PLUTONIUM-BEARING PARTICLES FROM FUEL REPROCESSING 109 



retention patterns from accidental exposures at Rocky Flats support the premise that 

 aerosols there are primarily pure compounds of plutonium. 



Ettinger, Moss, and Johnson (1971 ) developed a technique in 1971 to measure ^^^Pu 

 particles, which was a modification of the one used earlier by Moss, Hyatt, and Schulte 

 (1961), in which the particles were embedded in the emulsion. The samples were 

 collected from several ^^^Pu02 glove-box areas at Los Alamos Scientific Laboratory by 

 two-stage (cyclone-filter) air samplers and on gross filter samplers using Millipore filters. 

 Their modified technique permitted multiple exposures of aerosols to additional nuclear 

 track plates. Additional plates were placed against the plate containing the embedded 

 aerosols for shorter periods of time and thus increased the range of sensitivity by 

 providing both long and short exposures to the same particles. Ettinger felt that the alpha 

 tracks in the emulsion being symmetrical suggested that the plutonium was not attached 

 to inert aerosols. 



Hayden (1976), at Rocky Flats, was the first to combine alpha-particle and 

 fission-fragment tracks to isolate '^^^Pu-bearing particles from other fissile material in 

 1974. The sample was placed in intimate contact with a 10-jum -thick polycarbonate film. 

 A cellulose nitrate film was then placed on the polycarbonate film. The package was 

 allowed to set for a predetermined exposure time. The cellulose nitrate was removed, and 

 the remaining package was irradiated in a reactor for a desired neutron fluence. Both 

 films were then etched and examined for tracks. The fission-fragment tracks appeared in 

 the polycarbonate film and the alpha-particle tracks in the cellulose nitrate film. The 

 presence of fission-fragment and alpha-particle tracks indicated that the particle 

 contained ^^^Pu. The presence of fission-fragment tracks alone indicated that the particle 

 contained uranium. The Murri (Hayden, Murri, and Baker, 1972) equation was used to 

 calculate particle size from the fission-fragment track count, and the Leary (Leary, 1951) 

 equation was used to calculate particle size from the alpha-particle track count. However, 

 the sample could not be mounted with precise positioning of reference symbols so that a 

 specific particle could be evaluated. Thus the actual size of the particle or the presence or 

 composition of inert material could not be determined. 



Only two previous studies of plant effluents have been made, neither of which has 

 used autoradiographic techniques. The first was of effluent aerosols downstream from 

 high efficiency particulate air (HEPA) filters undertaken by Mishima and Schwendiman 

 (1972) in 1971 at the plutonium finishing plant at the Hanford site. Filter and cascade 

 impactor samples were taken of the stack gases and various exhaust systems of the plant 

 to determine the aerodynamic characteristics and distribution of plutonium-bearing 

 particles with their associated radioactivity. They found that the overall efficiency of the 

 exhaust system was high, that little, if any, of the alpha radioactivity leaving the stack 

 was being recycled back into the ventilation system, and that the plutonium present 

 appeared to be attached to large, nonradioactive particles. 



Systematic measurements and analyses of plutonium-bearing parficles in off-gas were 

 also made by Elder, Gonzales, and Ettinger (1974) and Seefeldt, Mecham, and Steindler 

 (1976) at Los Alamos Scientific Laboratory in 1972. They collected samples from five 

 operations — two research and development, two fabrication, and one recovery — where 

 isotopes of plutonium were handled at Rocky Flats, Mound Laboratory, and Los Alamos 

 Scientific Laboratory. The sampling stations were upstream from the HEPA filters, where 

 aerosol concentrations were adequately high. Particle size characteristics were determined 

 by radiometric analyses of the material deposited on each of the eight stages of Andersen 

 impactors and material deposited on a backup membrane filter that collected particles 



