Showing papers by "Japan Atomic Energy Research Institute published in 2007"

Best Practice Guidelines for the use of CFD in Nuclear Reactor Safety Applications

Abstract: In May 2002, an 'Exploratory Meeting of Experts to Define an Action Plan on the Application of Computational Fluid Dynamics (CFD) Codes to Nuclear Reactor Safety Problems' was held at Aix-en-Provence, France. One of three recommended actions was the formation of this writing group to report on the need for guidelines for use of CFD in single phase Nuclear Reactor Safety (NRS) applications. CSNI approved this writing group at the end of 2002, and work began in March 2003. A final report was submitted to GAMA in September 2004, summarizing existing Best Practice Guidelines (BPG) for CFD, and recommending creation of a BPG document for Nuclear Reactor Safety (NRS) applications. The present document is intended to provide an internally complete set of guidelines for a range of single phase applications of CFD to NRS problems. However, it is not meant to be comprehensive; it is recognized that for any specific application a higher level of specificity is possible on questions of nodalization, model selection, and validation. This document should provide direct guidance on the key considerations in known single phase applications, and general directions for resolving remaining details. The intent is that it will serve as a template for further application specific (e.g. PTS, induced break) BPG documents that will provide much more detailed information and examples. The document begins with a summary of NRS related CFD analysis in countries represented by the authors. Chapter 3 deals with definition of the problem and its solution approach. This includes isolation of the portion of the NRS problem most in need of CFD, and use of a classic thermal hydraulic (TH) safety code to provide boundary conditions for the CFD based upon less detailed simulation of the balance of plant. Chapter 4 provides guidance in choosing between various options, and also discusses use of a transient calculation with tightly coupled CFD and TH codes. Chapter 5 discusses selection of physical models available as user options. As is appropriate for single phase CFD, most of the emphasis is on selection of turbulence models. Recommendations are provided for high level selection between Reynolds Averaged Navier Stokes (RANS), Large Eddy Simulation (LES), and hybrid approaches such as Detached Eddy Simulation (DES). Chapter 7 focuses on the numerical approximations available to solve the flow equations. Guidelines are provided for nodalization, and for choice of discrete approximations to the differential equations. Guidance is also given on convergence of iterative solutions, and numerical techniques for following free surfaces. Chapter 7 discusses general assessment strategy. Chapter 8 covers approaches to limiting errors associated with discretization and numerical solution methods (verification). This step is a necessary precursor to quantifying errors associated with physical models (validation) as described in Chapter 9. Guidance on documentation is provided in Chapter 10. Chapter 11 provides some examples of NRS applications; the first two examples are boron dilution and pressurized thermal shock; the third example explores the use of Fluent for simulation of dry cask storage of spent fuel (this example is highly suited to single phase CFD analysis)

Recent Advances in Ce-Based Heavy-Fermion Superconductivity and Fermi Surface Properties

Abstract: We present the recent advances in Ce-based heavy fermion superconductivity. Heavy fermions are formed by the competition between the Ruderman–Kittel–Kasuya–Yosida interaction and the Kondo effect. ...

An Additional Insight into the Correlation between the Distribution Ratios and the Aqueous Acidity of the TODGA System

Abstract: Extraction of Eu(III) and Am(III) from HNO3 into the organic solvents using N,N,N′,N′‐tetraoctyl‐diglycolamide (TODGA) was investigated in order to study the detailed extraction reaction. The chemical species: 1:2 for metal:TODGA complex is present in polar diluents. On the other hand, the metal complexes need three or more TODGA molecules to remain stable in non‐polar diluents. The HNO3 concentration dependence on the distribution ratio suggests that HNO3 participates in the metal extraction. Infrared spectra indicate that the carbonyl oxygen coordinates with Eu(III), and luminescence lifetimes suggest that there are no water molecules in the inner coordination sphere of the extracted Eu‐complex.

Characterization of Electrode/Electrolyte Interface with X-Ray Reflectometry and Epitaxial-Film LiMn2O4 Electrode

Abstract: Structural changes at electrode/electrolyte interface of a lithium cell were studied by X-ray reflectometry and two-dimensional model electrodes with a restricted lattice plane of LiMn 2 O 4 . The electrodes were constructed with an epitaxial film synthesized by the pulsed laser deposition method. The orientation of the film depends on the substrate plane; the (111), (110), and (100) planes of LiMn 2 O 4 grew on the (111), (110), and (100) planes of the SrTiO 3 substrates, respectively. The ex situ reflectometry indicated that a thin impurity layer covered the lattice plane of the as-grown film. The impurity layer was dissolved and a solid-electrolyte-interface-like phase appeared after the electrode was soaked into the electrolyte. A defect layer was formed in the (111) plane, whereas no density changes were detected for the other lattice planes. The in situ observation clarified that the surface reactivity depended on the lattice planes of the spinel; the defect layer at the (111) plane was stable during the electrochemical reaction, whereas a slight decrease in the film thickness was observed for the (110) plane. Our surface characterization of the intercalation electrode indicated that the surface structure changes during the pristine stage of the change-discharge processes and these changes are dependent on the lattice orientation of LiMn 2 O 4 .

Stability and control of resistive wall modes in high beta, low rotation DIII-D plasmas

Abstract: Recent high-β DIII-D (Luxon J.L. 2002 Nucl. Fusion 42 64) experiments with the new capability of balanced neutral beam injection show that the resistive wall mode (RWM) remains stable when the plasma rotation is lowered to a fraction of a per cent of the Alfven frequency by reducing the injection of angular momentum in discharges with minimized magnetic field errors. Previous DIII-D experiments yielded a high plasma rotation threshold (of order a few per cent of the Alfven frequency) for RWM stabilization when resonant magnetic braking was applied to lower the plasma rotation. We propose that the previously observed rotation threshold can be explained as the entrance into a forbidden band of rotation that results from torque balance including the resonant field amplification by the stable RWM. Resonant braking can also occur naturally in a plasma subject to magnetic instabilities with a zero frequency component, such as edge localized modes. In DIII-D, robust RWM stabilization can be achieved using simultaneous feedback control of the two sets of non-axisymmetric coils. Slow feedback control of the external coils is used for dynamic error field correction; fast feedback control of the internal non-axisymmetric coils provides RWM stabilization during transient periods of low rotation. This method of active control of the n = 1 RWM has opened access to new regimes of high performance in DIII-D. Very high plasma pressure combined with elevated qmin for high bootstrap current fraction, and internal transport barriers for high energy confinement, are sustained for almost 2 s, or 10 energy confinement times, suggesting a possible path to high fusion performance, steady-state tokamak scenarios.

Japanese adult male voxel phantom constructed on the basis of CT images.

Abstract: A Japanese adult male voxel (volume pixel) phantom (hereinafter referred to as the JM phantom) was constructed on the basis of CT images of a healthy Japanese adult male volunteer. Body characteristics of the JM phantom were compared with those of a voxelised MIRD5 type phantom and a Japanese adult male voxel phantom which was previously developed. The voxel size of the JM phantom is 0.98 x 0.98 x 1 mm(3). The shapes of the organs of the JM phantom, even for small or complicated organs, such as thyroid and stomach, are more realistically reproduced as compared with the previous Japanese voxel phantom (voxel size: 0.98 x 0.98 x 10 mm(3)). Photon self-absorbed fractions (self-AFs) for brain, kidneys, spleen, pancreas, thyroid and urinary bladder wall of JM were evaluated and were compared with those of the other phantoms. In consequence, it was suggested that the mass, shape and thickness of organs are important factors for the determination of self-AFs.

Recent progress on the development and analysis of the ITPA global H-mode confinement database

Abstract: This paper describes the updates to and analysis of the International Tokamak Physics Activity (ITPA) Global H-Mode Confinement Database version 3 (DB3) over the period 1994–2004. Global data, for the energy confinement time and its controlling parameters, have now been collected from 18 machines of different sizes and shapes: ASDEX, ASDEX Upgrade, C-Mod, COMPASS-D, DIII-D, JET, JFT-2M, JT-60U, MAST, NSTX, PBX-M, PDX, START, T-10, TCV, TdeV, TFTR and TUMAN-3M. The database now contains 10382 data entries from 3762 plasma discharges, including data from deuterium–tritium experiments, low-aspect ratio plasmas, dimensionless parameter experiments and plasmas. DB3 also contains an increased amount of data from a range of diverted machines and further data at high triangularity, high density and high current. A wide range of physics studies has been performed on DB3 with particular progress made in the separation of core and edge behaviour, dimensionless parameter analyses and the comparison of the database with one-dimensional transport codes. The errors in the physics variables of the database have also been studied and this has led to the use of errors in variables fits. A key aim of the database has always been to provide a basis for estimating the energy confinement properties of next step machines such as ITER, and so the impact of the database and its analysis on such machines is also discussed.

Energetically deep defect centers in vapor-phase grown zinc oxide

Abstract: Vapor-phase grown ZnO crystals were investigated by means of DLTS measurements. The generation of defect center E4 subsequent to annealing in different ambients was monitored. By conducting electron irradiations with energies, where either both the Zn- and O-sublattice are damaged or according to [1] only the Zn-lattice, a chemical assignment to the defect centers E4 and E3 could be accomplished. DLTS investigations of ZnO samples under illumination give evidence that E4 is a negative-U center.

Quantum phase diagram of antiferromagnetism and superconductivity with a tetracritical point in Ce Rh In 5 in zero magnetic field

Abstract: We report on a pressure-temperature phase diagram of antiferromagnetism (AFM) and superconductivity (SC) in $\mathrm{Ce}\mathrm{Rh}{\mathrm{In}}_{5}$ studied by the nuclear-quadrupole-resonance measurements under pressure. It is demonstrated that an AFM phase transition takes place inside the superconducting state. This result reveals that a tetracritical point exists in the phase diagram of AFM and SC at zero magnetic field. The finding of unconventional SC characteristics in the uniformly coexisting phase of AFM and SC suggests that both phases may be mediated by the same magnetic interaction.

Cubic phases of B C 2 N : A first-principles study

Abstract: First-principles calculations are performed and analyzed to identify different cubic phases of $\mathrm{B}{\mathrm{C}}_{2}\mathrm{N}$ synthesized experimentally. With a proper choice of the supercell, cutoff energy, and sampling $k$ points, the cubic phases are found to be stable theoretically. The bulk modulus from elastic stiffness constants for each of the phases is in excellent agreement with available experimental data. All the phases are defect-free and do not possess any B\char21{}B or N\char21{}N bond. Two high-density phases with nearly degenerate energies are interpreted to represent two experimental systems of different x-ray patterns. The high-density phases are characterized by the existence of C\char21{}C bonds, whereas the low-density phase is characterized by the absence of C\char21{}C bonds. From the calculated equation of state and the available experimental data, we show that the unique feature of each of the cubic $\mathrm{B}{\mathrm{C}}_{2}\mathrm{N}$ phases is a direct result of the corresponding local electronic structure and chemical bonding in the system.

Status and Outlook of the Neutron Time-of-Flight Facility n_TOF at CERN

Abstract: The neutron time-of-flight facility n_TOF at CERN, fully operational since 2002, combines a high instantaneous neutron flux with high energy resolution. The wide energy range and the high neutron flux per time-of-flight burst result in a much enhanced signal to background ratio for neutron capture of radioactive isotopes and makes this facility well suited for the measurement of high quality neutron-induced reaction cross-sections. Neutrons are created by spallation reactions induced by a pulsed 20 GeV/c proton beam impinging on a lead target. A 5 cm water slab surrounding the lead target serves as a coolant and at the same time as a moderator of the spallation neutron spectrum, providing a wide energy spectrum from 0.1 eV to about 250 MeV. By the end of 2005, a first phase of data taking has been successfully terminated. Fission and capture experiments have been performed on a variety of isotopes of interest for nuclear astrophysics, advanced nuclear technologies and for basic nuclear physics. The instrumentation developed for this facility consists of parallel plate avalanche counter and fission ionization chamber detectors for the fission experiments and of low mass C6D6 detectors and a 4 pi BaF2 total absorption calorimeter for capture experiments. A new data acquisition system, based on sampling of the detector signals, has been developed to cope with the high count rates and to minimize the effective dead time to only a few tens of nanosecond. A second phase of data taking is planned to start in 2007, after an upgrade of the spallation target. On the longer term, the construction of a flight path at 20 m resulting in an increased neutron flux of about a factor of 100 opens new possibilities.

Crystal distortions in geometrically frustrated ACr2O4 (A = Zn,Cd)

Abstract: In this paper, we discuss neutron and synchrotron x-ray diffraction data obtained from single crystals of ACr2O4 (A = Zn, Cd). The Cr spinels undergo three-dimensional spin-Peierls transitions at low temperatures that involve cubic-to-tetragonal lattice distortions and magnetic long-range ordering. Our results show that the magnetic structures selected by these systems are closely related to the lattice distortions that are undertaken.

Processes for producing nano-space controlled polymer ion-exchange membranes

Abstract: A polymer film substrate is irradiated with ions to make a large number of nano-sized through-holes and the substrate may be further irradiated with ionizing radiation so that a functional monomer may be grafted or co-grafted onto a surface of the film and within the holes; in addition, sulfonic acid group(s) may be introduced into the graft chains to produce a polymer ion-exchange membrane that may have high oxidation resistance, dimensional stability, electrical conductivity and/or methanol resistance, as well as may have an ion-exchange capacity controlled over a wide range.

Pressure–Temperature Phase Diagram and Superconductivity in UIr

Abstract: Pressure-induced superconductivity is found in UIr without inversion symmetry. The pressure–temperature phase diagram has been investigated by means of the electrical resistivity, ac-susceptibility and magnetization measurements under high pressure. The phase diagram consists of three magnetic phases FM1–3 and a superconducting phase. The huge enhancement of residual resistivity and the negative magnetoresistance are found in the intermediate pressure region. These behavior may be induced by the pressure-induced structural phase transition and the accompanied phase separation in this pressure range. The superconducting phase with narrow pressure range is embedded in the FM3 phase, adjacent to zero-temperature FM3-to-nonmagnetic transition. The temperature dependence of resistivity above T SC follows non-Fermi liquid form of T 1.6 . From these experimental facts, superconductivity is considered to be associated with the ferromagnetic fluctuation.

Soft x-ray magnetic circular dichroism study of Ca 1 − x Sr x RuO 3 across the ferromagnetic quantum phase transition

Abstract: ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{RuO}}_{3}$, which is ferromagnetic for Sr concentration $xg0.3$, has been studied by x-ray magnetic circular dichroism (XMCD) in $\mathrm{Ru}\phantom{\rule{0.2em}{0ex}}3p$ and $\mathrm{O}\phantom{\rule{0.2em}{0ex}}1s$ core-level x-ray absorption. XMCD signals appear at $x$ $\ensuremath{\sim}$ 0.3 and monotonically increase with $x$ in the ferromagnetic phase. While the monotonic increase of the XMCD signals with $x$ is of a typical Stoner-type, the absence of appreciable change in the spectral line shapes of both the $\mathrm{Ru}\phantom{\rule{0.2em}{0ex}}3p$ and $\mathrm{O}\phantom{\rule{0.2em}{0ex}}1s$ XMCD spectra indicate that the itinerant-electron ferromagnetism in ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{RuO}}_{3}$ is influenced by strong electron correlation.

Density and structure of undercooled molten silicon using synchrotron radiation combined with an electromagnetic levitation technique

Abstract: X-ray diffraction and density measurements have been simultaneously performed to investigate the atomic structure of molten silicon in the undercooled temperature region with the use of an electromagnetic levitation technique. The density was obtained from the levitated sample shape by a non-contact method based on an image analysis technique. From structural analysis of the undercooled molten silicon, the first nearest neighbor coordination number and interatomic distance were determined to be about 5 and 2.48 A, respectively. There are no temperature dependence of both the first nearest neighbor coordination number and interatomic distance, but a small change observed on the side of the first peak with the structure factor in the temperature range of 1550–1900 K. From these results, we conclude that the short-range order based on tetrahedral bonds of the undercooled molten silicon did not change with the degree of undercooling, however, the medium-range order was changed by the degree of undercooling.

Elastic properties of filled-Skutterudite compounds probed by Mössbauer nuclei

Abstract: We have carried out Mossbauer spectroscopy and nuclear resonant inelastic scattering to elucidate the lattice dynamics in fi.lled-Skutterudite compounds, especially phosphides. The second-order Doppler shift obeys the Debye model in RFe4P12 Nuclear quadrupole interaction reveals an unusual temperature dependence in these compounds. An anomaly is observed in 57Fe nuclear resonant inelastic scattering of these compounds. The energy where the anomaly observed in SmFe4P12 agrees with the phonon excitation energy observed by 149Sm nuclear resonant inelastic scattering. We have also performed the 99Ru Mossbauer measurements SmRu4P12.

Transformation in intermediate-range structure of vitreous silica under high pressure and temperature

Abstract: The pressure dependence of the structure factor for vitreous silica was measured up to 8.3 GPa at 500 °C by means of an in situ x-ray diffraction method. The position of the first sharp diffraction peak (FSDP) moved to a higher momentum transfer as the pressure increased. It moved rapidly between 3.3 and 5.8 GPa, and then the slope of the FSDP position as a function of pressure decreased. The pressure dependence of the position is the same as that for a sample heated to 500 °C after room-temperature compression. On decompression at 500 °C, the position of the FSDP showed hysteresis. The pressure dependence of the FSDP position suggests that the permanent densification of vitreous silica is realized due to preservation of the intermediate-range structure stabilized at high pressure and temperature.