38 research outputs found
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Ultrafiltration evaluation with depleted uranium oxide
Scientists at the Los Alamos National Laboratory Plutonium Facility are using electrodissolution in neutral to alkaline solutions to decontaminate oralloy parts that have surface plutonium contamination. Ultrafiltration of the electrolyte stream removes precipitate so that the electrolyte stream to the decontamination fixture is precipitate free. This report describes small-scale laboratory ultrafiltration experiments that the authors performed to determine conditions necessary for full-scale operation of an ultrafiltration module. Performance was similar to what they observed in the ferric hydroxide system. At 12 psi transmembrane pressure, a shear rate of 12,000 sec{sup {minus}1} was sufficient to sustain membrane permeability. Ultrafiltration of uranium(VI) oxide appears to occur as easily as ultrafiltration of ferric hydroxide. Considering the success reported in this study, the authors plan to add ultrafiltration to the next decontamination system for oralloy parts
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Comparison of alpha spectroscopy procedures for measuring Pu, Am, and U swipeable contamination
An electrolytic decontamination process for removing Pu and Am contamination from U surfaces to levels less than 20dpm/100cm{sup 2} has been demonstrated. The process requires a quantitative analytical technique for measuring the remaining alpha activity by swiping the U surface. In this work, two alpha spectroscopy techniques were evaluated, one in which alpha spectroscopy was performed directly on the swipes, and another that requires chemical treatment of the swipe to remove all the contamination before counting. Along with differences in methodology, a comparison of the two techniques revealed differences in time, cost, and waste generation and handling. The chemical separation technique is pretty much the standard for alpha spectroscopy in which specific elements in the sample are isolated to minimize interference between the different alpha isotopes being analyzed. In comparison, direct counting of the swipe involves attenuation within the sample that causes tailing in the alpha peak. New {open_quotes}off the shelf{close_quote} software allows the authors to deconvolute the peaks and make a comparison of the two spectroscopy techniques
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Washing of Rocky Flats Combustible Residues (Conducted March - May 1995)
The scope of this project is to determine the feasibility of washing plutonium-containing combustible residues using ultrasonic disruption as a method for dislodging particulate. Removal of plutonium particulate and, to a lesser extent, solubilized plutonium from the organic substrate should substantially reduce potential fire, explosion or radioactive release hazards due to radiolytic hydrogen generation or high flammability. Tests were conducted on polypropylene filters which were used as pre-filters in the rich-residue ion-exchange process at the Los Alamos Plutonium Facility. These filters are similar to the Ful-Flo{reg_sign} cartridges used at Rocky Flats that make up a substantial fraction of the combustible residues with the highest hazard rating. Batch experiments were run on crushed filter material in order to determine the amount of Pu removed by stirring, stirring and sonication, and stirring and sonication with the introduction of Pu-chelating water-soluble polymers or surfactants. Significantly more Pu is removed using sonication and sonication with chelators than is removed with mechanical stirring alone
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Waste-form development for conversion to portland cement at Los Alamos National Laboratory (LANL) Technical Area 55 (TA-55)
The process used at TA-55 to cement transuranic (TRU) waste has experienced several problems with the gypsum-based cement currently being used. Specifically, the waste form could not reliably pass the Waste Isolation Pilot Plant (WIPP) prohibition for free liquid and the Environmental Protection Agency (EPA)-Toxicity Characteristic Leaching Procedure (TCLP) standard for chromium. This report describes the project to develop a portland cement-based waste form that ensures compliance to these standards, as well as other performance standards consisting of homogeneous mixing, moderate hydration temperature, timely initial set, and structural durability. Testing was conducted using the two most common waste streams requiring cementation as of February 1994, lean residue (LR)- and oxalate filtrate (OX)-based evaporator bottoms (EV). A formulation with a pH of 10.3 to 12.1 and a minimum cement-to-liquid (C/L) ratio of 0.80 kg/l for OX-based EV and 0.94 kg/L for LR-based EV was found to pass the performance standards chosen for this project. The implementation of the portland process should result in a yearly cost savings for raw materials of approximately $27,000 over the gypsum process
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Transpassive electrodissolution of depleted uranium in alkaline electrolytes
To aid in removal of oralloy from the nuclear weapons stockpile, scientists at the Los Alamos National Laboratory Plutonium Facility are decontaminating oralloy parts by electrodissolution in neutral to alkaline electrolytes composed of sodium nitrate and sodium sulfate. To improve the process, electrodissolution experiments were performed with depleted uranium to understand the effects of various operating parameters. Sufficient precipitate was also produced to evaluate the feasibility of using ultrafiltration to separate the uranium oxide precipitates from the electrolyte before it enters the decontamination fixture. In preparation for the experiments, a potential-pH diagram for uranium was constructed from thermodynamic data for fully hydrated species. Electrodissolution in unstirred solutions showed that uranium dissolution forms two layers, an acidic bottom layer rich in uranium and an alkaline upper layer. Under stirred conditions results are consistent with the formation of a yellow precipitate of composition UO{sub 3}{center_dot}2H{sub 2}O, a six electron process. Amperometric experiments showed that current efficiency remained near 100% over a wide range of electrolytes, electrolyte concentrations, pH, and stirring conditions
Influence of Smallmouth Bass Predation on Recruitment of Age-0 Yellow Perch in South Dakota Glacial Lakes
We estimated the influence of predation by Smallmouth Bass Micropterus dolomieu on recruitment of age-0 Yellow Perch Perca flavescens in two northeastern South Dakota glacial lakes. We estimated a likely range in consumption of age-0 Yellow Perch using Smallmouth Bass diet information from two time periods when age-0 Yellow Perch constituted high (2008) and low (2012 and 2013) proportions of Smallmouth Bass diets, and bass population size estimates as inputs in a bioenergetics model. The proportion of age-0 Yellow Perch consumed by the Smallmouth Bass populations was determined by comparing estimates of consumption with estimates of age-0 perch production. During 2008, age-0 Yellow Perch constituted between 0% and 42% of Smallmouth Bass diets by weight, whereas during 2012 and 2013, age-0 perch constituted between 0% and 20% of bass diets by weight. Across both lakes and time periods, production of age-0 Yellow Perch ranged from 0.32 to 1.78 kg.ha -1 week -1. Estimates of Smallmouth Bass consumption measured during the same intervals ranged from 0.06 to 0.33 kg.ha -1 week-1, equating to consumption of between 1% and 34% of the available Yellow Perch biomass. Given current conditions relative to Smallmouth Bass abundance and consumption dynamics and production of age-0 Yellow Perch, it does not appear that Smallmouth Bass predation acts as a singular factor limiting recruitment of age-0 Yellow Perch in our study lakes. However, future research and management initiatives should recognize that the long-term impact of Smallmouth Bass predation is not static and will likely fluctuate depending on environmental (e.g., temperature) and biotic (e.g., trends in macrophyte abundance, predator and prey population structure and abundance, and predatory fish assemblage dynamics) characteristics