Chemistry water

During bank-filtration of oxic river water a sequence of redox reactions occurs with increasing travel and reaction time of the infiltrating water. The Fe and particularly Mn content of the water can best describe the redox state of the system. Due to the complex flow behaviour and the natural heterogeneity of the sediments, the distribution of water constituents varies strongly. As an example. Fig. 11.3 shows the Fe concentration in January 2000 along the transect shown by Fig. 11.2. 

The redox sequence starts with the reduction of O2 and NO3 present in the river water. O2 and NOj are probably consumed within the first few m or even dm along the groundwater flow path since they are not observed in any of the observation wells (see also Massmann et al., 2001). 

As a result of Mn (hydr) oxide reduction, the Mn concentration of the water continuously increases from the river to a distance of 150 m, where it reaches a maxi- 

While the reduction of Mn (hydr) oxides is certainly the source for in solution, groundwater Mn concentration is controlled by the saturation of Mn carbonate (MnC03,rhodochrosite). Rhodochrosite is the most abundant reduced mineral in nature (Berner, 1980). It commonly precipitates in aquatic systems according to the reaction 

Whereas groundwater Mn concentration increases to 150 m from the river and then decreases to 620 m, the Fe concentration increases along the transect reaching a maximum of 2-5 mg L at 620 m. The redox conditions do not reach the post-oxic, ferrous precipitates, and SOl is not reduced, i.e. was not detected. The SO content of the groundwater is about 100 mg L, which is similar to the river water concentration. 

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Water chemistry oflightwater reactors pUCLEARREACTORS - WATERCHEMISTRYOFLIGHTWATERREACTORS] (Vol 17) Nuclear Regulatory Commission... 

Water chemistry of hghtwater reactors. Isotope separation. 

A variety of nuclear reactor designs is possible using different combinations of components and process features for different purposes (see Nuclear REACTORS, reactor types). Two versions of the lightwater reactors were favored the pressurized water reactor (PWR) and the boiling water reactor (BWR). Each requites enrichment of uranium in U. To assure safety, careful control of coolant conditions is requited (see Nuclearreactors, water CHEMISTRY OF LIGHTWATER REACTORS NuCLEAR REACTORS, SAFETY IN NUCLEAR FACILITIES). 

The BWR water chemistry parameters are given in Table 4 (19). Originally, no additives were made to feedwater—condensate or the primary water. The radiolytic decomposition of the fluid produced varying concentrations of O2 in the reactor vessel, ranging from about 200 ppb O2 in the reactor recirculation water to about 20 ppm O2 in the steam. Stoichiometric amounts of hydrogen were also produced, ie, 2 mL for each mL of O2. Feedwater O2 was about 30 ppb, hence the radiolytic decomposition of the water was a primary factor in determining the behavior of materials in the primary system and feedwater systems. 

Fig. 7. Radiation buildup at BWRs using normal water chemistry, A, and 2inc additions, B (12). To convert mGy to mrad, multiply by 100.

Water chemistry is important to the safe and reflable operation of a nuclear power plant. Improper conditions can lead to equipment and material failures which ia turn can lead to lengthy unscheduled shutdown periods for maintenance (qv) and repair operations. Water chemistry can also have an impact on the radiation levels duriag both power operations and shutdown periods. These affect the abiUty of personnel to perform plant functions. 

PWR Primary Water Chemistry Guidehnes Revision 2," Report NP-7077, Electdc Power Research Institute, Palo Alto, Calif., Nov. 1990. 

S. M. Ah, "An Updated Version of Computer Code CORA II for Estimation of Corrosion Product Mass and Activity Migration ia PWR Primary Circuits and Related Experimental Loops," Eourth International Conference on Water Chemistry of Nuclear Systems, Bournemouth, U.K., Oct. 1986, pp. 107-109. 

USSR Pat. 1,479,475 (May 15, 1989), S. S. Pesetskii and co-workers (to Institute of the Mechanics of Metal-Polymer Systems, Academy of Sciences, Belomssian S.S.R. Institute of CoUoidal and Water Chemistry, Academy of Sciences, Ukrainian S.S.R.). 

Other energy considerations for cooling towers include the use of two-speed or variable-speed drives on cooling-tower fans, and proper cooling-water chemistry to prevent fouling in users (see Water, industrial water treatment). Air coolers can be a cost-effective alternative to cooling towers at 50—90°C, just below the level where heat recovery is economical. 

Z. Amjad, ed.. Reverse Osmosis Membrane Technology, Water Chemistry and Industrial Applications, Van Nostrand Reiohold, New York, 1993. 

Scale control can be achieved through operation of the cooling system at subsaturated conditions or through the use of chemical additives. The most direct method of inhibiting formation of scale deposits is operation at subsaturation conditions, where scale-forming salts are soluble. For some salts, it is sufficient to operate at low cycles of concentration and/or control pH. However, in most cases, high blowdown rates and low pH are required so that solubihties are not exceeded at the heat transfer surface. In addition, it is necessary to maintain precise control of pH and concentration cycles. Minor variations in water chemistry or heat load can result in scaling (Fig. 12). 

Consensus on Operating Practicesfor The Control of Feedwater and Boiler Water Chemistry in Modem Industrial BoilerSs The American Society of Mechanical Engineers, New York, NY, 1994. 

Cooling Wa.ter. The primary rehabihty concern is that water chemistry must be maintained in a low fouling, noncorroding regime. In addition, water flow velocity must be maintained above a certain threshold (ca 0.5 m/s in tubeside flow) to avoid fouling and corrosion. 

Dumansky Institute of Colloid Chemistry and Water Chemistry ofNASU ... 

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