Repair of a heterogeneous weld joint
In 2012, the Service team from ŠKODA JS was the first in Central Europe to perform a unique repair, both technologically as well as in terms of organization, of the heterogeneous DN 1100 mm weld joint on the hot collector of the steam generator at the Dukovany NPP. The repaired weld joint was a workshop weld, which means that it was not expected it would ever be repaired at the power plant. Moreover, the weld involved the combination of two basic materials.
The entire project included preparation, trials and calculations, the removal of the faulty weld joint, the execution of the new weld, including continual non-destructive testing, and the management and coordination of a total of 15 subcontractors.
Preparation for the repair presented several issues. The first was putting together a team of service technicians, as due to the anticipated radiation situation on site and the length of the service task, the expected number of welding staff required was approx. 20 people. These workers had to undergo psychological testing required for work at the power plant as well as a number of professional exams. Of a total of 41 welders who took the professional exam, only 16 met the stringent criteria.
Another limiting factor was the length of time for the preparation of the project, which apart from the actual technical solutions also included the procurement of special jigs and materials as well as dozens of analyses and calculations. It was necessary to make preparations for the repair in record time. A special jig had to be developed and produced to prevent permanent deformation of and irreversible damage to the steam generator internals. Another issue requiring a solution was the stabilization of the primary circuit loop equipment to prevent its movement following the removal of the faulty weld joint.
The next stage involved the execution of inspected weld joints, whose successful result was a condition for the performance of the actual repair. A 1:1 scale repair stand was constructed for testing the beveling machine, staff training, etc.
The entire preparation was supervised by the State Office for Nuclear Safety. The preparation and the actual implementation took place with the participation of approx. 15 other organizations, with ČEZ a. s. and ŠKODA JS a.s. in charge of their management and coordination.
The repair itself was made during a scheduled outage of the main production unit and was executed on schedule (i.e., without any negative impact on the length of the outage) and to the required quality.
We made additional successful repairs of this kind on other steam generators at the Dukovany NPP in 2013 and 2016, and at the Temelín NPP in 2016.
The history of our cooperation
2012the first unique repair of a heterogeneous weld joint executed at the Dukovany NPP
2013the second repair of a heterogeneous weld joint executed at the Dukovany NPP
2016the third repair of a heterogeneous weld joint executed at the Dukovany NPP
2016the repair of a heterogeneous weld joint executed at the Temelín NPP