Topic 4 - Sources of Radiation

Summary of Radiation in the Environment

Sources of Radiation in the Environment

• Natural
  • Radionuclides
  • Radiation Fields
• Anthropogenic
  • Production & Processing of Nuclear Fuels
  • Power Reactors
  • Nuclear Weapons
  • Miscellaneous Other Sources

Naturally Occuring Radionuclides

• Radioactive Substances
  • Phosphate Fertilizers
  • Building Materials
  • Fossil Fuels
  • Induced Radionuclides
• External Sources
• Technological Enhancements

Technological Enhancements

• Building materials
• Smoking
• Natural Gas
• Mining Phosphate Minerals
• Poor disposal of uranium (U) mine wastes
• Thorium (Th) Lantern Mantles

Production & Reprocessing
of Nuclear Fuels

• Uranium (²³⁵U)
  • Belgian Congo
  • Great Bear Lake, Canada
  • Czechoslovakia
  • Colorado Plateau
• Thorium (²³²Th -> ²³³U)
  • Monazite Sands, Brazil
  • India

Uranium

• Underground and open pits
  •  Small (2 person to large (100) person) operation
  • In situ leaching has been used
  • radon & gaseous products a problem for workers - not much for general public
• Uranium Mills
  •  Ore ground to sand
  •  Acid/alkaline leach
  • Concentrated by ion exchange / solvent extraction

Uranium

• U₃0₈ is produced
• 95% of U is removed from ore
• ~100% of decay products remain in tailings & slurries
• Wastes are discharged into holding ponds/areas
• Most mills in dry areas
• Ponds dry out & residues are potentially mobile
• 1960 - 25 mills in operation
• 1990 - 2 mills operating, 14 “operable”

Uranium Mills

• Hazards from sites
  • Tailings piles
  • Emanation of radon
  • Dispersion by wind & water
  • Use of tailings in building construction
    •  Grand Junction
    •  Salt Lake City
    •  Others

Uranium Refining

•  Mill concentrates are converted
  •  Metal
  •  UO₃ (orange oxide)
  •  UF₄ (green salt)
•  Hazards include
  •  potential exposure of employees
  •  discharge of U dust
  •  radium residues (dependent on feed stock)
•  WWII - 31 operating plants
  •  1974 FUSRAP initiated

Isotopic Enrichment

• UF₄ (green salt) from refineries converted to UF₆ (uranium hexafluoride) at
  •  Gaseous diffusion plants
  •  Portsmouth, Ohio
  •  Paducah, Kentucky
  •  Oak Ridge, Tennessee
• Gas pumped through stages of porous barriers; each stage enriches the ²³⁵U
• Gaseous diffusion obsolete

Fuel Element Manufacture

• Limited releases (high cost of material, accountability concerns) but possible
  •  uranium metal is pyrophoric
  •  gases are caustic/reactive

Power Reactors

• Light-Water Reactors
  • PWR
  • BWR
  

• High Temperature Gas-Cooled Reactors
  • U.K. - since 1950s
  • U.S. - Ft. St. Vrain, CO
• Fast Reactors
  • No moderator
  • Breeds Pu
  • Limited Coolant Selection (can’t moderate) - choice: liquid Na
• Breeder Reactors
  • None constructed in U.S. (Clinch River Halted)

Low-Level Reactor Discharges from LWRs

• Fission Products
  • Confined to Fuels
  • Exceptions are Volatile F.P. (Iodines, Noble Gases)
  • Small quantities in aqueous wastes
  

Low-Level Reactor Discharges from LWRs

• Activation Products
  • Corrosion Products (⁶⁰Co, ⁵⁹Fe, ⁵¹Cr, ⁵⁴Mn, ⁵⁵Fe)
  • In coolant & moderator
• Wastes include:
  • liquid
    • accumulated
    • stripped / scrubbed / ionexchanged
    • monitored
    • released
    • ³H major release

Low-Level Reactor Discharges from LWRs

• Wastes include
  • Gaseous
    • Methods vary
  • PWR - condensed - holdup tanks
    • ⁸⁵Kr remains, may be released
  • BWR - gases boil off with the steam, pass through turbine & enter condenser - some leaks
    • Catalytic recombination of O and H has limited exhaust Refrigerated charcoal beds used to remove iodines and noble gases ⁸⁵Kr remains, may be released

Accidental Discharges
from Reactors

• SL1
• TMI
• Chernobyl