Repair of Class 1 Control Rod Drive and In-Core Housing Bottom Head Penetrations in BWRs

The ASME Section XI committee is developing a code case to permit repair of leakage on Boiling Water Reactor (BWR) bottom head penetrations with a mechanical roll expansion process. This technology has been successfully utilized for this application over the last two decades to address leakage due to Control Rod Drive (CRD) stub tube cracking. The code case defines the technical and administrative requirements for use of the mechanical roll expansion process for repair of Class 1 Control Rod Drive and Incore housing penetrations in the bottom head of BWRs. The code case specifies the process qualification, essential variables, process application, examination and pressure testing requirements for this process. The technical basis of the proposed code case includes detailed fracture mechanics analysis to evaluate the structural consequences of the cracking, metallurgical assessment and extensive testing to determine the load capability of the roll repair joint. Based on this assessment, the successful BWR field experience and the inspections/ qualifications required under the code case, the mechanical roll expansion repair can be used as a permanent repair option for addressing leakage in BWR CRD and In-core housing penetrations, The application of this code case will provide significant reduction in facility down time and will offer a reduction in personnel radiation exposure as compared to welded repair options.