Weld Repair of Irradiated Materials

Maintenance of an accelerator for production of tritium will require replacement or modification of components that have been exposed to neutron irradiation. A primary repair option is welding, but conventional repair welding processes produced severe cracking in irradiated stainless steel. Optical metallography, scanning electron microscopy, and transmission electron microscopy have shown that the cracks are: intergranular, primarily in the weld heat-affected zone, characterized by a dimple structure on the crack surface, and associated with helium bubbles that grow during welding. A model has been developed that qualitatively shows the interaction of three primary and three secondary variables producing helium embrittlement cracking. A shallow penetration overlay technique was successfully demonstrated to minimize cracking in irradiated 304 stainless steel that contained 10appm helium. The overlay technique provides a potential method for repair or modification of accelerator materials exposed to irradiation.