ESTABLISHING BOUNDING INTERNAL DOSE ESTIMATES FOR THORIUM ACTIVITIES AT ROCKY FLATS
As part of an evaluation of a Special Exposure Cohort petition filed on behalf of workers at the Rocky Flats Plant, the National Institute for Occupational Safety and Health (NIOSH) was required to demonstrate that bounding values could be established for radiation doses due to the potential intake of all radionuclides present at the facility. The main radioactive elements of interest at Rocky Flats were plutonium and uranium, but much smaller quantities of several other elements, including thorium, were occasionally handled at the site. Bounding potential doses from thorium has proven challenging at other sites due to the early historical difficulty in detecting this element through urinalysis methods and the relatively high internal dose delivered per unit intake. This paper reports the results of NIOSH’s investigation of the uses of thorium at Rocky Flats and provides bounding dose reconstructions for these operations. During this investigation, NIOSH reviewed unclassified reports, unclassified extracts of classified materials, material balance and inventory ledgers, monthly progress reports from various groups, and health physics field logbooks, and conducted interviews with former Rocky Flats workers. Thorium operations included: (1) an experimental metal forming project with 240 kg of thorium in 1960; (2) the use of pre-formed parts in weapons mockups; (3) the removal of 228Th from 233U; (4) numerous analytical procedures involving trace quantities of thorium; and (5) the possible experimental use of thorium as a mold coating compound. The thorium handling operations at Rocky Flats were limited in scope, well-monitored and documented, and potential doses can be bounded.
Role of membrane sialic acid and glycophorin protein in thorium induced aggregation and hemolysis of human erythrocytes.
Thorium-232 ((232)Th), a natural radionuclide from the actinide family, is abundantly present in monazite and other ores. It is used as one of the prime fuel materials in nuclear industry and may pose an exposure risk to nuclear workers and members of the public. Human erythrocytes, as a classical cellular membrane model, were coincubated with (232)Th in order to elucidate whether this naturally occurring important radionuclide produced perturbations to cell membrane. Present study revealed that erythrocytes underwent aggregation or lysis depending on the ratio of (232)Th to cell. Scanning electron micrographs showed that erythrocytes transformed into equinocytes and/or spherocytes after (232)Th treatment. Further examination of erythrocyte by atomic force microscopy suggested significant increase in surface roughness after (232)Th treatment. Experiments on neuraminidase treated and/or anti-GpA antibody blocked erythrocytes suggested significant role of membrane sialic acid and glycophorin A (GpA) protein in aggregation or hemolytic effects of (232)Th. Further results showed that (232)Th caused hemolysis by colloid osmotic mechanism, as evidenced by potassium efflux, osmotic protection and osmotic fragility studies. Osmoprotection experiments indicated that hemolysis get elicited through the formation of membrane pores of approximately 2.0 nm in size. Hemolysis studies in presence of inhibitors (TEA, bumetanide, DIDS and amiloride) revealed the role of K(+) channel, Na(+)/K(+)/2Cl(-) channel, Cl(-)/HCO(3)(-) anion exchanger and Na(+)/H(+) antiporter in (232)Th induced erythrolysis. Presence of non-diffusible cation (N-methyl d-glucasamine) or anion (gluconate) in erythrocyte suspending medium further confirm the role of Na(+) and Cl(-) influx in hemolytic effect of (232)Th. These findings provide significant insight in structural, biochemical and osmotic toxic effects of (232)Th on human erythrocytes.
Thermally Induced Dynamics of Satellite Solar Panels
Thermally induced structural motions are known to affect the attitude dynamics of low Earth orbiting satellites during eclipse transitions. Motions of e exible appendages such as solar panels lead to rigid body rotations of the entire satellite because the total angular momentum of the system is conserved. These potentially large attitude disturbances may violate pointing accuracy and jitter requirements. One type of thermally induced dynamics exhibited by solar panels is thermal snap. The Upper Atmosphere Research Satellite is a prominent example of a satellite that experiences thermal snap disturbances during eclipse transitions. This paper describes recent studies of thermally induced dynamicsof solarpanels, including an analysisofsatelliteattitudedynamics resulting from thermally induced structural motions and a laboratory investigation of the thermal-structural performance of a satellite solar panel. Analytical and experimental results demonstrate thermal bending deformations with acceleration transients that have characteristic thermal snap disturbance histories in response to rapid changes in heating. The studies show that solar panel thermal snap disturbances are caused by through-the-thickness temperature differences that vary at a nonconstant rate. Finite element analysis correctly predicts the thermal snap phenomenon observed in the solar panel experiments.