This document discusses three major nuclear accidents: Tokaimura, Japan in 1999; Three Mile Island, USA in 1979; and Fukushima, Japan in 2011. It outlines the key events and failures that led to each accident, including improper handling of nuclear material, loss of cooling systems, and natural disasters overwhelming safety systems. Lessons are highlighted around operator errors, poor emergency response, and design flaws that failed to adequately plan for all risks.

2. DISCLAIMER
Nuclear power plants are prominent and provide
approximately 5.7% of the world’s energy and 13% of
the world’s electricity.
There are about 437 nuclear power plants worldwide
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4. Level 0 Level 1 Level 2 Level 3 Level 4 Level 5 Level 6 Level
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LEVELS OF INTERNATIONAL NUCLEAR EVENTS
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5. Level 0 Level 1 Level 2 Level 3 Level 4 Level 5 Level 6 Level
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LEVELS OF INTERNATIONAL NUCLEAR EVENTS
Level 0
No threat to safety
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6. 6
Level 0 Level 1 Level 2 Level 3 Level 4 Level 5 Level 6 Level
7
LEVELS OF INTERNATIONAL NUCLEAR EVENTS
Level 4
• Release of radioactive material
• At lease one death from radiation
• 0.1% release of core inventory
• High probability of significant public exposure

7. 7
Level 0 Level 1 Level 2 Level 3 Level 4 Level 5 Level 6 Level
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LEVELS OF INTERNATIONAL NUCLEAR EVENTS
Level 7
• Major release of radioactive material
• Several deaths from radiation
• Widespread impact on environment and public health

8. Tokaimura, Japan
Three Mile Island, United States of America
Fukushima, Japan
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9. TOKAIMURA, JAPAN (1999)
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Uranium – 235
Design - Geometrical control

10. DIRECT CAUSE OF DISASTER
16 kg of high enriched uranium filled in precipitation
basin which can be filled with no more than 2.9 kg.
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11. TOKAIMURU PRECIPITATION TANK
Water-filled
cooling
jacket
Neutron
Moderation
Nuclear fission
reactions
occurring faster
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12. TOKAIMURU PRECIPITATION TANK
Water-filled
cooling
jacket
Neutron
Moderation
Nuclear fission
reactions
occurring faster
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13. POINT OF CRITICALITY?
Uncontrolled nuclear fission:
1. Self-sustaining
2. Intense gamma and neutron radiation
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14. LESSONS
Not designed to counter criticality (lack of geometrical design)
Built in the middle of residential area
Possibility of criticality accidents was not included when site review
was done
Unqualified workers
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15. THREE MILE ISLAND, USAUnclogging filter
Entry of waterCritical air pressure to
valves and pumps
lowered Computer shuts down
pumps
No water relieving the
reactor from heat
Pressure builds
Cadmium rods lowered
March 28, 1979
3:58 am
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Violent Shaking of pumps

16. DECISION?
Coolant turned off.
EFFECT
Core heating up to 2000OC +
At 5000OC rods would melt and burn through the 8 inch thick steel reactor into the
ground
CONCURRENT ACTIVITIESPoor communication between operators and experts due to single phone line
Radiation detected in control room March 28, 1979
7:15 am
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17. STILL TRYING TO STABILIZE
Radiation on top of containment high enough to kill a man
in 20 seconds
March 28, 1979
10:17 am
Radiation leaking out of the plantMarch 28, 1979
11:00 am
Contact made! Pumps restartedMarch 28, 1979
7:33 pm
Coolant sample required
to assess situation
Public given no details.
March 29, 1979
8:30 am
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18. Basement filled with radioactive water giving off radioactive gas
Ordered to vent gas into atmosphere
March 29, 1979
8:30 am
Evacuation!
March 30, 1979
8:00 am
Large amounts of hydrogen gas at the top of the containment
dome
April 1, 1979
10:00 am
Disaster averted.
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19. LESSONS
Know what each button and light represents in the control room
Poor planning
Designers were not accessible
Experts were not accessible
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20. FUKUSHIMA, JAPAN
Earthquake with 9.0 magnitude
5 nuclear plants in disaster zone (Fukushima was the largest)
Power loss  Emergency generators turned on
March 11, 2011
2:46 pm
Tsunami warning
March 11, 2011
2:55
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21. FUKUSHIMA, JAPAN
Earthquake with 9.0 magnitude
5 nuclear plants in disaster zone (Fukushima was the largest)
Power loss  Emergency generators turned on
March 11, 2011
2:46 pm
Tsunami warning
March 11, 2011
2:55
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22. Tsunami hits
All power lost
Two workers die
March 11, 2011
3:27 pm
Power plant evacuated – one team stayed behind
Required mobile power generators but transport was difficult
March 11, 2011
3:37 pm
Battery packs and car batteries used to make key readings
Pressure inside core rising
March 11, 2011
6:08 pm
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23. Tsunami hits
All power lost
Two workers die
March 11, 2011
3:27 pm
Power plant evacuated – one team stayed behind
Required mobile power generators but transport was difficult
March 11, 2011
3:37 pm
Battery packs and car batteries used to make key readings
Pressure inside core rising
March 11, 2011
6:08 pm
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24. Minister advised operators to release steam from the valvesMarch 11, 2011
7:03 pm
Valves had to opened manually, difficult to locate them
Cracked reactor (of 15 cm steel) was discovered
Plant will without power
March 11, 2011
9:00 pm
Pressure in reactor 1 was so high that it was feared that the
reactors might explode
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25. Evacuation!March 12, 2011
6:00 am
Poor communication between managers and operators
Valves still not open
March 12, 2011
7:00 pm
Valves opened
March 13, 2011
10:16 am
March 13, 2011
3:36 pm
Reactor 1 explodes
Reactor 2 and 3 damaged
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26. Fukushima 50 still has no control over the reactorMarch 13, 2011
11:01 pm
Explosion in building 4 causes a fireMarch 14, 2011
6:00 am
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27. LESSONS
Flaws in original design – more concerned with risk of Earthquake
Tsunami walls were too low
Poor location of diesel generators
Thin layer of Zirconium around the rods in the reactor which over
heated and became highly reactive
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28. • HTTPS://WWW.YOUTUBE.COM/WATCH?V=FYIBLYGNLCC
• HTTP://AMERICA.ALJAZEERA.COM/CONTENT/DAM/AJAM/IMAGES/ARTICLES_2014/06/EUROPEAN_NUCLEAR
_POWER_PLANT_A.JPG
• HTTPS://EN.WIKIPEDIA.ORG/WIKI/INTERNATIONAL_NUCLEAR_EVENT_SCALE
• HTTP://WWW.UCSUSA.ORG/CLEAN_ENERGY/OUR-ENERGY-CHOICES/ENERGY-AND-WATER-USE/WATER-
ENERGY-ELECTRICITY-COOLING-POWER-PLANT.HTML#.VK_AFYRIFUJ
• HTTP://WWW.UCSUSA.ORG/CLEAN_ENERGY/OUR-ENERGY-CHOICES/ENERGY-AND-WATER-USE/WATER-
ENERGY-ELECTRICITY-NUCLEAR.HTML#.VK_AGYRIFUJ
• HTTPS://EN.WIKIPEDIA.ORG/WIKI/FUKUSHIMA_DAIICHI_NUCLEAR_DISASTER
• HTTPS://WWW.YOUTUBE.COM/WATCH?V=GWPNJANZVJI
• HTTP://WWW.PRN.USM.MY/OLD_WEBSITE/MAINSITE/HEADLINE/POISON/OCT99.HTML
• HTTP://WWW.WORLD-NUCLEAR.ORG/INFO/SAFETY-AND-SECURITY/SAFETY-OF-PLANTS/TOKAIMURA-
CRITICALITY-ACCIDENT/
• HTTP://WWW.ENERGYADVOCATE.COM/TOKAI.HTM
REFERENCES
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