ML20134G764
| ML20134G764 | |
| Person / Time | |
|---|---|
| Site: | Bellefonte  |
| Issue date: | 07/29/1985 |
| From: | Hufham J TENNESSEE VALLEY AUTHORITY |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| REF-PT21-85, REF-PT21-85-380-000 NCR-4277, NCR-4352, PT21-85-380, PT21-85-380-000, NUDOCS 8508280074 | |
| Download: ML20134G764 (2) | |
Text
TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 37401 1630 Chestnut Street Tower II B5t,"c7 A8: 22 July 29, 1985 BLRD-50-438/85-21 BLRD-50-439/85-20 U.S. Nuclear Regulatory Commission Region II Attn:
Dr. J. Nelson Grace, Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
Dear Dr. Grace:
BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 - FAILURE OF BBC BROWN BOVERI LIMIT SWITCHES ON MEDIUM-VOLTAGE CIRCUIT BREAKERS - BLRD-50-438/85-21 ANL BLRD-50-439/85 FINAL REPORT The subject deficiency was initially reported to NRC-OIE Inspector Linda Watson on July 3, 1985 in accordance with 10 CFR 50.55(e) as NCR 4277 and 4352. Enclosed is cur final report. We consider 10 CFR Part 21 applicable to this deficiency.
If you have any questions, please get in touch with R. H. Shell at FTS 858-2688.
Very truly yours, TENNESSEE VALLEY AUTHORITY M
. W. Hufham, Manager Licensing and Risk Protection Enclosure i
cc:
Mr. James Taylor, Director (Enclosure) office of Inspection and Enforcement
,+
U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Records Center (Enclosure) l Institute of Nuclear Power Operations i
1100 circle 75 Parkway, Suite 1500 Atlanta, Georgia 30339 i
l l
OS002%h p
i PU8
%(k s
An Equal Opportunity Employer fgg 7 L
c.
ENCLOSURE BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 FAILURE OF BBC BROWN B0 VERI LIMIT SWITCHES ON MEDIUM-VOLTAGE CIRCUIT BREAKERS BLRD-50-438/85-21, BLRD-50-439/85-20 NCRs 4277 AND 4352 10 CPR 50.55(e)
FINAL REPORT Description of Deficiency Two safety-related BBC Brown Boveri, Incorporated (Springhouse, Pennsylvania), medium-voltage circuit breakers failed to electrically close at Bellefonte Nuclear Plant (BLN) during routine maintenance. The circuit breakers are used in the class 1E 6.9-kV switchgear. Failure was caused by a dislodged spring and contact in the circuit breaker limit switch model number 191921-T6. Dislodgement of the limit switch spring and contact renders the circuit breakers unable to electrically close.
The cause of this deficiency is a flaw in the model number 191921-T6 limit switch design. The contacts become loose due to the shock created by control level overtravel when the breaker is tripped. This flaw is limited to circuit breakers manufactured between March 1974 and July 1978 inclusive.
Safety Implications The deficient circuit breakers can be closed manually, but manual operation is not an acceptable alternative to the sequential electrical closing that is required during abnormal plant conditions and which was assumed in the plant safety analysis. Failure of circuit breakers to close electrically as required in redundant safety-related power systems could cause unavailability of electrical power to redundant essential safety-related systems.
Therefore, if this condition had remained uncorrected, the safe operation of the plant could have been adversely affected.
Corrective Action Corrective action for the deficient circuit breakers will be in accordance with Brown Boveri, Incorporated, recommendations and Instruction Book IB 8303 revision 1.
This action will involve the installation of a 2-17/32-inch control lever stop in place of the 2-25/32-control lever stop found on most of the affected circuit breaker limit switches. The shorter lever stop will limit lever travel to reduce the shock to the contacts.
Also, the mechanism will be adjusted to meet dimensional requirements specified in Instruction Book IB 8303 revision 1.
In order to prevent future failues of this nature, all Brown Boveri, Incorporated, medium-voltage circuit breakers at Bellefonte Nuclear Plant will be modified and adjusted as stated above. Since the limit switch deisgn after 1978 does not have this problem, no further actions to prevent recurrence are required.
All action to correct the deficient condition for units 1 and 2 will be completed by March 1 1987.
,