Determination of particle size for airborne UO2 dust at a fuel fabrication work station and its implication on the derivation and use of ICRP Publication 30 derived air concentration values.

Abstract

When internal radiation exposure occurs via the inhalation route, the activity deposition in the respiratory tract is dependent on the particle size distribution of the radioactive aerosol. This fact has been recognized by ICRP Publication 30 in which annual limit of intake (ALI) and derived air concentration (DAC) values have been calculated for a variety of radionuclides based upon an activity median aerodynamic diameter (AMAD) of 1 micron. When radioactive aerosols have AMADs not equal to 1 micron, ICRP Publication 30 suggests the use of correction factors to calculate the appropriate ALI and DAC values. This work describes the measurement of particle size distribution for UO2 dust at a fuel fabrication work station by means of a cascade impactor. Measurements were made on 39 d spread over a 10-mo period to determine if the particle size distribution was stable over a year. The results of this study indicate that for this work station the measured AMAD values are not stable over a year. A discussion is provided on the treatment of such particle-size distribution data with the objective of extracting a representative particle-size distribution value, upon which an ALI and a DAC value can be determined. The observations made in this study have implications on the application of ICRP Publication 30 recommendations to operational health physics practice.