MWDS-2016: THE SLOW DISSOLUTION RATE FOR PLUTONIUM NITRATE INTAKES AT THE MAYAK FACILITY

Area of Science:

• Radiological protection
• Inhalation toxicology
• Biokinetics of inhaled radionuclides

Background:

• The slow dissolution rate of lung-deposited material significantly impacts radiation dose.
• Discrepancies exist between measured slow dissolution rates for plutonium nitrate from volunteer/USTUR studies and Mayak worker autopsies.

Purpose of the Study:

• To investigate and resolve discrepancies in the slow dissolution rate of plutonium nitrate.
• To establish a reliable dissolution rate parameter for the Mayak Worker Dosimetry System (MWDS-2016).

Main Methods:

• Bayesian analysis applied to multiple datasets: Public Health England (PHE) volunteer data, Beagle dog data, United States Transuranium and Uranium Registries (USTUR) case 0269, and Mayak worker autopsy data.
• Testing competing hypotheses including slower interstitial dissolution, a third dissolution component, and aerosol composition (oxide vs. nitrate).

Main Results:

• Volunteer and USTUR data suggest slow dissolution rates of 10-40 × 10-4 d-1.
• Mayak worker data indicate slower rates of approximately 2.4 × 10-4 d-1.
• A mixture of plutonium oxide and nitrate, with ~14% oxide, best explains the Mayak worker dissolution rates.

Conclusions:

• The Mayak worker dissolution rate is best explained by a mixed oxide-nitrate material composition.
• This finding reconciles disparate dissolution rate values without conflicting with other study parameters.
• Accurate dosimetry for Mayak workers requires accounting for this mixed material composition.