ML20111B848
| ML20111B848 | |
| Person / Time | |
|---|---|
| Site: | Bellefonte  |
| Issue date: | 01/07/1985 |
| From: | Hufham J TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| NUDOCS 8503130258 | |
| Download: ML20111B848 (3) | |
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TENNESSEE VALLEY AUTHORITY CHATTANOOG A, TENNESSEE 37401 400 Chestnut Street Tower II BLRDMpfli38M f1,! 459)82-27 U.S. Nuclear Regulatory Commission Region II Attn:
Mr. James P. O'Reilly, Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
Dear Mr. O'Reilly:
BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 - NONCONSERVATIVE CALCULATION METHOD FOR GENERAL CONSTRUCTION SPECIFICATION G-32 VIOLATIONS - FINAL REPORT The subject deficiency was initially reported to NRC-0IE Inspector D. Quick on May 28, 1982 in accordance with 10 CFR 50.55(e) as NCR WBN SWP 8208. Related NCR GEN CEB 8205 was also determined to be report-able under 10 CFR 50.55(e). This was followed by our interim reports dated July 2 and October 12,1982; April 12 and November 17,1983; and February 15 and June 18, 1984. Enclosed is our final report.
If you have any questions concerning this matter, please get in touch with R. H. Shell at FTS 858-2688.
Very truly yours, TENNESSEE VALLEY AUTHORITY e x. Hu ham anager i ensing an Regulations Enclosure oc (Enclosure):
Mr. Richard C. DeYoung, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Records Center Institute of Nuclear Power Operations 1100 Circle 75 Parkway, Suite 1500 Atlanta, Georgia 30339 8503130258 850107 PDR ADOCK 05000438 cmCIA1. COPY S
PDR An Equal Opportunity Employer
ENCLOSURE WATTS BAR NUCLEAR PLANT UNITS 1 AND 2 NONCONSERVATIVE CALCULATION METHOD FOR GENERAL CONSTRUCTION SPECIFICATION G-32 SPACING VIOLATIONS BLRD-50-438/82-41, -439/82-27 10 CFR 50.55(e)
FINAL REPORT Description of Deficiency This deficiency concerns embedded plates with a potentially inadequate factor of safety against concrete failure. The reduced factor of safety could have resulted from incorrect evaluation of the pullout capacity of the concrete when the welded stud anenors on the embedded plate were spaced closer than the normally applied minimum spacing. The incorrect evaluation could have resulted because the requirements given in Civil Design Standard DS-C6.1 were stated but the method for implementing the requirement did not specify that a factor of safety must be applied. Also, the method given resulted in a factor of safety of 4.0 for ASTM A307 bolts but resulted in lower factors of safety against concrete failure for higher strength materials. For the ASTM A108 materials used for the welded studs, the design methods in the design standard resulted in a factor of safety against concrete failure of 3.1 for service load conditions.
(It should be noted that a factor of safety of 3.1 for ASTM A108 material is acceptably conservative.)
In the introduction of DS-C6.1, it specified that the factor of safety against the concrete failure mechanism (pullout of a spall of concrete) should be 4.0 if a steel failure mechanism could not be assured. For some work on Watts Bar Nuclear Plant (WBN) where the welded studs were spaced closer than the normally applied minimum spacing, the designer compared the applied load to the calculated concrete pullout capacity without application of a factor of safety. Since the deficiency related to a design standard which was also used by Bellefonte Nuclear Plant (BLN), TVA considered the problem to be generic and included BLN in the scope of the nonconformance report (NCR).
Safety Implications TVA's review of the existing strip plates at Bellefonte Nuclear Plant (BLN) has determined that an adequate level of safety against concrete failure exists. However, because of the ambiguity of DS-C6.1, there was no assurance that future checks of attachments on strip plates with closely spaced stud anchors would have incorporated acceptable safety factors.
As such, there j
was a potential for the overloading of concrete which could have caused the I
subsequent failure of the attachments and respective safety-related piping.
Corrective Action A sample of 48 embedded plates with significantly loaded multiple attachments was randomly selected at the site in order to provide information for the evaluation of this NCR and NCR GEN CEB 8208 (BLRD 50-438/82-67, -439/82-60), as TVA had determined that this type sample would provide a conservative method for
cvalunting tha in-place factors-of-safety against concrete failure for welded 3
stud Enchors. Tha sample was originally intended to consist of 60 embedded plates with multiple attachments but only 48 could be located which had significantly loaded multiple attachments.
(The difficulty in obtaining the entire sample indicates that the problem at BLN is not as significant as it was for WBN.)
The 48 plates were analyzed to determine the factor-of-safety against concrete failure for the welded stud anchors, and all but one sample (No.!24) had a factor-of-safety against concrete failure of 3.1.
Sample No. 24 had a factor-of-safety of 3.04, but the documented increase in concrete strength with age from 20 to 30 percent will increase sample No. 24's factor-of-safety to a point above the required 3.1.
Since the sample indicates that an adequate level of safety against concrete failure exists for all embedded plates in the sample, no corrective action is required and the embedded plates may be used as-is.
To prevent any potential 3
problems with future attachments, however, TVA has issued DS-C1.7.1 which clarifies the use of correct factors-of-safety for plates having closely spaced stud anchors (DS-C1.7.1 replaces DS-C6.1).
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