Hyeun Min Kim

A REVIEW OF HELIUM GAS TURBINE TECHNOLOGY FOR HIGH-TEMPERATURE GAS-COOLED REACTORS

Current high-temperature gas-cooled reactors (HTGRs) are based on a closed Brayton cycle with helium gas as the working fluid. Thermodynamic performance of the axial-flow helium gas turbines is of critical concern as it considerably affects the overall cycle efficiency. Helium gas turbines pose some design challenges compared to steam or air turbomachinery because of the physical properties of helium and the uniqueness of the operating conditions at high pressure with low pressure ratio. This report present a review of the helium Brayton cycle experiences in Germany and in Japan. The design and availability of helium gas turbines for HTGR are also presented in this study. We have developed a new throughflow calculation code to calculate the design-point performance of helium gas turbines. Use of the method has been illustrated by applying it to the GTHTR300 reference.

STIRRING FREE SURFACE FLOWS DUE TO HORIZONTAL CIRCULATORY OSCILLATION OF A PARTIALLY FILLED CONTAINER

Mixing in a partially filled beaker or conical flask using oscillator shaker tables is routinely used for cultivation of biological cells. The present study seeks to gain a better understanding of fluid flow inside a beaker on a shaker table and the fluid motion influence on the mixing of cells within the fluid medium used for their cultivation. The imposed oscillatory motion on the beaker induces free surface deformations, which may cause laminar and low shear flow environments thus uniformly mixing the fluid medium. The low shear and uniformly mixed cell culture medium are requirements necessary for optimum cellular growth. In this study, fluid flow due to periodic and horizontal circulatory oscillations at a beaker boundary has been analyzed both numerically and experimentally. A partially filled beaker was modeled as a circular cylinder, and the cell culture medium was modeled as an incompressible fluid with a free and deformable liquid interface. The three-dimensional numerical model that can resolve the free surface deformation was based on finite difference scheme based on the “Marker-and-Cell” method. The method was used to determine the free surface deformation, its coupling to the flow dynamics within the beaker, and the resulting stirring effects. To verify the numerical model and validate the results, a simple flow visualization experiment was performed using an ion laser sheet to optically section flow chamber and reveal the flow pattern. The flow patterns obtained using numerical simulations were similar to those obtained experimentally through flow visualization. This study provides useful information that can be used to optimize the operation of a shaker table necessary to mix uniformly the cell culture, ensuring cell growth. In addition, this model can be extended to study the mixing processes in any chemical reactions within a partially filled container subjected to oscillatory forces.

Analysis of power spectrum density in the PWR fuel assembly using the 3-D LES turbulent model of fluent 6

Trublence-induced vibration is an important concern in the design of the spacer grids of nuclear power plants. This study addresses numerically and statistically the effects of random pressures due to turbulent flows upon the fluctuating responses to the power spectrum density in one-dimensional nuclear fuel rod supported simply by the spacer grids. The dynamic forces produced by the pressure fluctuation on the rod surface are calculated by the 3-dimensional large eddy simulation turbulent model in Fluent 6 to simulate the flow field in the same as being measured empirically via pressure transducers. To acquire response to fluctuating pressure, the mode response equation of vibration is used in case of a cylindrical rod in one-dimensional case. The first modal longitudinal joint acceptance integral including a coherence function is also an important parameter affecting the displacement in the form of the r.m.s. of modal responses along with the damping ratio. The root mean square of the lateral displacement in addition to the natural frequency is studied using the PSD and the longitudinal joint acceptance integral in a fundamental mode. The random pressure PSD on the middle point of the rod shows the typical turbulence pattern: the PSD energy decreases slightly in a low frequency region, but decreases rapidly and linearly with frequency as the frequency exceeds a certain value. The PSD in a very high frequency region is obtained assuming the slope is constant in a logarithmic graph after smoothing the PSD. It turns out that the r.m.s. displacement ranges from 15 to 40 micro-meter at the maximum value using the mode response equation under the modal damping ration ranging from 0.01 to 0.05.Copyright

HORIZON EXPANSION OF THERMAL-HYDRAULIC ACTIVITIES INTO HTGR SAFETY ANALYSIS INCLUDING GAS-TURBINE CYCLE AND HYDROGEN PLANT

We present three nuclear/hydrogen-related R&D activities being performed at KAIST: air-ingressed LOCA analysis code development, gas turbine analysis tool development, and hydrogen-production system analysis model development. The ICE numerical technique widely used for the safety analysis of water-reactors is successfully implemented into GAMMA, with which we solve the basic equations for continuity, momentum conservation, energy conservation of the gas mixture, and mass conservation of 6 species (He, N2, O2, CO, CO2, and H2O). GAMMA has been extensively validated using data from 14 test facilities. We developed a tool to predict the characteristics of HTGR helium turbines based on the throughflow calculation with a Newton- Raphson method that overcomes the weakness of the conventional method based on the successive iteration scheme. It is found that the current method reaches stable and quick convergence even under the off-normal condition with the same degree of accuracy. The dynamic equations for the distillation column of HI process are described with 4 material components involved in the HI process: H2O, HI, I2, H2. For the HI process we improved the Neumann model based on the NRTL (Non-Random Two-Liquid) model. The improved Neumann model predicted a total pressure with 8.6% maximum relative deviation from the data and 2.5% mean relative deviation, and liquid-liquid-separation with 9.52% maximum relative deviation from the data.

Assessment of HTGR Helium Compressor Analysis Tool Based on Newton-Raphson Numerical Application to Throughflow Analysis

This study describes the development of a computer program for analyzing the off-design performance of axial flow helium compressors, which is one of the major concerns for the power conversion system of a high temperature gas-cooled reactor (HTGR). The compressor performance has been predicted by the aerodynamic analysis of meridional flow with allowances for losses. The governing equations have been derived from Euler turbomachine equation and the streamline curvature method, and then they have been merged into linearized equations based on the Newton-Raphson numerical method. The effect of viscosity is considered by empirical correlations to introduce entropy rises caused by primary loss sources. Use of the method has been illustrated by applying it to a 20-stage helium compressor of the GTHTR300 plant. As a result, the flow throughout the stages of the compressor has been predicted and the compressor characteristics have been also investigated according to the design specification. The program results show much better stability and good convergence with respect to other through-flow methods, and good agreement with the compressor performance map provided by JAEA. (authors)