There are over 100 nuclear power plants operating in the U.S., which generate approximately 20% of the nation’s electricity. These plants range from 15 to 40 years old. Extending the service lives of the current fleet of nuclear power plants beyond 60 years is imperative to allow for the environmentally-sustainable energy infrastructure being developed and matured. Welding repair of irradiated nuclear reactor materials (such as austenitic stainless steels) is especially challenging because of the existence of large amounts of helium in the steel matrix after intense neutron exposure. Under the influence of high temperatures and high tensile stresses during welding, rapid formation and growth of helium bubbles can occur at grain boundaries, resulting in intergranular cracking in the heat-affected zone (HAZ). Over the past decades, a fundamental understanding has been established for the mechanism of stress evolution during welding and the detrimental effects of weld stresses on weld cracking. However, practical methods for weld repair of irradiated materials are still evolving.
This task was to develop the initial baseline version of weld computational model that can be used to determine the optimum welding conditions to manage the weld stresses during welding and suppress helium induced cracking during weld repair of helium containing irradiated materials. This model was to be used for quantitative understanding of the temperature and stress evolution in the weld HAZ. The initial results obtained using the baseline computational model for proactive welding stress management to suppress helium induced cracking during weld repair are reported as follows.