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At least 1,351 records · Page 75Linked to original sources
PubMed2002

Simultaneous separation and detection of actinides in acidic solutions using an extractive scintillating resin.

An extractive scintillating resin was evaluated for the simultaneous separation and detection of actinides in acidic solutions. The transuranic extractive scintillating (TRU-ES) resin is composed of an inert macroporous polystyrene core impregnated with organic fluors (diphenyloxazole and 1,4-bis-(4-methyl-5-phenyl-2-oxazolyl)benzene) and an extractant (octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide in tributyl phosphate). The TRU-ES resin was packed into FEP Teflon tubing to produce a flow cell (0.2-mL free column volume), which is placed into a scintillation detection system to obtain pulse height spectra and time series data during loading and elution of actinides onto/from the resin. The alpha-particle absolute detection efficiencies ranged from 77% to 96.5%, depending on the alpha energy and quench. In addition to the on-line analyses, off-line analyses of the effluent can be conducted using conventional detection methods. The TRU-ES resin was applied to the quantification of a mixed radionuclide solution and two actual waste samples. The on-line characterization of the mixed radionuclide solution was within 10% of the reported activities whereas the agreement with the waste samples was not as good due to sorption onto the sample container walls and the oxidation state of plutonium. Agreement between the on-line and off-line analyses was within 35% of one another for both waste samples.

Acids↗
PubMedDate not supplied

From models to performance assessment: the conceptualization problem.

Today, models are ubiquitous tools for ground water analyses. The intent of this paper is to explore philosophically the role of the conceptual model in analysis. Selection of the appropriate conceptual model is an a priori decision by the analyst. Calibration is an integral part of the modeling process. Unfortunately a wrong or incomplete conceptual model can often be adequately calibrated; good calibration of a model does not ensure a correct conceptual model. Petroleum engineers have another term for calibration; they refer to it as history matching. A caveat to the idea of history matching is that we can make a prediction with some confidence equal to the period of the history match. In other words, if we have matched a 10-year history, we can predict for 10 years with reasonable confidence; beyond 10 years the confidence in the prediction diminishes rapidly. The same rule of thumb applies to ground water model analyses. Nuclear waste disposal poses a difficult problem because the time horizon, 1000 years or longer, is well beyond the possibility of the history match (or period of calibration) in the traditional analysis. Nonetheless, numerical models appear to be the tool of choice for analyzing the safety of waste facilities. Models have a well-recognized inherent uncertainty. Performance assessment, the technique for assessing the safety of nuclear waste facilities, involves an ensemble of cascading models. Performance assessment with its ensemble of models multiplies the inherent uncertainty of the single model. The closer we can approach the idea of a long history with which to match the models, even models of nuclear waste facilities, the more confidence we will have in the analysis (and the models, including performance assessment). This thesis argues for prolonged periods of observation (perhaps as long as 300 to 1000 years) before a nuclear waste facility is finally closed.

Calibration↗
PubMedDate not supplied

Factors affecting the trapping performance of xenon holdup--filters in nuclear medicine applications.

Activated charcoal traps are used in nuclear medicine departments to capture exhaled radioactive xenon gas. In the present study, the trapping performance of charcoal was investigated for different physical qualities in experimental and clinical situations. Various factors affecting the trapping capacity are identified, such as the charcoal mass, moisture and carbon-dioxide concentrations in the sweep gas, gas-flow rate through the trap, and temperature. Improper drying of the exhaled air prior to passage through the charcoal bed appears to be a critical factor, leading to a much earlier breakthrough of xenon. Commercial xenon traps intended for ambient temperature operation were found to be useful only for a limited number of patients due to an early breakthrough point. By refrigerating the trap, however, a much larger capacity was achieved. If correctly managed, xenon traps constitute a useful alternative for isolating radioactive xenon wastes in clinical and experimental applications.

Air Pollution, Radioactive↗
PubMed1990

Review of biotechnology applications to nuclear waste treatment.

This paper gives an overview of the feasibility of the application of biotechnology to nuclear waste treatment. The contents are based on a report which PA Technology carried out for the Department of the Environment (DoE Reference: DoE/RW/88.008 Sector No 2.3). Many living and dead organisms accumulate heavy metals and radionuclides. The controlled use of this phenomenon forms the basis for the application of biotechnology to the removal of radionuclides from nuclear waste streams. Indeed, biotechnology offers a series of new opportunities for removal of radionuclides from dilute aqueous process effluents. Such technology is already used for heavy metal removal on a commercial basis and could be optimised for radionuclide removal. An overview of biotechnology areas, namely the use of biopolymers and biosorption using biomass applicable to the removal of radionuclides from industrial nuclear effluents is given. The potential of biomagnetic separation technology, genetic engineering and monoclonal antibody technology is also to be examined. The most appropriate technologies to develop for radionuclide removal in the short term appear to be those based on biosorption of radionuclides by biomass and the use of modified and unmodified biopolymers in the medium term.

Biotechnology↗
PubMed2002

Leachability of radionuclides from cement-solidified waste form produced at Korean nuclear power plant.

The leach test of radionuclide in cement-solidified waste form was performed. After leach test, compressive strength of waste form was measured. Cement-solidified waste form produced at Korean nuclear power plant, Kori (PWR) was chosen for the leach test. Specimens were cored out from a full-scale waste form (2001 drum size). The leach test procedure used for this study was ANSI/ANS 16.1 procedure. The leach ability indexes for cesium and cobalt isotopes were determined. Semi-infinite model was used for analysis of the controlling mechanism in the release of isotopes. Release mechanism of cesium was dominated by diffusion but release of cobalt behaved somewhat differently from the diffusion controlled release. Averaged leachability indexes were 8.6 for cesium and 11.4 for cobalt. Compressive strength after leach/ immersion test was 7.34 MPa for the sample immersed in simulated seawater and 8.34MPa for the sample immersed in deionized water.

Cesium Radioisotopes↗
PubMed2005

Confocal micrometer-scale X-ray fluorescence and X-ray absorption fine structure studies of uranium speciation in a tertiary sediment from a waste disposal natural analogue site.

Investigations by micrometer-scale X-ray fluorescence and X-ray absorption fine structure (micro-XRF and micro-XAFS) recorded in a confocal geometry on a bore core section of a uranium-rich tertiary sediment are performed in order to assess mechanisms leading to immobilization of the uranium during diagenesis. Results show uranium to be present as a tetravalent phosphate and that U(IV) is associated with As(V). Arsenic present is either As(V) or As(O); we found no evidence for As(III). The As(O) is observed to be intimately associated with the surface of Fe(II) nodules and likely arsenopyrite. A hypothesis for the mechanism of uranium immobilization is proposed, where arsenopyrite acted as reductant of groundwater-dissolved U(VI), leading to precipitation of less soluble U(IV) and thereby forming As(V).

Absorptiometry, Photon↗
PubMed2004

Colloid formation in Hanford sediments reacted with simulated tank waste.

Solutions of high pH, ionic strength, and aluminum concentration have leaked into the subsurface from underground waste storage tanks atthe Hanford Reservation in Washington State. Here, we test the hypothesis that these waste solutions alter and dissolve the native minerals present in the sediments and that colloidal (diameter < 2 microm) feldspathoids form. We reacted Hanford sediments with simulated solutions representative of Hanford waste tanks. The solutions consisted of 1.4 or 2.8 mol/kg NaOH, 0.125 or 0.25 mol/kg NaAlO4, and 3.7 mol/kg NaNO3 and were contacted with the sediments for a period of 25 or 40 days at 50 degrees C. The colloidal size fraction was separated from the sediments and characterized in terms of mineralogy, morphology, chemical composition, and electrophoretic mobility. Upon reaction with tank waste solutions, native minerals released Si and other elements into the solution phase. This Si precipitated with the Al present in the waste solutions to form secondary minerals, identified as the feldspathoids cancrinite and sodalite. The solution phase was modeled with the chemical equilibrium model GMIN for solution speciation and saturation indices with respect to sodalite and cancrinite. The amount of colloidal material in the sediments increased upon reaction with waste solutions. At the natural pH found in Hanford sediments (pH 8) the newly formed minerals are negatively charged, similar to the unreacted colloidal material present in the sediments. The formation of colloidal material in Hanford sediments upon reaction with tank waste solutions is an important aspect to consider in the characterization of Hanford tank leaks and may affect the fate of hazardous radionuclides present in the tank waste.

Aluminum Oxide↗
PubMed1997

Healthful radiation.

This title of this article sounds paradoxical to most people because the general public is not fully aware of the many benefits radiation has brought to people's healthcare. Radiation has provided the most effective means of noninvasive diagnosis of many diseases, thus reducing the need for exploratory surgery, at significantly reduced risks. Furthermore, radiotherapy has been effective in treating many diseases without surgical removal of the diseased part. The breast is one excellent example of the benefits of radiation in both diagnosis and treatment with preservation. Yet the public still regards radiation as mysterious and dangerous, while trained experts regard it as beneficial with manageable risks. This article suggests ways of presenting this material to the public in a manner that is interesting and informative.

Breast Diseases↗
PubMed2003

Comparison of doses and risks obtained from dose reconstructions for historical operations of federal facilities that supported the development, production, or testing of nuclear weapons.

Five dose reconstruction projects focusing on historical public exposures from U.S. government nuclear facilities have been completed in the last 12 y (Fernald, Hanford, Nevada Test Site, Oak Ridge, Rocky Flats). Using information available in published reports, doses and excess health risks of the most serious contaminants in each study are compared for representative maximally and typically exposed individuals. For both the representative maximally exposed individual and the representative typically exposed individual, the highest excess risks of cancer incidence were from 131I released from Hanford, Nevada Test Site, and Oak Ridge and 222Rn released from Fernald (with central estimates for maximally exposed individuals approaching or exceeding 10(-2)); the lowest risks for both maximally and typically exposed individuals were from 239/240Pu and carbon tetrachloride released from Rocky Flats. Excess health risks to the representative maximally exposed individual were at or below 10(-40 for releases from Rocky Flats. For representative typically exposed individuals, the excess risks from releases of mixed radionuclides in the Clinch River (Oak Ridge), PCBs in East Fork Poplar Creek (Oak Ridge), and both plutonium and carbon tetrachloride released from Rocky Flats were mostly below 10(-5).

Air Pollutants, Radioactive↗
PubMed1999

A description of factors affecting hazardous waste workers' use of respiratory protective equipment.

This article describes the first phase of a study that was designed to gain an understanding of hazardous waste workers' attitudes and beliefs about the use of respiratory protective equipment. Exploratory, open-ended interviews were conducted among 28 respirator users at a US Department of Energy facility. Subjects were asked to describe their knowledge, attitudes, and beliefs about their risks to hazards at their worksites and to discuss their use of respiratory protective equipment. A detailed content analysis of the interviews resulted in the generation of a taxonomy of issues and concerns which fell into three general categories: 1) Knowledge, Beliefs, and Attitudes, 2) Physical and Psychological Effects, and 3) External Influences. Knowledge, Beliefs, and Attitudes included Training, Fit Testing, Medical Clearance, Work Exposures, Respirator Use, and Vulnerability to Disease. Physical and Psychological Effects included Somatic/Health Effects, Personal Comfort, Visual Effects, Fatigue, Communication, and Anxiety. External Influences included Structural Environment, Quality and Availability of Equipment, Other PPEs, Co-Worker Influence, Supervisor Influence, and Organizational Culture. The findings from this study have important implications to training and education programs. Effective respiratory protection programs depend on a knowledge of the factors that affect workers' use of equipment. This study suggests that efforts to assure equipment comfort and fit, to assist workers who see and hear less well as a result of their equipment, and to develop strategies to allay worker anxiety when wearing equipment should all be components of a program. An organizational culture that supports and abets the appropriate use of equipment is also a critical element in a successful program.

Adult↗
PubMed1990

Radionuclide uptake and growth of barn swallows nesting by radioactive leaching ponds.

Populations of barn swallows (Hirundo rustica) nested seasonally near the Test Reactor Area (TRA) radioactive leaching ponds on the Idaho National Engineering Laboratory (INEL). These birds utilized leaching pond arthropods as a food source and contaminated mud for nest construction and thus accumulated radioactive materials. Over 20 fission and activation products were detected in immature and adult TRA birds. The radionuclide exhibiting the highest mean concentration in adult birds was 51Cr, with 16.1 Bq g-1 (435 pCi g-1). Mean concentrations of detectable radionuclides were used to calculate internal dose rates. Approximately 72% of the total dose rate of 219 microGy d-1 (22 mrad d-1) for adult birds was due to 24Na. Swallow thyroids contained a mean 131I concentration of 3330 Bq g-1. An average dose rate to the thyroid was calculated to be 4300 microGy d-1 or 450 mGy (45 rad) for the entire breeding season. Data from LiF-700 thermoluminescent dosimeters in swallow nests indicated that average dose rates were 840 microGy d-1 for eggs and 2200 Gy d-1 for nestlings, for a total of 54 mGy (5.4 rad) during the nesting period. The breeding biology and growth rate were investigated for TRA swallows and comparison group located 15 km and 100 km away. Total mortality rates for the comparison group vs. 1976 and 1977 TRA populations were not found to be significantly (p greater than 0.9) different. Nonlinear regression was used to fit individual growth curves and estimate parameters using a logistic model. First clutch TRA swallows were found to have a significantly (p less than 0.05) lower mean growth rate compared to either the first clutch comparison group or the second clutch of TRA birds. Mean asymptotic weights achieved by immature TRA birds were also found to be significantly (p less than 0.05) lower than those achieved by comparison group birds. Both growth rate and asymptotic weights for TRA birds were within the normal range reported in the literature. The cause for the statistical difference in growth rate between the comparison group and TRA first clutch populations could not be determined.

Animals↗