The material presented in this article summarizes the results from phase 2 of a larger Electric Power Research Institute (EPRI) study to determine if permanently mounted strain sensors can be used to monitor and quantify the presence and growth characteristics of flaw indications in primary loop piping in light water nuclear power reactors (LWRs). The samples utilized in this phase 2 work consisted of butt welded sections of austenitic 304 stainless steel pipe segments. Axial and circumferential notches, intended to simulate service flaws of varying depths and lengths, were generated into the inner diameter (ID) of the samples. Resistive strain gauges were applied in longitudinal (axial) and transverse (hoop) orientations, on the outer diameter (OD) in the vicinity of the notch locations. The axial notches perpendicularly intersected the weld while circumferential notches were generated along the weld fusion planes on one side (15 deg from the radial direction). The notch morphologies, strain gauge placement details, and a summary of the strains measured during pressurization tests are presented in this article. Based on the strain data obtained, transverse strain measurements may be sufficient to allow online monitoring (OLM) of axial and circumferential flaws in the vicinity of welds in the LWR pressurized primary coolant loop austenitic stainless steel piping and components.

Time-of-flight neutron diffraction and energy-resolved imaging each provide unique perspectives into material properties. Neutron diffraction is useful for assessing microstructural parameters such as phase composition, texture, and dislocation densities, though it typically provides averaged data over the sampled volume. Energy-resolved imaging, on the other hand, offers both spatial and spectral information by detecting Bragg edges and neutron absorption resonances, which enables detailed mapping of microstructure and isotopic composition. When combined, these techniques have the potential to enrich our understanding of material behavior across different scales, enhancing our understanding of complex materials. Traditionally, these modalities are conducted on separate instruments, which is time-consuming and poses challenges for data integration. Here, we report the integration of the LumaCam, an event-mode energy-resolved neutron imaging camera with the HIPPO time-of-flight diffractometer at LANSCE. This integration enables simultaneous diffraction and imaging across the full spectrum, with analysis optimized for diffraction and Bragg-edge imaging in the thermal range (0.45–10 Å) and resonance imaging in the epithermal range (0.5–3000 eV), facilitating comprehensive multi-modal analysis. We demonstrate its capabilities through case studies, including spatial mapping of grain orientations in a steel sample and accurate thickness estimations for irregular samples including a depleted uranium cylinder and a natural silver-containing mineral specimen. The combined setup enhances real-time sample alignment and provides comprehensive data for crystal structure, texture, and isotopic composition analysis. This approach opens new possibilities for advanced applications in nuclear engineering, archaeology, and materials science.

Ultrasonic diffuse field absorption, a nondestructive evaluation technique that has been shown to be sensitive to radiation-induced microstructural and microchemical features in materials, was utilized to characterize integrated internal friction in service-irradiated austenitic stainless steel samples cut from baffle plates extracted from the Jose Cabrera Nuclear Power Station, often referred to as Zorita nuclear power plant. Measurements were performed on broken compact tension (CT) samples with 9.4 to 41.5 dpa of neutron damage in the asirradiated condition and after annealing at either 400 degrees C or 1050 degrees C. Since the microstructural and microchemical evolution of 304 stainless steels at Zorita-relevant irradiation conditions saturates at relatively low dpa levels, it was not surprising that the changes in internal friction in the as-extracted material also saturated. When the as-irradiated specimens were subjected to annealing at temperatures that resulted in either mild coarsening or total dissolution of as-irradiated microstructure, measurable changes were observed in the internal friction, that could be explained by invoking previously observed microstructural and microchemical phenomena from other studies, confirming the responsiveness of this technique to changing internal structure. The diffuse field ultrasonic absorption measurement technique therefore appears to show promise in nondestructive evaluation of irradiation microstructural features known to affect physical properties in light water nuclear power reactor internals. Further destructive post-irradiation and subsequent post-annealing examination studies on these specimens are required to relate full details of microstructural and microchemical evolution to observed concurrent changes in physical properties using the ultrasonic diffuse field absorption technique.

Grade 91 steel has been used in nuclear and fossil power plants since the 1970s. Manufacturing variabilities resulting from manufacturing, repair, and management activities have been attributed to lowered creep and fatigue life. This paper characterizes the elastic, thermal, and anelastic properties of P91 steel with different microstructures. Eight different microstructural conditions were identified as acceptable, gross, and gradual degradations. Ultrasonic testing was used to measure velocities, and resonant ultrasound spectroscopy was used to measure internal friction. The thermal diffusivity was measured along with Vicker's hardness and grain size. A model for internal friction was used to combine the measured elastic and thermal properties. The results suggest that the current understanding of internal friction and its sources may be incomplete for complex microstructures like grade 91. From an nondestructive evaluation perspective, the results suggest that the internal friction has the highest sensitivity to microstructure changes, compared to elastic and thermal properties.

Microstructural variability from manufacturing and post-fabrication activities have been attributed to a significant portion of failure in grade 91 steels. For example, heat treatment from welding can change the microstructure locally, which can change the hardness, phase content and grain size. This article explores the use of ultrasonic coda waves to detect microstructural changes in martensitic grade 91 steel. Tube samples with eight different microstructural conditions were simulated using different heat treatments and were tested using coda waves. Six different differential features were extracted from the coda wave signals. Only three features: Loss of correlation, differential curve length and coda wave interferometry showed accuracy > 50%. Further, clustered analysis to test the ability of the features to classify good, mid-level and bad microstructures showed that only loss of correlation had good accuracy. Overall, the study suggests that coda waves can be used to detect subtle changes in microstructure.

Destructive techniques to monitor nuclear reactor component health may not always be available during service, as they are time-consuming and often require pre-installed inspection coupons. Non-destructive evaluation (NDE) techniques can bridge this gap by rapidly identifying the state of mission-critical reactor components, via inference between NDE-measurable material properties and those of ultimate interest, such as ductility and toughness. Here, we demonstrate one such inference about the health of thermally aged cast austenitic stainless steels. Observations of surface acoustic wave peak (SAW) splitting correlate with spinodal decomposition-induced embrittlement as destructively measured by Charpy impact energy. Elastodynamic calculations and molecular dynamics simulations of the effects of spinodal decomposition on elastic moduli support that the new acoustic modes present are due to stiffening in the δ-ferrite domains. This discovery enables one to probe structure-property relationships in materials in a greatly accelerated manner, suggesting that similar inference methods can be used to determine material fitness-for-service, or to quickly uncover new structure-property relationships.

A significant portion of failures in grade 91-92 steels have been attributed to poor fabrication that results from a high production variability and repair/management activities such as post weld heat treatment. This can result in microstructures which are detrimental to creep and fatigue properties of the structure. The objective of this article is to use Rayleigh wave nonlinear ultrasonics to differentiate and classify the different microstructures. Eight different microstructures were chosen for testing with as-received, gradual and gross degradation in the microstructure. The nonlinear 2nd and 3rd harmonics were measured for each microstructural condition and used for analysis. The destructive analysis included hardness measurement and microscopy to get the average grain sizes. The hardness was used to calculate the dislocation density, which was further correlated with the 2nd and 3rd harmonic nonlinear parameters. The results suggest that the 3rd harmonic is better at classifying the microstructures compared to the 2nd harmonic or the linear Rayleigh wave velocity. Conjectures were developed destructive and nondestructive results.

Primary loop piping integrity is a regulatory and safety concern for the long-term operation (LTO) commercial light water reactor (LWR) nuclear power plants (NPPs). Typically, primary loop piping in existing LWRs was manufactured from cast or wrought austenitic stainless steel alloy material and operates at a pressure of ~2250 psi (16MPa) for a pressurized water reactor (PWR) design type and ~1000 psi (7 MPa) for a boiling water reactor (BWR). The objective of this research was to determine if measurement of surface strains can be used to characterize inner diameter flaws. For this feasibility study, wrought carbon steel Alloy A106 Grade B material was selected in lieu of stainless steel. This research was performed on pre-notched, 10 in. (25 cm) nominal outer diameter (OD) Schedule 120 (0.844 in. [21.4 mm) wall thickness) pipe samples of 24 in. (61 cm) length. The notches were made using electrical discharge machining (EDM) on the inner diameter (ID) of the pipe samples, with notch features two-dimensional (2D) and planar in nature to simulate cracking. The surface strains in the samples were evaluated under increasing hydrostatic pressure, up to a maximum of 2300 psi (16MPa) to determine their response to flaws with variable depth. Reusable end caps were utilized in lieu of welded caps for the pressure testing. This article describes the test procedure for the pressure testing and results of the feasibility study, which is the first phase of research with the end goal of the development of online crack monitoring capability for use at operating NPPs.

The Electric Power Research Institute (EPRI) Nuclear Sector and US Department of Energy Light Water Reactor Sustainability Program are committed to engaging in research and development endeavors to address materials aging issues specific to long term operation of light water power reactors. To this effect, EPRI launched an industry initiative to develop nondestructive evaluation systems for online monitoring of existing cracks in light water reactor primary coolant loop piping and components. One of the goals of this initiative is to develop a sensor system (or systems) that can determine nondestructively if cracks are growing or arrested and, in the case of the former, to characterize their growth rates. A missing component of this initiative is an experimental assessment of how sensors and adhesive couplants will perform in service when exposed to chronic energetic neutron radiation, particularly at the primary coolant loop hot and cold leg dissimilar metal welds, which join the primary loop piping to the reactor pressure vessel and reside in the vicinity of the reactor core. The objective of this experimental study was to determine how ultrasonic transducers and adhesive couplants perform when exposed to irradiation in a test reactor to simulate and accelerate in-service exposure. To achieve this objective, the signal stability of piezoelectric transducers and performance of adhesive couplants as a function of accumulated fast neutron fluence were characterized by collecting ultrasonic data in-situ during irradiation. Of particular interest were the ultrasonic signal quality and time decay of the amplitude of acoustic reflections as a function of fast neutron fluence. The results of the study showed that, of the 8 transducer/substrate sample assemblies tested, only 3 generated usable ultrasonic signals through the conclusion of the irradiation campaign. It was found that high temperature epoxy tends to ultrasonically couple the sensors to the substrates better than three types of refractory ceramic cements studied, as is supported by post irradiation examination. The results obtained through this experimental study will be utilized in the achievement of the overall goal of development of a sensor system to perform online monitoring of primary loop components.This manuscript has been authored in part by UT-Battelle, LLC, under contract DE AC05-00OR22725 with the US Department of Energy (DOE). The publisher acknowledges the US government license to provide public access under the DOE Public Access Plan (https://energy.gov/downloads/doe-public-access-plan [energy. gov]).

The US code of Federal Regulations mandates regular inspection of centrifugally cast austenitic stainless steel pipe, commonly used in primary cooling loops in light-water nuclear power plants. These pipes typically have a wall thickness of ~8 cm. Unfortunately, inspection using conventional ultrasonic techniques is not reliable as the microstructure strongly attenuates ultrasonic waves. Work is ongoing to simulate the behavior of acoustic waves in this microstructure and ultimately develop an acoustic inspection method for reactor inspections. In order to account for elastic anisotropy in the material, the texture in the steel was measured as a function of radial distance though the pipe wall. Experiments were conducted on two 10 × 12.7 × 80 mm radial sections of a cast pipe using neutron diffraction scans of 2 mm slices using the HIPPO time-of-flight neutron diffractometer at the Los Alamos Neutron Science Center (LANSCE, Los Alamos, NM, USA). Strong textures dominated by a small number of austenite grains with their (100) direction aligned in the radial direction of the pipe were observed. ODF analysis indicated that up to 70% of the probed volume was occupied by just three single-grain orientations, consistent with grain sizes of almost 1 cm. Texture and phase fraction of both ferrite and austenite phases were measured along the length of the samples. These results will inform the development of a more robust diagnostic tool for regular inspection of this material.

This research combines linear and nonlinear ultrasound to examine the microstructural and microchemical changes in five large, highly irradiated cold-worked ANSI 304 stainless steel coin specimens cut from two hexagonal cross section blocks with radiation damage levels ranging from -0.4 to -33 dpa following irradiation in the EBR-II fast reactor. Both linear (velocity) and nonlinear ultrasonic (beta) measurements were conducted in a hot cell using an automated fixture device specially designed to hold the sensor for repeatable measurements in an environment where direct human access is limited, demonstrating their potential to more fully investigate the complex defect ensemble introduced by irradiation. The measurements were performed at the Westinghouse Churchill site hot cell facility. The linear measurements agree very well with previous measurements employing a different sensor application technique. The ultrasonic nonlinearity parameters measured after irradiation increased by more than 100% from the unirradiated state and show a level of random variation below 4.7%. These ultrasonic nonlinearity parameters also show a spatial dependence on measurement location across each of the specimens in agreement with the spatial inhomogeneity of microstructure and microchemical distribution previously observed in adjacent, nominally identical specimens using transmission electron microscopy (TEM) and atom probe tomography (APT). It is proposed that the inhomogeneous distribution of microstructural and microchemical features including Frank loops, and both intragranular and grain boundary precipitates, as well as their different nonlinearity generation efficiencies are responsible for the spatial dependence of the measured ultrasonic nonlinearity parameters. The major and dominant component of the microstructure of these specimens at 20-30 dpa is vacancy agglomerations called voids, previously observed by microscopy and measurable using either linear ultrasonic velocity or linear attenuation, but which are not readily visible using nonlinear ultrasound. Components such as Frank loops, which are one of the other major microstructural components, do not contribute significantly to changing the linear ultrasonic velocity. Using this combination of linear and nonlinear measurements allows for the examination of microstructural/microchemical components whose linear ultrasonic interactions are overshadowed by voids, especially Frank loops and various radiation-induced precipitates. The changes in ultrasonic nonlinearity parameters in these specimens are thought to arise from two major sources. The smaller contribution is due to carbide pinning of dislocations in the grain boundary walls and the few line dislocations present in the grain interior. The largest contribution appears to come from segregation of Ni and Si to the perimeter of the very high density of Frank loops, leading to the formation of Ni3Si precipitates which are thought to be very efficient at pinning the Frank loops. These results on two hex blocks provide an ideal, though not completely realistic, test case to demonstrate the sensitivity of nonlinear ultrasound to two different microstructure sources. (C) 2020 Elsevier B.V. All rights reserved.

An important topic for long-term operation of nuclear plants is aging of plant concrete structures. The containment building, biological shielding, and support concrete are examples of concrete structures that are of primary importance in the operation of a nuclear plant. These and other safety-related structures must be capable of maintaining structural capability for the operating life of the plant. Demonstration of the satisfactory condition of the concrete structures is required for safe operation, particularly when plant operation beyond 60 years is considered. The concrete biological shield (CBS) wall is particularly important because of its shielding and structural functions and that it is irradiated due to its proximity to the reactor pressure vessel. Demonstrating that the concrete remains structurally able to perform its intended function is vital in effective aging management. Neutron irradiation above certain thresholds can cause loss of tensile and compressive strength of the concrete and volumetric expansion. If the irradiation level exceeds the threshold, both loss of strength and volumetric expansion should be evaluated. Methods to reliably evaluate the effects of the loss of strength and volumetric expansion are required.

The Electric Power Research Institute (EPRI) has been engaged in collaborative research and development activities related to concrete in nuclear applications over the past several years in concert with the nuclear generation industry, foreign and domestic national laboratories and regulatory bodies and universities. The EPRI Long Term Operations program is focused on performing research activities that will help the industry extend operation beyond the first period of license renewal, which for US plants means operation beyond 60 years. In this overview talk, three subjects will be addressed-radiation damage in boiling and pressurized water reactor concrete biological shields, boric acid attack of pressurized water reactor spent fuel pool concrete substructures and alkali-silica reaction degradation of concrete structures. The results of these and other studies are expected to support utilities as they demonstrate technical bases to regulatory bodies for long term operation of commercial nuclear plants.

The objective of this research is to use nonlinear resonance ultrasound spectroscopy (NRUS) to evaluate the sensitivity of the nonclassical hysteretic nonlinearity parameter, a to microscopic material damage in metallic specimens. The proposed NRUS procedure uses both a noncontact source and receiver - an air-coupled piezoelectric transducer source and a laser vibrometer receiver - to excite and detect the axial motion of a slender rod. This fully noncontact configuration avoids mechanical contact which can adversely influence the measurements. This NRUS procedure measures a(f) and a(Q) by calculating the amount of the shift of the resonance frequency and the change of quality factor (Q) as a function of increasing excitation amplitudes. The sensitivity of this NRUS measured a parameters to small changes in microstructure is demonstrated on a series of thermally aged 17-4 PH stainless steel samples. These hysteretic nonlinearity (a(f) and a(Q)) results are then compared to (quadratic) acoustic nonlinearity parameter (beta) values previously measured on these same 17-4 PH samples to demonstrate the sensitivity of the hysteretic nonlinearity parameters to changes in microstructure due to precipitate formation.

This research conducts in situ nonlinear ultrasonic (NLU) measurements for real time monitoring of load-induced damage in concrete. For the in situ measurements on a cylindrical specimen under sustained load, a previously developed second harmonic generation (SHG) technique with non-contact detection is adapted to a cylindrical specimen geometry. This new setup is validated by demonstrating that the measured nonlinear Rayleigh wave signals are equivalent to those in a flat half space, and thus the acoustic nonlinearity parameter, beta can be defined and interpreted in the same way. Both the acoustic nonlin-earity parameter and strain are measured to quantitatively assess the early-age damage in a set of concrete specimens subjected to either 25 days of creep, or 11 cycles of cyclic loading at room temperature. The experimental results show that the acoustic nonlinearity parameter is sensitive to early-stage microcrack formation under both loading conditions-the measured beta can be directly linked to the accumulated microscale damage. This paper demonstrates the potential of NLU for the in situ monitoring of mechanical load-induced microscale damage in concrete components. (C) 2018 Elsevier B.V. All rights reserved.

Nonlinear ultrasound (NLU) has been shown to be sensitive to microstructural features including precipitates and dislocations. The heat-affected zone (HAZ) of welded austenitic stainless steels can be susceptible to intergranular stress corrosion cracking (IGSCC). This research uses NLU to evaluate the microstructure of the HAZ with an emphasis on dislocations, precipitates, grain size/morphology and sensitization, which is the formation of chromium carbide precipitates at the grain boundaries. The results show that there is a large increase in the measured acoustic nonlinearity parameter in the vicinity of the HAZ, which can be used to monitor changes in microstructure such as sensitization. (C) 2017 Elsevier B.V. All rights reserved.

Austenitic stainless steels have a wide range of applications in the energy industry, but the corrosion resistance of these stainless steels can be reduced by sensitization, particularly in the heat affected zones in welds. Sensitization is the formation of chromium carbide precipitates along the grain boundaries, causing the formation of a zone of chromium depletion around the grain boundary. Since chromium is the primary alloying element that makes stainless steel corrosion resistant, this chromium depleted zone is susceptible to intergranular stress corrosion cracking (IGSCC). Sensitization occurs when a stainless steel is exposed to a high temperature for an extended time period, such as during welding. The objective of this research is to determine the sensitivity of nonlinear ultrasound to the presence of sensitization by using nonlinear Rayleigh waves to quantitatively track the sensitization of 304 and 304L stainless steels as a function of holding time at 675°C. The effect of the carbon content of the alloys (304 versus 304L) to the sensitization process and the measured nonlinearity parameter, β are investigated. Annealing of these specimens isolates the effect of just sensitization, removing the presence of cold work which can also affect the material nonlinearity. Complementary electrochemical potentiodynamic reactivation (EPR) measurements and microscopy are used to confirm the absence or presence of sensitization. The results show that the acoustic nonlinearity parameter is sensitive to the presence of chromium carbide precipitates in sensitized austenitic stainless steels.