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

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? Series of events in Reactor 4 resulting in: Catastrophic “Steam Explosion” Nuclear meltdown Graphite fire

Series of Events - April 25 th pm: 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 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 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 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

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

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 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 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 Worst Accident in history of commercial Nuclear power in AmericaWorst Accident in history of commercial Nuclear power in America Accident unfolded over 5 daysAccident unfolded over 5 days World’s worst civilian disaster until Chernobyl 7 years laterWorld’s worst civilian disaster until Chernobyl 7 years later No injuries or deathsNo injuries or deaths

Where is Three Mile Island Plant? United States of AmericaUnited States of America Dauphin County,Dauphin County,Pennsylvania Three miles downThree miles down river from near by town, Harrisburg (Hence the name)

Power Plant 2 Pressurised Water Reactors: TMI-1 and TMI-22 Pressurised Water Reactors: TMI-1 and TMI-2 TMI-1 : 850 MWe capacityTMI-1 : 850 MWe capacity Individual containmentIndividual containment buildings per reactor Reactors connected byReactors connected by cooling towers

What Happened? A series of malfunctions resulting in:A series of malfunctions resulting in: Rupturing of quench tank relief diaphragmRupturing of quench tank relief diaphragm Small explosion in containmentSmall explosion in containmentbuilding Melting of half of the coreMelting of half of the core

Series of malfunctions March 27 th 1979 Plants main feed water pumps failPlants main feed water pumps fail Turbine and reactor shut downTurbine and reactor shut down Extra heat causes rise in steam production and increase in pressureExtra heat causes rise in steam production and increase in pressure Pilot operated pressuriser relief valve was opened and jammed – cooling water escapedPilot operated pressuriser relief valve was opened and jammed – cooling water escaped Pressuriser indicator gave false reading and water was cut off from reactorPressuriser indicator gave false reading and water was cut off from reactor Reactor core became uncovered causing reaction between fuel rods and steam – producing explosionReactor core became uncovered causing reaction between fuel rods and steam – producing explosion

Immediate Aftermath 7am: Site area emergency was declared7am: Site area emergency was declared 7:24am: Upgraded to “general emergency”7:24am: Upgraded to “general emergency” 8pm: primary loop pumps turned back on and reactor core found to have melted8pm: primary loop pumps turned back on and reactor core found to have melted Steam and Hydrogen removed using recombinerSteam and Hydrogen removed using recombiner Controversial vent used to expel radioactive hydrogen and steam straight into atmosphereControversial vent used to expel radioactive hydrogen and steam straight into atmosphere 13 million curies of radioactive noble gases released13 million curies of radioactive noble gases released

Clean up Started in 1979 and officially ended in 1993Started in 1979 and officially ended in 1993 Cost: $975 millionCost: $975 million Removal of 100 tonnes of radioactive fuel between 1985 and 1990Removal of 100 tonnes of radioactive fuel between 1985 and 1990

Ecological and Human Effects Possible link between lung cancer and offsite exposures, but not conclusivePossible link between lung cancer and offsite exposures, but not conclusive No member of public was injured by the accidentNo member of public was injured by the accident Average radiation dose to people within 10km radius: 8 millirem; equal to single X-rayAverage 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 radiationRadiation dose no more than 100 millirem; equal to 1/3 background radiation

Decommissioning Reactor gradually dismantled and mothballed by 1993Reactor gradually dismantled and mothballed by 1993 De-fuelling completed in 1988De-fuelling completed in 1988 Damaged reactor safely removed and disposed in 1993Damaged reactor safely removed and disposed in 1993 Unit 1 permitted to resume operations in 1985 following licence suspensionUnit 1 permitted to resume operations in 1985 following licence suspension Unit 2 maintained and monitored since by various companies: currently Exelon nuclearUnit 2 maintained and monitored since by various companies: currently Exelon nuclear

Long Term Aftermath Public approval of nuclear power in the U.S fell from 70% to 50%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 industryOnly 53 of 123 newly approved plants were ever completed: demise in nuclear industry Federal requirements became more stringentFederal requirements became more stringent Local opposition became more stringentLocal opposition became more stringent Construction time severely lengthenedConstruction time severely lengthened