Estimating Uncertainty in Actinide Intake Due to Unknown Time of Exposure

Bioassay of radiation workers handling actinides in powder form is carried out annually under routine monitoring program. In case of routine monitoring, as the day of intake is unknown, it is assumed that intake has occurred at the midpoint of monitoring interval. However, an uncertainty is introduced in intake estimation due to this assumption. In the present work, uncertainties were evaluated due to unknown time of intake of Type M and S compounds of Pu and U for annual and biennial monitoring interval. Lung and excreta monitoring methods were considered for uncertainty estimation along with the spread of ±1 month or ±2 months in measurements, at the end of monitoring interval. Annual lung monitoring is found to be the most robust and accurate method for assessment of intake of Type S compounds of Pu, Am and U when time of intake is unknown and Pu is detected using 241Am as a tracer. For Type M compounds, uncertainty was found to be higher than 3 for biennial monitoring interval. Uncertainty is found to be less than 3 for Type S compounds of Pu and U and also for Type M compounds of Pu for both, annual and biennial monitoring intervals using urine analysis. It is higher than 3 for Type M compounds of U for both the monitoring intervals. It is greater than 3 for both Type M and S compounds of Pu and U for both the monitoring intervals using fecal analysis. •Uncertainties due to unknown time of intake of Type M and S compounds of Pu and U are evaluated.•For lung measurements, uncertainty is found to be less than 3 for Type S but greater than 3 for Type M compounds.•For urine bioassay of Type M and S compounds of Pu and Type S compounds of U, uncertainty is found to be less than 3.•For fecal bioassay, uncertainty is found to be greater than 3 for both Type M and S compounds of Pu and U.