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AbstractThe U.S. Nuclear Regulatory Commission has undertaken a program to lay the groundwork for defining proactive actions to manage degradation of materials in light water reactors (LWRs). This proactive management of materials degradation (PMMD) program examines LWR component materials and the degradation phenomena that affect them. Of particular interest is how such phenomena can be monitored and data can be used to predict degradation and prevent component failure. Some forms of degradation, including some modes of stress corrosion cracking, are characterized by a long initiation time followed by a rapid growth phase, and monitoring such long-term degradation will require new nondestructive evaluation methods and measurement procedures. As reactor lifetimes are extended, degradation mechanisms previously considered too long-term to be of consequence (such as concrete and wiring insulation degradation) may become more important. This paper explains the basic principles of PMMD and its relationship to in-service inspection, condition-based maintenance, and advanced diagnostics and prognostics. It then reviews the phases for degradation development and technologies with potential for sensing and monitoring degradation in its early stages.

Studies conducted at the Pacific Northwest National Laboratory (PNNTL) in Richland, Washington, have focused on developing and evaluating the reliability of nondestructive testing (NDT) approaches for coarse- grained stainless steel reactor components. The objective of this work is to provide information to the United States Nuclear Regulatory Commission (NRC) on the utility, effectiveness and limitations of NDT techniques as related to inservice testing of primary system piping components in pressurized water reactors. We examined cast stainless steel pipe specimens containing thermal and mechanical fatigue cracks located close to the weld roots and having inner and outer diameter surface geometrical conditions that simulate several water reactor primary piping configurations. In addition, segments of vintage centrifugally cast piping were examined to characterize the inherent acoustic noise and scattering caused by grain structures and to deter- mine the consistency of ultrasonic responses when propagating through differing microstructures. Advanced ultrasonic phased array techniques were applied from the outside surface of these specimens using automated scanning devices and water coupling. The phased array approach was implemented with a modified instrument operating at low frequencies, and composite volumetric images of the specimens were generated. Results from laboratory studies for assessing crack detection effectiveness in cast stainless steel as a function of frequency are discussed in this paper. [ABSTRACT FROM AUTHOR]

Assesses the remote visual testing system capabilities for the detection of service induced cracking. Determination of the maximum visual acuity of an analog or digital video system; Identification of the image sharpness produced by mechanical visual systems; Observation of the current volumetric and surface techniques.

Continuous on-line monitoring of active and passive systems, structures and components in nuclear power plants will be critical to extending the lifetimes of nuclear power plants in the US beyond 60 years. Acoustic emission and guided ultrasonic waves are two tools for continuously monitoring passive systems, structures and components within nuclear power plants and are the focus of this study. These tools are used to monitor fatigue damage induced in a SA 312 TP304 stainless steel pipe specimen. The results of acoustic emission monitoring indicate that crack propagation signals were not directly detected. However, acoustic emission monitoring revealed crack formation prior to visual confirmation through the detection of signals caused by crack closure friction. The results of guided ultrasonic wave monitoring indicate that this technology is sensitive to the presence and size of cracks. The sensitivity and complexity of guided ultrasonic wave (GUW) signals is observed to vary with respect to signal frequency and path traveled by the GUW relative to the crack orientation.