Microscopic evaluation of weld defects using different welding techniques in zircaloy end plug welds

Zircaloy is selected as a reference structural material for thermal reactors due to its properties like better corrosion resistance, low neutron absorption cross section, good mechanical strength at room temperature as well as at reactor operating temperature and its weldability. Radiometallurgy Division was involved in development and fabrication of zircaloy cladded fuel pins for loop irradiation work for Boiling Water Reactor (BWR) and Pressurized Heavy Water Reactor (PHWR). The welding of the above thin walled tube and solid plug was a challenging task due to its thin-thick geometry. It was successfully carried out by Tungsten Inert Gas welding to avoid harmful effect of deleterious gases to the weld joint. Due to chemical toxicity and radiological hazards, top end plug closure welding has been carried out in leak tight glove box. Standard ASTM metallographic practice has been adopted to prepare the end plug welds and they have been evaluated using optical microscope. This paper describes the typical weld defects observed during development and fabrication of experimental fuel pins for loop irradiation test. This paper also depicts the defects encountered during development of zircaloy end plug welds by Resistance welding and Laser welding. (author)