TMI Accidents

7/30/2019 TMI Accidents

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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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