Non-destructive examination and fracture mechanical assessments of RPV internals

Mångård, Daniel; Kiwa Inspecta; Sweden

Gunnars, J.; Kiwa Inspecta Technology AB; Sweden
Mångård, D.; Kiwa Inspecta Technology AB; Sweden
Poznić, M.; Kiwa Inspecta Sweden AB / WesDyne; Sweden

ID: ECNDT-0523-2018
Session: Nuclear Industry 1
Room: H2
Date: 2018-06-13
Time: 10:50 - 11:10

In-service inspection of stress corrosion cracks (SCC) in reactor pressure vessel (RPV) internals has attracted great attention from the NDE community. One particular concern is whether SCC initiated in the attachment and buttering welds, connecting the core shroud support legs to the reactor tank, could propagate into the vessel steel. SCC have been indicated by visual inspection (VT) and characterized by ultrasonic testing (UT). EDM boat sampling was used in an attempt to remove the SCC although qualified moulding (AVT) reveals that small segments remain.

Numerically predicted weld residual stresses (WRS), validated by experimental measurements, have shown to be a principal contributor to the total stress state in the attachment and buttering welds during normal and upset loading. Detailed FEM-analyses show that the EDM removal locally increases the WRS. This makes defect characteristics such as location, orientation and extension essential when performing a damage tolerant assessment. The margin against plastic collapse and fracture have been evaluated.