[en] An antiferromagnetic (AF)-weakly ferromagnetic (WF) crossover has been found for UO₂-TiO_x multi-phase systems, (1-y)UO₂+yTiO_x (y=0.05-0.72, x=0, 1.0, 1.5 and 2.0), when these mixtures are heat treated at high temperature in vacuum. From the powder X-ray diffraction and electron-microprobe analyses, their phase assemblies were as follows: for x=0, 1.0 and 1.5, a heterogeneous two-phase mixture of UO₂+TiO_x; for x=2.0, that of UO₂+UTi₂O₆ for y<0.67, showing characteristic microstructures, and for y>0.67 that of UTi₂O₆+TiO₂ (plus residual minor UO₂). Magnetic susceptibility (χ) of the present UO₂ powder was confirmed to exhibit an antiferromagnetic sharp drop at T_N (=30.5 K). In contrast, χ of these multi-phase systems was found to exhibit a sharp upturn at the respective T_N, while their T_N values remained almost constant with varying y. This χ upturn at T_N is most pronounced for UO₂+Ti-oxide (titania) systems (x=1.0, 1.5 and 2.0) over the wide mixture ratio above y∼0.10. These observations indicate that an AF-WF crossover is induced for these multi-phase systems, plausibly due to the interfacial magnetic modification of UO₂ in contact with the oxide partners

No abstract available

[en] Actinide series elements, as their main and common solid oxide phase, form oxides with the fluorite structrure. Thermodynamic properties of these fluorite oxides are of prime importance in their practical application as nuclear fuels. In the present paper, high temperature thermodynamics of these actinide fluorite oxides is discussed mainly focusing on the relationship of their nonstoichiometric composition with oxygen potential, g-bar(O₂)=h-bar(O₂)-Ts-bar(O₂), as a basic parameter to describe and characterize the system. Based on the available literature data on their composition versus g-bar(O₂), h-bar(O₂) and s-bar(O₂), and related properties on these systems, a unified thermodynamic representation of all these systems is pursued in terms of the point defect thermodynamical methods. The results obtained show that in spite of wide varieties of both nonstoichiometric composition and these thermodynamic quantities of oxygen, their unified common description is basically possible by incorporating several kinds of point defects relevant to the respective systems and the defect-defect interaction parameters common to all these systems. (N.K.)

[en] An experimental investigation was performed to study the mass transfer in an annular, as the first step of the heat transfer in non-coaxial double tube for the purposes of the safety in nuclear reactors and the improvement of heat exchangers. Mass transfer coefficients between a flowing solution and the inside tube wall in annular were measured using an electrochemical method by mean of the redox reaction of ferricyanide/ferrocyanide couple. The Reynolds number was varied from 1,300 to 40,000 with six kinds of Schmidt number and three kinds of the ratio of inner and outer tube diameters in an experimental condition. The correlation of mass transfer data in annuli was expressed as follows: Sh = 0.015(Re) sup(0.8)(Sc) sup(0.4)(Do/Di) sup(0.53) This is reasonably agreed with previous heat transfer correlations by mean of the analogy for heat and mass transfer. (author)

[en] A concise review is given on a new chemical approach to high Tc superconductivity recently proposed by the present author, the multi-valence resonance-condensation (MVRC) model. The MVRC state of super-conductivity is a Bose condensate of the resonance hybrids between two kinds of multivalence states of the chemical species (Cu^1,2,3+, Bi^3,4,5+, etc.) responsible for the superconductivity, which is realized macroscopically through the self-organization (valence fluctuation -> valence ordering -> resonance-condensation) process of the electron system as the fundamental chemical bonding force. This is demonstrated to provide a possible unified picture of the super-conducting state of various high T_c systems for both the so-called 'hole' and 'electron' type superconductors in a symmetrical manner. In this paper, through the analysis of oxygen nonstoichiometry dependence of the superconductivity of YBa₂Cu₃O_7-x, these main features of the model are delineated, emphasizing the importance of the combined defect-chemical and quantum-chemical consideration on the mixed (multi) valence of high T_c systems. (author). 28 refs.; 5 figs.; 1 tab

[en] The prominent feature of the thermodynamic data of PuO_2-x and CeO_2-x is the strong sigmoidal variation of anti h(O₂) and anti s(O₂) with x. In this paper, in search for a possible basic mechanism for the onset of such feature of anti h(O₂) and anti s(O₂) in these hypostoichiometric fluorite-type oxides, a defect-thermodynamic formulation is put forward based on the local Pu³⁺ (Ce³⁺)-V₀ interaction model in the mutual first nearest neighbor coordination sphere. Under some simplified assumptions on the V₀ arrangement on the oxygen sublattice the number of the local defect-defect configurations is reduced to 16, and using the virtual Gibbs formation energies of these 16 local configurations as the basic parameter the explicit analytical expressions are derived for their concentrations and for the thermodynamic quantities of oxygen ( anti g(O₂), anti h(O₂) and anti s(O₂)). The numerical evaluations show that such sigmoidal shape of both anti h(O₂) and anti s(O₂) as observed in these systems is interpreted and reproduced well by the present approach as a result of the coupled local defect-defect configurational changes between Pu(Ce) and O sites. Discussions are also made on the validity and the limitation of the present model. (orig.)

[en] Thermodynamic analysis on point defects of UO_2+x at relatively small deviation from stoichiometry, 0≤x≤0.05 between 600 and 1400⁰C has been made based on the available literature data on the relative partial molar thermodynamic quantities of oxygen in UO_2+x; anti g(O₂), anti h(O₂) and anti s(O₂) as a function of nonstoichiometry, x at these temperatures. In the model, as majority defects, Frenkel disorder between oxygen vacancy and oxygen interstitial cluster with predominant electronic disorder was assumed. Numerical evaluation of the theoretical model shows that the model reproduces almost quantitatively the microcalorimetrically measured anti h(O₂)-x curve at 1100⁰C and also gives the theoretical log P^*_O2-x curves which agree with reported data within their experimental scatters. It was also found that both theoretical anti h(O₂) and anti σ(O₂) exhibit strong temperature dependences at approximately x< or approx.0.02, contrary to the majority of the published experimental data on these quantities. (orig.)

[en] A complete set of thermodynamic parameters of UO_2+x - the relative partial molar thermodynamic quantities of oxygen anti g(O₂), anti h(O₂) as a function of nonstoichiometry x and temperature T - have been determined with sufficient accuracy by the precise emf measurements of the solid state galvanic cell of the type Ni, NiO/Stabilized ZrO₂/UO_2+x, at 0.003≤x≤0.23 between 500 and 1100⁰C. Nonstoichiometry x was controlled and determined by the coulometric titration of oxide ions at 1000⁰C by using NiO in the Ni/NiO reference mixture as a source of oxygen. UO_2+x samples of two different preparation procedures give almost identical results and show that anti g(O₂) versus T plots at various compositions x are not a linear function of temperature, but curve downwards with temperature in the composition and temperature ranges studied. This tendency becomes more pronounced with decreasing nonstoichiometry x and indicates that both anti h(O₂) and anti s(O₂) of UO_2+x increase with temperature, their temperature dependence becoming stronger with decreasing nonstoichiometry x. (orig./TW)

[en] Hamaoka Nuclear Power Station No.5 (No.5) is being built. It is ABWR and 1350000 kW electric outputs. In the paper, the characteristics of the water circulating system and hydraulic characteristics of discharge pit are stated. New design, inspection items and outline of intake and outtake system are described. The water circulating system of No.5 is set by two siphon break valves at the water circulating pipe of the outlet of building and at the regulator. The discharge pit is cost down and compact by using only the orifice method for controlling water level. The change of water surface of the discharge pit is very small. The orifice is able to determine the flow coefficient. It was confirmed that the water circulation is filled with water. (S.Y.)

[en] A thermodynamic model of hyperstoichiometric uranium dioxide, UO_2+x is presented. The model takes four kinds of oxygen interstitial defect clusters into account and in addition treats the remaining excess enthalpy term as the molar volume dependent parts of both the defect formation energies and the phenomenological interaction energy between the defects. The model gives a consistent and satisfactory description of the full set of thermodynamic data of oxygen in UO_2+x, anti g(O₂), anti h(O₂) and anti s(O₂) reported by the present autors. (orig.)