Three Mile Island Research Paper
INTRODUCTION
Three Mile Island Nuclear Generating Station (TMI) is a civilian nuclear power plant (NPP) 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. The TM-1 is a pressurized water reactor with a net generating capacity of 852 MWe while TMI-2 was also a pressurized water reactor but with slightly larger output of 906 MWe. 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. The partial meltdown resulted in the release of small amounts of radioactive gases and radioactive iodine into the environment. However, …show more content…
Epidemiology studies have not linked a single instance of cancer with the accident. Figure 1 : Satellite view of Three Mile Island Figure 2 : Aerial view of Three Miles Island Nuclear Power Plant. The left side of the figure show the already deactivated TMI-2
THE TM-2 ACCIDENT
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 …show more content…
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.
Figure 3 : Overall view of the TM-2 Reactor operating system
Diagram 1 : Overall flow on how the reactor should work
Diagram 2 : The feedwater pumps failed to operate and causes the power plant to overheat
Diagram 3 : The zirconium cladding ruptured and half of the core melted
CHRONOLOGY OF THE ACCIDENT
Date
Event
1968–1970
Construction
April 1974
Reactor-1 online
Feb 1978
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 (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
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.
EFFECTS TO ENVIRONMENT
Radioactivity
Within hours of the accident the United States Environmental Protection Agency (EPA) began daily sampling of the environment at the three stations closest to the plant.
Radioactive gases from the reactor cooling system built up in the makeup tank in the auxiliary building. Operators used a system of pipes and compressors to move the gas to waste gas decay tanks. The compressors leaked, and some radioactive gas was released to the environment. These went through high-efficiency particulate air (HEPA) filters and charcoal filters which removed most of the radionuclides, except for the noble gases, the estimated total of which was about 370 PBq (the Kemeny Commission said ‘a maximum of 480 PBq noble gases’ and NRC also quotes 1.6 PBq of krypton rlelease in July). With short half-life and being biologically inert, these did not pose a health hazard. 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.
The Hydrogen Bubble ( Aftermath Explosion )
When the reactor 's core was uncovered, on the morning of 28 March, a high-temperature chemical reaction between water and the zircaloy metal tubes holding the nuclear fuel pellets had created hydrogen gas. In the afternoon of 28 March, a sudden rise in reactor building pressure shown by the control room instruments indicated a hydrogen burn had occurred. Hydrogen gas also gathered at the top of the reactor vessel.
From 30 March through 1 April operators removed this hydrogen gas "bubble" by periodically opening the vent valve on the reactor cooling system pressuriser. For a time, regulatory (NRC) officials believed the hydrogen bubble could explode, though such an explosion was never possible since there was not enough oxygen in the system.
Health Effect
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.
For the record also, the nuclear power industry claims that there were no deaths, injuries or adverse health effects from the accident, and a report by Columbia University epidemiologist Maureen Hatch agrees with this finding.
Economic Effect
The TMI-2 accident had caused the US government a total loss of more than US$ 3 billion and had caused the loss of confidence towards nuclear-powered energy among the US people. The TMI-1 that was unaffected by the disaster had also being shutdown until 1985 where the reactor had restarted but with a much improve operating system.
EMERGENCY RESPONSE AND ACTION TAKEN TO SOLVE THE ACCIDENT
Short-term Solution
Long-term Solution
The cleanup of the damaged nuclear reactor system at TMI-2 took nearly 12 years and cost approximately US$973 million. The cleanup was uniquely challenging technically and radiologically. Plant surfaces had to be decontaminated. Water used and stored during the cleanup had to be processed. And about 100 tonnes of damaged uranium fuel had to be removed from the reactor vessel -- all without hazard to cleanup workers or the public.
A cleanup plan was developed and carried out safely and successfully by a team of more than 1000 skilled workers. It began in August 1979, with the first shipments of accident-generated low-level radiological waste to Richland, Washington. In the cleanup 's closing phases, in 1991, final measurements were taken of the fuel remaining in inaccessible parts of the reactor vessel. Approximately one percent of the fuel and debris remains in the vessel. Also in 1991, the last remaining water was pumped from the TMI-2 reactor. The cleanup ended in December 1993, when Unit 2 received a license from the NRC to enter Post Defueling Monitored Storage (PDMS).
Early in the cleanup, Unit 2 was completely severed from any connection to TMI Unit 1. TMI-2 today is in long-term monitored storage. No further use of the nuclear part of the plant is anticipated. Ventilation and rainwater systems are monitored. Equipment necessary to keep the plant in safe long-term storage is maintained.
Defueling the TMI-2 reactor vessel was the heart of the cleanup. The damaged fuel remained underwater throughout the defueling. In October 1985, after nearly six years of preparations, workers standing on a platform atop the reactor and manipulating long-handled tools began lifting the fuel into canisters that hung beneath the platform. In all, 342 fuel canisters were shipped safely for long-term storage at the Idaho National Laboratory, a program that was completed in April 1990. It was put into dry storage in concrete containers.
TMI-2 cleanup operations produced over 10.6 megalitres of accident-generated water that was processed, stored and ultimately evaporated safely.
In February 1991, the TMI-2 Cleanup Program was named by the National Society of Professional Engineers as one of the top engineering achievements in the U.S. completed during 1990.
In 2010 the generator was sold by FirstEnergy to Progress Energy to upgrade its Shearon Harris nuclear power plant in North Carolina. It was shipped in two parts, the rotor, which weighs 170 tonnes, and the stator, which weighs about 500 tonnes.
CONCLUSION
As a conclusion, while it is one of the best energy resources but when it comes to dealing with nuclear energy, we must know that we have little room for error. The TMI-2 accident shows us how a small flaw of in operation system had almost cause a life-threatening radioactive disaster towards the surrounding area. The TMI-2 accident also took billions of dollars out of US government in order to solve the issue. However, this accident has teaches us a lesson on how to improve the usage of nuclear energy. Intensive research had been made and the upgrade had been installed towards the nearby TMI-1 reactor which had restarted its operation in 1985 and is still continuing the operation until today where more than 800 000 houses gains electricity from it. This shows us that even though nuclear energy is very dangerous to take care of, but we cannot simply right off the profit and how ‘green’ and environmentally friendly it can be if we can keep its power in check.
REFERENCES http://en.wikipedia.org/wiki/Three_Mile_Island_accident http://en.wikipedia.org/wiki/Three_Mile_Island_Nuclear_Generating_Station
http://www.world-nuclear.org/info/Safety-and-Security/Safety-of-Plants/Three-Mile-Island-accident/
Three Mile Island Nuclear Generating Station (TMI) is a civilian nuclear power plant (NPP) 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. The TM-1 is a pressurized water reactor with a net generating capacity of 852 MWe while TMI-2 was also a pressurized water reactor but with slightly larger output of 906 MWe. 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. The partial meltdown resulted in the release of small amounts of radioactive gases and radioactive iodine into the environment. However, …show more content…
Epidemiology studies have not linked a single instance of cancer with the accident. Figure 1 : Satellite view of Three Mile Island Figure 2 : Aerial view of Three Miles Island Nuclear Power Plant. The left side of the figure show the already deactivated TMI-2
THE TM-2 ACCIDENT
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 …show more content…
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.
Figure 3 : Overall view of the TM-2 Reactor operating system
Diagram 1 : Overall flow on how the reactor should work
Diagram 2 : The feedwater pumps failed to operate and causes the power plant to overheat
Diagram 3 : The zirconium cladding ruptured and half of the core melted
CHRONOLOGY OF THE ACCIDENT
Date
Event
1968–1970
Construction
April 1974
Reactor-1 online
Feb 1978
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 (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
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.
EFFECTS TO ENVIRONMENT
Radioactivity
Within hours of the accident the United States Environmental Protection Agency (EPA) began daily sampling of the environment at the three stations closest to the plant.
Radioactive gases from the reactor cooling system built up in the makeup tank in the auxiliary building. Operators used a system of pipes and compressors to move the gas to waste gas decay tanks. The compressors leaked, and some radioactive gas was released to the environment. These went through high-efficiency particulate air (HEPA) filters and charcoal filters which removed most of the radionuclides, except for the noble gases, the estimated total of which was about 370 PBq (the Kemeny Commission said ‘a maximum of 480 PBq noble gases’ and NRC also quotes 1.6 PBq of krypton rlelease in July). With short half-life and being biologically inert, these did not pose a health hazard. 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.
The Hydrogen Bubble ( Aftermath Explosion )
When the reactor 's core was uncovered, on the morning of 28 March, a high-temperature chemical reaction between water and the zircaloy metal tubes holding the nuclear fuel pellets had created hydrogen gas. In the afternoon of 28 March, a sudden rise in reactor building pressure shown by the control room instruments indicated a hydrogen burn had occurred. Hydrogen gas also gathered at the top of the reactor vessel.
From 30 March through 1 April operators removed this hydrogen gas "bubble" by periodically opening the vent valve on the reactor cooling system pressuriser. For a time, regulatory (NRC) officials believed the hydrogen bubble could explode, though such an explosion was never possible since there was not enough oxygen in the system.
Health Effect
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.
For the record also, the nuclear power industry claims that there were no deaths, injuries or adverse health effects from the accident, and a report by Columbia University epidemiologist Maureen Hatch agrees with this finding.
Economic Effect
The TMI-2 accident had caused the US government a total loss of more than US$ 3 billion and had caused the loss of confidence towards nuclear-powered energy among the US people. The TMI-1 that was unaffected by the disaster had also being shutdown until 1985 where the reactor had restarted but with a much improve operating system.
EMERGENCY RESPONSE AND ACTION TAKEN TO SOLVE THE ACCIDENT
Short-term Solution
Long-term Solution
The cleanup of the damaged nuclear reactor system at TMI-2 took nearly 12 years and cost approximately US$973 million. The cleanup was uniquely challenging technically and radiologically. Plant surfaces had to be decontaminated. Water used and stored during the cleanup had to be processed. And about 100 tonnes of damaged uranium fuel had to be removed from the reactor vessel -- all without hazard to cleanup workers or the public.
A cleanup plan was developed and carried out safely and successfully by a team of more than 1000 skilled workers. It began in August 1979, with the first shipments of accident-generated low-level radiological waste to Richland, Washington. In the cleanup 's closing phases, in 1991, final measurements were taken of the fuel remaining in inaccessible parts of the reactor vessel. Approximately one percent of the fuel and debris remains in the vessel. Also in 1991, the last remaining water was pumped from the TMI-2 reactor. The cleanup ended in December 1993, when Unit 2 received a license from the NRC to enter Post Defueling Monitored Storage (PDMS).
Early in the cleanup, Unit 2 was completely severed from any connection to TMI Unit 1. TMI-2 today is in long-term monitored storage. No further use of the nuclear part of the plant is anticipated. Ventilation and rainwater systems are monitored. Equipment necessary to keep the plant in safe long-term storage is maintained.
Defueling the TMI-2 reactor vessel was the heart of the cleanup. The damaged fuel remained underwater throughout the defueling. In October 1985, after nearly six years of preparations, workers standing on a platform atop the reactor and manipulating long-handled tools began lifting the fuel into canisters that hung beneath the platform. In all, 342 fuel canisters were shipped safely for long-term storage at the Idaho National Laboratory, a program that was completed in April 1990. It was put into dry storage in concrete containers.
TMI-2 cleanup operations produced over 10.6 megalitres of accident-generated water that was processed, stored and ultimately evaporated safely.
In February 1991, the TMI-2 Cleanup Program was named by the National Society of Professional Engineers as one of the top engineering achievements in the U.S. completed during 1990.
In 2010 the generator was sold by FirstEnergy to Progress Energy to upgrade its Shearon Harris nuclear power plant in North Carolina. It was shipped in two parts, the rotor, which weighs 170 tonnes, and the stator, which weighs about 500 tonnes.
CONCLUSION
As a conclusion, while it is one of the best energy resources but when it comes to dealing with nuclear energy, we must know that we have little room for error. The TMI-2 accident shows us how a small flaw of in operation system had almost cause a life-threatening radioactive disaster towards the surrounding area. The TMI-2 accident also took billions of dollars out of US government in order to solve the issue. However, this accident has teaches us a lesson on how to improve the usage of nuclear energy. Intensive research had been made and the upgrade had been installed towards the nearby TMI-1 reactor which had restarted its operation in 1985 and is still continuing the operation until today where more than 800 000 houses gains electricity from it. This shows us that even though nuclear energy is very dangerous to take care of, but we cannot simply right off the profit and how ‘green’ and environmentally friendly it can be if we can keep its power in check.
REFERENCES http://en.wikipedia.org/wiki/Three_Mile_Island_accident http://en.wikipedia.org/wiki/Three_Mile_Island_Nuclear_Generating_Station
http://www.world-nuclear.org/info/Safety-and-Security/Safety-of-Plants/Three-Mile-Island-accident/