Simulation and Validation Studies in Zircaloy-4 End Cap Welding of Pressurized Heavy Water Reactor Fuel Element

Pressurized Heavy Water Reactors (PHWR) are fuelled with assemblies containing elements filled with natural uranium di-oxide pellets encapsulated in Zircaloy-4 tube and hermitically sealed with end caps. Any breach in end cap weld joint, being the first barrier for radioactive containment, results in release of radioactivity in to the reactor environment. The weld joint shall be of stringent quality for reliable performance of the fuel bundle in the reactor. Resistance welding is used extensively for joining all the components in the manufacturing of the fuel bundle with stringent quality and integrity requirements. Resistance upset welding process is a multi-physics phenomenon where electric current and force are applied simultaneously for formation of end cap weld joint. The weld quality depends on critical process parameters like current, resistance, force, time and their interactions. In this study, a coupled electrical–mechanical-thermal finite element simulation of end cap welding process is carried out. Validation studies are done using a high speed dedicated online data acquisition system for capturing weld deformation and its variation during the 250 ms weld cycle. Predicted deformation and shape of the weld joint matched well with the measured deformation during experimentations and shape of the weld joint seen in microscopy respectively. Validated model will be used for generation of data by varying process parameters towards defect characterization studies.