The Three Mile Island accident in 1979 was caused by failures in the non-nuclear systems that prevented the removal of heat from the reactor core. The pilot-operated relief valve failed to close which caused the loss of coolant and overheating of the reactor. This led to a partial meltdown of the nuclear fuel. The accident highlighted issues with plant design, operator training, emergency response, and strengthened safety requirements. It cost over $500 million to decontaminate and over $2-3 billion in additional capital expenditures but resulted in no deaths and only small amounts of radiation release.

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CONTENT
• INTRODUCTION
• MEDIA
• THE ACCIDENT
• ACCIDENT ANALYSIS
• IMPACT OF ACCIDENT
• RADIATION
• FINANCIAL IMPACT
• CORRECTIVE ACTIONS
• CONCLUSION

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INTRODUCTION
• Located on Susquehanna river in
Pennsylvania, USA
• Two units of PWR
 TMI-1: 800 MWe (1974)
 TMI-2: 906 MWe (1978)

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Date of Accident: March 28, 1979
INTRODUCTION (Cont.)

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MEDIA

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THE ACCIDENT
• Experienced failure in the non-nuclear
section of the plant.
• Central feed water pumps terminated
and prevented the steam generators
from removing heat.
• Turbine and reactor shut down,
caused an increase in pressure.

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THE ACCIDENT (Cont.)
• The pilot-operated relief valve was
never closed and no signal was
generated.
• Valve poured out cooling water to
assist in the lowering of pressure and
caused the reactor to overheat.
• The designed indicators installed was
malfunctioning.

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THE ACCIDENT (Cont.)
• No indicator was displaying the level
of coolant and signal of relief valve.
• Alarms went off due to the loss of
coolant and confused the operator.
• The overheating caused a rupture in
the zirconium cladding and melting of
the fuel pellets.

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ACCIDENT ANALYSIS
DIRECT CAUSE
• The pressurizer
relief valve stuck
open.
• Emergency core
cooling system was
stopped by operator.
ROOT CAUSE
• Design Deficiencies
• Man – Machine
Interface
• Multiple latent
deficiencies like
organization,
maintenance, quality

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IMPACT OF
ACCIDENT Promoted upgrading and strengthening of
plant design and equipment requirements.
 Identified human performance as a
critical part of plant safety.
 Revamped operator training and staffing
requirements.
 Improved instruction to avoid the
confusing signals that plagued operations
during the accident.

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IMPACT OF ACCIDENT
(Cont.)
 Enhanced emergency preparedness.
 Forced regular analysis of plant
performance.
 Expanded performance-oriented as well
as safety-oriented inspections.
 No death occurred
 Small amount of radiation

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RADIATION

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FINANCIAL IMPACT
Some Funds Available Quickly
• Advanced money to evacuated families to
cover living expenses.
• Immediately paid pregnant women and
pre-school age children who evacuated five-
mile area
– 3,000 claimants
– $1.4 million for living expenses
and lost wages

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FINANCIAL IMPACT (Cont.)
Immediate Litigation and Partial Settlement
• Within weeks, class action filed for
businesses and residents within 25 miles of
the plant
– >2,000 personal injury claims
Other claims:
Lost wages, evacuation costs, loss of
property value, loss of profits

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FINANCIAL IMPACT (Cont.)
NOTE: Total TMI-2 “clean up” cost = $973 million
Total TMI-2 “clean up” time =12 Years

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FINANCIAL ANALYSIS
“The companies had to spend $500-600
million to decontaminate and repair the
damaged nuclear reactor and related facilities
while continuing to fund an additional $2 to 3
billion in capital expenditures to insure
reliable electric service to their customers.”
- Published on July 7, 1980

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CORRECTIVE ACTIONS
• R&D programs to improve the knowledge
available in core melt and other related
issues.
• Carry out of Safety Analysis Procedures.
• Adaptation of secondary safety display
system, alarm ranking system etc.
• Exchange of information at international
level.
• Improvement of operators training.

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CONCLUSION
 The accident was the result of equipment
malfunctions, worker errors and design
related problems that ultimately led to
partial core meltdown and small release of
radioactivity.
The case highlighted the need for
changes in emergency response planning,
reactor operator training, human factors
engineering and radiation protection.

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“The sun is the only safe nuclear
reactor, situated as it is some ninety-
three million miles away”
– Stephanie Mills