Sodium-water interaction

FAST REACTOR ENGINEERING 6.5.1. Sodium-water interaction 

Sodium-water steam generator design features. One of the principal problems in the development of the sodium-water steam generator (SG) design is the choice of the tube bundle characteristics. 

Besides, there are certain limitations on temperature conditions for some steels (for example, stability of mechanical properties of 2V4CrlMo steel can only be guaranteed at temperature not exceeding 520°C). It should be also noted that practically all of the above steels have adequate corrosion resistance in pure sodium and all corrosion problems take place on the steam-water side. So it is seen that choosing tube material is rather complicated problem. 

Taking into account various properties of steels and contradictory requirements imposed to them, the SG design features, such as unit heat capacity, tube bundle characteristics, maintainability, etc. sometimes play decisive role in the choice of structural materials. To date, there are examples of implementation of all the above steels. 

Speaking about design features, small tube-to-tube distance in the tube bundle should be mentioned, since micro defect present in one tube would result in rapid failures of the adjacent tubes. 

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The cause of one of the leaks remained uncertain. At the BN-350 a rupture of the electromagnetic pump channel wall of the secondary circuit auxiliary system. A possible cause of this event was corrosion resulting from prolonged operation of the pump at pumping of coolant strongly contaminated with sodium-water interaction products. 

Thus, sodium-water interaction is rather complicated multistage process including successive reactions with sodium hydroxide and hydrogen formation followed by their interaction with sodium. The final concentration of water-sodium interaction products is determined by thermodynamic equilibrium conditions and the time of reaching equilibrium state in the course of the reaction. 

In the USA sodium was chosen as LMC as it possessed the better thermo-hydraulic characteristics. The ground-based test facility-prototype of the NPI and the experimental nuclear submarine Sea Wolf were constructed. Yet the operation experience has pointed that the choice of coolant which was chemically active with respect to oxygen and water has not justified itself. After several sodium water interaction, the RI was decommissioned together with the compartment and replaced by the pressurized water RI. 

In 1979, tests were carried out in the micro-modular steam generator SG-1 to study sodium-water interaction processes in case of small (up to 0.2 g/s) and large (up to 0.25 kg/s) water leaks. The main results of tests ... 

With respect to secondary-circuit operation problems arose by the steam generator leaks in 1973-1975. For ensuring the required coolant quality after the leaks prolonged operation of coolant-purification systems was called for. A great quantity of impurities, mainly of sodium-water interaction products, had accumulated in cold traps so that the operating efficiency of the traps began to decrease. To restore purification system performance, regeneration work on four secondary circuit cold traps and coolant preparation system cold traps was carried out. 

Sodium is a chemical that has been used extensively and has an established record of safe handling on a large scale. The PRISM reactor has been designed with the potential for sodium-water reaction in mind. The primary sodium system is entirely encompassed within the reactor vessel and surroxmded by the containment vessel, to eliminate the potential for loss of primary coolant and to reduce the potential for sodium-water reaction. The IHTS transports heat from the primary system to the SG where the heat is transferred to the cooling water. The sodium-water interaction is mitigated in the SG with the pressure cap inert gas and the SGIS as described in Section 6.4.5.I. 

In contrast, solid sodium chloride dissolves readily in water at room temperature and without a large heat effect. This can only mean that the water interacts strongly with the ions—so strongly that aqueous ions are about as stable as are ions in the crystal. In fact, water interacts... 

Fig. 12 (A) The d(CGCGAATTCGCG)2 duplex with a narrow groove and a sodium ion coordinated at the ApT step. (I) The DNA is shown in stick representation and the ion in space-filling size. Left view is directly into the central minor groove. Right view left view rotated 90° counterclockwise and tilted 30° to show the ion in the minor groove. (II) The base pair views are of the central ApT step. Top view is down the helix axis, bottom view is directly into the minor groove. (B) The DNA duplex with a phosphate-oxygen pair-sodium ion interaction and a water molecule coordinated at the ApT step. (II) Views as in Fig. 12A for the phosphate-ion-water-base complex at the AT site. Reproduced with permission from Ref. (42). Copyright 2000, American Chemical Society.

W. Meyerhofler said that under the conditions here described, the salt pair, barium nitrite and sodium chloride, is stable within its interval of change, and that in the presence of water it will separate as a third salt, while barium chloride and sodium nitrite will remain in soln. To prevent this an excess of sodium nitrite is necessary. J. Matuschek showed that hydrated barium chloride and sodium nitrite, interact when pounded together, and that these salts react in molecular proportion in aq. soln. at 100° if only a limited amount of water is present. The yield of barium nitrite approaches the theoretical when the amount of water added as solvent is one-third of the weight of the nitrite which would be formed if the reaction were quantitative. 

By decreasing the water content in the core (Wo < 15), a decrease in the hydrated electron concentration occurs. At low values (Wo < 6) all molecules of water interact very strongly with the micelle core and electrons are less attracted in the process of hydration. At Wo values lower than 5, no solvation of the electrons has been observed in reverse micelles. When Wo increases, the water in the center of the pool is partially attracted by the hydration process of electrons. The absorption spectra of hydrated electrons in the core of the micelle are shifted toward short wavelengths compared to bulk water, thus showing that the water in the pool is different from the bulk water. This could be due to the fact that the sodium cations are very active in interaction with electrons (Llor and Rigny, 1986 Pileni, 1989b Pileni et al., 1982 Wong et al., 1976). 

The computed radial distribution functions (g(r)) are shown in Fig. 18. The g(r) between the Ca ions, the Na and the 02 type atoms (carboxylic PGA oxygen) exhibits a sharp, well defined peak at about 2.5 A The calcium plot is markedly more pronounced than the sodium one. This suggests calcium ions play a relevant bridging role between the chains while sodium mainly interacts with the peripheral carboxyl groups. The Ca-OW and Na-OW g(r) (OW= water oxygen) are very similar and shows two well defined hydration shells at about 2.5 and 4.5 A. The sodium one is a little more pronounced on the second peak, suggesting its water shell is more lasting and complete. 

Lipophilic linkers (Salager, 1998) and hydrophilic linkers (Uchiyama, 2000 Acosta, 2002) are used to increase the value of SP and decrease y. Lipophilic linkers are long-chained alcohols (above C8) and their low oxyethylenation products that increase the surfactant-oil interaction. The most effective ones have hydrophobic chain lengths that are an average of the hydrophobic chain length of the surfactant and the chain length of the alkane oil. Hydrophilic linkers increase the surfactant-water interaction. Examples are mono- and dimethylnaphthalene sulfonates and sodium octanoate... 

Transition Interval.—double salt, we learned (p. 242), when brought in contact with water at the transition point undergoes partial decomposition with separation of one of the constituent salts and only after a certain range of temperature (transition interval) has been passed, can a pure saturated solution of the double salt be obtained. A similar behaviour is also found in the case of reciprocal salt-pairs. In the case of each salt-pair there will be a certain range of temperature, called the transition interval, within which, if excess of the salt-pair is brought into contact with water, interaction will occur and one of the salts of the reciprocal salt-pair will be deposited. For the salt-pair which is stable below the transition point, the transition interval will extend down to a certain temperature below the transition point and for the salt-pair which is stable above the transition point, the transition interval will extend up to a certain temperature above the transition point. Only when the temperature is below the lower limit or above the upper limit of the transition interval, will it be possible to prepare a solution saturated only for the one salt-pair. In the case of ammonium chloride and sodium nitrate the lower limit of the transition interval is 5 5 , so that above this temperature and up to that of the transition point (unknown), ammonium chloride and sodium nitrate in contact with water will give rise to a third salt by double decomposition, in this case to sodium chloride. ... 

Since water interacts with the one-half amount of sodium produced in this reaction, sodium yield cannot exceed 50% of theoretical value. In other electrolysis reactions, the yield of sodium could be even lower. Metallic sodium production by electrolysis of molten NaCl having melting point about 800°C is the most wide spread method. In order to reduce melting temperature such salts as CaCb, Na2COs, etc. are used. For instance, mixture consisting of 40% NaCl and 60% CaCU has melting temperature of 580"C, while mixture of 35.6% NaCl and 64.4% Na2C03 melts at 600°C. 

Physical phenomena of sodium-water reaction. Sodium-water chemical interaction proceeds in two stages at the first stage the reaction proceeds at a high rate with release of gaseous hydrogen and heat ... 

Fig. 13. The effect of temperature on the solubility in micellar bile acid solution of fatty acid (top), monoglyceride (center), and sodium soap (bottom). The data of Figs. 6, 8, and 10 have been plotted with the coordinates switched and the axes reversed. Fatty acid solubility increases markedly at a temperature close to the melting point of the anhydrous acid. Monoglyceride solubility increases at a temperature close to that of the transition temperature of monoglyceride in water. Thus, for both fatty acids and soap, the temperature at which a marked increase in solubility occurs is determined chiefly by lipolytic product-water interaction. With sodium soaps, the temperature range over which the solubility increases is much broader, and a significant depression is caused by bile acids. For a given acyl radical, the temperature at which solubility increases is lowest for soap, intermediate for monoglyceride, and highest for fatty acid.

Since the alkaline agent/connate water interactions were not the major concern of this study, it was decided to eliminate the magnesium hydroxide and calcium hydroxide precipitation. Therefore, the PW was softened by filtering through a resin column saturated with sodium (Na) and chloride (Cl) ions. Thus, the divalent cations (Mg" and Ca " ) in the PW were exchanged with the monovalent cations (Na ). Note that the term "produced water (PW)" will be used to refer to the softened produced water in the remainder of this paper. 

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