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Nuclear Reactor Disasters

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

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  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 Ukraine’s 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%) • 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

  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 • “exclusion zone” became wildlife haven

  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

  12. 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

  14. 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 • World’s worst civilian disaster until Chernobyl 7 years later • No injuries or deaths

  16. 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)

  17. 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 • 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

  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

  23. 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

  24. 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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