Uncertainty of the tritium dose conversion factor.

Environmental releases of tritium oxide at a number of Department of Energy nuclear weapons facilities contribute to a significant portion of environmental dose. Several conversion factors are utilized in the estimation of human impact from these releases, e.g., dispersion coefficients, consumption rates, uptake factors, transport factors, dose conversion factors, and risk coefficients. A probabilistic determination of the tritium dose conversion factor was generated in this work to assess the uncertainty of the internal dosimetry required to estimate dose equivalent given an intake of tritium oxide. The tritium dose conversion factor was found to vary by a factor of about 15 with a median value of 2.2 x 10(-11) Sv Bq(-1) when considering orthovoltage x rays as the standard for estimating the relative biological effectiveness of tritium. The median dose conversion factor increases by about 50%; however, when gamma radiation is considered as the standard. The current deterministic estimate of the tritium dose conversion factor published by the DOE and the EPA is 1.7 x 10(-11) Sv Bq(-1), 25-50% lower than the median probabilistic values. The tritium oxide dose conversion factor model was found to be most sensitive to biological half-life and quality factor and is highly dependent on the standardizing radiation for RBE assessments.