ML19281A675
| ML19281A675 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 03/16/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Gary R TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| References | |
| NUDOCS 7903300003 | |
| Download: ML19281A675 (1) | |
Text
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^^A pn *= coq UNITE D STATES l
NUCLEAR REGULATORY COMMISSION
[
REGtONIV n
5, G11 RYAN PLAZA DRIVE SUITE 1000 AR LINGTON, TE XAS 70011 March 16, 1979 In Reply Refer To:
RIV Docket Nos.
50-445/IE Circular flo. 79-04 50-446/IE Circular No. 79-04 Texas Utilities Generating Company ATTH: Mr. R. J. Gary, Executive Vice President and General Manager 2001 Bryan Tower Dallas, Texas 75201 Gentlemen:
The enclosed IE Circular 79-04 is forwarded to you for information.
If there are any questions related to your understanding of the suggested actions, please contact this office.
Sincerely, wb Jj/
t Karl V. Seyfrit -
Director
Enclosures:
1.
IE Circular No. 79-04 2.
List of IE Circulars Issued in Last 12 Months 7903300003
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 IE Circular No. 79-04 Date:
March 16, 1979 Page 1 of 2 LOOSE LOCKING NUT ON LIMITORQUE VALVE OPERATORS Description of Circumstances:
On December 8,1978, Fort Calhoun Station Unit No.1 reported that 30 out of 65 Limitorque Type SMB valve operators did not have the locking nut fastened securely in accordance with the manufacturer's recommendation.
If this locking nut is not secure, it can loosen and allow the stem nut to move axially to the point that the splines are disengaged; resulting in a loss of drive to the valve stem.
The licensee reported that several locking nuts were slightly loose but in no instance had the stem nut backed out e' lough to affect the operation of the valve.
This licensee was made aware of the potential problem by a letter of July 28, 1978, from the NSSS supplier, Combustion Engineering, Inc.
Other plants have reported similar findings.
On April 27, 1977, Davis-Besse Nuclear Power Station Unit No.1 reported that two valve 2
operability failures had been caused by locking nuts loosening and falling off.
During the ensuing inspection program, a total of 65 out of 144 safety-related valve operators required staking.
Arkansas Nuclear One (ANO), Unit 2, reported on June 29, 1978, that several valve operators required staking. A subsequent inspection at ANO Unit 2 was made by an IE inspector who identified records that 15 out of 17 SMB o provided by the NSSS supplier (Combustion Engineering Inc.)perators required staking.
Valve operability failures, resulting from loosened lccking nuts, have also been reported by Cooper Nuclear Station (Unusual Event Report 75-5), Browns Ferry Unit 2 report of March 6,1974, and Three Mile Island Nuclear Station Unit 1 reports of March 13, 1976, and October 20, 1976. The corrective action by the licensee in each case was to stake the locking nut.
In June 1978, the Limitorque Corporation issued a supplement to the October 1977, issue of the Type SMB Instruction and Maintenance Manual SMBI-170 that called for the crimping or staking of the locking nuts.
The 1971 issue of the manual had statements for crimping and staking of the lock nuts incorporated into the manual.
The stem nut specification drawing provided by Limitorque for Unit Types SMB-000, SMB-00, SMB-0, SMB-1, SMB-2, SMB-3, and SMB-4 directs the customer to a Limitorque 19CG7 lCoh b PR