A Study of Remote Visual Methods to Detect Cracking in Reactor Components (NUREG/CR-6943)
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Manuscript Completed: August 2007
Date Published: October 2007
S.E. Cumblidge, M.T. Anderson, S.R. Doctor,
F.A. Simonen, A.J. Elliott
Pacific Northwest National Laboratory
P.O. Box 999
Richland, WA 99352
W.E. Norris, NRC Project Manager
Division of Fuel, Engineering and Radiological Research
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code Y6604
The U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research funded a multiyear program at the Pacific Northwest National Laboratory (PNNL) to evaluate the reliability and accuracy of nondestructive evaluation techniques employed for inservice inspection. Recently, the U.S. nuclear industry proposed replacing current volumetric and/or surface examinations of certain components in commercial nuclear power plants, as required by the American Society of Mechanical Engineers Boiler and Pressure Vessel Code Section XI, "Inservice Inspection of Nuclear Power Plant Components," with a simpler visual testing (VT) method. The advantages of VT are that these tests generally involve much less radiation exposure and time to perform the examination than do volumetric examinations such as ultrasonic testing. Therefore, the issues relative to the reliability of VT in determining the structural integrity of reactor components were examined.
Certain piping and pressure vessel components in a nuclear power station are examined using remote VT to reduce occupational exposure as they are in high radiation fields. Other components are examined using VT because the geometry precludes the use of ultrasonic testing (UT). Nuclear utilities employ remote VT with radiation-hardened video systems to find cracks in pressure vessel cladding in pressurized water reactors and core shrouds in boiling water reactors and to investigate leaks in piping and reactor components. The utilities perform these visual tests using a wide variety of procedures and equipment, including the use of submersible closed-circuit video cameras for the remote examination of reactor components and welds.
To evaluate the reliability and effectiveness of the testing, PNNL conducted a parametric study that examined the important variables influencing the effectiveness of remote VT. The tested variables included lighting techniques, camera resolution, camera movement, and magnification. PNNL also conducted a limited laboratory test using a commercial visual testing camera system to experimentally determine the ability of the camera system to detect cracks of various widths under ideal conditions. The results of these studies and their implications are presented in this report.