Y.H Kim

Extension of Analytic Function Expansion Nodal Method to Multigroup Problems in Hexagonal- Z Geometry

The analytic function expansion nodal (AFEN) method has been successfully applied to two-group neutron diffusion problems. However, the current AFEN method cannot treat complex eigenmodes, which appear in the general multigroup equations. The AFEN method is extended such that complex eigenmodes are treated within the framework of the original AFEN method for any type of geometry. Also, a suite of new nodal codes based on the extended AFEN theory is developed for hexagonal-z geometry and applied to several benchmark problems. Numerical results obtained attest to their accuracy and applicability to practical problems.

Parallel solution of the neutron diffusion equation with the domain decomposition method on a transputer network

The neutron diffusion equation in reactor physics is solved on a multiple-instruction, multiple-data parallel computer network composed of five transputers. A parallel variant of the Schwarz alternating procedure for overlapping subdomains is used for domain decomposition. The parallel Schwartz algorithm with the concept of underrelaxation in pseudo-boundary conditions is applied to two types of reactor benchmark problems: fixed-source problems and eigenvalue problems. Results of parallel computation for these problems are reported and compared with results of sequential computation. The results show that a very high speedup can be achieved in fixed-source problems in spite of the small problem size and that a relatively high speedup, although lower than that of fixed-source problems, can be obtained in eigenvalue problems.

Graphite-filled mixed-oxide fuel design for fully loaded PWR cores

Abstract In order to maximize the benefit of plutonium recycling in the current light water reactor (LWR) cores, recently, many researches have been performed for 100% mixed-oxide (MOX) core. However, when the LWR core is fully loaded with MOX fuel, several problems arise due to the spectrum hardening effect of the plutonium isotopes. In order to overcome the spectrum hardening effect, we propose a new fuel design for full MOX core, that consists of annular fuel material filled internally with graphite. The new design is compatible with the conventional assembly in its overall geometry, and therefore it may require only minor modifications from the conventional fuel technology. The results of assembly and core analysis with the graphite-filled MOX fuel rods indicate that the new fuel design provides desirable characteristics, namely, higher burnup with less fuel inventory, faster depletion of plutonium and less production of actinides, and better safety features in fuel temperature, control rod worth, boron worth, moderator temperature coefficient (MTC), and shutdown margin. These beneficial results come from the enhanced moderation of the neutrons due to the moderating power of graphite and its contribution to the increased moderator/fuel volume ratio.

Parallel schwarz algorithm with under-relaxed pseudo boundary conditions in domain decomposition method

The parallel Schwarz algorithm for solving partial differential equations in a two-subdomain case and its convergence feature are summarized. Under-relaxation in pseudo-boundary conditions as an acceleration scheme is introduced and its convergence is analyzed in this paper. In addition, several iteration strategies which exploit the attractive feature of the under-relaxation scheme in pseudo-boundary conditions are investigated via numerical experiments. The results show that superlinear speedup can easily be obtained if adequate iteration strategies are adopted.