RBG-21706, Revised Response to Violation 85-40-01, High Strength Steel Bolts Preload, Noted in Insp Rept 50-458/85-40.Condition Does Not Present Safety Issue.Addl Actions Not Required to Achieve Full Compliance
| ML20135A565 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 07/26/1985 |
| From: | Deddens J GULF STATES UTILITIES CO. |
| To: | Martin R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| Shared Package | |
| ML20135A519 | List:
|
| References | |
| RBG-21706, NUDOCS 8509100196 | |
| Download: ML20135A565 (4) | |
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GULF STATES UTILITIES COMPANY RIVER BEND STATION POST Of FICE BOX 220 ST FRANCISVILLE. LOUISLANA 70775 ARE A CODE 504 635 6094 346-8651 July 26, 1985 RBG-21706 File Nos. G9.5, G15.4.1 Mr. Robert D. Martin, Regional Administrator U.S. Nuclear Regulatory Comtission Region IV
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611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76011 N-lE
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Dear Mr. Martin:
River Bend Station - Unit 1 Refer to: Region IV Docket No 50-458/ Report 85-40 This letter is a revised response to the Notice of Violation 85-40-01 contained in NRC I&E Inspection Report No.
50-458/85-40.
The inspection was perfonned by Mr. W. M. McNeill during the period April 15-19 and April 29 - May 3, 1985, of activities authori: ed by NPC Construction Permit CPPR-145 for River Bend Station Unit No.1.
Gulf States Utilities Canpany's (GSU's) revised response to the Notice of Violation 85-40-01, "High Strength Steel Bolts Preload," is provided in the enclosed attachment.
This carpletes GSU's response to the Potice of Violation.
Sincerely,
.ht h w J. C. Deddens Vice President River Bend Nuclear Group JCD/ TOC /PJD/amg Attachment t
8509100196 850906 PDR ADOCK 05000458 PDR e
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ATTACIIMENT July 26, 1985 RBG-21706 Response to Notice of Violations Reference Notice of Violations - E. II. Johnson letter to W. J. Cahill, dated May 28, 1985.
Refer to Docket 50-458/85-40.
Response to 85-40-01 High Strength Steel Bolts Preload A smple of 200 7/8-in.~ bolts were inspected at River Bend Station (RBS) using job inspection torque (JIT), which was developed at the time this lot of. bolts was installed. Of these 200 bolts, 8 failed to achieve JIT and recorded a residual. torque.approximately 27 percent to 88 percent of JIT.
This_ demonstrated that 96 percent of the sample met or exceeded the accep-tance criteria (90% of JIT) established for the NRC inspection.
We believe that the results of the torque testing of the bolts by the NIC indicate satisfactory _ bolt installation, as required to meet the design conditions. The following are the bases for this conclusion.
a)
' Installation and inspection of bolts were performed in' accordance with the Research Council for Riveted and Bolted Structural Joints (RCRBSJ), which requires an inspection'of two bolts per connection selected at randan. This inspection is intended to provide assur-ance that the connection has been properly tightened.
(Note: _1he inspection sampling frequency is not intended to detect every bolt that may exist below the 'JIT, but rather to lend confidence that the ccnnection was installed properly, based on the two bolts.
inspected in a connection shosed ccmpliance).
7herefore, the-existence of eight bolts that' failed to meet JIT out _of 200 bolts -
total is consistent with industry standards, b)
JIT'is the average. torque measured in the testing of three bolts in a lot. Industry test on torque tension relationship shows that-bolts fran the.same lot yielded an extreme value of bolt tension-
+30. percent fran the mean tension desired. The average variation was in general +10 percent. As a result, bolts that have 70 per-cent of the JIT could provide the mininum fastener tension.
c)
Friction connections installed'in accordance with'BCRBSJ specifi-cation give a minimun factor of safety of 1.52 against slip for full capacity'of connection in' accordance with the AISC
Page 2 July 26, 1985 RBG-21706 seventh edition.
Also, the eighth edition recognizes the higher friction coefficient of roughened galvanized surfaces, which adds approximately 20 percent to the safety margin. This essentially provides a friction capacity significantly higher than that required by design.
d)
Conservatively, all the connections at RBS have been designated as friction type. The safety significance of the nest critical (worst load) connection losing its friction capacity (e.g., loss of 100% torque) is not a concern at River Bend because in the unlikely event that friction wculd be overccam, the connection would act as a bearing connection. Performance of bearing connec-tions is not dependent on high bolt pretension.
It should be noted that connection holes are noninally 1/16 in. larger than the bolt diameter. Therefore, the maximum slip that can occur in a joint is equal to 1/8 in. However, the joint movments are rarely as large as 1/8 in, and average less than 1/32 in, according to industry e:perience.
In many situations, the joint will not slip at all under live loads because the joint is often in bearing by the time the bolts are tightened.
This ocrurs due to small misalignments inherent to the fabrication process or due to slip occurring under the dead load before the bolts in joint are tightened.
'Iherefore, torque has insignificant effect on the stability of the structure.
River Bend structural connection design utilizes A325 bolts in the majority of applications.
'Ihe AISC allowable shear values for friction connection are the same as allowable for connection in bearing. For higher strength bolts, the allowable bearing capacity is slightly higher than that for friction connection. Therefore, if the connection results in bearing con-nection, the design capacity is not ccrprcmised. It should be noted that the performance of bearing connections is not dependent on the high bolt pretension.
Corrective Steps Which Have Been Taken and Results Achieved Not Applicable.
Corrective Steps Which Will Be Taken To Avoid Further Violations Not Applicable.
Date When Full Cmpliance Will Be Achieved Based upon the above considerations, the condition identified by the NBC does not present a safety issue at RBS. Therefore, additional actions are not required to achieve full empliance with progrannatic and technical requirments.
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l UNITED STATES OF ABERICA NUCLEAR EEGULATOET ColetISSION STATE OF LOUISIANA 5
PARISH OF WEST FELICIANA 5
In the Matter of Docket Nos. 50-458 GULF STATES UTILITIES COMPANT 5
(River Bend Station, Unit 1) e AFFIDAVIT J.
C.
Deddens, being duly sworn, states that he is a Vice President of Gulf States Utilities Company; that he is authorized on the part of said Company to sign and file with the Nuclear Regulatory Connaission the documents attached hereto; and that all such documents are true and correct to the best of his knowledge, information and belief.
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J. C. Dedfiens
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Subscribed and sworn to before me, 1 Notary Public in and for the State and Parish above named, this day of h//
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oan W. Middlebro6ks Notary Public in and for West Feliciana Parish, Louisiana My Commission is for Life.
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