Three Mile Island nuclear accident - Revision history

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	[[Category:Done ~~2015~~-07-24]]		[[Category:Done 2018-07-20]]
	[[File:tmi.jpg\|300px\|thumb\|Figure 1. Three mile island nuclear facility.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/0/09/Three_mile_island_062010.jpg</ref>]]		[[File:tmi.jpg\|300px\|thumb\|Figure 1. Three mile island nuclear facility.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/0/09/Three_mile_island_062010.jpg</ref>]]

	<onlyinclude>'''Three Mile Island nuclear accident''' occurred at the Three Mile Island [[nuclear power plant]] ~~in [[nuclear reactor]] number 2 (TMI-2) on March 28, 1979~~, located near Middletown, Pa., U.S.A.<Ref name=nrc>U.S. NRC. (June 17 2015). ''Backgrounder on the Three Mile Island accident'' [Online], Available: http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/3mile-isle.html</ref> A partial [[meltdown]] occurred in the reactor ~~core~~, and caused the most serious accident in civilian U.S. nuclear power history~~; although~~ the small release of [[radioactivity\|radioactive materials]] had no detectable health effects on the public.</onlyinclude><ref name=nrc/><Ref name=wna>World Nuclear Association. (June 17 2015). ''Three Mile Island Accident'' [Online], Available: http://www.world-nuclear.org/info/Safety-and-Security/Safety-of-Plants/Three-Mile-Island-accident/</ref> The [[SL-1]] disaster was more serious, as it killed the three people operating the reactor, but SL-1 was a military reactor, not a civilian one.		<onlyinclude>'''Three Mile Island nuclear accident''' occurred on March 28, 1979 at the Three Mile Island [[nuclear power plant]], located near Middletown, Pa., U.S.A.<Ref name=nrc>U.S. NRC. (June 17 2015). ''Backgrounder on the Three Mile Island accident'' [Online], Available: http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/3mile-isle.html</ref> A partial [[meltdown]] occurred in the core of [[nuclear reactor]] number 2 (TMI-2), and caused the most serious accident in civilian U.S. nuclear power history. However, the small release of [[radioactivity\|radioactive materials]] had no detectable health effects on the public.</onlyinclude><ref name=nrc/><Ref name=wna>World Nuclear Association. (June 17 2015). ''Three Mile Island Accident'' [Online], Available: http://www.world-nuclear.org/info/Safety-and-Security/Safety-of-Plants/Three-Mile-Island-accident/</ref> The [[SL-1]] disaster was more serious, as it killed the three people operating the reactor, but SL-1 was a military reactor, not a civilian one.

	In the aftermath of the event, sweeping changes were made to regulation and operation of nuclear power plants. Operator training, emergency response systems, engineering, radiation protection, and many other areas were addressed and significantly improved.<ref name=nrc/>		In the aftermath of the event, sweeping changes were made to regulation and operation of nuclear power plants. Operator training, emergency response systems, engineering, radiation protection, and many other areas were addressed and significantly improved.<ref name=nrc/>
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	===Events===		===Events===

	To start the chain of events, a mechanical or electrical fault prevented the main water pumps from receiving [[steam]] from the core~~, which~~ caused the steam [[turbine]] and [[generator]] to shut down followed by a shutdown of the core.		To start the chain of events, a mechanical or electrical fault prevented the main water pumps from receiving [[steam]] from the core. This caused the steam [[turbine]] and [[generator]] to shut down followed by a shutdown of the core—which increased the temperature and [[pressure]] in the primary section (Figure 2). In response, the pressure relief valve opened, and ''should have'' closed after the pressure returned to normal. However, it got stuck and the operators were unaware of this fact. This caused a '[[loss of coolant accident]]', which meant the coolant drained and nothing was cooling down the fuel inside the core.<ref name=nrc/>

	~~This caused an increase of temperature and [[pressure]] in the primary section (Figure 2), which was responded~~ to ~~by the opening of a pressure relief valve. The valve should have closed after the pressure was relieved to normal levels~~, ~~however it became stuck and~~ the operators were unaware of ~~this fact. This caused~~ a ~~[[loss~~ of ~~coolant accident]], in~~ which the primary coolant ~~was drained which should have been cooling~~ down the ~~fuel inside~~ the core.<ref name=nrc/>		Due to inadequate alarm signals, the operators were unaware of the real problem and began to make a series of actions which made the situation worse.<Ref name=nrc/> Since they thought that the primary section had sufficient amount of coolant circulating, they shut down any input of coolant from the secondary section. However, the core was in fact starved of coolant, and in turn overheated.<ref name=nrc/>

	~~Due to inadequate alarm signals, the operators were unaware~~ of the ~~real problem~~ and began to ~~make~~ a ~~series~~ of ~~actions which made~~ the ~~situation worse~~.<~~Ref~~ name=nrc/> ~~Since they thought that~~ the ~~primary section had sufficient amount of coolant circulating~~, ~~they shut down any input of coolant from~~ the ~~secondary section. However~~ the core ~~was in fact starved of coolant~~, ~~and in turn overheated~~.~~<ref name=nrc/>~~		The fuel assemblies inside of the core ruptured, and the [[uranium]] fuel pellets began to melt. Even though around half of the core experienced a meltdown, the effects outside of the plant were minimal.<ref name=nrc/> Within a few hours response teams investigated the site, with non-essential personnel evacuated. By the evening, the core appeared to be adequately cooled, however, the problems were not over yet.

	~~The fuel assemblies inside of~~ the ~~core ruptured~~, and the ~~[[uranium]] fuel pellets began to melt. Even though around half~~ of ~~the core experienced~~ a ~~meltdown, the effects outside of~~ the plant ~~were minimal~~.<ref name=nrc/> ~~Within~~ a ~~few hours response teams investigated~~ the ~~site~~, ~~with non-essential personnel evacuated~~. ~~By the evening the core appeared~~ to be ~~adequately cooled, however the problems were not over yet~~.		Authorities were worried for the population's safety, and advised pregnant women and children to leave the area of a 5 mile radius around the plant.<ref name=nrc/> Furthermore, through [[chemical reaction]]s inside of the core, a large [[hydrogen]] bubble formed in the pressure vessel—which had the potential to burn or explode. An explosion, worst case scenario, would release containments. However, on April 1<sup>st</sup> it was deemed to be decreasing in size and posed no threat.<ref name=nrc/>

	~~Authorities were worried for the population's safety, and advised pregnant women and children to leave the area of a 5 mile radius around the plant.<ref name~~=nrc/> Further, through [[chemical reaction]]s inside of the core, a large [[hydrogen]] bubble had formed in the pressure vessel which had potential of burning or exploding. An explosion could compromise containment and would be the worst possible scenario, however on April 1<sup>st</sup> it was deemed to be decreasing in size and posed no threat.<ref name=~~nrc/>~~		==Aftermath==

	=~~=Aftermath==~~		After the accident, public confidence in nuclear energy drastically declined, especially in the United States. This resulted in the decline of construction in the U.S. during the 80's and 90's. Skewed communication on the effects of the accident caused confusion and worry among the population—as misunderstood reports stated radiation doses in the area being much larger than they actually were.<ref name=wna/>

	~~After the accident, public confidence in nuclear energy drastically declined, especially in the United States~~. ~~This resulted in~~ the ~~decline of construction in the U.S. during the 80~~'~~s and 90~~'s. ~~Skewed communication of~~ the ~~effects~~ of the ~~accident caused confusion~~ and ~~worry among~~ the ~~population, as misunderstood reports told people of~~ the ~~radiation doses in the area being much larger than they actually~~ were.<ref name=~~wna~~/>		Health effects were essentially negligible. Approximately 2 million people received about 10 [[sievert\|microsieverts]] above the normal background radiation dose—6x ''less'' than a what a chest x-ray would expose someone to.<Ref name=nrc/> Many well respected organizations, such as Columbia University and the University of Pittsburgh, conducted experiments on the nearby area, and all came to the conclusion that health effects on humans and the environment were negligible.<ref name=nrc/>

	~~Health effects were essentially negligible~~. ~~Approximately 2 million people received about 10 [[sievert\|microsieverts]] above~~ the ~~normal background radiation dose, which is 6x ''less'' than~~ a ~~chest x-ray would expose someone to.<Ref name=nrc/> Many well respected organizations~~, ~~such as Columbia University~~ and the ~~University~~ of ~~Pittsburgh, conducted experiments on~~ the ~~nearby area~~, ~~and all came to~~ the ~~conclusion that health effects on humans and the environment were negligible~~.<ref name=~~nrc~~/>		As mentioned before, this event caused the improvement in many areas of safety and operation. Power plants all over the world had to live up to a higher standard, and if all of the measures were taken by the operators of the [[Chernobyl]] nuclear reactor, the disaster could have had a far lesser impact.<ref name=can>AECL. (June 16 2015). ''Chernobyl - A Canadian Perspective'' [Online]. Available: https://canteach.candu.org/Content%20Library/19910101.pdf</ref>

	~~As mentioned before, this event caused the improvement in many areas~~ of ~~safety and operation. Power plants all over the world had to live up to a higher standard, and if all of the measures were taken by the operators of the~~ Chernobyl nuclear ~~reactor, the disaster could have had~~ a ~~far lesser impact.<ref name=can>AECL. (June 16 2015). ''Chernobyl - A Canadian Perspective''~~ [~~Online~~]~~. Available: https://canteach.candu.org/Content%20Library/19910101.pdf</ref>~~		==For Further Reading==
			*[[Nuclear power plant]]
			*[[Nuclear reactor]]
			*[[Loss of coolant accident]]
			*[[Radioactivity]]
			*[[Chernobyl nuclear accident]]
			*Or explore a [[Special:Random\|random page]]

	==References==		==References==
	{{reflist}}		{{reflist}}
	[[Category:Uploaded]]		[[Category:Uploaded]]

J.williams: 1 revision imported

2015-08-26T21:31:44Z

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J.williams at 17:00, 12 August 2015

2015-08-12T17:00:17Z

New page

[[Category:Done 2015-07-24]]
[[File:tmi.jpg|300px|thumb|Figure 1. Three mile island nuclear facility.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/0/09/Three_mile_island_062010.jpg</ref>]]

<onlyinclude>'''Three Mile Island nuclear accident''' occurred at the Three Mile Island [[nuclear power plant]] in [[nuclear reactor]] number 2 (TMI-2) on March 28, 1979, located near Middletown, Pa., U.S.A.<Ref name=nrc>U.S. NRC. (June 17 2015). ''Backgrounder on the Three Mile Island accident'' [Online], Available: http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/3mile-isle.html</ref> A partial [[meltdown]] occurred in the reactor core, and caused the most serious accident in civilian U.S. nuclear power history; although the small release of [[radioactivity|radioactive materials]] had no detectable health effects on the public.</onlyinclude><ref name=nrc/><Ref name=wna>World Nuclear Association. (June 17 2015). ''Three Mile Island Accident'' [Online], Available: http://www.world-nuclear.org/info/Safety-and-Security/Safety-of-Plants/Three-Mile-Island-accident/</ref> The [[SL-1]] disaster was more serious, as it killed the three people operating the reactor, but SL-1 was a military reactor, not a civilian one.

In the aftermath of the event, sweeping changes were made to regulation and operation of nuclear power plants. Operator training, emergency response systems, engineering, radiation protection, and many other areas were addressed and significantly improved.<ref name=nrc/>

==Events leading to the disaster==

===Summary===

At 4:00 am, the reactor was running at 97% power when a fairly minor problem in the secondary section (See Figure 2) caused the [[temperature]] of the primary coolant to rise. This caused the reactor to shutdown immediately, which occurred in a couple of seconds. The fault occurred when a relief valve failed to close, went undetected by the workers, and caused a large amount of the [[loss of coolant accident|coolant to drain away]]. This caused the core to overheat, resulting in partial meltdown and severe damage. A combination of equipment malfunction, design problems, and worker error led to the partial meltdown in TMI-2.<ref name=wna/>

[[File:tmi2.png|800px|center|thumb|Figure 2. Layout of the TMI-2 reactor.<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/3/39/Tmi-2_schematic.svg</ref>]]

===Events===

To start the chain of events, a mechanical or electrical fault prevented the main water pumps from receiving [[steam]] from the core, which caused the steam [[turbine]] and [[generator]] to shut down followed by a shutdown of the core.

This caused an increase of temperature and [[pressure]] in the primary section (Figure 2), which was responded to by the opening of a pressure relief valve. The valve should have closed after the pressure was relieved to normal levels, however it became stuck and the operators were unaware of this fact. This caused a [[loss of coolant accident]], in which the primary coolant was drained which should have been cooling down the fuel inside the core.<ref name=nrc/>

Due to inadequate alarm signals, the operators were unaware of the real problem and began to make a series of actions which made the situation worse.<Ref name=nrc/> Since they thought that the primary section had sufficient amount of coolant circulating, they shut down any input of coolant from the secondary section. However the core was in fact starved of coolant, and in turn overheated.<ref name=nrc/>

The fuel assemblies inside of the core ruptured, and the [[uranium]] fuel pellets began to melt. Even though around half of the core experienced a meltdown, the effects outside of the plant were minimal.<ref name=nrc/> Within a few hours response teams investigated the site, with non-essential personnel evacuated. By the evening the core appeared to be adequately cooled, however the problems were not over yet.

Authorities were worried for the population's safety, and advised pregnant women and children to leave the area of a 5 mile radius around the plant.<ref name=nrc/> Further, through [[chemical reaction]]s inside of the core, a large [[hydrogen]] bubble had formed in the pressure vessel which had potential of burning or exploding. An explosion could compromise containment and would be the worst possible scenario, however on April 1<sup>st</sup> it was deemed to be decreasing in size and posed no threat.<ref name=nrc/>

==Aftermath==

After the accident, public confidence in nuclear energy drastically declined, especially in the United States. This resulted in the decline of construction in the U.S. during the 80's and 90's. Skewed communication of the effects of the accident caused confusion and worry among the population, as misunderstood reports told people of the radiation doses in the area being much larger than they actually were.<ref name=wna/>

Health effects were essentially negligible. Approximately 2 million people received about 10 [[sievert|microsieverts]] above the normal background radiation dose, which is 6x ''less'' than a chest x-ray would expose someone to.<Ref name=nrc/> Many well respected organizations, such as Columbia University and the University of Pittsburgh, conducted experiments on the nearby area, and all came to the conclusion that health effects on humans and the environment were negligible.<ref name=nrc/>

As mentioned before, this event caused the improvement in many areas of safety and operation. Power plants all over the world had to live up to a higher standard, and if all of the measures were taken by the operators of the Chernobyl nuclear reactor, the disaster could have had a far lesser impact.<ref name=can>AECL. (June 16 2015). ''Chernobyl - A Canadian Perspective'' [Online]. Available: https://canteach.candu.org/Content%20Library/19910101.pdf</ref>

==References==
{{reflist}}
[[Category:Uploaded]]