Chernobyl source term, atmospheric dispersion, and dose estimation

Area of Science:

• Nuclear Safety and Environmental Science
• Atmospheric Dispersion Modeling
• Radiological Assessment

Background:

• The Chernobyl accident released a substantial source term into the atmosphere, necessitating detailed analysis for long-range transport.
• Previous reactor accident source terms (Windscale, TMI) were orders of magnitude smaller than Chernobyl's.
• Comparison with radionuclide releases from atmospheric nuclear weapon tests is crucial for context.

Purpose of the Study:

• To estimate the Chernobyl source term available for long-range atmospheric transport.
• To model the dispersion of radionuclides across the Northern Hemisphere.
• To assess inhalation doses from direct cloud exposure.

Main Methods:

• Integration of radiological measurements with atmospheric dispersion modeling.
• Estimation of radionuclide inventory in the Chernobyl reactor core.
• Application of WASH-1400 release fractions for specific chemical groups.

Main Results:

• Release estimates: nearly all noble gases, 60% radioiodines, 40% radiocesium, 10% tellurium, <1% refractory elements.
• Dispersion modeling showed cloud segmentation, with transport towards Scandinavia, Asia, Japan, North Pacific, and North America.
• Estimated inhalation doses: >10 mGy near Chernobyl, 0.001-0.1 mGy in Europe, <0.00001 mGy in the US.

Conclusions:

• The Chernobyl source term was significantly larger than previous reactor accidents but smaller than atmospheric nuclear weapon tests for key isotopes like Cesium-137, Iodine-131, and Strontium-90.
• Atmospheric dispersion modeling effectively predicted the global transport pathways of Chernobyl radionuclides.
• Inhalation dose assessments highlight the localized high-risk zone near Chernobyl and reduced risks in North America and most of Europe.