The NRU reactor at Chalk River Laboratories is one of the largest and oldest research reactors in the world. It has been the world’s largest producer of medical isotopes, which are used in cancer treatments, nuclear medicine and other diagnostic procedures. The NRU reactor was shut down in May 2009 when a heavy water leak was detected in the reactor building. Subsequent inspections indicated that the reactors aluminum vessel corroded at various locations resulting in heavy water seeping through the reactor vessel.
The extent of the damage required a complex pattern of internally applied weld overlays in numerous areas. Weld repair was further complicated by concerns over the effect of radiation hardening of the aluminum and compositional changes (irradiation induced transmutation of aluminum to silicon). Considering the deformation and stress associated with welding aluminum plate (Figure 1) and the aggressive return to service schedule, Atomic Energy of Canada (AECL) commissioned an extensive Computational Weld Mechanics (CWM) campaign to guide the repair design and optimize structural integrity. This paper describes the technical issues encountered in the design of the weld repair processes and how CWM was used in selecting welding strategies. Traditionally, welding pattern, progression and sequence are determined through a combination of trial and error on mock ups along with welders experience and analyzed by computer after the fact. To the authors knowledge, this is the first weld repair that used CWM to assess proposed designs of welds.
