Plants dissolution

Konoplev and Bulgakov (1999) used these observations to estimate the fraction of undissolved fuel particles present in soils in the Chernobyl 30 km exclusion zone. They found that the unoxidized fuel particles, deposited from the initial explosion in a plume to the west of Chernobyl, are more resistant to leaching and dissolution than the oxidized fuel particles released during the subsequent fire and deposited to the north, northeast, and south of the plant. Dissolution rates for the unoxidized fuel particles were about one-third those of oxidized particles, with 27-79% remaining undissolved in 1995, while only 2-30% of the oxidized fuel remained. Fuel particle dissolution rates also increased with increasing soil acidity and with decreasing particle size (Kashparov et al, 1999 Konoplev and Bulgakov, 1999). 

In this paragraph we briefly describe some of the largest anthropogenic sources causing far field effects, i.e. nuclear weapons tests and nuclear power plant accidents. The cause of the releases is discussed in Chapter 19. Chapter 22 discusses both near and far field effects in further detail, particulary with regard to chemical properties liquid releases from nuclear power plants, dissolution of solidified nuclear waste and of fall-out particles, migration in the environment, and possible consequences. 

Neste patented an industrial route to a cellulose carbamate pulp (90) which was stable enough to be shipped into rayon plants for dissolution as if it were xanthate. The carbamate solution could be spun into sulfuric acid or sodium carbonate solutions, to give fibers which when completely regenerated had similar properties to viscose rayon. When incompletely regenerated they were sufficientiy self-bonding for use in papermaking. The process was said to be cheaper than the viscose route and to have a lower environmental impact (91). It has not been commercialized, so no confirmation of its potential is yet available. 

Fluorozirconate Crystallization. Repeated dissolution and fractional crystallization of potassium hexafluorozirconate was the method first used to separate hafnium and zirconium (15), potassium fluorohafnate solubility being higher. This process is used in the Prinieprovsky Chemical Plant in Dnieprodzerzhinsk, Ukraine, to produce hafnium-free zirconium. Hafnium-enriched (about 6%) zirconium hydrous oxide is precipitated from the first-stage mother Hquors, and redissolved in acid to feed ion-exchange columns to obtain pure hafnium (10). 

Fuel Dissolution. In the American and British plants, LWR fuel pieces typically fall directly from the shear into a dissolver basket, which fits inside the dissolver vessel. A soluble poison such as gadolinium is added to the nitric acid to prevent criticahty. The massive end fittings are sometimes separated from the fuel pieces before the latter enter the dissolver. The French have installed continuous rotary dissolvers in the UP3 and UP2-800 plants at La Hague. The units each consist of a dmm rotating within a geometrically favorable slab tank (13). 

The metal dissolves readily in concentrated HCl, H PO, HI, or HCIO. Nitric acid (qv) forms a protective oxide skin on the metal and can be removed by ca 0.05 Af HF. Dissolution of Pu metal in HNO —HF mixtures is common practice in scrap-recovery plants. The metal does not dissolve readily in H2SO4 because passivation of the metal surface occurs. The reaction of water and Pu metal is slow compared to that in HCl, HI, or HCIO. ... 

Australian Vanadium—Uranium Ore. A calcareous camotite ore at YeeHrrie, AustraHa, is iU-suited for salt roasting and acid leaching. Dissolution of vanadium and uranium by leaching in sodium carbonate solution at elevated temperature and pressure has been tested on a pilot-plant scale... 

Agronomic Properties and Nutrient Release Mechanism. The conversion of UF reaction products to plant available nitrogen is a multistep process, involving dissolution and decomposition. Materials are slow to enter the soil solution by virtue of their low solubiUty. Longer polymer chain products are less soluble than shorter chains and take longer to become available to the plants. 

Stress corrosion can arise in plain carbon and low-alloy steels if critical conditions of temperature, concentration and potential in hot alkali solutions are present (see Section 2.3.3). The critical potential range for stress corrosion is shown in Fig. 2-18. This potential range corresponds to the active/passive transition. Theoretically, anodic protection as well as cathodic protection would be possible (see Section 2.4) however, in the active condition, noticeable negligible dissolution of the steel occurs due to the formation of FeO ions. Therefore, the anodic protection method was chosen for protecting a water electrolysis plant operating with caustic potash solution against stress corrosion [30]. The protection current was provided by the electrolytic cells of the plant. 

Bar-code readers (like those in grocery stores) are to identify equipment in a plant. Suggest a way that this may be used to check the temperature, acid type and quantity, and aluminum quantity for acid dissolution of aluminum. 

Plants handling aqua regia Aqua regia is used extensively in the extraction and refining of the precious metals, and tantalum, as one of the few metals resistant to this medium, is used for dissolution/evaporation pans, reactor lids and all immersed ancillary equipment. 

Thermal oxide reprocessing plant, 6, 885 Thermal reactor fuels, 6,926 dissolution, 6,927 irradiated... 

The spent salt from MSE is currently sent to an aqueous dissolution/carbonate precipitation process to recover plutonium and americium. Efforts to recover plutonium and americium from spent NaCl-KCl-MgCl2 MSE salts using pyrochemistry have been partially successful (3). Metallothermic reductions using Al-Mg and Zn-Mg alloys have been used in the past to recover plutonium and americium, and produce salts which meet plant discard limits. Attempts at direct reductions of MSE salts using... 

D. L. Jones, P. R. Darrah, and L. V. Kochian, Critical evaluation of organic acid mediated iron dissolution in the rhizo.sphere and its potential role in root iron uptake. Plant Soil 180 51 (1996). 

P. Hinsinger and R. J. Gilkes, Dissolution of phosphate rock in the rhizosphere of five plant species grown in an acid, P-fixing mineral substrate. Geoderma 75 231 (1997). 

D. L. Jones and L. V. Kochian, Aluminum-organic acid interactions in acid soils. 1. Effect of root-derived organic acids on the kinetics of A1 dissolution. Plant Soil 782 221 (1996). 

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