particularly about the possibility and severity of off-site radiation releases. Scranton held a press conference in which he was reassuring, yet confusing, about this possibility, stating that though there had been a "small release of radiation...no increase in normal radiation levels" had been detected. These were contradicted by another official, and by statements from Met Ed, who both claimed that no radiation had been released. In fact, readings from instruments at the plant and off-site detectors had detected radiation releases, albeit at levels that were unlikely to threaten public health as long as they were temporary, and providing that containment of the then highly contaminated reactor was maintained.

Angry that Met Ed had not informed them before conducting a steam venting from the plant, and convinced that the company was downplaying the severity of the accident, state officials turned to the NRC
Nuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...

. After receiving word of the accident from Met Ed, the NRC had activated its emergency response headquarters in Bethesda, Maryland
Bethesda, Maryland
Bethesda is a census designated place in southern Montgomery County, Maryland, United States, just northwest of Washington, D.C. It takes its name from a local church, the Bethesda Meeting House , which in turn took its name from Jerusalem's Pool of Bethesda...

 and sent staff members to Three Mile Island. NRC chairman Joseph Hendrie
Joseph Hendrie
Joseph M. Hendrie is a former Chairman of the U.S. Nuclear Regulatory Commission. On August 9, 1977 he was named to a four-year term on the Commission and designated as its Chairman by President Jimmy Carter...

 and commissioner Victor Gilinsky initially viewed the accident, in the words of NRC historian Samuel Walker, as a "cause for concern but not alarm". Gilinsky briefed reporters and members of Congress on the situation and informed White House staff, and at 10 am met with two other commissioners. However, the NRC faced the same problems in obtaining accurate information as the state, and was further hampered by being organizationally ill-prepared to deal with emergencies, as it lacked a clear command structure and the authority to tell the utility what to do, or to order an evacuation of the local area.

In a 2009 article, Gilinsky wrote that it took five weeks to learn that "the reactor operators had measured fuel temperatures near the melting point". He further wrote: "We didn't learn for years—until the reactor vessel was physically opened—that by the time the plant operator called the NRC at about 8 am, roughly ½ of the uranium fuel had already melted."

It was still not clear to the control room staff that the primary loop water levels were low and that over half the core was exposed. A group of workers took manual readings from the thermocouples and obtained a sample of primary loop water. Seven hours into the emergency, new water was pumped into the primary loop and the backup relief valve was opened to reduce pressure so that the loop could be filled with water. After 16 hours, the primary loop pumps were turned on once again, and the core temperature began to fall. A large part of the core had melted
Nuclear meltdown
Nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. The term is not officially defined by the International Atomic Energy Agency or by the U.S. Nuclear Regulatory Commission...

, and the system was still dangerously radioactive.

On the third day following the accident, a hydrogen bubble was discovered in the dome of the pressure vessel, and became the focus of concern. A hydrogen explosion might not only breach the pressure vessel, but, depending on its magnitude, might compromise the integrity of the containment vessel leading to large scale release of radiation. However, it was determined that there was no oxygen present in the pressure vessel, a prerequisite for hydrogen to burn or explode. Immediate steps were taken to reduce the hydrogen bubble, and by the following day it was significantly smaller. Over the next week, steam and hydrogen were removed from the reactor using a catalytic recombiner and, controversially, by venting straight to the atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

.

Radioactive material release


Once the first line of containment is breached during a reactor plant accident, there is a possibility that the fuel or the fission products held inside can be released into the environment. Although the zirconium fuel cladding has been breached in other nuclear reactors without generating a release to the environment, at TMI-2 operators permitted fission products to leave the other containment barriers. This occurred when the cladding was damaged while the PORV was still stuck open. Fission products were released into the reactor coolant. Since the PORV was stuck open and the loss of coolant accident was still in progress, primary coolant with fission products and/or fuel was released, and ultimately ended up in the auxiliary building. This auxiliary building was outside the containment boundary.

This was evidenced by the radiation alarms that eventually sounded. However, since very little of the fission products released were solids at room temperature, very little radiological contamination was reported in the environment. No significant level of radiation was attributed to the TMI-2 accident outside of the TMI-2 facility. According to the Rogovin report, the vast majority of the radioisotopes released were the noble gases, Xenon and Krypton. The report stated, "During the course of the accident, approximately 2.5 million curies of radioactive noble gases and 15 curies of radioiodines were released." This resulted in an average dose of 1.4 mrem to the two million people near the plant. The report compared this with the additional 80 mrem per year received from living in a high altitude city such as Denver.

Within hours of the accident the United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

 (EPA) began daily sampling of the environment at the three stations closest to the plant. By April 1, continuous monitoring at 11 stations was established and was expanded to 31 stations two days later. An inter-agency analysis concluded that the accident did not raise radioactivity far enough above background levels to cause even one additional cancer death among the people in the area. The EPA found no contamination in water, soil, sediment or plant samples.

Researchers at nearby Dickinson College—which had radiation monitoring equipment sensitive enough to detect Chinese atmospheric atomic weapons testing—collected soil samples from the area for the ensuing two weeks and detected no elevated levels of radioactivity, except after rainfalls (likely due to natural radon
Radon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...

 plate out, not the accident). Also, white-tailed deer tongues harvested over 50 mi (80.5 km) from the reactor subsequent to the accident were found to have significantly higher levels of Cs-137 than in deer in the counties immediately surrounding the power plant. Even then, the elevated levels were still below those seen in deer in other parts of the country during the height of atmospheric weapons testing. Had there been elevated releases of radioactivity, increased levels of Iodine-131 and Cesium-137 would have been expected to be detected in cattle and goat's milk samples. Yet elevated levels were not found.

A later scientific study noted that the official emission figures were consistent with available dosimeter
Dosimeter
Dosimeters measure an individual's or an object'sexposure to something in the environment — particularly to a hazard inflicting cumulative impact over long periods of time, or over a lifetime...

 data, though others have noted the incompleteness of this data, particularly for releases early on.

According to the official figures, as compiled by the 1979 Kemeny Commission from Metropolitan Edison and NRC data, a maximum of 480 petabecquerels (13 million curie
Curie
The curie is a unit of radioactivity, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit,...

s) of radioactive noble gas
Noble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...

es (primarily xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...

) were released by the event. However, these noble gases were considered relatively harmless, and only 481–629 GBq
Becquerel
The becquerel is the SI-derived unit of radioactivity. One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The Bq unit is therefore equivalent to an inverse second, s−1...

 (13–17 curies) of thyroid cancer
Thyroid cancer
Thyroid neoplasm is a neoplasm or tumor of the thyroid. It can be a benign tumor such as thyroid adenoma, or it can be a malignant neoplasm , such as papillary, follicular, medullary or anaplastic thyroid cancer. Most patients are 25 to 65 years of age when first diagnosed; women are more affected...

-causing iodine-131
Iodine-131
Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical...

 were released. Total releases according to these figures were a relatively small proportion of the estimated 370 E Bq
Becquerel
The becquerel is the SI-derived unit of radioactivity. One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The Bq unit is therefore equivalent to an inverse second, s−1...

 (10 billion curie
Curie
The curie is a unit of radioactivity, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit,...

s) in the reactor. It was later found that about ½ the core had melted, and the cladding around 90% of the fuel rods had failed, with 5 ft (1.5 m) of the core gone, and around 20 ST (18.1 t) of uranium flowing to the bottom head of the pressure vessel, forming a mass of corium
Corium (nuclear reactor)
Corium, also called fuel containing material or lava-like fuel containing material , is a lava-like molten mixture of portions of nuclear reactor core, formed during a nuclear meltdown, the most severe class of a nuclear reactor accident...

. The reactor vessel—the second level of containment after the cladding—maintained integrity and contained the damaged fuel with nearly all of the radioactive isotopes in the core.

Anti-nuclear political groups disputed the Kemeny Commission's findings, claiming that independent measurements provided evidence of radiation levels up to five times higher than normal in locations hundreds of miles downwind from TMI. According to Randall Thompson, a health physics technician employed to monitor radioactive emissions at TMI after the accident, radiation releases were hundreds if not thousands of times higher. Some other insiders, including Arnie Gundersen
Arnold Gundersen
Arnold "Arnie" Gundersen is chief engineer of energy consulting company Fairewinds Associates and a former nuclear power industry executive, and who has questioned the safety of the Westinghouse AP1000, a proposed third-generation nuclear reactor. Gundersen has also expressed concerns about the...

, a former nuclear industry executive who is now an expert witness in nuclear safety issues, make the same claim; Gundersen offers evidence, based on pressure monitoring data, for a hydrogen explosion shortly before 2 pm on March 28, 1979, which would have provided the means for a high dose of radiation to occur. Gundersen cites affidavits from four reactor operators according to which the plant manager was aware of a dramatic pressure spike, after which the internal pressure dropped to outside pressure. Gundersen also notes that the control room shook and doors were blown off hinges. However official NRC reports refer merely to a "hydrogen burn." The Kemeny Commission referred to "a burn or an explosion that caused pressure to increase by 28 pounds per square inch in the containment building". The Washington Post
The Washington Post
The Washington Post is Washington, D.C.'s largest newspaper and its oldest still-existing paper, founded in 1877. Located in the capital of the United States, The Post has a particular emphasis on national politics. D.C., Maryland, and Virginia editions are printed for daily circulation...

reported that "At about 2 pm, with pressure almost down to the point where the huge cooling pumps could be brought into play, a small hydrogen explosion jolted the reactor."

Voluntary evacuation


Twenty-eight hours after the accident began, William Scranton III, the lieutenant governor
Lieutenant Governor of Pennsylvania
The Lieutenant Governor is a constitutional officer of the Commonwealth of Pennsylvania. The Lieutenant Governor is elected every four years along with the Governor. Jim Cawley of Bucks County is the incumbent Lieutenant Governor...

, appeared at a news briefing to say that Metropolitan Edison, the plant's owner, had assured the state that "everything is under control". Later that day, Scranton changed his statement, saying that the situation was "more complex than the company first led us to believe". There were conflicting statements about radiation releases. Schools were closed and residents were urged to stay indoors. Farmers were told to keep their animals under cover and on stored feed.

Governor Dick Thornburgh
Dick Thornburgh
Richard Lewis "Dick" Thornburgh is an American lawyer and Republican politician who served as the 41st Governor of Pennsylvania from 1979 to 1987, and then as the U.S...

, on the advice of NRC Chairman Joseph Hendrie
Joseph Hendrie
Joseph M. Hendrie is a former Chairman of the U.S. Nuclear Regulatory Commission. On August 9, 1977 he was named to a four-year term on the Commission and designated as its Chairman by President Jimmy Carter...

, advised the evacuation "of pregnant women and pre-school age children...within a five-mile radius of the Three Mile Island facility." The evacuation zone was extended to a 20 mile radius on Friday March 30. Within days, 140,000 people had left the area. More than half of the population within the 20-mile radius remained in that area. According to a survey conducted in April 1979, 98% of the evacuees had returned to their homes within three weeks.

Post-TMI surveys have shown that less than 50% of the American public were satisfied with the way the accident was handled by Pennsylvania State officials and the NRC, and people surveyed were even less pleased with the utility (General Public Utilities) and the plant designer.

Investigations


Several state and federal government agencies mounted investigations into the crisis, the most prominent of which was the President's Commission on the Accident at Three Mile Island, created by Jimmy Carter
Jimmy Carter
James Earl "Jimmy" Carter, Jr. is an American politician who served as the 39th President of the United States and was the recipient of the 2002 Nobel Peace Prize, the only U.S. President to have received the Prize after leaving office...

 in April 1979. The commission consisted of a panel of twelve people, specifically chosen for their lack of strong pro- or anti-nuclear views, and headed by chairman John G. Kemeny, president of Dartmouth College
Dartmouth College
Dartmouth College is a private, Ivy League university in Hanover, New Hampshire, United States. The institution comprises a liberal arts college, Dartmouth Medical School, Thayer School of Engineering, and the Tuck School of Business, as well as 19 graduate programs in the arts and sciences...

. It was instructed to produce a final report within six months, and after public hearings, depositions, and document collection, released a completed study on October 31, 1979. The investigation strongly criticized Babcock and Wilcox, Met Ed, GPU, and the NRC for lapses in quality assurance and maintenance, inadequate operator training, lack of communication of important safety information, poor management, and complacency, but avoided drawing conclusions about the future of the nuclear industry. The heaviest criticism from the Kemeny Commission concluded that "fundamental changes were necessary in the organization, procedures, practices 'and above all – in the attitudes' of the NRC [and the nuclear industry.]" Kemeny said that the actions taken by the operators were "inappropriate" but that the workers "were operating under procedures that they were required to follow, and our review and study of those indicates that the procedures were inadequate" and that the control room "was greatly inadequate for managing an accident."

The Kemeny Commission noted that Babcock and Wilcox's PORV valve had previously failed on 11 occasions, nine of them in the open position, allowing coolant to escape. More disturbing, however, was the fact that the initial causal sequence of events at TMI had been duplicated 18 months earlier at another Babcock and Wilcox reactor, the Davis-Besse Nuclear Power Station owned at that time by Toledo Edison. The only difference was that the operators at Davis-Besse identified the valve failure after 20 minutes, where at TMI it took 80 minutes; and the Davis-Besse facility was operating at 9% power, against TMI's 97%. Although Babcock engineers recognised the problem, the company failed to clearly notify its customers of the valve issue.

Upon his return to Dartmouth, Kemeny addressed Dartmouth college students. When asked what caused the meltdown, he replied that the proximate cause
Proximate cause
In the law, a proximate cause is an event sufficiently related to a legally recognizable injury to be held the cause of that injury. There are two types of causation in the law, cause-in-fact and proximate cause. Cause-in-fact is determined by the "but-for" test: but for the action, the result...

 would probably never be known. The Government Affairs Vice President confirmed that the Metropolitan Edison Company, which operated the company, had shortly before received a warning from the Nuclear Regulatory Commission
Nuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...

 (NRC) that Babcock and Wilcox
Babcock and Wilcox
The Babcock & Wilcox Company is a U.S.-based company that provides design, engineering, manufacturing, construction and facilities management services to nuclear, renewable, fossil power, industrial and government customers worldwide. B&W's boilers supply more than 300,000 megawatts of installed...

 reactor valves were vulnerable to failure under certain conditions. He said he had sent it on to the Vice President of Engineering, who confirmed that he had read it. Shortly after that, the two men met at the water cooler where the Government Affairs VP asked the Engineering VP a question. The Government Affairs VP remembered the question as "Is there a problem here?" The Engineering VP thought the question was "Have you solved the problem?" Both VPs agreed that the answer was "no". One walked away believing that the problem was solved. The other believed that he had informed his bosses that there was a problem. The issue was never resolved. Kemeny told the students that he believed it never would be. The proximate cause of the meltdown remains unknown and no proof of negligence was ever uncovered.

The Pennsylvania House of Representatives
Pennsylvania House of Representatives
The Pennsylvania House of Representatives is the lower house of the bicameral Pennsylvania General Assembly, the legislature of the U.S. state of Pennsylvania. There are 203 members, elected for two year terms from single member districts....

 conducted its own investigation, which focused on the need to improve evacuation procedures.

In 1985, a television camera was used to see the interior of the damaged reactor. In 1986, core sample
Core sample
A core sample is a cylindrical section of a naturally occurring substance. Most core samples are obtained by drilling with special drills into the substance, for example sediment or rock, with a hollow steel tube called a core drill. The hole made for the core sample is called the "core hole". A...

s and samples of debris were obtained from the corium
Corium (nuclear reactor)
Corium, also called fuel containing material or lava-like fuel containing material , is a lava-like molten mixture of portions of nuclear reactor core, formed during a nuclear meltdown, the most severe class of a nuclear reactor accident...

 layers on the bottom of the reactor vessel and analyzed.

Effect on nuclear power industry


According to the IAEA, the Three Mile Island accident was a significant turning point in the global development of nuclear power. From 1963–1979, the number of reactors under construction globally increased every year except 1971 and 1978. However, following the event, the number of reactors under construction in the U.S. declined every year from 1980-1998. Many similar Babcock and Wilcox
Babcock and Wilcox
The Babcock & Wilcox Company is a U.S.-based company that provides design, engineering, manufacturing, construction and facilities management services to nuclear, renewable, fossil power, industrial and government customers worldwide. B&W's boilers supply more than 300,000 megawatts of installed...

 reactors on order were canceled; in total, 51 American nuclear reactors were canceled from 1980–1984.

The 1979 TMI accident did not, however,initiate the demise of the U.S. nuclear power industry. As a result of post-oil-shock
1973 oil crisis
The 1973 oil crisis started in October 1973, when the members of Organization of Arab Petroleum Exporting Countries or the OAPEC proclaimed an oil embargo. This was "in response to the U.S. decision to re-supply the Israeli military" during the Yom Kippur war. It lasted until March 1974. With the...

 analysis and conclusions of overcapacity, 40 planned nuclear power plants had already been canceled between 1973 and 1979. No U.S. nuclear power plant had been authorized to begin construction since the year before TMI. Nonetheless, at the time of the TMI incident, 129 nuclear power plants had been approved; of those, only 53 (which were not already operating) were completed. Federal requirements became more stringent, local opposition
Anti-nuclear movement in the United States
The anti-nuclear movement in the United States consists of more than 80 anti-nuclear groups which have acted to oppose nuclear power or nuclear weapons, or both, in the United States. These groups include the Abalone Alliance, Clamshell Alliance, Institute for Energy and Environmental Research,...

 became more strident, and construction times were significantly lengthened to correct safety issues and design deficiencies.

Globally, the cessation of increase in nuclear power plant construction came with the more catastrophic Chernobyl disaster
Chernobyl disaster
The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...

 in 1986 (see graph).

Cleanup


Three Mile Island Unit 2 was too badly damaged and contaminated to resume operations; the reactor was gradually deactivated and permanently closed. TMI-2 had been online only 13 months but now had a ruined reactor vessel and a containment building that was unsafe to walk in. Cleanup started in August 1979 and officially ended in December 1993, with a total cleanup cost of about $1 billion. Benjamin K. Sovacool
Benjamin K. Sovacool
Benjamin K. Sovacool is a Visiting Associate Professor at Vermont Law School and founding Director of the Energy Justice Program at their Institute for Energy and Environment. He was formerly an Assistant Professor and Research Fellow at the National University of Singapore.Sovacool's research...

, in his 2007 preliminary assessment of major energy accidents, estimated that the TMI accident caused a total of $2.4 billion in property damages.

Initially, efforts focused on the cleanup and decontamination of the site, especially the defueling of the damaged reactor. Starting in 1985, almost 100 ST (90.7 t) of radioactive fuel were removed from the site. The first major phase of the cleanup was completed in 1990, when workers finished shipping 150 ST (136.1 t) of radioactive wreckage to Idaho for storage at the Department of Energy's National Engineering Laboratory. However, the contaminated cooling water that leaked into the containment building had seeped into the building's concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

, leaving the radioactive residue impractical to remove. In 1988, the Nuclear Regulatory Commission announced that, although it was possible to further decontaminate the Unit 2 site, the remaining radioactivity had been sufficiently contained as to pose no threat to public health and safety. Accordingly, further cleanup efforts were deferred to allow for decay of the radiation levels and to take advantage of the potential economic benefits of retiring both Unit 1 and Unit 2 together.

Health effects and epidemiology


In the aftermath of the accident, investigations focused on the amount of radiation released by the accident. According to the American Nuclear Society
American Nuclear Society
The American Nuclear Society is an international, not-for-profit 501 scientific and educational organization with a membership of approximately 11,000 scientists, engineers, educators, students, and other associate members. Approximately 900 members live outside the United States in 40 countries....

, using the official radiation emission figures, "The average radiation dose to people living within ten miles of the plant was eight millirem, and no more than 100 millirem to any single individual. Eight millirem is about equal to a chest X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

, and 100 millirem is about a third of the average background level of radiation received by US residents in a year."

Based on these emission figures, early scientific publications on the health effects of the fallout estimated one or two additional cancer deaths in the 10 mi (16.1 km) area around TMI. Disease rates in areas further than 10 miles from the plant were never examined. Local activism in the 1980s, based on anecdotal reports of negative health effects, led to scientific studies being commissioned. A variety of studies have been unable to conclude that the accident had substantial health effects.

The Radiation and Public Health Project
Radiation and Public Health Project
Radiation and Public Health Project is a nonprofit educational and scientific organization founded in 1985 by Jay M. Gould, a statistician and epidemiologist, and Ernest Sternglass...

 cited calculations by Joseph Mangano—who has authored 19 medical journal articles and a book on Low Level Radiation and Immune Disease—that reported a spike in infant mortality in the downwind communities two years after the accident. Anecdotal evidence also records effects on the region's wildlife. For example, according to one anti-nuclear activist, Harvey Wasserman
Harvey Wasserman
Harvey Franklin Wasserman is an American journalist, author, democracy activist, and advocate for renewable energy. He has been a strategist and organizer in the anti-nuclear movement in the United States for over 30 years. He has been a featured speaker on Today, Nightline, National Public Radio,...

, the fallout caused "a plague of death and disease among the area's wild animals and farm livestock", including a sharp fall in the reproductive rate of the region's horses and cows, reflected in statistics from Pennsylvania's Department of Agriculture, though the Department denies a link with TMI.

Activism and legal action



The TMI accident enhanced the credibility of anti-nuclear groups, who had predicted an accident, and triggered protests around the world.

Members of the American public, concerned about the release of radioactive gas from the TMI accident, staged numerous anti-nuclear demonstrations across the country in the following months. The largest demonstration was held in New York City in September 1979 and involved 200,000 people, with speeches given by Jane Fonda
Jane Fonda
Jane Fonda is an American actress, writer, political activist, former fashion model, and fitness guru. She rose to fame in the 1960s with films such as Barbarella and Cat Ballou. She has won two Academy Awards and received several other movie awards and nominations during more than 50 years as an...

 and Ralph Nader
Ralph Nader
Ralph Nader is an American political activist, as well as an author, lecturer, and attorney. Areas of particular concern to Nader include consumer protection, humanitarianism, environmentalism, and democratic government....

. The New York rally was held in conjunction with a series of nightly “No Nukes” concerts
No Nukes (album)
No Nukes: The Muse Concerts For a Non-Nuclear Future was a 1979 triple live album that contained selections from the September 1979 Madison Square Garden concerts by the Musicians United for Safe Energy collective, with Jackson Browne, Graham Nash, Bonnie Raitt, and John Hall being the key...

 given at Madison Square Garden
Madison Square Garden
Madison Square Garden, often abbreviated as MSG and known colloquially as The Garden, is a multi-purpose indoor arena in the New York City borough of Manhattan and located at 8th Avenue, between 31st and 33rd Streets, situated on top of Pennsylvania Station.Opened on February 11, 1968, it is the...

 from September 19–23 by Musicians United for Safe Energy
Musicians United for Safe Energy
Musicians United for Safe Energy, or MUSE, is an activist group founded in 1979 by Jackson Browne, Graham Nash, Bonnie Raitt, and John Hall. The group advocates against the use of nuclear energy, forming shortly after the Three Mile Island nuclear accident in March 1979...

. In the previous May, an estimated 65,000 people—including California Governor Jerry Brown
Jerry Brown
Edmund Gerald "Jerry" Brown, Jr. is an American politician. Brown served as the 34th Governor of California , and is currently serving as the 39th California Governor...

—attended a march and rally against nuclear power in Washington, D.C.

In 1981, citizens' groups succeeded in a class action suit against TMI, winning $25 million in an out-of-court settlement. Part of this money was used to found the TMI Public Health Fund. In 1983, a federal grand jury indicted Metropolitan Edison on criminal charges for the falsification of safety test results prior to the accident. Under a plea-bargaining agreement, Met Ed pleaded guilty to one count of falsifying records and no contest to six other charges, four of which were dropped, and agreed to pay a $45,000 fine and set up a $1 million account to help with emergency planning in the area surrounding the plant.

According to Eric Epstein, chair of Three Mile Island Alert, the TMI plant operator and its insurers paid at least $82 million in publicly documented compensation to residents for "loss of business revenue, evacuation expenses and health claims". Also according to Harvey Wasserman, hundreds of out-of-court settlements have been reached with alleged victims of the fallout
Fallout
Fallout or nuclear fallout is the residual radiation hazard from a nuclear explosion.Fallout may also refer to:*Fallout , a 1997 post-apocalyptic computer role-playing game released by Interplay Entertainment...

, with a total of $15m paid out to parents of children born with birth defects. However, a class action lawsuit alleging that the accident caused detrimental health effects was rejected by Harrisburg U.S. District Court
United States district court
The United States district courts are the general trial courts of the United States federal court system. Both civil and criminal cases are filed in the district court, which is a court of law, equity, and admiralty. There is a United States bankruptcy court associated with each United States...

 Judge Sylvia Rambo. The appeal of the decision in front of U.S. Third Circuit Court of Appeals also failed.

Design changes


The PORV position indicator design flaw was corrected, and more PORV testing was done. Dedicated instruments directly measure core water level. Vents were added at the top of the pressure vessel.

Lessons learned


The Three Mile Island accident inspired Charles Perrow
Charles Perrow
Charles B. Perrow is an emeritus professor of sociology at Yale University and visiting professor at Stanford University. He is the author of several books and many articles on organizations, and is primarily concerned with the impact of large organizations on society.-Academic appointments:After...

's Normal Accident Theory, in which an accident occurs, resulting from an unanticipated interaction of multiple failures in a complex system. TMI was an example of this type of accident because it was "unexpected, incomprehensible, uncontrollable and unavoidable". But Perrow's conclusion that the accident was unavoidable is belied by the fact that a TMI control room operator wrote a memo warning of "a very serious accident" if the condensate system problems were not properly addressed. He stated that "the resultant damage could be very significant." Additionally, James Cresswell, an NRC inspector, warned for two years that a design flaw with U-shaped tubes could prevent coolant circulation and cause an accident like that which would occur at TMI. His warnings were ignored until the NRC met with him six days before the accident at TMI.

The China Syndrome


The accident at the plant occurred twelve days after the release of the movie The China Syndrome
The China Syndrome
The China Syndrome is a 1979 American thriller film that tells the story of a reporter and cameraman who discover safety coverups at a nuclear power plant. It stars Jane Fonda, Jack Lemmon, Michael Douglas, Scott Brady, James Hampton, Peter Donat, Richard Herd, and Wilford Brimley.The film was...

. The film features Jack Lemmon
Jack Lemmon
John Uhler "Jack" Lemmon III was an American actor and musician. He starred in more than 60 films including Some Like It Hot, The Apartment, Mister Roberts , Days of Wine and Roses, The Great Race, Irma la Douce, The Odd Couple, Save the Tiger John Uhler "Jack" Lemmon III (February 8, 1925June...

 as a supervisor at a nuclear plant who uncovers evidence of a potential nuclear catastrophe and Jane Fonda
Jane Fonda
Jane Fonda is an American actress, writer, political activist, former fashion model, and fitness guru. She rose to fame in the 1960s with films such as Barbarella and Cat Ballou. She has won two Academy Awards and received several other movie awards and nominations during more than 50 years as an...

 as a television news reporter at a California television station. In the film, a major nuclear plant crisis takes place while Fonda's character and her cameraman (Michael Douglas
Michael Douglas
Michael Kirk Douglas is an American actor and producer, primarily in movies and television. He has won three Golden Globes and two Academy Awards; first as producer of 1975's Best Picture, One Flew Over the Cuckoo's Nest, and as Best Actor in 1987 for his role in Wall Street. Douglas received the...

) are at the plant producing a series on nuclear power
Nuclear power
Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...

. Fonda and Lemmon proceed to raise awareness regarding the unsafe conditions at the plant.

After the release of the film, Fonda began lobbying against nuclear power. In an attempt to counter her efforts, Edward Teller
Edward Teller
Edward Teller was a Hungarian-American theoretical physicist, known colloquially as "the father of the hydrogen bomb," even though he did not care for the title. Teller made numerous contributions to nuclear and molecular physics, spectroscopy , and surface physics...

, a nuclear physicist and long-time government science adviser nicknamed the "father of the hydrogen bomb", personally lobbied in favor of nuclear power.

Current status


Unit 1 had its license temporarily suspended following the incident at Unit 2. Although the citizens of the three counties surrounding the site voted by a margin of 3:1 to permanently retire Unit 1, it was permitted to resume operations in 1985. General Public Utilities Corporation, the plant's owner, formed General Public Utilities Nuclear Corporation (GPUN) as a new subsidiary to own and operate the company's nuclear facilities, including Three Mile Island. The plant had previously been operated by Metropolitan Edison Company (Met-Ed), one of GPU's regional utility operating companies. In 1996, General Public Utilities shortened its name to GPU Inc. Three Mile Island Unit 1 was sold to AmerGen Energy Corporation, a joint venture between Philadelphia Electric Company (PECO), and British Energy
British Energy
British Energy was the UK's largest electricity generation company by volume, before being taken over by Électricité de France in 2009. British Energy operated eight former UK state-owned nuclear power stations and one coal fired power station....

, in 1998. In 2000, PECO merged with Unicom Corporation to form Exelon Corporation
Exelon
Exelon Corporation is an electricity generating and distributing company headquartered in the Chase Tower in the Chicago Loop area of Chicago. It was created in October, 2000 by the merger of PECO Energy Company and Unicom, of Philadelphia and Chicago respectively. Unicom owned Commonwealth Edison...

, which acquired British Energy's share of AmerGen in 2003. Today, AmerGen LLC is a fully owned subsidiary of Exelon
Exelon
Exelon Corporation is an electricity generating and distributing company headquartered in the Chase Tower in the Chicago Loop area of Chicago. It was created in October, 2000 by the merger of PECO Energy Company and Unicom, of Philadelphia and Chicago respectively. Unicom owned Commonwealth Edison...

 Generation and owns TMI Unit 1, Oyster Creek Nuclear Generating Station
Oyster Creek Nuclear Generating Station
Oyster Creek nuclear power station is a single unit 636 MWe boiling water reactor power plant located on an 800 acre site adjacent to the Oyster Creek in the Forked River section of Lacey Township in Ocean County, New Jersey. The facility is currently owned and operated by Exelon Corporation and...

, and Clinton Power Station
Clinton Nuclear Generating Station
The Clinton Power Station is located near Clinton, Illinois, USA. The nuclear power station has a General Electric boiling water reactor on a site with an adjacent cooling reservoir, Clinton Lake. Due to inflation and cost overruns, Clinton's final construction cost exceeded $2.6 billion...

. These three units, in addition to Exelon's other nuclear units, are operated by Exelon Nuclear Inc., an Exelon subsidiary.

General Public Utilities was legally obliged to continue to maintain and monitor the site, and therefore retained ownership of Unit 2 when Unit 1 was sold to AmerGen in 1998. GPU Inc. was acquired by FirstEnergy
FirstEnergy
FirstEnergy Corp. , is a diversified energy company headquartered in Akron, Ohio. Its subsidiaries and affiliates are involved in the generation, transmission, and distribution of electricity, as well as energy management and other energy-related services...

 Corporation in 2001, and subsequently dissolved. FirstEnergy then contracted out the maintenance and administration of Unit 2 to AmerGen. Unit 2 has been administered by Exelon Nuclear since 2003, when Exelon Nuclear's parent company, Exelon, bought out the remaining shares of AmerGen, inheriting FirstEnergy's maintenance contract. Unit 2 continues to be licensed and regulated by the Nuclear Regulatory Commission in a condition known as Post Defueling Monitored Storage (PDMS).

Today, the TMI-2 reactor is permanently shut down with the reactor coolant system drained, the radioactive water decontaminated and evaporated, radioactive waste shipped off-site, reactor fuel and core debris shipped off-site to a Department of Energy facility, and the remainder of the site being monitored. The owner says it will keep the 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.

Timeline

Date Event
Construction
Reactor-1 online
Reactor-2 online
March 1979 TMI-2 accident occurred. Containment coolant and unknown amounts of radioactive contamination released into environment.
April 1979 Containment steam vented to the atmosphere in order to stabilize the core.
July 1980 Approximately 1,591 TBq
Becquerel
The becquerel is the SI-derived unit of radioactivity. One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The Bq unit is therefore equivalent to an inverse second, s−1...

 (43,000 curie
Curie
The curie is a unit of radioactivity, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit,...

s) 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 Defueling 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 Defueling 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 Post-Defueling Monitoring Storage began.
Oct. 2009 TMI-1 license extended from April 2014 until 2034.

See also

  • Nuclear Policy of the United States
    Nuclear policy of the United States
    The nuclear energy policy of the United States developed within two main periods, from 1954–1992 and 2005–2010. The first period saw the ongoing building of nuclear power plants, the enactment of numerous pieces of legislation such as the Energy Reorganization Act of 1974, and the implementation of...

  • International Nuclear Events Scale
  • Nuclear and radiation accidents
    Nuclear and radiation accidents
    A nuclear and radiation accident is defined by the International Atomic Energy Agency as "an event that has led to significant consequences to people, the environment or the facility...

  • Lists of nuclear disasters and radioactive incidents
  • Chernobyl disaster
    Chernobyl disaster
    The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...

  • Fukushima I nuclear accidents
  • Forked River Nuclear Power Plant
    Forked River Nuclear Power Plant
    The Forked River Nuclear Power Plant was a proposed nuclear power plant in Lacey Township in Ocean County, New Jersey. It was proposed as a single 1,070 MW reactor in 1969 to be built by Combustion Engineering and operated by Jersey Central Power and Light...

  • Process control
    Process control
    Process control is a statistics and engineering discipline that deals with architectures, mechanisms and algorithms for maintaining the output of a specific process within a desired range...

  • Human-machine interaction
    Human-machine interaction
    Human–machine Interaction is the interaction between machines and the persons who operate them. An old-fashioned term is is Man-machined Interaction - Related terms:...

  • Generation II reactor
    Generation II reactor
    A generation II reactor is a design classification for a nuclear reactor, and refers to the class of commercial reactors built up to the end of the 1990s...

  • List of articles about Three Mile Island
  • List of books about nuclear issues
  • List of civilian nuclear accidents
  • Nuclear accidents in the United States
    Nuclear accidents in the United States
    According to a 2010 survey of energy accidents, there have been at least 56 accidents near nuclear reactors in the United States . The most serious of these was the Three Mile Island accident in 1979...

  • Nuclear power whistleblowers
    Nuclear power whistleblowers
    The GE Three are three nuclear engineers who "blew the whistle" on safety problems at nuclear power plants in the United States in 1976. The three nuclear engineers gained the attention of journalists and the anti-nuclear movement. The GE Three returned to prominence in 2011 during the Fukushima...

  • Nuclear safety
    Nuclear safety
    Nuclear safety covers the actions taken to prevent nuclear and radiation accidents or to limit their consequences. This covers nuclear power plants as well as all other nuclear facilities, the transportation of nuclear materials, and the use and storage of nuclear materials for medical, power,...

  • Nuclear safety in the U.S.
  • Three Mile Island accident health effects
    Three Mile Island accident health effects
    The health effects of the 1979 Three Mile Island nuclear accident are widely, but not universally, agreed to be very low level. According to the official radiation release figures, average local radiation exposure was equivalent to a chest X-ray, and maximum local exposure equivalent to less than a...

  • Three Mile Island: Thirty Minutes to Meltdown
    Three Mile Island: Thirty Minutes to Meltdown
    Three Mile Island: Thirty Minutes to Meltdown is a 1982 book by Daniel Ford. Ford presents a "meticulous post-mortem of the events that nearly led to a meltdown" at the Metropolitan Edison station near Harrisburg in March 1979. He analyses the complex of people, technology, customs and regulations...

  • TMI 25 Years Later: The Three Mile Island Nuclear Power Plant Accident and Its Impact
    TMI 25 Years Later: The Three Mile Island Nuclear Power Plant Accident and Its Impact
    TMI 25 Years Later: The Three Mile Island Nuclear Power Plant Accident and Its Impact is a 2004 book which reviews the Three Mile Island accident and its causes, and the subsequent cleanup process which lasted more than a decade...

  • Robert Del Tredici
    Robert Del Tredici
    Robert Del Tredici is a Canadian photographer, artist and teacher, who documented the impact of the 1979 Three Mile Island accident on the community. His first book of photographs and interviews, The People of Three Mile Island , was a sociological critique of nuclear power...


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