Improvement of LBW quality of Zircaloy-4 Spacer Grids for PWR Fuel Assembly

Kim, Soo-Sung; Song, Kee-Nam; Han, Hyoung-Jun

Journal of KWJS 2006;24(5):22-28.
Published online January 4, 2007.

경수로 원전연료용 지르칼로이-4 지지격자 레이저용접품질 개선

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Improvement of LBW quality of Zircaloy-4 Spacer Grids for PWR Fuel Assembly

Soo-Sung Kim, Kee-Nam Song, Hyoung-Jun Han

Abstract

A spacer grid assembly, which is an interconnected array of slotted grid straps and is welded at the intersections to form an egg crate structure, is one of the main structural components of the nuclear fuel assembly for Pressurized Water Reactors (PWRs). The weld quality of spacer grids in PWRs fuel is extremely important for the fuel assembly performance in the nuclear reator. The spacer grid welds are currently evaluated mainly by the metallographic examination although it reveals only cross-points which are welded by the laser beam. This experiment is also to compare the weldability of Zircaloy-4 spacer grids using by the GTA and LB. The effect of node geometries of spacer grids for the GTAW and LBW has been studied and optimum conditions of spacer grid welding have been found. Microstructures and micro-hardness of the GTA and LB welded zones have been also compared.

Key Words: Spacer grid, Nd:YAG Laser welding, Zircaloy-4, Nuclear fuel, Penetration depth