Joon-kyoo Park

STRUCTURAL INTEGRITY EVALUATION OF NUCLEAR FUEL WITH REDUCED WELDING CONDITIONS

Welding is required for a connection between two different components in the nuclear fuel of a pressurized water reactor. This work relies on a mechanical experiment and analytic results to investigate the structural integrity of nuclear fuel in a situation where some components are not welded to each other. A series of lateral vibration tests are performed in a test facility, and the test structures are examined in terms of dynamic behavior. In the tests, the displacement signal at every grid structure that sustains fuel rods is measured and processed to identify the dynamic properties. The fluid-elastic stability of the structure is also analyzed to evaluate susceptibility to a cross flow with an assumed conservative cross flow distribution. The test and analysis results confirm that the structural integrity can be maintained even in the absence of some welding connections.

Fatigue Characteristics of Laser Welded Zirconium Alloy Thin Sheet

The spacer grid is one of the main structural components in a fuel assembly. It supports fuel rods, guides cooling water and maintains geometry from external impact load and cyclic stress by the vibration of nuclear fuel rod, it is necessary to have sufficient strength against dynamic external load and fatigue strength. In this study, the mechanical properties and fatigue characteristics of laser beam welded zircaloy thin sheet are examined. The material used in this study is a zirconium alloy with 0.66 mm of thickness. The fatigue strength under cyclic load was evaluated at stress ratio R

Analysis of Spacer Grid Spring Load-Deflection Characteristic for PWR Fuel Assembly

Spacer grid springs support fuel rods so that the rods keep the position laterally and axially in pressurized water reactor fuel assemblies. The spring load-deflection characteristic, i.e. spring force and stiffness, is needed to evaluate the rod support conditions in the case of fuel assembly manufacturing, shipping and handling. In general, the load-deflection characteristic of grid spring is obtained by mechanical test, but it takes long time to get the new designed grid specimen because the grid manufacturing process comprises strip material manufacturing, stamping die and punch preparation, heat treatment and welding, etc. Therefore the analytic method such as finite element method (FEM) is tried to predict the nonlinear load-deflection characteristic of new designed grid. The spring characteristic mechanical test is simulated with unit cell model and analyzed by FEM tool. Comparing the results between test and analysis shows that more details are needed in the modeling because the boundary conditions of the spring are very complicated and the spring material thickness is changed by the stamping process. The analysis of modified model including expanded cells and thickness changed springs is performed. Using the analytic method of the work to obtain the load-deflection characteristic of spacer grid spring is expected to be useful in the prediction of the characteristic of new designed grids.Copyright