AEROSOL SIZE DISTRIBUTION IN URANIUM PROCESSING FACILITY FOR APPLICATION IN THE ASSESSMENT OF INTERNAL EXPOSURE.

In circumstances of inhalation exposure the radiotoxicity of radionuclide depends on the fractional deposition of inhaled activity, which is governed by the aerodynamic characteristics of the particles. Although International Commission on Radiological Protection (ICRP) provides default size distribution parameters for work place aerosols, inhaled aerosol characteristics may be different depending on the physical and chemical conditions of aerosol generation process. The present study is undertaken to determine the particle activity-size distribution during operation of various significant processes of uranium metal production facility of Bhabha Atomic Research Centre (BARC). Activity median aerodynamic diameter (AMAD) and its geometric standard deviation (GSD) were estimated for these process areas for uranium aerosol particles. The AMAD varied from 3.2 to 10.06 µm and GSD ranged from 1.5 to 3.0. Also, the obtained size distribution was tested by Pearson's chi-squared distribution test method to ascertain the assumption that the particle size distribution is best described by log-normal relationship.

Preliminary radiological safety assessment for decommissioning of thoria dissolver of the ²³³U pilot plant, Trombay.

The thoria dissolver, used for separation of (233)U from reactor-irradiated thorium metal and thorium oxide rods, is no longer operational. It was decided to carry out assessment of the radiological status of the dissolver cell for planning of the future decommissioning/dismantling operations. The dissolver interiors are expected to be contaminated with the dissolution remains of irradiated thorium oxide rods in addition to some of the partially dissolved thoria pellets. Hence, (220)Rn, a daughter product of (228)Th is of major radiological concern. Airborne activity of thoron daughters (212)Pb (Th-B) and (212)Bi (Th-C) was estimated by air sampling followed by high-resolution gamma spectrometry of filter papers. By measuring the full-energy peaks counts in the energy windows of (212)Pb, (212)Bi and (208)Tl, concentrations of thoron progeny in the sampled air were estimated by applying the respective intrinsic peak efficiency factors and suitable correction factors for the equilibration effects of (212)Pb and (212)Bi in the filter paper during the delay between sampling and counting. Then the thoron working level (TWL) was evaluated using the International Commission on Radiological Protection (ICRP) methodology. Finally, the potential effective dose to the workers, due to inhalation of thoron and its progeny during dismantling operations was assessed by using dose conversion factors recommended by ICRP. Analysis of filter papers showed a maximum airborne thoron progeny concentration of 30 TWLs inside the dissolver.