Approach for improvement of maintenance technology of BMI

Primary water stress corrosion cracking (PWSCC) has been concerned in Bottom Mounted Instrumentation (BMI) of Reactor Pressure Vessel with alloy 600 for the last two decades. Generally the Rules on Fitness for Service for Nuclear Power Plants of JSME are applied for flaw evaluation after detecting defects in the operating nuclear plants. However in the case that a crack is detected in a complex configuration area such as J-groove weld, it is needed to perform a fracture mechanics approach using FE analysis because of different geometry and stress field from piping or vessels. The core support structure guidelines of JANSI have been revised to apply FE analysis for calculation of a precise stress intensity factor K of J-groove weld of BMI. The revision includes the notices of FE modeling, used material and K calculation method. The summary of this guideline is introduced in this paper. (author)