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Nondestructive Examination (NDE) Detection and Characterization of Degradation Precursors

The U.S. Department of Energy’s (DOE) Light Water Reactor Sustainability (LWRS) Program is developing the fundamental scientific basis to understand, predict, and measure changes in materials and systems, structure, and components (SSCs) as they age in environments associated with long-term operations (LTO) of operating commercial nuclear power reactors. The push towards safe long-term operations of light-water reactor (LWR) nuclear power plants (NPPs) brings significant challenges because aging of components can limit the operating lifetime of critical systems (Bond 2010; Bond et al. 2011a). A key element of LTO of LWRs is therefore expected to be the management of aging and degradation in materials that make up the passive safety system components. If not managed, degradation and aging have the potential to reduce the safety margin of nuclear components.

Within the LWRS Program, the Materials Aging and Degradation research and development (R&D) pathway conducts R&D to develop the scientific basis for understanding and predicting long-term environmental degradation behavior of materials in NPPs. These R&D products will be used to define operational limits and aging mitigation approaches for materials in NPP SSCs that are subject to long- term operating conditions. In parallel, the pathway is developing technologies for the assessment of the condition of these materials in a nondestructive fashion, as such assessments will be necessary to assure adequate safety margins and ensure that an effective aging management program can be set up for LTO.

One class of passive components of concern for LTO are metallic Class 1 components (pressure vessel, primary piping, etc.), because these systems and structures are not easily or economically upgraded when degradation is detected (Bond et al. 2008). Current approaches to detecting material degradation in LWRs use nondestructive in-service inspection methods (such as ultrasonic and eddy current inspection) periodically, typically during refueling outages. These techniques have been shown to be reliable for detecting large cracks or significant areas of corrosion in materials currently used in NPP construction. However, approaches to mitigating the growth of large cracks are limited; and for sustainable long-term operations, the need is to detect and assess degradation before the onset of large- scale cracking. Such an approach provides sufficiently early notice of potential component failure and enables proactive actions to be taken to mitigate and control degradation growth. To meet this need, nondestructive measurement methods are needed that are sensitive to the small-scale changes in material microstructure that occur as degradation accumulates.

This project addresses these issues by developing and evaluating nondestructive methods for their sensitivity to material degradation precursors. The present report describes progress towards this objective in FY 2012.

The report is organized as follows. Section 2 discusses the measurement needs and briefly reviews the state of the art in nondestructive methods for degradation precursor detection. Section 3 briefly describes the experimental setup used for this preliminary assessment. Section 4 presents a discussion of the results to date and the implications of the results. Finally, Section 5 briefly summarizes the work to date, and describes planned follow-on research activities.