Defects have been found on the class 1 BOSS welds in Loop 1 pressure boundary in domestic PWRs

such as

incomplete fusion

slag inclusion

blowhole and so on. an analysis is made from the aspects of the type

position and reason of the defects

two treatment solutions are formulated

one is grinding and repairing

one is cutting and replacing. Through the design and development of special tools

the technical difficulties

including the control for grinding residual wall thickness

the control for cutting to prevent foreign matters and the argon protection for weld back

have been conquered. All of these are successfully applied in Ningde

Fuqing

Fang Chenggang and Changjiang NPPs

which provide reference for the treatments of the welding defects of BOSS and other similar structures.