Acceptance criteria for reactor coolant pumps and valves

Each of the six primary coolant loop systems of the Savannah River Site (SRS) production reactors contains one reactor coolant pump, one pump suction side motor operated valve, and other smaller valves. The pumps are double suction, double volute, and radially split type pumps. The valves are different size shutoff and control valves rated from ANSI B16.5 construction class 150 to class 300. The reactor coolant system components, also known as the process water system (PWS), are classified as nuclear Safety Class 1 components. These components were constructed in the 1950's in accordance with then prevailing industry practices. No uniform construction codes were used for design and analysis of these components. However, no pressure boundary failures or bolting failures have ever been recorded throughout their operating history. Over the years, the in-service inspection (ISI) was limited to visual inspection of the pressure boundaries, and surface and volumetric examination of the pressure retaining bolts. Efforts are now underway to implement ISI requirements similar to the ASME Section 11 requirements for pumps and valves. The new ISI requirements call for volumetric examination of the pump casing and valve body welds. However, the volumetric examination of the such welds is extremely difficult due to the limited access and high radiation exposure difficulties. Therefore, fracture evaluations based on ASME code case N-481, which provides a method for relaxing these requirements, are performed. Conservative throughwall initial flaws are postulated and CEGB R6 type analyses are performed to establish flaw stability. The analyses show that detectable size throughwall flaws will remain stable at the operating conditions and volumetric examinations can be relaxed