Effect of uranium concentration

Figure 15 The effect of uranium concentration on uranium extraction from H2S04 by 0.1 M HDEHP in kerosene.106 The curves are labelled with U concentration (g dm-3)...

Fig. 3-18. The effects of uranium concentration and type of radiation on the initial H2 yield from irradiated UO2SO4 solutions.

Fig. 10 6. Effect of uranium concentration and reactor diameter on fuel cost in one-region reactors. 300 Mw of electricity, 1000 Mw of heat, Avg. reactor temperature = 330°C, U02S04-Li2S04-D20 solution with dissolved Pu, molar ratio of Li2S04 to UO2SO4 = 1, optimum poisons = 5%.

The effects of uranium in animal experiments were also compound-dependent, the more water-soluble compounds (e.g., uranyl nitrate) causing much greater renal toxicity than insoluble compounds (e.g., uranium dioxide) when the dose contained equivalent amounts of uranium. ATSDR has determined that the toxicity database for uranium justifies the derivation of separate MRLs for soluble and insoluble forms of uranium for certain durations and routes of exposure. This is based on toxicokinetic evidence that absorption of uranium (and concentration in target tissue) is significantly greater during exposure to the more water-soluble compounds. Soluble forms include uranyl fluoride, uranium tetrachloride and uranyl nitrate hexahydrate insoluble forms include uranium tetrafluoride, uranium dioxide, uranium trioxide, and triuranium octaoxide. Where the database is not extensive enough to allow separate MRLs, the MRL for the soluble form should be protective for health effects due to all forms of uranium. 

Waite DT, Joshi SR, Sommerstad H. 1988. The effect of uranium mine tailings on radionuclide concentrations in Langley Bay, Saskatchewan Canada. Arch Env Contam Tox 17 373-380. 

Sims R., Lawless R., Alexander L, Bennett D., and Read D. (1996) Uranium migration through intact sandstone effect of pollutant concentration and the reversibihty of uptake. J. Contamin. Hydrol. 21, 215-228. 

The 2.54-cm diameter Electropulse Column shown in Figure 1, after completion of uranium runs, was installed at Battelle Memorial Institute (Columbus, Ohio) for uranium-plutonium partition tests. Six electrolytic runs were made under conditions corresponding to partitioning in the first process cycle to determine the effect of uranium reduction efficiency R(u) on t le separation process. The organic feed contained 80 to 83 grams/L of uranium and 0.71 to 0.82 grams/L of plutonium. The nitric acid concentration in the aqueous feed was 2.5 to 2.8 M and in the organic feed 0.2 to 0.3 M. 

Figure 10.9 illustrates the effect of uranium saturation of solvent on distribution coefficients, at nitric acid concentrations approximately those in the extracting and scrubbing sections. The ratio of plutonium distribution coefficient to fission products is improved at high uranium loadings, a condition sought at the feed point. 

Figure 9.20 The effect of agent concentration in the organic phase on viscosity for solutions containing no uranium (uncomplexed agent) and solutions previously equilibrated with aqueous uranium solution (complexed agent).17 (Organic phase Alamine 336 dissolved in Aromatic 150).

Figure 9.21 The effect of agent concentration on the uranium flux through a coupled transport membrane calculated from Equations 13 and 24. The measured flux data are shown for comparison.17 (Membrane Celgard 2400/Alamine 336 dissolved in Aromatic 150. Feed 0.2% Uranium, pH 1.0. Product pH 4.5).

Gonzalez-Luque and Streat [45] determined the isotherms for the sorption and desorption of uranium from synthetic phosphoric acid solutions in the presence of interfering cations, such as Fe(II) and Ca(II), with these different impregnated resins and one commercial aminophosphinic acid ion-exchange resin. The effect of phosphoric concentration on uranium... 

The occupational exposure values for the inhalation of uranium have been compiled by the American Conference of Governmental Industrial Hygienists (ACGIH) [14]. These are air concentration exposure limits based on the chemical effects of uranium. In contrast, the International Commission on Radiological Protection (ICRP) has developed the annual limit on intake (ALI) for ingestion and inhalation of uranium compounds based solely on the radiation doses received by tissues and organs of the body [12,15]. Whether the primary concern is the chemical toxicity or radiation dose, the occupational limits take the solubility of the uranium compound into consideration. The occupational limits are summarized in Table 3. It must be emphasized that the air concentration exposure limits are for the typical 8-hr day (see Abbrevi-... 

The total daily ingestion of uranium can vary markedly due to the local concentration in drinking water or the consumption of mineral waters. The range of uranium concentrations in potable surface waters is 0.03-15 p,g/liter (0.4-185 mBq/liter) [19], and while public groundwater supplies are generally <10 JLg/liter (<125 mBq/liter), a few exceed 10(X) p,g/liter [20]. Because of the extreme variability in uranium concentration in potable waters, no global average has been adopted by the United Nations Scientific Committee for the Effects of Atomic Radiation (UNSCEAR). Mineral waters in three European nations have been reported to contain 0.04-70 xg U/liter (0.5-870 mBq/liter) [21]. 

Last but not least, an excellent comprehensive document that covers practically all facets of environmental behavior of uranium was published by the Canadian Council of Ministers of the Environment (Environment 2007). The chemical and physical properties of uranium were reviewed and its distribution in the environment and bio-accumulation in various flora and biota were discussed. For example, guidelines for the permissible uranium concentration in soil were set according to the intended land use. Eor agricultural use and commercial land use, the maximum uranium concentration was 33 mg kg" for residential and parkland uses it was 23 mg kg , and a value of 300 mg kg" was set for industrial land use. This document also contains many tables that summarize the toxicological effects of uranium on humans and the uranium content in several food products, vegetation, soil, water, etc. In addition, a summary of the analytical methods that are used for the determination of uranium in a variety of environmental samples, very similar to Table 3.1, is given (Environment 2007). 

There are somewhat contradictary reports and studies on the genaal health effects of uranium and particularly on the effects on kidney functions. In the comprehensive study of 325 people of a Finnish pt ulation that regularly consume large amounts of uranium in their drinking wato (Kurttio et al. 2002), it was shown that continuous uranium intake frran drinking water, evai at relatively high exposures, did not have cytotoxic effects on kidneys in humans. In that study, the median uranium concentration in drinking water... 

A special case of radiological effects of uranium is when a criticality incident occurs. A criticality accident, or an uncontrolled nuclear chain reaction, may inadvertently occur if a sufficient amount of accumulates under certain conditions. The criteria for criticality control are known by the acronym MAGIC MF.RV for Mass, Absorption, Geometry, Interaction, Concentration, Moderation, Enrichment, Reflection, and Volume (for more details, see Frame 1.3 in Chapter 1). The result would be the emission of neutrons and ganuna radiation, as occurred in Tokai-Mura, Japan, in 1999, and resulted in the death of two of the plant employees (WNA 2007). A brief discussion on the units for measuring radiation and exposure of the public is presented in Frame 4.3. 

Uranium occurs naturally in variable concentrations in all soils, minerals, rocks and waters. It can also be derived from several anthropogenic sources. Uranium is weakly radioactive and human exposure to the element has long been considered to pose a radiological as well as toxic hazard (WHO, 2004 2008 Smedley et al., 2006). This dissolved toxic radioactive metal may poison drinking water sources and the food chain via contaminated surfaces and groundwater. In recent years, there has been increasing concern that the chemical effects of uranium may also pose a potential hazard to exposed populations. However, there are few if any epidemiological studies that have been able to demonstrate any resultant harm, even in occupational contexts (The Royal Society, 2001). 

Studies of the kinetics of the thermal decomposition of peroxide in uranyl sulfate solutions [43] have shown the rate to be first order with respect to peroxide concentration in the range from 0.4 to 5 X 10 M, independent of uranium concentration in the range from 4.5 X 10 to 0.65 M, and independent of the acidity from pH 1.6 to 3.3. Traces of certain ions showed pronounced catalytic effects. The rate of decomposition could be expressed by... 

Hydrogen ion concentration (pH). Orban of Mound Laboratory [48,56] studied the acidity of uranyl sulfate solutions from 25 to 60 C. Orban has also reported the pH values for uranyl sulfate solutions containing excess UO3 at temperatures up to 60°C [49,56]. Secoy has compiled information concerning the effects of uranium sulfate concentration upon pH as reported by a number of investigators [59]. Marshall has utilized the relationship between pH and concentration to determine the solubility of UO3 in sulfuric acid at elevated temperatures [7]. Table 3-13 shows the effect of sulfate concentration on pH at 25.00°C for various ratios of UO3 to sulfate as found by Marshall. 

The concentration of uranium in the analyzed sample, as well as the effectiveness of digestion of the examined materials and the effect of caning material needs to be considered. 

---