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TOPIC
THREE MILE ISLAND NUCLEAR ACCIDENT
PRESENTED BY:
HAFIZ AMANAT ALI
12-MS-FT-TSE-09
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Three Mile Island Nuclear Generating
Station is a civilian nuclear power plant
(NPP)
Located on Three Mile Island in the
Susquehanna River, south of Harrisburg,
Pennsylvania.
TMI-1 (Unit-1) TMI-2 (Unit-2)
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The Three Mile Island Unit-1 is apressurized water reactor designed byBabcock and Wilcox
Net generating capacity of 802 MWUnit-1 first came online on April 19, 1974,
and began commercial operations onSeptember 2, 1974
Closed-cycle cooling system for its maincondenser using two natural draft coolingtowers.
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The Three Mile Island Unit-2 was also a
pressurized water reactor constructed by
B&W
Net generating capacity of 906 MW
Operating on February 8, 1978, and
began commercial operation on December
30, 1978
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On March 28,1979,TMI-2 suffered a partial
meltdown
At 36 seconds past 4:00 a.m. the first of a
series of pumps feeding water to thesteam generators at the Three Mile Island
nuclear plant stopped functioning.
The steam produced by the reactor runsthe generators to produce electricity
Also serves to cool down the reactor core,
reducing the risk of a meltdown
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CONT..
When the flow of the water stopped, thetemperature inside the reactor core increased
This caused the water inside the reactor toexpand, increasing the pressure inside the
pressurizer to 2200 psi, 100 psi more then thenormal
As designed the increase in pressure caused thePilot Operated Relief Valve to open (PORV)
draining the steam and water from the reactor core Despite the opening of the PORV the pressure
continued to rise, 9 seconds into the accident thecontrol rods automatically lowered as designed tohalt the fission reaction.
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CONT..
The latent heat of the radioactive materialcontinued to heat the water
The light indicating that the PORV was shut
off, leading the operators to assume that thePORV had was now closed
In reality the PORV was stuck open andsteam and water was escaping from thereactor
This is known as a Lost Of CoolantAccident (LOCA)
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CONT.
2 Minutes into the accident the EmergencyInjection Water (EIW) to be automatically activated
This sent about 1000 gallons of water per minute
into the reactor coolant system But fearing that the core would have too muchwater, Operator Fredrick turned off one of the EIWpumps, reducing the flow of water into the core toless then 100 gallons per minute
8 Minutes into the accident it was discovered thatthe emergency feed water was not reaching thecore because of the closed valves
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CONT.
Once the core over heats the zirconium alloy of the fuel rodcladding reacts with the steam to produce hydrogen gas
Hydrogen produced flammable, but the diminishment ofthe fuel rod cladding increases the risk of radioactive
contamination Based on increasing radiation levels, at around 7:00 a.m. a
site emergency was declared, indicating the threat ofrelease of radioactivity into the surrounding environment
At 7:24 a general emergency was declared at the TMI-2site and the site began to be evacuated
Technicians were forced to wear face masks to block anyair Bourne radioactive particles.
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Component failures
Fee water pumps stopped working
Design deficiencies
Stuck-open pilot-operated relief valve (PROV)
Personnel error
Operator Fredrick turned off one of the EIW pump,
reducing the flow of water into the core.
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VOLUNTARYEVACUATION The situation was "more complex than the company first
led to believe Schools were closed and residents were urged to stay
indoors. Farmers were told to keep their animals undercover and on stored feed
INVESTIGATIONS President's Commission on the Accident at Three Mile
Island, created by Jimmy Carter in April 1979 The commission consisted of a panel of twelve people It was instructed to produce a final report within six
months Complete study released on October 31, 1979,the
investigation strongly criticized Babcock and Wilcox
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Health effectsApproximately 2.5 million curies of radioactive
gases, and approximately 15 curies of iodine-131was released into the environment. According to the
American Nuclear Society Based on these emission figures, early scientific
publications on the health effects of the falloutestimated one or two additional cancer deaths in
the 16 km area around TMIA variety of studies have been unable to conclude
that the accident had substantial health effects, orthat it didn't
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The Three Mile Island accident is one of the
factors cited for the decline of new reactor
construction
Significant turning point in the globaldevelopment of nuclear power
From 1963-1979 the number of reactors under
construction globally increased every year
The number of reactors under construction inthe U.S. declined every year from 1980-1998.
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Design flaws with U-shaped tubes that
could prevent coolant circulation that
caused an accident. (as mentioned by
NRC inspector before the accident)
Human factor was also involved because
control room was not properly working
We may say that the accidents are notunexpected or unavoidable but damages
can be minimized by proper management.
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