Weld repair of irradiated materials

Maintenance of an accelerator for production of tritium will require replac ement or modification of components that have been exposed to neutron irrad iation. 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 micr oscopy have shown that the cracks are: intergranular, primarily in the weld heat-affected zone, characterized by a dimple structure on the crack surfa ce, and associated with helium bubbles that grow during welding. A model ha s been developed that qualitatively shows the interaction of three primary and three secondary variables producing helium embrittlement cracking. A sh allow penetration overlay technique was successfully demonstrated to minimi ze cracking in irradiated 304 stainless steel that contained 10appm helium. The overlay technique provides a potential method for repair or modificati on of accelerator materials exposed to irradiation. (C) 1999 Westinghouse S avannah River Company. Published by Elsevier Science Inc. All rights reserv ed.