Detection and characterization of indications in segments of reactor pressure vessels

Studies have been conducted to estimate flaw density in segments cut from light water reactor (LWR) pressure vessels as part of the Oak Ridge National Laboratory's Heavy-Section Steel Technology (HSST) Program. Segments from the Hope Creek Unit 2 vessel and the Pilgrim Unit 2 vessel were purchased from salvage dealers. Hope Creek was a boiling water reactor (BWR) design and Pilgrim was a pressurized water reactor (PWR) design. Neither were ever placed in service. Objectives were to evaluate these LWR segments for flaws with ultrasonic and liquid penetrant techniques and to compare the results with current assumptions related to probabilistic risk assessment. Both objectives were successfully completed. Ultrasonic techniques beyond those required by the 1986 edition of the ASME Boiler and Pressure Vessel Code were necessary for the detection and reporting of the detected discontinuities. Extra care and analysis must be exercised when conducting ultrasonic examination through cladding. The detection of the discontinuities in the arbitrarily selected sections implies that the Marshall report estimates (and others) are nonconservative for such small flaws. 8 refs., 9 figs.