1. Three Mile Island Unit 1
     Incidents  

2. Three Mile Island Unit 2
    Accident  Unit 2 Generator 

3. Post-accident

4. Closure

5. Seismic risk

6. See also

7. References

8. External links

The reactor core of TMI-2 has since been removed from the site, but the site has not been decommissioned.^[8] In July 1998, Amergen Energy (now Exelon Generation) agreed to purchase TMI-1 from General Public Utilities for $100 million.^[9]

Three Mile Island is so named because it is located three miles downriver from Middletown, Pennsylvania.^[10] The plant was originally built by General Public Utilities Corporation, later renamed GPU Incorporated.^[11] 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.^[12]

The NRC defines two emergency planning zones around nuclear power plants: a plume exposure pathway zone with a radius of {{convert|10|mi}}, concerned primarily with exposure to, and inhalation of, airborne radioactive contamination, and an ingestion pathway zone of about {{convert|50|mi}}, concerned primarily with ingestion of food and liquid contaminated by radioactivity.^[13]

The 2010 U.S. population within {{convert|10|mi}} of Three Mile Island was 211,261, an increase of 10.9 percent in a decade, according to an analysis of U.S. Census data for msnbc.com. The 2010 U.S. population within {{convert|50|mi}} was 2,803,322, an increase of 10.3 percent since 2000. Cities within 50 miles include Harrisburg (12 miles to city center), York (13 miles to city center), and Lancaster (24 miles to city center).^[14]

Exelon has been operating Unit 1 at Three Mile Island at a loss since 2015.^[15] On May 30, 2017, the company said it would consider ceasing operations at Unit 1 in 2019 due to high costs of operating the plant unless there was government action.^[16][17]

Unit 2, which has been dormant since the accident in 1979, is still owned by FirstEnergy, and it is estimated to close in 2036.^[18]

Three Mile Island Unit 1

The Three Mile Island Unit 1 is a pressurized water reactor designed by Babcock & Wilcox with a net generating capacity of 819 MW_e. The initial construction cost for TMI-1 was {{nowrap|US$400 million}}, equal to ${{Formatprice|{{Inflation|US|0.400|1974|r=2}}}} billion today.^[19] Unit 1 first came online on April 19, 1974, and began commercial operations on September 2, 1974.^[20] TMI-1 is licensed to operate for 40 years from its first run, and in 2009, was extended 20 years, which means it may operate until April 19, 2034.^[21][22] TMI-1 has a closed-cycle cooling system for its main condenser using two natural draft cooling towers. Makeup water is drawn from the river to replace the water lost via evaporation in the towers. Once-through cooling with river water is used for the service water system which cools auxiliary components and removes decay heat when the reactor is shutdown. When TMI-2 suffered its accident in 1979, TMI-1 was offline for refueling. It was brought back online in October 1985, after public opposition, several federal court injunctions, and some technical and regulatory complications.^[23]

Incidents

In February 1993, a man drove his car past a checkpoint at the TMI nuclear plant, then broke through an entry gate. He eventually crashed the car through a secure door and entered the Unit 1 turbine building. The intruder, who had a history of mental illness, hid in the turbine building and was apprehended after four hours.

On November 21, 2009, a release of radioactivity occurred inside the containment building of TMI-1 while workers were cutting pipes. Exelon Corporation stated to the public that "A monitor at the temporary opening cut into the containment building wall to allow the new steam generators to be moved inside showed a slight increase in a reading and then returned to normal. Approximately 20 employees were treated for mild radiation exposure."^[24] {{As of|2009|11|22|df=US}}, it is believed that no radiation escaped the containment building and the public is not in any danger. The inside airborne contamination was caused by a change in air pressure inside the containment building that dislodged small irradiated particles in the reactor piping system. Some of the small particles became airborne inside the building and were detected by an array of monitors in place to detect such material. The air pressure change occurred when inside building ventilation fans were started to support outage activities. The site has modified the ventilation system to prevent future air pressure changes. Work continued on the project the following day. On January 24, 2010, TMI-1 was brought back online.^[25]

Three Mile Island Unit 2

The Three Mile Island Unit 2 was also a pressurized water reactor constructed by B&W, similar to Unit 1. The only difference was that TMI-2 was slightly larger with a net generating capacity of 906 MW_e, compared to TMI-1, which delivers 819 MW_e. Unit 2 received its operating license on February 8, 1978, and began commercial operation on December 30, 1978. TMI Unit 2 has been permanently shut off after the Three Mile Island accident in 1979.^[26]

Accident

On March 28, 1979, there was a cooling system malfunction that caused a partial melt-down of the reactor core. This loss-of-coolant accident resulted in the release of an amount of radioactivity, estimated at 43,000 curies (1.59 PBq) of radioactive krypton-85 gas (half life 10 yrs), but less than 20 curies (740 GBq) of the especially hazardous iodine-131 (half life 8 days), into the surrounding environment.^[3]

Nearly 2 million people were exposed to a small amount of radiation from the accident.^[27] A review by the World Nuclear Association concluded that no deaths, injuries or adverse health effects resulted from the accident,^[28] and a report by Columbia University epidemiologist Maureen Hatch confirmed this finding.^[4][29] Because of the health concerns, the Pennsylvania Department of Health kept a registry of more than 30,000 people that lived within 5 miles of TMI at the time of the accident. The registry was kept for nearly 20 years until 1997, when no evidence was found of unusual health effects.^[30] Further epidemiology studies have not shown any increase in cancer as a result of the accident.^[5][6][7] However, almost $25 million was paid in insurance settlements to people who then agreed not to discuss their injuries in ongoing litigation.^[31]{{better source|date=January 2019}}

Unit 2 has not been operational since the accident occurred.^[32]

The New York Times reported on August 14, 1993, 14 years after the accident, that the clean up had been finished. According to the United States NRC, 2.3 million gallons of waste water had been removed.^[33]

The incident was widely publicized internationally, and had far-reaching effects on public opinion, particularly in the United States. The China Syndrome, a movie about a nuclear disaster, which was released just 12 days before the incident and received a tepid reception from the movie-going public, became a blockbuster hit.^[34]

Unit 2 Generator

On January 22, 2010, officials at the NRC announced the electrical generator from the damaged Unit 2 reactor at TMI will be used at Shearon Harris Nuclear Plant in New Hill, North Carolina. The generator was transported in two parts, weighing a combined 670 tons. It was refurbished and installed during a refueling outage at Shearon Harris NPP in November 2010. TMI's Unit 2 reactor has been shut down since the partial meltdown in 1979.^[35]

Post-accident

Closure

On June 20, 2017, Exelon Generation, the owners of Three Mile Island's Unit 1 sent to the Nuclear Regulatory Commission a formal notice of its intention to shut down the plant on September 30, 2019,^[42] unless the Pennsylvania legislature rescues the nuclear industry, which is currently{{when|date=December 2017}} struggling to compete in a world where newfound natural gas resources have driven down electricity prices.^[48] Exelon Generation's Senior Vice President Bryan Hanson noted that once Three Mile Island is closed, it can never be reopened for use again.^[42] Hanson explicitly stated the reason for the shutdown is because of the unprofitability of Unit 1. Unit 1 has lost the company over 300 million dollars over the last half-decade despite its being one of Exelon's best-performing power plants. 

Shut down of Unit 1 can go in two possible directions, the first being the immediate dismantlement immediately after the radioactive fuel has been moved away from the plant. The dismantlement can proceed after the spent fuel is removed from the casks. Dismantling the plant this way will take anywhere from 8 to 10 years.^[43] The second option Exelon could take is the long-term storage, which involves mothballing the plant and letting the radiation decay for up to 60 years on its own to a harmless level before completely dismantling the buildings. The advantage to the long term storage is the lack of radiation when the dismantlement would begin but the disadvantage would be the possible lack of qualified workers at the time of dismantlement. Exelon would also have to pay for limited maintenance and security of the plant over the potential sixty years.^[43] The entirety of the spent fuel will be moved to the Londonderry Township facility, which is another process that could take decades to complete.^[42]

Mike Pries, a Dauphin County Commissioner says the value of the property, and the $1 million a year Exelon pays in property taxes, would plummet the moment Unit 1 shuts down, which would harshly hurt Pennsylvania's economy.^[44] The Unit 1 plant manager says that the 675 workers remain committed to operating the plant safely and efficiently even though their future employment is uncertain.^[44]

It is currently{{when|date=December 2017}} unknown if Pennsylvania legislators are willing to pay for the costs of nuclear energy. About 70 legislators signed the industry-inspired Nuclear Caucus this year{{when|date=December 2017}} but have made no commitments.^[44]

Seismic risk

The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Three Mile Island was 1 in 25,000, according to an NRC study published in August 2010.^[45][46]

See also

• Chernobyl disaster
• Fukushima Daiichi nuclear disaster

References

External links

• Three Mile Island page on the operator's website
• Three Mile Island – Three Mile Island Alert

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