Kazuyoshi Miki

A domain decomposition and overlapping method for the generation of three-dimensional boundary-fitted coordinate systems

Abstract A new method is presented for numerically generating boundary-fitted coordinate systems for arbitrarily shaped three-dimensional regions. In the method, the three-dimensional region of interest is decomposed into several hexahedrons, each of which has two grid surfaces overlapped with each of the neighboring hexahedrons. Based on this method, a new computer program GRID-3D has been developed, which allows the generation of an unlimitted number of different types of coordinate systems. Application to a variety of geometries confirms that GRID-3D is a convenient and efficient tool in the generation of boundary-fitted coordinate systems even for a considerably complicated configuration consisting of many different components.

Numerical generation of boundary-fitted curvilinear coordinate systems for arbitrarily curved surfaces

Abstract A new method is presented for numerically generating boundary-fitted coordinate systems for arbitrarily curved surfaces. The three-dimensional surface has been expressed by functions of two parameters using the geometrical modelling techniques in computer graphics. This leads to new quasi-one- and two-dimensional elliptic partial differential equations for coordinate transformation. Since the equations involve the derivatives fo teh surface expressions, the grids generated by the equations distribute on the surface depending on its slope and curvature. A computer program GRID-CS based on the method was developed and applied to a surface of the second order, a torus and a surface of a primary containment vessel for a nuclear reactor. These applications confirm that GRID-CS is a convenient and efficient tool for grid generation on arbitrarily curved surfaces.

Numerical solution of Poisson's equation with arbitrarily shaped boundaries using a domain decomposition and overlapping technique

A direct-solution scheme for numerically solving the 3-dimensional Poissons problem with arbitrarily shaped boundaries ∇ · (λ∇φ) = S on Ω, C1φ + C2n · (λ∇φ) = C3 on ∂Ω, has been developed by using a boundary-fitted coordinate transformation. The scheme also used the technique of decomposing the closed domain Ω into several hexahedron subdomains and then overlapping neighboring hexahedrons to deal with complicated geometries. A large system of linear equations derived from discretizing the Poissons equation was solved by using a biconjugate gradient method with incomplete LU factorization of the nonsymmetric coefficient matrix as preconditioning. The convergence behavior of the different domain decompositions was demonstrated for a numerical experiment. Application to the electrostatic field problem in the electron gun of a color picture tube confirms that the present numerical scheme should provide an efficient and convenient tool for solving many important large-scale engineering problems.

Deformation analysis of fuel pins within the wire-wrap assembly of an LMFBR

Abstract Deformation of fuel pins within the wire-wrap fuel assembly of a fast breeder reactor is analyzed by two computational codes, the subchannel deformation analysis code SHADOW and the thermal-hydraulic analysis code DIANA. Coupling these codes makes it possible to analyze percisely the mechanical interactions between all fuel pins in an assembly, and the deviation of coolant temperature distribution in deformed flow channels from the nominal distribution. In this paper, particular attention is paid to the effect on fuel pin deformation of the following factors: dimensional changes in the fuel assembly components, displacement of wrapper tube walls and changes in the radial power gradients.

A Conceptual Design of a Fuel Bundle for Extended Burnup in Boiling Water Reactors

A new design concept of a boiling water reactor (BWR) fuel bundle for extended burnup was proposed to improve the capacity factor without increasing the fuel cycle cost. Some effects, which are raised from higher burnup, such as strong pellet-cladding interaction due to enhanced fuel swelling and changes in neutronic characteristics due to increased fuel enrichment, are minimized by a reduction in the maximum fuel temperature to below 1200/sup 0/C and an increase in the moderator-to-fuel ratio. To realize these concepts, a 9 X 9 lattice design with a reduced fuel rod diameter and annular pellets was proposed. The proposed fuel bundle design offers advantages in fuel cycle improvements through extension of achievable burnup and reduction of fuel inventory. The core, loaded with the proposed fuel bundles which achieve 30% higher burnup by the full power month, has a potential for natural uranium savings of about 20% per unit power and a reduction in the amount of reprocessing of about 40% per unit power, compared with the current BWR design when coupled with other improvements such as refueling pattern optimization, natural uranium axial blankets, and spectral shift with flow control.

Reduction of fission gas release at extended burnups in light water reactors by decreasing fuel temperature

Abstract The effects of fuel temperature on fission gas release in light water reactor UO2 fuel at extended burnups of up to 56 effective full power months (EFPMs) are evaluated using a simple fission gas release mechanistic model. The model is first described and then model validation comparisons are made against experimental fission gas release date. The study shows that by decreasing the maximum operating fuel temperature to below 1200°C, it is possible to reduce the amount of released fission gas at 56 EFPMs to less than that at the current design burnup of 36 EFPMs.

3D electron optics simulation method for cathode ray tubes

A numerical simulation method for 3D electron optics in an electromagnetic field is described. The method features the following: (1) electric field analysis by a boundary-fitted coordinate transformation method in conjunction with a domain decomposition and overlapping technique; (2) consideration of the space-charge effect due to the electron beam in a self-consistent electric field; (3) magnetic field analysis based on a current sheet and a boundary-element method; and (4) interactive geometric modeling and numerical grid generation based on the same method used for electric field analysis. The method has been applied to electron optics simulation for the electron gun of a cathode-ray tube with a typical deflection yoke. A comparison between computed and measured screen spot profiles verifies the method and demonstrates its capabilities. >

A new approach to electron beam analysis using a domain decomposition and overlapping method in a three-dimensional boundary-fitted coordinate system

Abstract A new method is described for an electron beam analysis in a three-dimensional self-consistent field. The method has been developed based on a boundary-fitted coordinate transformation. The scheme also used the technique of decomposing the domain surrounded by electrodes into several hexahedrons and then overlapping neighboring hexahedrons. The computer code developed for the method can treat electron beam optics in complicated electrode shapes with a practicably sized CPU memory. Numerical results for an axisymmetric electron gun verified the code capability and feasibility.