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.
Decorporation and therapeutic efficacy of liposomal-DTPA against thorium-induced toxicity in the Wistar rat
Purpose: This study examined the effect of liposomal encapsulation of 99mTc-labeled diethylenetriaminepentaacetic acid (metastable technetium labeled DTPA) on its organ distribution and therapeutic effect of optimized neutral liposomal-DTPA against thorium (232Th)-induced liver toxicity and its accumulation in rat animal model. Materials and methods: 99mTc-DTPA was encapsulated in neutral (dipalmitoylphosphatidylcholine:cholesterol) and positively (dipalmitoylphosphatidylcholine:cholesterol:stearylamine) charged liposomes using thin film hydration method. Comparative efficacy of liposomal and free DTPA (11.2 mg/kg) was examined in terms of its effect on 232Th accumulation and subsequent toxicity in the liver and blood of rat administered with 232Th-nitrate (600 μg/kg). Organ distribution of free or liposomal 99mTc-DTPA was determined by solid scintillation counting and 232Th accumulation by Inductively Coupled Plasma-Atomic Emission Spectroscopy. Results: Neutral liposomes encapsulated with 99mTc-DTPA showed more uptake in liver, spleen and blood than with positively charged liposomal- and free- 99mTc-DTPA. Administration of 232Th-nitrate to rat significantly increased the levels of liver toxicity markers and of oxidative injury, which were found to be restored more significantly by neutral liposomal-DTPA than free-DTPA. The accumulation of 232Th in liver and blood of contaminated mice was found to be decreased more significantly by neutral liposomal-DTPA than by free-DTPA. Conclusions: Decorporation and consequent mitigation of 232Th induced toxicity may be significantly improved by liposomal encapsulation of DTPA, a chelating agent.
Thermodynamic Evaluation of Solar Integration into a Natural Gas Combined Cycle Power Plant
The term integrated solar combined-cycle (ISCC) has been used to define the combination of solar thermal energy into a natural gas combined-cycle (NGCC) power plant. Based on a detailed thermodynamic cycle model for a reference ISCC plant, the impact of solar addition is thoroughly evaluated for a wide range of input parameters such as solar thermal input and ambient temperature. It is shown that solar hybridization into an NGCC plant may give rise to a substantial benefit from a thermodynamic point of view. The work here also indicates that a significant solar contribution may be achieved in an ISCC plant, thus implying substantial fuel savings and environmental benefits.