An Assessment of Remote Visual Testing in the Nuclear Industry

The ASME Boiler and Pressure Vessel Code, Section XI, requires that volumetric and/or surface examinations be periodically conducted for certain safety-related components in commercial nuclear power plants. Recently, the U.S. nuclear industry has proposed replacing some of these volumetric and surface examinations with a simpler visual testing (VT) method. PNNL researchers conducted a study of the capabilities of remote visual testing (VT) as related to detecting surface-breaking cracks in nuclear components. This paper describes remote visual testing, performance demonstration standards for camera systems, typical dimensions for service induced cracks in reactor components, and an assessment of the reliability of camera systems at finding these cracks. Included is a discussion of the reliability of visual acuity guidelines for calibration of remote visual systems using two crossed 12- (micro)m diameter wires as a performance demonstration standard. Also, the average dimensions of various types of service-induced cracks in nuclear components are reviewed, with the most critical of these being the crack opening dimension (COD). Because many of these cracks have very small (approximately 30 (micro)m) CODs, the reliability of remote VT may not be adequate to insure component integrity, given the capabilities of current VT systems and application practices