[en] Sensitivity study of Sodium-Water Reaction (SWR), which will occur in a steam generator of a liquid sodium cooled fast reactor when a heat transfer tube is failed, have been carried out using the multi-dimensional and multi-phase analysis code SERAPHIM. An influence of the interfacial area density and the sodium hydroxide (NaOH) evaporation on the SWR phenomena is investigated. The interfacial area density much affects the heating (reaction) zone. However, it is less influential on the maximum temperature. In the analysis, the hydrogen gas produced by the SWR covers over the interface between the liquid sodium and the water vapor and thus suppresses the reaction quickly. Consequently, the maximum temperature has a ceiling regardless of the interfacial area density. When one takes into account the evaporation of NaOH, the maximum temperature tends to decrease, whereas it has a little influence on the heating zone. The latent heat of NaOH evaporation in the standard state is considerably high compared with the reaction heat in which liquid NaOH is generated in the SWR. Therefore, the maximum temperature decreases due to the latent heat. It is concluded that the evaporation of NaOH is quite important and has a great effect to the temperature investigation in the SWR. (author)

[en] A vector finite volume method (VFVM) has been developed for an electromagnetic flow analysis. In the VFVM, the governing equations of magnetic flux density and electric field intensity are solved separately so as to reduce the computational cost caused by an iterative procedure that is required to satisfy the solenoidal condition. In the present paper, a suppression of temperature fluctuation of liquid sodium after a T-junction has also been investigated with a simplified two dimensional numerical analysis by adding an obstacle (turbulence promoter) or a magnetic field after the junction. (author)

[en] The deposition of catalyst metals in ceramic breeders could enhance the release rate of tritium due to the promotion of isotope exchange reactions taking place at the interface of the breeder surface and the sweep gas. In this work, the authors examined the effects of catalytic active metal deposited on lithium titanate on the isotope exchange reactions. With respect to the virgin lithium titanate, it was found that the rate of the isotope exchange reactions taking place on the surface is quite low. However, the deposition of palladium greatly increased the exchange reaction rate. The effect of the amounts of deposited palladium on the isotope exchange reaction rate was also investigated. The results indicate that the exchange reactions are still enhanced even if the amounts of deposited palladium are as low as 0.04%

[en] Sodium fire is one of the key issues for plant safety of sodium-cooled fast reactor (SFR) regardless of its size. In general, a concrete structure, which includes free and bonding water inside, is used in a reactor building. Accordingly, water vapor will release from the concrete during sodium fire incident due to temperature increase resulting in a hydrogen generation even in a dry air condition. Since a surface area ratio of concrete wall per compartment volume will increase in accordance with a decrease of the dimension of the comportment, which corresponds to a small and medium sized or modular reactor (SMR), the probability of hydrogen generation may increase due to an increase of a concentration of water vapor that will be released from the concrete. A numerical investigation of a small leakage sodium pool fire has been carried out by changing a dimension of compartment. Furthermore, numerical challenges to enhance a prediction accuracy of hydrogen generation during sodium fire has also been discussed in the paper. (author)

[en] Numerical methodology for sodium combustion has been developed for the safety evaluation of a liquid metal cooled fast reactor. Sodium reactions with oxygen and water vapor are complicated phenomena of reacting fluid flow and the physical and chemical processes are not well understood in detail. The phenomenological scale in sodium fire varies in wide range. It is not practical to consider all the scales in one simulation. Hence in computer codes, empirical parameters are often utilized in a conservative manner. From the viewpoint of safety analysis, use of the parameters are to be avoided otherwise verified based on appropriate experiments. In this paper multi-level or multi-scale simulation technique of the sodium fire is presented. Detailed-level analysis can develop numerical correlations useful in macroscopic safety analysis. Experimental validation of the computer codes is also given by comparing the results with experimental data. (author)

[en] Polarized Raman scattering from NdBa₂Cu₃O_y and Nd_1.6Ba_1.4Cu₃O_y single crystals is reported. Single-phonon peaks have been observed in NdBa₂Cu₃O_y at 136, 168, 316, 448, 508, and 580 cm^-1 at room temperature where the 316- and 580-cm^-1 peaks are strong in the (x,x) while the 448- and 508-cm^-1 peaks are strong in the (z,z) configurations. The 316-cm^-1 peak is found to separate into two peaks at 290 and 323 cm^-1 at 4 K, which are assigned as in-phase and out-of-phase vibration of oxygen atoms in the Cu-O plane, respectively. The polarization dependence of the scattering peaks has been explained on the basis of the characteristics of the electronic transitions. The energy shift of peaks when Ba is substituted by Nd has also been discussed

No abstract available

[en] We investigate the effect of Zn substitution for Cu on the lattice parameters and the temperature dependences of resistivity and susceptibility in YBa₂Cu₄O₈. Samples of YBa₂(Cu_1-xZn_x)₄O₈ with x=0 to 0.1 were prepared by a high-oxygen-pressure technique. As the Zn context is increased, the lattice parameters of the a and b axes increase, but that of the c axis decreases. The oxygen content is independent of the Zn concentration. The superconducting transition temperature T_c decreases monotonically with increasing Zn concentration, with a coefficient of -21 K/at.%, and superconductivity vanishes at x=0.037. The Zn doping induces the local moment coming from Cu²⁺, and the normal-state susceptibility shows Curie-Weiss-like behavior. Some possible explanations for the suppression of T_c by Zn doping are provided

No abstract available

[en] JAEA has developed sodium fire analysis codes SPHINCS and AQUA-SF for numerical evaluation of the consequence of a sodium fire accident, which is one of key issues in sodium-cooled fast reactor (SFR) plant. This paper describes a PIRT (Phenomena Identification and Ranking Table) process for a sodium fire event. The present PIRT is aimed to utilize for validation of the sodium fire analysis codes. Because a sodium fire accident in an SFR plant involves complex phenomena, various figures of merit (FOMs) for importance ranking could exist in the PIRT process. Therefore, the FOMs are specified through factor analysis. Associated phenomena in a sodium fire event are identified through the element- and sequence-based phenomena analyses. Importance of each associated phenomenon is evaluated by considering the sequence-based analysis of associated phenomena related to the FOMs. Then, ranking table in a sodium fire event is established. In order to validate models corresponding to the identified important phenomena in the sodium fire analysis codes, an assessment matrix of important phenomena and experiments is completed finally. (author)