ML20097J859
| ML20097J859 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 08/30/1984 |
| From: | Tucker H DUKE POWER CO. |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| RO-369-83-35, RO-369-83-65, RO-369-83-82, RO-369-83-97, NUDOCS 8409240066 | |
| Download: ML20097J859 (3) | |
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DUKE Powza GOMPANY P.O. BOX 33180 CHAMLOrrTE, N.C. 28242 IfAL II.Tt CKER Tetzenoxx 34 g sepap, goy om.oa, s
/ Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
Subject:
McGuire Nuclear Station, Unit 1 Docket No. 50-369 LER/RO-369/83-97 LER/RO-369/83-82 LER/RO-369/83-65 LER/RO-369/83-35
Dear Mr. O'Reilly:
The following is additional information relating to Reportable Occurrence Reports R0-369/83-35, 83-65, 83-82, and 83-97 which were submitted by my letters dated June 28, August 31, October 11, and November 4, 1983, respectively. During 1983, failures of pressurizer heater group 1B resulted in four Reportabic Occurrence Reports (as noted above). Efforts have been made to locate the sources of the problems to prevent further occurrences.
Duke Power Company has completed an investigation into the cause of the failures and has located the source of the problem. Details of the actions taken to locate and repair the intermittent problem in pressurizer heater group 1B are given below.
Located within each vacuum contactor control panel is a vacuum contactor (Electric Machinery Industrial Controls Corporation. Type VBS3AD630D1). The vacuum contactor is comprised of a main frame, a steel L-shaped armature, three vacuum switches (one per phase), opening springs, closing springs, and auxiliary contacts. The springs, acting against the armature, hold the vacuum switches in the normally open position. When the coil energizes, the L-shaped armature plate is attracted horizontally to the magnetic pole of the coil, compressing the springs. The armature pivots transmitting movement by a bell-crank action, alicwing the vacuum switches to close under the effect of atmos-pheric pressure acting on the bellows. The failures of pressurizer heater group 1B to energiz' were suspected to be caused by a component in the con-tactor control circuit. The contactor control circuit was checked several times and no problems were found.
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Mr. James P. O'Reilly, Regional Administrator August-30, 1984 Page Two On May 2, 1984 technicians troubleshooting pressurizer heater group 1B to determine the cause of the failures noticed the voltage and current measurements in each phase were inconsistent and at times were not correct. These symptoms indicated that the vacuum contacts were not making proper contact in two of the three phases ("Y" phase measured consistently good). On May 7, 1984 the "Y" phase tension insulator stud was found to be too tight, causing poor contact in the "X" and "Z" phase power, The tension insulator studs on all three phases were adjusted per the " Instruction Manual for Slimline Vacuum Contactor," and pressurizer heater group 1B was placed back in service and operated for several hours. It was rechecked and the problem still existed.
It was decided to move the vacuum contactor (the assembly) from pressurizer heater group 1B to group 1D.
On May 8, 1984, the vacuum contactor from pressurizer heater group 1D was moved to group 1B (if the problem cleared in IB and appeared in ID, it would verify the vacuum contactor to be faulty). After several hours the vacuum contactor in group 1D failed to energize. Pressurizer heater group 1B functioned properly and has not failed since the contactor change-out on May 8, 1984. A new vacuum contactor has been ordered to replace the one in pressurizer heater group 1D.
The problem with the vacuum contactor appears to be directly related to temperature.
I The contactor functions properly with the cabinet door open but fails after several I
hours with the cabinet door closed (neither exterior or interior cabinet temperatures were above rated temperature for the contactor). A fan was installed outside the pressurizer heater group 1D cabinet to blow ambient air into the cabinet, but this additional cooling has been unsuccessful. This is only temporary and will be removed when the new vacuum contactor is installed.
Pressurizer heater groups 1A and IB receive essential power with IC and ID receiving non-essential power. Technical Specification 3.4.3 requires that tiro groups of pressurizer heaters be operable. Since group 1B receives essential power, its operability and reliability was improved by the swap from group 1D.
Relocating the vacuum contactor from pressurizer group 1B to 1D verified that the problem was the contactor. Pressurizer heater group 1B has not failed since the change on May 8, 1984.
Very truly yours, d
I /
w Hal B. Tucker a
TBN:scs cc: Document Control Desk M&M Nuclear Consultants U. S. Nuclear Regulatory Commission 1221 Avenue of the Americas Washington, D. C.
20555 New York, New York 10020 Records Center American Nuclear Insurers Institute of-Nucicar Power Operations c/o Dottie Sherman, ANI Library 1100 circle 75 Parkway, Suite 1500 The Exchange, Suite 245 Atlanta, Georgia 30339 270 Farmington Avenue Farmington, CT 06032
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-Mr. James'P.'O'Reilly, Regional Adm'inistrator-
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-August:30, 1984-1Page Three.
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