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Studies conducted at the Pacific Northwest National Laboratory in Richland, Washington, have focused on assessing the effectiveness and reliability of novel approaches to nondestructive examination (NDE) for inspecting coarse-grained, cast stainless steel reactor components. The primary objective of this work is to provide information to the U.S. Nuclear Regulatory Commission on the effectiveness and reliability of advanced NDE methods as related to the inservice inspection of safety-related components in pressurized water reactors (PWRs). This report provides progress, recent developments, and results from an assessment of low frequency ultrasonic testing (UT) for detection of inside surface-breaking cracks in cast stainless steel reactor piping weldments as applied from the outside surface of the components.Vintage centrifugally cast stainless steel piping segments were examined to assess the capability of low-frequency UT to adequately penetrate challenging microstructures and determine acoustic propagation limitations or conditions that may interfere with reliable flaw detection. In addition, welded specimens containing mechanical and thermal fatigue cracks were examined. The specimens were fabricated using vintage centrifugally cast and statically cast stainless steel materials, which are typical of configurations installed in PWR primary coolant circuits.Ultrasonic studies on the vintage centrifugally cast stainless steel piping segments were conducted with a 400-kHz synthetic aperture focusing technique and phased array technology applied at 500 kHz, 750 kHz, and 1.0 MHz. Flaw detection and characterization on the welded specimens was performed with the phased array method operating at the frequencies stated above. This report documents the methodologies used and provides results from laboratory studies to assess baseline material noise, crack detection, and length-sizing capability for lowfrequency UT in cast stainless steel piping.iii Foreword Cast stainless steel (CSS) material was used extensively in the primary pressure boundary of pressurized water reactors (PWRs) due to its relatively low cost and resistance to corrosion. The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code requires periodic inservice inspection (ISI) of welds in the primary pressure boundary. Because of background radiation and access limitations, inspection personnel use ultrasonic testing (UT) techniques rather than radiography to inspect these welds. In most applications, UT can reliably detect and accurately size flaws that may occur during service. This is not the case for CSS material.The coarse-grained and anisotropic microstructure of CSS material makes it difficult to inspect CSS components such as statically cast elbows, statically cast pump bowls, and centrifugally cast stainless steel piping. Similar inspection problems exist for dissimilar metal welds and weld-overlay-repaired pipe joints. The large grain sizes of these materials strongly affect the propagation of ultrasoun...

Executive SummaryThe response of the nuclear industry and regulators to issues of materials degradation in the past generally has been to develop and approve mitigation actions after the degradation has occurred. These mitigation actions have involved increases and improvements in in-service inspection, changes in designs, materials, and operating conditions, and replacement of degraded components. This reactive approach has maintained the safety of operating reactors but has proved to be an inefficient and expensive way of managing materials degradation issues for the industry.To address the issue of "reactive management of materials degradation", the NRC has initiated a program to assess the potential to identify early the components that are potentially susceptible to future degradation, so that mitigation and/or monitoring and repair actions can be proactively developed, assessed, and implemented before the degradation process could adversely impact structural integrity or safety. Two processes can be envisioned for the Proactive Management of Materials Degradation (PMMD) programs. The processes are (a) implementation of actions to mitigate or eliminate the susceptibility to materials degradation, and (b) implementation of effective inspection, monitoring, and timely repair of degradation. This study concentrated on an identification of components susceptible to future degradation and an assessment of the existing knowledge level for potential development of mitigation actions, that is, process (a) only. The Pacific Northwest National Laboratory conducted the research to find and develop the PMMD information contained in this technical letter report. This technical letter report concisely explains the basic principles of PMMD and its relationship to prognostics, provides a review of programs related to PMMD being conducted worldwide, and provides an assessment of the technical gaps in PMMD and prognostics that need to be addressed.Degradation and aging are terms used to describe both the deterioration and aging of components, but it is useful to distinguish between them. Degradation is immediate or gradual deterioration of characteristics of systems, structures, and components (SSCs) that could impair their ability to function within acceptance criteria. Aging is a general process in which characteristics of an SSC gradually change with time or use. When aging processes are known, they can be monitored through an appropriate aging management program and plant life management (PLiM) program and potentially mitigated.Aging degradation mechanisms are usually classified into two main categories, which are those that (1) affect the internal microstructure or chemical composition of the material and thereby change its intrinsic properties (thermal aging, creep, irradiation damage, etc.), and (2) impose physical damage on the component either by metal loss (corrosion, wear) or by cracking or deformation (stress-corrosion, deformation, cracking). As can be seen above, the phenomenon of aging degradation in nuclear p...

The Pacific Northwest Laboratory is conducting a four-phase program for measuring and evaluating the effectiveness and reliability of in-service inspection (lSI} performed on the primary system piping welds of commercial light water reactors (l..WRs). Phase I of the program is complete. A survey was made of the state of practice for ultrasonic rsr of LWR primary system piping ·Nelds. Fracture mechanics calculations 'Nere made to establ-ish required nondestru:tive testing sensitivities. In general, it was found that fatigue flaw·s less t11an 25% of wall :hic!

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