Kee-Nam Song

Fretting wear of laterally supported tube

The fretting wear of a tube, which is in contact with a lateral support, is examined experimentally. A fretting wear tester is specifically designed. Elastic springs are used as the support, which can simulate the contact between a spacer grid and a fuel rod in pressurized water reactor fuel. The tubes and the springs are made of Zircaloy-4. The experiments are conducted in air at room temperature. The experimental conditions, i.e. the normal and shear forces on the contact, the slip range and the number of cycles, are set to be the same. To investigate the influence of the contact geometry on the wear, the spring supports have a concave, a flat or a convex contour. The influence on the axial and transverse slip directions is investigated to incorporate the actual tube motion caused by such a flow-induced vibration in the reactor. The wear on the tube is examined by the surface roughness tester, which measures the depth, and the contour of the worn surface of the tube. Since the shape and the distribution of wear are found arbitrary, a method for evaluating the wear volume is proposed using the signal processing technique. It is found that wear can be restrained when the slip direction is transverse, and if the support has a concave contour.

PERFORMANCE EVALUATION OF NEW SPACER GRID SHAPES FOR PWRS

A spacer grid, which is one of the most important structural components in a PWR fuel assembly, supports its fuel rods laterally and vertically. Based on in-house design experience, scrutiny of the design features of advanced nuclear fuels and the patents of other spacer grids, KAERI has devised its own spacer grid shapes and acquired patents. In this study, a performance evaluation of KAERIs spacer grid shapes was carried out from mechanical/structural and thermohydraulic view points. A comparative performance evaluation of commercial spacer grid shapes was also carried out. The comparisons addressed the spring characteristics, fuel rod vibration characteristics, fretting wear resistance, impact strength characteristics, CHF enhancement, and the pressure drop level of the spacer grid shapes. The results show that the performances of KAERIs spacer grid shapes are as good as or better than those of the commercial spacer grid shapes.

Design improvement of an OPT-H type nuclear fuel rod support grid by using an axiomatic design and an optimization

A nuclear fuel rod support grid is an important structural part of a nuclear fuel assembly which is used in a pressurized light water reactor. It provides a flexible support for the nuclear fuel rods which experience a severe thermal expansion and a contraction caused by the harsh operational conditions in the core of a reactor. Diverse design requirements should be set for the performances of the multidisciplinary natures such as an impact resistance, spring characteristics, possible amount of a fretting wear on the fuel rods, the coolant flow and heat transfer around it, and so on. In this paper, an effort is reported to improve the impact resistance of an OPT-H type support grid, a high performance spacer grid developed by the Korea Atomic Energy Research Institute. A systematic approach by using an axiomatic design and optimization is utilized for this purpose.

Axial-flow-induced vibration for a rod supported by translational springs at both ends

Abstract An axial-flow-induced vibration model was proposed for a rod supported by two translational springs at both ends in order to evaluate the sensitivity to spring stiffness on the FIV for a PWR fuel rod. For developing the model, a one-mode approximation was made based on the assumption that the first mode was dominant in vibration behavior of the single span rod. The first natural frequency and mode shape functions for the flow-induced vibration, called the FIV, model were derived by using Lagranges method. The vibration displacements were calculated by both of the spring-supported rod and the simple-supported (SS) one. As a result, the vibration displacement for the spring-supported (50 kN m −1 ) rod was 15–20% larger than that of the SS rod when the rods are in axial flow of 5–8 m s −1 velocity. The discrepancy between both displacements became much larger as flow velocity increased, and that of the rod having the short span length was larger than that of the rod having the long span length although the displacement value itself of the long span rod was larger than that of the short one. The vibration displacement for the spring-supported rod appeared to decrease with the increase of the spring constant. Since single span beam supported by the two translational springs are focused on in this paper, further study will be needed to reflect more realistic supporting conditions of the PWR fuel rod such as two springs and four dimples and cross or swirling flow caused by the mixing vane of the spacer grid.

Measurement of Weld Mechanical Properties of SUS316L Plate Using an Instrumented Indentation Technique

Different microstructures in the weld zone of a metal structure such as a fusion zone or heat affected zone are formed as compared to the parent material. Thus, the mechanical properties in the weld zone are different from those in the parent material. As the basic data for reliably understanding the structural characteristics of welded PCHE prototype made of SUS316L, the mechanical properties in the weld zone and parent material for a SUS316L plate are measured using an the instrumented indentation technique in this study.

Measurement of Weld Material Properties of Alloy 617 Using an Instrumented Indentation Technique

Abstract Different microstructures in the weld zone of a metal structure such as a fusion zone or heat affected zone are formed as compared to the parent material. Thus, the mechanical properties in the weld zone are different from those in the parent material. As the basic data for reliably understanding the structural characteristics of a welded PCHE specimen to be made of Alloy 617, the mechanical properties in the weld zone and parent material for a Alloy 617 plate are measured using an instrumented indentation technique in this study.Key Words : Instrumented indentation technique, Mechanical property, PCHE(Printed Circuited Heat Exchanger), Very high temperature reactor 1. 서 론 용접은 단품으로 이루어진 부품들을 원하는 형상의 구조물로 용이하게 형상화할 수 있는 편리한 접합 방법이다. 그런데 용접된 구조물의 용접 부위는 용접시에 투입된 열로 인하여 용융부 및 열영향부(Heat Affected Zone; HAZ)가 형성된다. 용융부 및 HAZ에서는 모재와는 다른 미세조직이 형성되고 용접에 의한 잔류응력 등으로 인하여 이 부위의 기계적 물성치도 모재와는 다를 수 있다 1) . 모재, HAZ, 용융부 등의 기계적 물성치가 다를 수 있기 때문에 용접된 구조물이 하중을 받을 경우, 거시적으로 보면 구조물의 구조특성 및 기계적 거동이 단일 물성치로 이루어진 구조물의 구조특성 및 기계적 거동과는 사뭇 다를 수 있다

Investigation of FIV Characteristics on a Coaxial Double-tube Structure

A Very High Temperature Gas Cooled Reactor (VHTR) has been selected as a high energy heat source of the order of 950 for nuclear hydrogen generation, which can produce hydrogen from ℃ water or natural gas. A primary hot gas duct (HGD) as a coaxial double-tube type cross vessel is a key component connecting a reactor pressure vessel and an intermediate heat exchanger in the VHTR. In this study, a structural sizing methodology for the primary HGD of the VHTR is suggested in order to modulate a flow-induced vibration (FIV). And as an example, a structural sizing of the horizontal HGD with a coaxial double-tube structure was carried out using the suggested method. These activities include a decision of the geometric dimensions, a selection of the material, and an evaluation of the strength of the coaxial double-tube type cross vessel components. Also in order to compare the FIV characteristics of the proposed design cases, a fluid-structure interaction (FSI) analysis was carried out using the ADINA code.

IMPACT ANALYSIS AND TEST FOR THE SPACER GRID ASSEMBLY OF A NUCLEAR FUEL ASSEMBLY

A spacer grid assembly is one of the main structural components of the nuclear fuel assembly for a Pressurized light Water Reactor (PWR). The spacer grid assembly supports and aligns the fuel rods, guides the fuel assemblies past each other during a handling and, if needed, sustains lateral seismic loads. The ability of a spacer grid assembly to resist these lateral loads is usually characterized in terms of its dynamic and static crush strengths, which are acquired from tests. In this study, a finite element analysis on the dynamic crush strength of spacer grid assembly specimens is carried out. Comparisons show that the analysis results are in good agreement with the test results to within about a 30 % difference range. Therefore, we could predict the crush strength of a spacer grid assembly in advance, before performing a dynamic crush test. And also a parametric study on the crush strength of a spacer grid assembly is carried out by adjusting the weld penetration depth for a sub-sized spacer grid, which also shows a good agreement between the test and analysis results.

Macroscopic High-Temperature Structural Analysis of PHE Prototypes Considering Weld Material Properties

®-X is being conducted on in a small-scale nitrogen gas loop at the Korea Atomic Energy Research Institute. Previous research on the macroscopic high-temperature structural analysis of PHE prototypes had been performed using base material properties owing to a lack of weld material properties. In this study, macroscopic high-temperature structural analyses considering the weld material properties were performed and the results were compared with those of a previous study.

High-Temperature Structural Analysis of a Medium-Scale Process Heat Exchanger Prototype

A process heat exchanger (PHE) in a nuclear hydrogen system is a key component for transferring the considerable heat generated in a very high temperature reactor (VHTR) to a chemical reaction that yields a large quantity of hydrogen. A performance test on a medium-scale PHE prototype made of -X is scheduled in a small-scale gas loop at the Korea Atomic Energy Research Institute. In this study, as a preliminary study before carrying out the performance test in the gas loop, high-temperature structural analysis modeling and macroscopic thermal and structural analysis of the medium-scale PHE prototype by imposing the established displacement boundary constraints were carried out under the gas loop test condition. The results obtained in this study will be compared with the performance test results of the medium-scale PHE prototype in the gas loop.