Kyung Ho Yoon

Impact Analysis and Test on the Spacer Grid Assembly for PWRs

A spacer grid assembly is one of the main structural components of the fuel assemblies of Pressurized light Water Reactors. The spacer grid assembly is structurally required to have enough buckling strength under various kinds of lateral loads acting on the fuel assembly so as to keep the fuel assembly straight. The structural performance of the spacer grid assembly is characterized in terms of its dynamic crush strength, which is usually acquired from the test. In this study, a dynamic buckling test and a finite element analysis on the KAERI designed spacer grid assembly are carried out. The pendulum-type tester was used in the test. In the finite element analysis, we proposed an analysis methodology that could predict the dynamic failure behavior of the spacer grid assembly using a commercial finite element code ABAQUS/explicit with appropriate boundary conditions. As a result of the comparisons, the analysis result is in good agreement with the test result to within a 10% difference range. Therefore, we could predict the dynamic behaviors of a spacer grid assembly in advance before performing the dynamic buckling test.

Finite Element Analysis Model for Estimating the Dynamic Crush Strength of the Spacer Grid Assembly for PWRs

The spacer grid assembly, which is an interconnected array of slotted grid straps and welded at the intersections to form an egg crate structure, is one of the main structural components of the nuclear fuel assemblies of a Pressurized light Water Reactor (PWR). The spacer grid assembly is structurally required to have enough crush strength under lateral loads due to lateral seismic accelerations, lateral Loss Of Coolant Accident (LOCA) blowdown forces, and shipping and handling loads so that the fuel rods are maintained within a coolable geometry, and that the control rods are able to be inserted. The ability of the spacer grid assembly to resist the lateral loads is usually characterized in terms of its dynamic and static crush strengths, which are acquired from the relevant tests. In this study, dynamic buckling tests and finite element analyses on spacer grid assembly specimens are carried out. As a result of the comparisons, the analysis results are in good agreement with the test results to within an 8 % difference range. Therefore, we could predict the crush strength of a spacer grid assembly in advance before performing the dynamic buckling test.

Experimental Study on the Fluctuating Pressure Acting on a 5x5 Partial Fuel Assembly in a Parallel Flow

A 5x5 partial fuel assembly was used for a comparative design evaluation test of a newly developed spacer grid from a mechanical/hydraulic vibration aspect. Axial flow pattern along this rod bundle in the test was very complex due to the intermediate spacers and the mixing vane; Understanding of this flow field of a dynamic pressure is a preliminary step for a theoretical analysis of a vibratory behavior of a partial fuel assembly. Since a fluctuating pressure induced by the randomly-varying flow turbulence cannot be accurately predicted by an analysis alone, it has to be measured directly on the surface over the rod or in an accessible vicinity of the bundle. In this study, the fluctuating pressure acting on a partial fuel assembly with a spacer grid and a mixing vane was measured. The measured PSD showed different spectral features from the results of the literatures and had a series of periodic pulsations with sidebands over the specific frequency ranges; it is believed that the periodic components in the PSD have to do with the design of the spacer grid and the mixing vane. And, the exciting force function for the theoretical analysis of a partial fuel assembly with spacers and a mixing vane was estimated as a possible PSD form.