Alexander L. Shimkevich

Self-diffusion in liquid potassium

The natural line of the incoherent quasi-elastic neutron scattering law of liquid potassium has been obtained from experimental double-differential scattering cross-sections at the temperatures of 340, 440, and 550 K for wavevector transfers in the range of . The full width at half maximum of this line as a function of has been analysed on the basis of several diffusion models. It has been found that the self-diffusion process in liquid potassium has an individual and activationless character and can be approximately described by means of the mode-coupling theory at temperatures noticeably more than the melting point.

On composition converting liquid metal alloys

For studying the effect of impurity on the structure of basic component in the solvent, three-component molecular-dynamics model for liquid PbK and NaPb is represented. The analysis of atomic configurations is performed by statistical-geometry method. It is shown that with increasing potassium concentration in liquid lead more than 14% at., a microstructure transition is possible. The lead influence to liquid sodium does not make an impact on the NaPb structure up to 20% at. of the lead.

Study of the Microdynamics of Liquid Lithium and Lithium-Hydrogen Melt by Inelastic Neutron Scattering

The frequency spectra of vibrations of Li atoms at temperatures of 22, 227, 397, and 557°C and the lithium-hydrogen melt (98 at % 7Li, 2 at % H) at 557°C have been obtained from the experimental neutron inelastic scattering data. On the basis of the frequency spectra, the temperature dependences of the mean-square displacement of Li atoms, the mean-square amplitudes of atomic vibrations, and the velocity autocorrelation function of atoms have been calculated. The speed of sound in liquid lithium has been estimated within the Debye model. The frequency spectra of lithium-hydrogen melt and solid lithium hydride are compared. A generalized frequency spectrum of vibrations of hydrogen atoms in lithium-hydrogen melt is obtained.

On Water Density Fluctuations with Helices of Hydrogen Bonds

An adaptive model is developed here for the liquid water density fluctuations as momentary dense clusters with helices of hydrogen bonds and nondense tetrahedral clusters of ice. This model can be useful for explanation of liquid water structural anomalies including the high quantity of hydrogen bonds with quasitetrahedral orientation in the nonordered liquid water. The topology of such clusters is essentially differed from the one of the crystalline ice. From this and only this point of view, the liquid water can be considered as a two-structural fluid by dynamic forming the two topological kinds of clusters as a consequence of condensed-matter density fluctuations. Another feature of the dense-water-part clusters is helical ordering of protons which can realize coherent vibrations. A spectral series of such vibrations is determined as a function of the number of molecules into the helical cluster.

Aqueous Nanofluid as a Two-Phase Coolant for PWR

Density fluctuations in liquid water consist of two topological kinds of instant molecular clusters. The dense ones have helical hydrogen bonds and the nondense ones are tetrahedral clusters with ice-like hydrogen bonds of water molecules. Helical ordering of protons in the dense water clusters can participate in coherent vibrations. The ramified interface of such incompatible structural elements induces clustering impurities in any aqueous solution. These additives can enhance a heat transfer of water as a two-phase coolant for PWR due to natural forming of nanoparticles with a thermal conductivity higher than water. The aqueous nanofluid as a new condensed matter has a great potential for cooling applications. It is a mixture of liquid water and dispersed phase of extremely fine quasi-solid particles usually less than 50 nm in size with the high thermal conductivity. An alternative approach is the formation of gaseous (oxygen or hydrogen) nanoparticles in density fluctuations of water. It is possible to obtain stable nanobubbles that can considerably exceed the molecular solubility of oxygen (hydrogen) in water. Such a nanofluid can convert the liquid water in the nonstoichiometric state and change its reduction-oxidation (RedOx) potential similarly to adding oxidants (or antioxidants) for applying 2D water chemistry to aqueous coolant.

On Voltage-Sensitive Managing the Redox-Potential of MSR Fuel Composition

The principles for optimal managing a composition of base solutions for the molten-salt reactor are formulated here for ensuring the given properties and exchange processes as a selective extracting of salt components. The correction of melt properties can be carried out by means of impurity additives parallel with the forced and controllable variation of reduction-oxidation (redox) potential of the non-stoichiometric salts. The accent is done on a possible application of the potentiometer for monitoring and managing of the properties of MSR fuel compositions. For this, one can use the precision methods of e.m.f and the coulomb-metric titration of sodium (lithium) in a galvanic cell upon the base of Na+ (Li+ )-β″ -Al2 O3 solid electrolyte with cation conductivity.Copyright

Collective dynamics of liquid potassium studied by inelastic neutron scattering

Abstract Dispersion curves of collective excitations have been obtained from the data on inelastic scattering on liquid potassium at 340 and 550 K for the wave-vector transfer region of 1.0 ⩽ Q ⩽ 1.3 A −1 . Experimental points were described in the frame of a model for longitudinal collective modes. In using the values of model paramters ωE and r0, the shear modulus and the high-frequency sound velocity have been evaluated. The latter seems to exceed the adiabatic sound velocity beyond the hydrodynamic limit ( Q > 0.1 A −1 ) near the melting point due to the effects of shear relaxation. This is the characteristic feature of liquid alkali metals.

Eutectic Na–Tl And Pb–Mg Alloys As Liquid-metal Coolants For Fast Nuclear Reactors

The liquid-metal microstructure is a correct subdivision of Delaunay simplexes (triangular pyramids with atoms in their vertexes). Its dense part consists of almost regular tetrahedrons connected by faces in ramified clusters. Any metal additive (as a second component of alloy) can be outside of these tetrahedral clusters or into them as a constituent of dense liquid part. These structural states of liquid alloy convert to each other at its eutectic composition. Such the polymorphic conversion of the liquid-metal alloy is approved by moleculardynamics simulating the Pb–K alloy and can be applied to any eutectic, for example, Na0.93Tl0.07 with the melting point of 64 C. At the sodium side of this point, a homogeneous solution of thallium is formed in liquid sodium which becomes the colloidal one with clusters, (Na6Tl)n, when it is passing the eutectic point. Such the modified sodium coolant enriched by the isotope, 205 Tl, can appear attractive for inhibiting the chemical activity of this coolant maintained by oxygen-free technology. An alternative liquid-metal coolant for fast nuclear reactors is eutectic, Pb0.83Mg0.17, with the melting point of 248 C. This liquid alloy as a modified lead coolant maintained by the same oxygen-free technology can appear attractive for inhibiting the high corrosion activity of molten lead.

Molecular Dynamics Simulation of the Clustering of Minor Lead Additives in Liquid Sodium

A strong influence of minor lead additives on the liquid sodium microstructure is revealed in the molecular dynamics (MD) simulation of the Na0.98Pb0.02 alloy. The obtained results can be explained by the existence of lead-sodium clusters in liquid sodium built up by ionic bonds, Na

On Enhancing Water Heat Transfer by Nanofluids

Conventional coolants such as water have, in general, poorer heat-transfer properties than most liquid metals. A clear need exists today to develop new strategies in improving the effective heat-transfer behavior of the water coolant. Recent development in technology has created a new class of liquids called “nanofluids” which are two-phase mixtures of liquid matrix and dispersed systems consisting of nanoparticles usually less than 50 nm in size. A material of these particles can be a metal, oxide, or another compound. The subject of this research is a microstructure modification of fine suspension in liquids. Such the studying can be useful for motivated choosing a composition of coolant suspension, developing technology for the effective nanofluid operation in the first circuit of pressure water reactors (PWR). These investigations are important for purposeful modifying the water composition, its deterministic operation under non-isothermal conditions. In this paper, the author has attempted to estimate an effect of a fractal structure of nanoparticles for enhancing thermal conductivity of water.Copyright