Nuclear Reactor Disasters

1
Nuclear Reactor Disasters

• Chernobyl
• 1986
• Three Mile Island
• 1979
• Andrew Cornwall

2
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
• Affected Western Soviet Union, Eastern, Central
  and Northern Europe, and Eastern and Northern
  America
• 336,000 people evacuated and resettled elsewhere

3
Where is the Chernobyl Plant?

• Ukraine
• 18km northwest of Chernobyl town
• 110km north of Kiev

4
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 Ukraines electricity at time of
  accident
• 2 additional reactors under construction at time
  of accident

5
What Happened?

• Series of events in Reactor 4 resulting in
• Catastrophic Steam Explosion
• Nuclear meltdown
• Graphite fire

6
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)
• 123am 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 put100 times normal
• Fuel pellets explode roof blown off air sucked
  in causing fire

7
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

8
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

9
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

10
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

11
Causes?

• 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

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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

13
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

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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

15
Three Mile Island

• Worst Accident in history of commercial Nuclear
  power in America
• Accident unfolded over 5 days
• Worlds worst civilian disaster until Chernobyl 7
  years later
• No injuries or deaths

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Where is Three Mile Island Plant?

• United States of America
• Dauphin County,
• Pennsylvania
• Three miles down
• river from near
• by town, Harrisburg
• (Hence the name)

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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

18
What Happened?

• A series of malfunctions resulting in
• Rupturing of quench tank relief diaphragm
• Small explosion in containment
• building
• Melting of half of the core

19
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

20
Immediate Aftermath

• 7am Site area emergency was declared
• 724am 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

21
Clean up

• Started in 1979 and officially ended in 1993
• Cost 975 million
• Removal of 100 tonnes of radioactive fuel between
  1985 and 1990

22
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

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Decommissioning

• 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

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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

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