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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...

A set of circumferentially oriented thermal fatigue cracks (TFCs) were implanted into three cast austenitic stainless steel (CASS) pressurizer (PZR) surge-line specimens (pipe-to-elbow welds) that were fabricated using vintage CASS materials formed in the 1970s, and flaw responses from these cracks were used to evaluate detection and sizing performance of the phased-array (PA) ultrasonic testing (UT) methods applied. Four different custom-made PA probes were employed in this study, operating nominally at 800 kHz, 1.0 MHz, 1.5 MHz, and 2.0 MHz center frequencies. The CASS PZR surge-line specimens were polished and chemically etched to bring out the microstructures of both pipe and elbow segments. Additional studies were conducted and documented to address baseline CASS material noise and observe possible ultrasonic beam redirection phenomena.

Executive SummarySafe, efficient, and economic operation of nuclear systems (nuclear power plants, fuel fabrication and storage, used fuel processing, etc.) relies on accurate and reliable measurements. Newer types of sensors, and sensors to monitor non-traditional parameters, are expected in next-generation nuclear power plant (NPP) and fuel-cycle environments. A number of factors (besides changes in the monitored variable) affect the measured signals, resulting in effects such as signal drift and response time changes, requiring techniques to distinguish between signal changes from plant or subsystem performance deviations and those from sensor or instrumentation issues. Advanced algorithms that continuously monitor sensor responses can address this issue and facilitate automated monitoring and control of plant and subsystem performance.Currently, periodic sensor recalibration is performed to avoid problems with signal drift and sensor performance degradation. Periodic sensor calibration involves (1) isolating the sensor from the system, (2) applying an artificial load and recording the result, and (3) comparing this "As Found" result with the recorded "As Left" condition from the previous recalibration to evaluate the drift at several input values in the range of the sensor. If the sensor output is found to have drifted from the previous condition, then the sensor is adjusted to meet the prescribed "As Left" tolerances. However, this approach is expensive and time-consuming, and unnecessary maintenance actions can potentially damage sensors and sensing lines. Online monitoring (OLM) can help mitigate many of these issues, while providing a more frequent assessment of calibration and signal validation. However, widespread utilization of traditional OLM approaches is lacking with the need to better quantify OLM uncertainty a key factor in this.Sources of uncertainty in OLM can be roughly categorized as (1) process noise, (2) measurement uncertainty, (3) electronic noise, and (4) modeling uncertainty. Approaches to uncertainty quantification (UQ) that are data-driven may be capable of providing estimates of uncertainty that are time-varying as the quantities being measured vary with time. Such a capability provides the option of adjusting acceptance criteria and, potentially, setpoints in a time-varying fashion to meet the needs of the nuclear power system.A Gaussian Process (GP) model is proposed in this study for addressing the UQ issue. The advantage of this approach is the ability to account for spatial and temporal correlations among the sensor measurements that are used in OLM. The GP model, as proposed, may be considered an extension of a commonly used OLM model and, therefore, the hypothesis is that the UQ methodology may be readily extended to accommodate commonly used OLM models.Two approaches were taken for generating the data sets needed for evaluating the proposed model. Experimental data was acquired using an instrumented flow loop, with varying test conditions. In addition, a simulation model of a ...

This report documents a literature survey of so-called "Model Assisted Probability of Detection" (MAPOD) approaches that may be useful in determining the probability of detection (POD), a metric for quantifying the performance of nondestructive evaluation (NDE) methods. The objective of this report is to summarize MAPOD concepts that have been proposed to date in order to assess specific approaches that may be appropriate for application to improve estimates of POD for field NDE of nuclear power plant components. The limitations of laboratory-based studies to replicate actual field conditions are well-recognized and not limited to the nuclear power industry. Probability of detection estimates based on laboratory studies generally provide ideal environments for performing examinations as compared field settings, which typically will result in non-conservative estimates of POD for field applications. As a consequence of this effort, the authors conclude that use of MAPOD concepts to improve estimates of field NDE performance may require access to certain field data, or alternatively, may require significant laboratory studies to assess the influence of human and environmental shaping factors. If the necessary field data cannot be made available, it is proposed that laboratory efforts will have greater chance of success by focusing on a specific examination technique and component application. The authors also find that MAPOD concepts may have a more immediate contribution to the nuclear power industry through their use in extending personnel and procedure qualifications beyond established limits. Finally, another basis was identified that may be used to adjust POD curves generated in previous reliability studies and performance demonstrations. Many of the previous studies calculated POD as the average of performance data which may be inappropriate for many applications, as the calculation may be nonconservative. A more conservative approach to estimating POD would include basing the calculation on a lower statistical quantile of the data set. v