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Nuclear Reactor Disasters

Nuclear Reactor Disasters

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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