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Nuclear Reactor Disasters. Chernobyl 1986 Three Mile Island 1979 Andrew Cornwall. Chernobyl. Worst accident ever in the history of Nuclear power Released more than 100 times the radiation produced by the atom bombs of Hiroshima and Nagasaki

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nuclear reactor disasters

Nuclear Reactor Disasters



Three Mile Island


Andrew Cornwall

  • Worst accident ever in the history of Nuclear power
  • Released more than 100 times the radiation produced by the atom bombs of Hiroshima and Nagasaki
  • Affected Western Soviet Union, Eastern, Central and Northern Europe, and Eastern and Northern America
  • 336,000 people evacuated and resettled elsewhere
where is the chernobyl plant
Where is the Chernobyl Plant?
  • Ukraine
  • 18km northwest of Chernobyl town
  • 110km north of Kiev
power plant
Power Plant
  • 4 reactors of type – RBMK-1: now obsolete class of graphite moderated nuclear reactor
  • Reactor capacity – 1Gigawatt (total plant capacity: 4 Gigawatt)
  • Provided 10% of Ukraine’s electricity at time of accident
  • 2 additional reactors under construction at time of accident
what happened
What Happened?

Series of events in Reactor 4 resulting in:

  • Catastrophic “Steam Explosion”
  • Nuclear meltdown
  • Graphite fire
series of events april 25 th 1986
Series of Events - April 25th 1986
  • 11pm: Control rods were lowered to reduce reactor output for planned turbine test) BUT too quickly - almost complete shut down
  • 1am: control rods raised to increase reactor activity for the test (12%)
  • 1:23am: Reactor overheats; water coolant turns to steam
  • 6 control rods left; minimum safe number = 30
  • Emergency shut down button pressed
  • Control rods re-inserted BUT fault causes power surge in reactor; Out put:100 times normal
  • Fuel pellets explode; roof blown off; air sucked in causing fire
immediate aftermath
Immediate Aftermath
  • Area evacuated, but quite slowly - “exclusion zone”
  • Tragedy made worse by poor preparation, equipment and assessments
  • Radiation estimated at 20,000 Rontgen/hr (lethal dose = 100 R/hr)
  • True radiation unknown
  • Fire burned until helicopters

extinguished it by dropping

water, sand, lead and boron

  • Radioactive cloud observed
clean up
  • Liquidators sent in to open sluice gates to vent reactor water
  • Worst radioactive debris collected in remains of reactor core
  • Covered with bags of sand,

lead and boric acid

(5000 tonnes in first

week after explosion)

  • Giant concrete sarcophagus

erected to seal off reactor

and its contents

ecological effects
Ecological Effects
  • Radioactive cloud floated in easterly direction
  • Radiation travelled as far as Sweden (1100km)
  • Initial Soviet Union reports: 60% contamination in Belarus
  • River Pripyat and Dnieper river-reservoir system

contaminated (reduced after initial period)

  • Fresh water fish contaminated

to several times the safe

limits (reduced after

initial period)

  • Pine forest within 4km

radius turned

ginger brown

and died: Red Forest

  • “exclusion zone”

became wildlife haven

human effects
Human Effects
  • 336,000 people evacuated and resettled
  • 237 suffered

from acute

radiation sickness

  • 31 deaths within

3 months

  • 9,000 cancer deaths expected as direct

result of radiation exposure

  • 4,000 thyroid cancer

cases among children by 2002

  • 1986 IAEA Report: Plant Operators to blame
  • 1991 Valeri Legasov:

Reactor design flaws to blame

  • 1993 IAEA Report:

revoked original report and placed

blame with flawed reactor design

flawed reactor design
Flawed Reactor Design
  • High void coefficient: weaken convection currents
  • Graphite tipped control rods: increase activity for short period
  • Vertical water channels in core: temperature gradient in core
  • Partial containment measurements to save costs
  • Operational for 1 year – stored fission by products
  • Reactor vessel warped under intense heat, preventing insertion of control rods
long term aftermath
Long Term Aftermath
  • Construction of reactor 5 and 6 terminated
  • 200m of concrete built to isolate contaminated reactor from operational buildings
  • Reactors 1,2 and 3 continued to operate due to energy shortage in Ukraine
  • 1991: Fire in reactor 2 – damaged beyond repair and taken offline
  • 1996: IAEA recommended the termination of operations at plant – reactor 3 decommissioned
  • 2000: Reactor 3 and entire plant shut down
current situation
Current Situation
  • Sarcophagus not effective permanent containment method – strong wind could dislodge roof, and water leaks in through gaping holes
  • Rising humidity levels inside sarcophagus cause erosion of concrete and steel
  • Chernobyl Shelter Fund

started in 1997 for

Shelter Implementation Plan

  • Planned construction of

“New Safe Confinement” (NSC)

  • Large movable arch:

Span: 250m

Height: 100m

Length: 150m

  • Cost: $1.2 Billion
three mile island
Three Mile Island
  • Worst Accident in history of commercial Nuclear power in America
  • Accident unfolded over 5 days
  • World’s worst civilian disaster until Chernobyl 7 years later
  • No injuries or deaths
where is three mile island plant
Where is Three Mile Island Plant?
  • United States of America
  • Dauphin County,


  • Three miles down

river from near

by town, Harrisburg

(Hence the name)

power plant1
Power Plant
  • 2 Pressurised Water Reactors: TMI-1 and TMI-2
  • TMI-1 : 850 MWe capacity
  • Individual containment

buildings per reactor

  • Reactors connected by

cooling towers

what happened1
What Happened?
  • A series of malfunctions resulting in:
  • Rupturing of quench tank relief diaphragm
  • Small explosion in containment


  • Melting of half of the core
series of malfunctions march 27 th 1979
Series of malfunctions March 27th 1979
  • Plants main feed water pumps fail
  • Turbine and reactor shut down
  • Extra heat causes rise in steam production and increase in pressure
  • Pilot operated pressuriser relief valve was opened and jammed – cooling water escaped
  • Pressuriser indicator gave false reading and water was cut off from reactor
  • Reactor core became uncovered causing reaction between fuel rods and steam – producing explosion
immediate aftermath1
Immediate Aftermath
  • 7am: Site area emergency was declared
  • 7:24am: Upgraded to “general emergency”
  • 8pm: primary loop pumps turned back on and reactor core found to have melted
  • Steam and Hydrogen removed using recombiner
  • Controversial vent used to expel radioactive hydrogen and steam straight into atmosphere
  • 13 million curies of radioactive noble gases released
clean up1
Clean up
  • Started in 1979 and officially ended in 1993
  • Cost: $975 million
  • Removal of 100 tonnes of radioactive fuel between 1985 and 1990
ecological and human effects
Ecological and Human Effects
  • Possible link between lung cancer and offsite exposures, but not conclusive
  • No member of public was injured by the accident
  • Average radiation dose to people within 10km radius: 8 millirem; equal to single X-ray
  • Radiation dose no more than 100 millirem; equal to 1/3 background radiation
  • Reactor gradually dismantled and mothballed by 1993
  • De-fuelling completed in 1988
  • Damaged reactor safely removed and disposed in 1993
  • Unit 1 permitted to resume operations in 1985 following licence suspension
  • Unit 2 maintained and monitored since by various companies: currently Exelon nuclear
long term aftermath1
Long Term Aftermath
  • Public approval of nuclear power in the U.S fell from 70% to 50%
  • Only 53 of 123 newly approved plants were ever completed: demise in nuclear industry
  • Federal requirements became more stringent
  • Local opposition became more stringent
  • Construction time severely lengthened