US Transuranium and Uranium Registries case study on accidental exposure to uranium hexafluoride

Area of Science:

• Radiological Science
• Occupational Health
• Toxicology

Background:

• A whole-body donor (Case 1031) with a history of acute uranium hexafluoride (UF6) inhalation exposure 65 years prior to death was studied.
• United States Transuranium and Uranium Registries (USTUR) autopsy tissue samples revealed long-term uranium retention in lungs and lymph nodes.

Observation:

• Tissue measurements were combined with historical bioassay data for analysis.
• International Commission on Radiological Protection (ICRP) respiratory tract and systemic models for uranium were employed.
• Maximum likelihood and Bayesian statistical methods were utilized to estimate intakes and model parameters.

Findings:

• Maximum likelihood analysis estimated an occupational intake of 79 mg uranium, comprising 86% soluble (Type F) and 14% insoluble (Type S) material.
• Bayesian analysis, using a revised respiratory tract model, estimated a mean intake of 160 mg uranium and provided case-specific lung dissolution parameters.
• Derived dissolution parameters indicated predominantly soluble uranium with a significant insoluble component, yielding effective dose estimates 2-7 times higher than current ICRP coefficients.

Implications:

• The study highlights the potential underestimation of effective dose from insoluble uranium components in UF6 mixtures.
• Case-specific dissolution parameters derived from Bayesian analysis may offer more accurate dose assessments for radiation protection.
• Findings emphasize the need to refine ICRP models for exposures involving mixed-solubility uranium compounds.