Eddy current analysis round robin using the NRC steam generator mockup. Page: 3 of 14
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EDDY CURRENT ANALYSIS ROUND ROBIN USING THE NRC
STEAM GENERATOR MOCKUP
D. S. Kupperman, J. Muscara, S. Bakhtiari, J. Y Park and W. J. Shack
One major outcome of regulatory activity over the past 10 years intended to develop guidance
for tube integrity assessments is the development and implementation of two key concepts,
condition monitoring and operational assessment. Condition monitoring is an assessment of the
current state of the steam generator (SG) relative to the performance criteria of structural
integrity. An operational assessment is an attempt to assess what will be the state of a generator
relative to the structural integrity performance criteria at the end of the next operating cycle. The
predictions of the operational assessment from the previous cycle can be compared with the
results of the condition monitoring assessment to verify the adequacy of the methods and data
used to perform the operational assessment. The reliability of the in-service inspection (ISI) is
critical to the effectiveness of the assessment processes. Quantitative information on probability
of detection (POD) and sizing accuracy of flaws for the inservice inspection techniques are
needed for conditional monitoring and operational assessment. Eddy-current (EC) inspection
techniques are the primary means of ISI for assessing the condition of SG tubes in current use.
Detection of flaws by EC depends on detecting the changes in impedance produced by the flaw.
However, many other variables, including tube material properties, tube geometry, and
degradation morphology, can produce impedance changes, and the accuracy of distinguishing
between the changes produced by such artifacts and those produced by flaws is strongly
influenced by EC data analysis and acquisition practices (including human factors). Similarly,
although it can be shown that there is a relationship between the depth of a defect into the tube
wall and the EC signal phase response, in practice, those things that affect detection also affect
The approach chosen for this program was to develop an SG tube bundle mock-up that simulates
the key features of operating SGs so that the inspection results from the mock-up would be
representative of those for operating SGs. Considerable effort was expended in preparing
realistic flaws and verifying that their EC signals and morphologies are representative of those
from operating SGs. The mock-up includes stress corrosion cracks of different orientations and
morphologies at various locations in the mock-up and simulates the artifacts and support
structures that may affect the EC signals. In this exercise all analysts examine the same data
provided on copies of optical disks that contain the data to be analyzed. The team-to-team
variation in detection capability is the result of analyst variability in interpretation of eddy
current signals. The fits to the POD data and the subsequent lower 95% confidence limits are
influenced by the uncertainty in crack depth determined by a multiparameter algorithm and the
number of cracks in the sample set. In this report, the probabilities of detecting flaws of various
types and at various locations are presented as logistic fit curves to the raw data, along with
lower 95% confidence limits.
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Kupperman, D. S.; Muscara, J.; Bakhtiari, S.; Park, J. Y. & Shack, W. J. Eddy current analysis round robin using the NRC steam generator mockup., article, February 20, 2002; Illinois. (digital.library.unt.edu/ark:/67531/metadc741237/m1/3/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.