CHARACTERIZATION OF PLUTONIUM AEROSOL COLLECTED DURING AN ACCIDENT

Abstract

This study determined the plutonium particle size distribution and dissolution rate of PuO2 aerosol collected during the 16 March 2000 release of an undetermined amount of PuO2 in a room within a plutonium facility at Los Alamos National Laboratory. The facility has been in operation since 1978 to support the development, fabrication, and testing of Pu heat sources for the U.S. Department of Energy. Several workers were in the room at the time of the release and in vivo study of five of the workers began the day after the exposure event. Four of the subjects subsequently received chelation therapy. Over 30 fixed air filter samplers (FASs) and four continuous air monitors (CAMs) were operating in the room during the radiological release. One 47-mm-diameter glass fiber FAS filter and one 25-cm-diameter mixed cellulose ester CAM filter containing Pu aerosol from the incident were examined in the study described here. Total alpha radioactivity on the filters was determined by gross alpha counting. Isotopic identification of the Pu was made by alpha spectrometry. Film autoradiography was used to characterize the spatial distribution of alpha-emitting particles on the filters. Track-etch autoradiography was used to estimate the distribution of alpha radioactivity in individual plutonium particles on the filters for particle size measurement. The glass fiber filter was then cut into six sections. Particles from two sections were resuspended in alcohol, dispersed as an aerosol using a Lovelace nebulizer, and characterized by aerodynamic diameter using a Lovelace Multi-jet cascade impactor. The measured activity median aerodynamic diameter from the cascade impactor was 4.8 mum with a geometric standard deviation of 1.5. That agreed with the size distribution obtained from the alpha track detection technique. The remaining four filter sections were used in an in vitro dissolution study with synthetic serum ultrafiltrate. The retention of undissolved Pu was consistent with a biphasic exponential function. The majority of the Pu dissolved with a half-time of 900 d. The information on particle size distribution and solubility from this study was useful in assigning a radiation dose to the exposed workers, supporting the decision to administer chelation therapy, and providing a model for characterizing accident-associated aerosols in the future.