ML19273C366
Text
E([.n UNITED STATES g
NUCLEAR REGULATORY COMMISSION
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- p WASHINGTON. D. C. 20555
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pgg 14 B80 MEMORANDUM FOR:
L. C. Shao, Acting Assistant Director for Engineering Programs, D0R FROM:
V. S. Noonan, Chief, Engineering Branch Division of Operating Reactors
SUBJECT:
GENERIC IMPLICATIONS OF RECENT EDDY CURRENT TESTING EXPERIENCE AT POINT BEACH UNIT 1 By memorandum dated January 4,1980, you requested that we determine if the decreased sensitivity of single frequency eddy current testing (ECT) near the top of the tubesheet represents a generic safety problem and develop a plan to upgrade industry and NRC inspection techniques in the tubesheet and similar areas.
Regarding the first subject, we have been and are continuing to evaluate the generic implications of the recent experience with ECT at Point Beach Unit 1.
Based on available literature and discussions with vendors, utilities and our consultants, we have concluded that multifrequency ECT is superior to single frequency ECT,particularly in the tubesheet and tube support plate regions.
The multifrequency technique can provide enhenced capability to detect tube defects and quantify their magnitude.
Naturally, this improved sensitivity is desirable and multifrequency inspection should be encouraged throughout the industry.
However, a word of caution is necessa ry.
As inspection techniques become more sensitive we must establish corresponding)ymore discriminate acceptance criteria.
Using more sensitive techniques, many defects which would have previously gone un-detected will be categorized as pluggable under current tube plugging cri teri a.
Testing by the vendors and by Pacific Northwest Laboratory, under contract to the Office of Nuclear Regulatory Research, indicate that many of these defects would maintain their integrity under normal and postulated accident conditions. This is largely because current tube plugging criteria consider only one parameter; i.e., defect depth.
More discriminating tube plugging criteria would also consider defect length and defect volume.
Westinghouse maintains with sound technical basis that the five tubes at Point Beach Unit 1 which were categorized as defective at or above the tubesheet are small volume defects which would not have failed under accident conditions.
This hypothesis is borne out in part by the fact that the tubes maintained their integrity during pre-plugging hydrostatic tests simulating LOCA pressure differentials.
Westinghouse has further indicated that defects of a magnitude that would lead to failure of a tube during postulated MSLB or LOCA loadings would be detectable in the tubesheet er tube support plate regions even using single frequency ECT.
Contact:
J. R. Strosnider
.N27356 003050 % {
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L. C. Shao In sunmary, before a conclusion can be reached regarding the generic implications of single frequency ECT in the tubesheet and tube support plate regions, its sensitivity to significant defects (defects which could fail under postulated accident loadings) in these regions must be evaluated.
With respect to this matter, we are planning a trip to R. E.
Ginna where we will review the comparative performance of single fraquency and multifrequency ECT in a steam generator mock up.
The mock up ir-cludes the tubesheet and tube support plates.
This effort along with careful review of available information will allow us to reach a conclu-sion about the generic safety implications of the Point Beach Unit 1 ECT experience.
With regard to a plan for upgrading industry and NRC requirements for inspection techniques, improved NDE methods should be encouraged; how-ever, development and implementation of such requirements should occur through a well planned and organized effort.
Discussions with our ECT consultant from Oak Ridge National Laboratory indicate that it would be premature to require multifrequency ECT on an industry wide basis at this time.
As mentioned previously, requirements for improved inspection techniques may also require corresponding changes in areas such as tube plugging criteria.
Without an integrated approach, the industry may actually be discourage from developing improved inspection techniques.
Furthermore, severe logistics problem could develop if the technology of multifrequency ECT is not properly transferred from the development stage to widespread industrial use.
One significant problem would be the shortage of equipment and trained operators.
For these reasons, the most appropriate context in which to address this subject is Task Action Plans A-3, A-4, and A-5 (TAPS) regarding steam generator tube integrity.
Evaluation of ISI methods is already included in subtask B.3 of the TAPS.
Following the staff trip to R. E. Ginna and review of available information, we will provide our final conclusions regarding generic safety implications of single frequency ECT.
Based on these conclusions we will proceed with the actions necessary to address this subject through t a. TAPS.
S N
n Engineering Branch Division of Operating Reactors cc:
See next page
a L. C Shao cc:
H. R. Dent o, NRR R. J, Budnitz, RES E. G Case, NRR D. G, Eisenhut, NRR T
E. Murley, RES C Z Serpan, RES S, Hanauer, NRR J. P. Knight, NRR 3
D. Liaw, NRP, L. Frank, NRR F, M. Almeter, NRR E. Murphy, NRR J. R. Strosnider, NRR
.