Ecological and Toxicological Aspects of the Partial Meltdown of the Chernobyl Nuclear Power Plant Re

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Ecological and Toxicological Aspects of the
Partial Meltdown of the Chernobyl Nuclear Power
Plant Reactor

• Presented by Clair Morris

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Outline

• Background of the accident
• Release, dispersion and deposition of
  radionuclides
• Dose estimates
• Local effects
• Non-local effects
• Conclusion

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Radiation Units

• Bq Becquerel
• measure of Activity
• Gy Gray
• measure of Absorbed Dose
• Sv Sievert
• measure of Dose Equivalent

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Chernobyl Nuclear Power Plant

• 80 miles North of Kiev in Ukraine
• 4 nuclear reactors, 2 more under construction at
  time of accident

• Pripyat (pop. 49,000) 1½ miles from reactor
• Total population 125,000 within 30km radius of
  reactor

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Reasons for the Reactor Meltdown

• Mismanaged electrical-engineering experiment
• Human error
• Operators overrode built-in safety mechanisms
• Ignored plant safety rules
• Poor reactor safety design

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The Accident 123am April 26th 1986

• Reaction accelerated out of control
• Reactor exploded - unit 4
• Plume of smoke, radioactive fission products,
  debris from core building sent up to 1 mile
  high
• Heavy debris deposited close to site
• Lighter components (fission products noble
  gases) blown to NW of site

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Fires at reactor

• Conventional fire
• Extinguished within 4 hours
• More than 100 firefighters
• Graphite fire
• Extinguished after 10 days
• Uncertainty about firefighting measures
• May have led to high releases of radionuclides
  after 1 week

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Release of Reactor Core Products

• Noble gases 100 released
• 131I 50-60 released (1760 PBq)
• 134Cs 20-40 released (54 PBq)
• 137Cs 20-40 released (85 PBq)
• 132Te 25-60 release (1150 PBq)
• Other elements in reactor core released to lesser
  extent

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Dispersion Deposition of Radionuclides

• Largest particles (fuel particles) deposited by
  sedimentation within 60 miles of reactor
• Smaller particles carried by wind large distances
  deposited primarily by rainfall

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Release Rate of Radionuclides Following the
Accident
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137Cs Deposition Ukraine, Belarus Russia
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European Plumes of Contamination
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Local Response to Exposure

• Town of Pripyat evacuated April 27th
• All people within 30km of reactor (135,000) were
  later evacuated
• Exposure prevention in surrounding areas began
• Wetting areas to reduce dust
• Cleaning and washing streets, buildings
• Efforts mostly unsuccessful

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Relative Contribution From Individual
Radionuclides to Absorbed Dose Rate Following the
Accident
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Dose Estimates - Liquidators

• Liquidators
• Power plant staff people who participated in
  clean-up operations
• Up to 800,000 people
• Workers in plant April 26th 400 people
• All dosimeters worn over-exposed
• Whole-body doses between 1 16 Gy
• Thyroid dose up to 20 Sv

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Dose Estimates Liquidators

• Cleanup operations
• 1986 170 mSv
• 1987 130 mSv
• 1988 30 mSv
• 1989 15 mSv
• Small group working inside plant
• Whole body doses 0.5 to 13 Gy

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Dose Estimates - Evacuees

• Evacuees
• Nearby residents evacuated from 30km zone
• Exposed to internal irradiation from 131I and
  other radionuclides
• Thyroid doses
• 1 Sv small children
• 70 Sv adults
• Whole body doses average 15 mSv

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Dose Estimates former SU

• People who lived in the contaminated areas of the
  former Soviet Union
• Consumption of cows milk with 131I
• Internal exposure
• Thyroid doses up to 40 Sv
• Activity of 137Cs deposited on ground
• External exposure
• Doses 5 to 250 mSv
• Dependent of food control

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Dose Estimates - Europe

• Variable based on deposition
• Exposures higher if rainfall occurred during
  passage of radioactive cloud
• Annual Dose Estimates
• Southeastern Europe 1.2 mSv
• Northern Europe 0.97 mSv
• Central Europe 0.93 mSv
• (Former Soviet Union 0.81 mSv)

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Local Effects - Human

• Acute Effects
• 31 people died within 3 months
• Acute radiation doses gt 4 Gy
• 137 treated for acute radiation sickness

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131I Milk

• 131I more hazardous radionuclide
• Easily transferred pasture ? animal ? milk
  pathway
• Rapidly concentrates in thyroid gland
• High specific activity
• 131I half-life
• 3.9 days pasture grass
• 5 days cows milk

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Local Effects - Human

• Chronic Effects
• Psychological effects
• Increase in thyroid cancers
• More prevalent in children aged 0 to 5 at time of
  accident in high 131I contaminated areas

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Local Effects - Trees

• 1 stand of pine forest (400 ha) died
• Dose 80100 Gy
• Other stands with 3-4 Gy dose
• 95 necrotization of young shoots
• Leafy trees undamaged
• More radioresistant than pines

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Local Effects - Animals

• Fish
• High levels of 134Cs 137Cs in young fish
• Game animals
• Moved into area because of evacuation
• Rodents
• High deaths in areas of high contamination
• Populations recovered 1 year later

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Non-local Effects

• Plants
• Wildlife
• Domestic animals
• Aquatic life

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Plant Uptake of Radiation

• Plant uptake of radiation dependent on
• Exposed surface area
• Developmental season of the plant
• External morphology
• Type of radionuclide affects uptake
• Chemical similarity to essential nutrient
• Example Cs and K

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Non-local Effects - Plants

• Mosses and lichens
• Some areas of central Norway - concentrations gt
  100,000 Bq/kg in lichens
• Alpine trees, lichens, lake sediments
• Agricultural crops had high 137Cs activity
• Some harvests rejected

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Key Species - Reindeer

• Key species in transfer of radioactivity from
  environment to humans
• High transfer from feed to muscle
• High percentage of diet is lichen
• Diet not significantly supplemented with food low
  in radioactivity

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Reindeer Exposure

• Annual estimated dose estimate (Norwegian
  reindeer) 500 mSv
• 1986 1987 75 Swedish reindeer meat unfit for
  human consumption (gt300 Bq/kg)
• 1987 increased permissible level
• 1987 1999 25 still exceeded limit (gt1500
  Bq/kg)

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Non-local Effects Reindeer

• Calf survival
• Decreased 25 in 2 Norwegian herds with high
  contamination
• Chromosomal aberrations
• Female reindeer showed aberrations positively
  correlated with 137Cs flesh
• Calf aberrations decreased over time showing
  dose-dependent induction

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Non-local Effects Other Wildlife

• Mutagenicity in mice (Sweden) increased
• Increased tissue concentrations of radionuclides
  found in
• Caribou Quebec
• Moose - Sweden

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Biomagnification

• Little or no food chain biomagnification measured
• Wolverine, lynx arctic fox (Norway)
• Radioactivity
• Highest in muscle
• Lowest in fat
• Lower levels of radioactivity in top-level
  carnivores than at lower trophic levels

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Transfer Coefficient of Radionuclides

• Transfer Coefficient proportion of
  radioactivity transferred from diet to muscle
• Radiocesium transfer coefficient
• 2.5 adult cattle
• 16 calves

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Non-local Effects Domestic Animals

• Radiocesium isotopes transferred easily to farm
  grazing animals
• Radiocesium ingested concentrated in muscle
• Radiocesium activity in milk increased
• Transfer coefficients vary by species
• Cattle 2.5
• Sheep 24

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Non-local Effects - Sheep

• Sheep absorbed high 137Cs from food
• 4.25 million sheep in UK initially restricted for
  movement and slaughter
• 438,000 by January 1994
• Decreases in 137Cs activity dependent on food
  source (in study after 115 days)
• Contaminated pasture 13 of initial
• Uncontaminated pasture 3.5 of initial

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Non-local Effects Aquatic Life

• Consumption fishing declined
• Radiocesium concentrations in fish muscle
• Increased 3-5 times in southern Baltic Sea
• Increased 5 times in Danube river
• Bioconcentration in some species

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Chernobyl Now?

• Sarcophagus erected over reactor, completed
  November 1986

• Ukraine reluctantly shut down Chernobyl power
  plant in December 2000, over 14 years after the
  accident

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Conclusion

• Accident at Chernobyl was preventable
• Large amounts of radionuclides were released
• Contamination found across Northern Hemisphere
• Long-term effects of the accident are still being
  evaluated

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References

• Book chapter 24 Hoffman et. al. 1995. Handbook
  of Ecotoxicology. Lewis Press, Boca Raton, FL.
• NEA Committee on Radiation Protection and Public
  Health, Nov. 1995. Chernobyl 10 years on
  Radiological and Health Impact.
  http//www.nea.fr/html/rp/chernobyl/c01.html
• NEA Committee on Radiation Protection and Public
  Health, April 2001. Chernobyl 15 years on. USA
  Health Physics Soc. Newsletter.
• Meyers, Robert A. (Ed.), (1999) The Wiley
  Encyclopedia of Environmental Pollution and
  Cleanup. Vol.s 1 2. J. Wiley Sons, New York,
  NY.
• Liu, David and Bela Liptak (Eds.), (1997)
  Environmental Engineers Handbook (2nd Edn.) Lewis
  Publ., Boca Raton, FL.

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Questions

• Why is it that young cattle absorb ( retain in
  their tissue) a higher proportion of ingested
  radiocesium than adult cattle?
• Why were the exposures to radioiodine mostly
  short-term compared to the exposures from
  radiocesium?

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