ML20087P318
| ML20087P318 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 03/30/1984 |
| From: | Beckham J GEORGIA POWER CO. |
| To: | Deyoung R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| REF-PT21-84 NED-84-074, NED-84-74, NUDOCS 8404060286 | |
| Download: ML20087P318 (3) | |
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. Georgia Power Company,
- 333 Piedmon) Avenue Attenta, cecrgia 30308,
Telephone 404 526 7020 Mailing Address -
Post Offce Box 4545 Atlanta, Georgia 30302 Georgia Power The sot 4 hem electnc System J. T. Beckharn, Jr.
Vice Presdent and General Manager.
Nuclear Generation March 30,1984 U. S. Nuclear Regulatory Commission
REFERENCE:
Office of Inspection and Enforcement Wash.: RCD Washington, D. C.
20555 50-366 Limitorque Motor Defect ATTENTION: Richard C. DeYoung GENTLIMEN:
On June 2, 19tt3 and then again on August 3, 1983 Plant Hatch Unit 2 experienced a failure of a Limitorque Model SMB-4 motorized operator to close a safety-related valve.
The second event was mported on September 1, 1983 by Licensee Event Report (LER) No. 50-366/1983-076; however, the earlier event was never reported to the NRC since the plant was in a Cold Shutdown Condition t.t the time and the affected valve was not required to be operable.
Georgia Power Company (GPC) has determined that the two failures were similar.in origin and that both fall within the critieria for reportability under 10 CFR 21.
Therefore, the details of the June 2, 1983 event are included in the-enclosed Evaluation of a Substantial Safety Hazard, along with infonsation m1ating this failure to the August 3,1983 event and other infonsation not included in the above referenced LER.
In-addition, GPC is mporting the details of both ' events to the vendor. for these-motors (Limitorque Corporation) so that appropriate action is taken to reduce -the potential for future occurrences of this type.
This submittal concludes reporting by GPC for. this event, - barring any future occurmnces' of this type or discovery of any new information relating to this problem. -
Sincerely yours,
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[J.T.Beckham,Jr CBS l
L Enclosure
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J. P O'Reilly 8404060786 840330 P. D. Rice PDR ADOCK 05000366-H. C._ Nix, Jr.
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EVALUATION OF A SUBSTANTIAL SAFETY HA2ARD LIMITORQUE M070RIZED VALVE OPERATDilS-Parch 30, 1984 Initial Events and Reporting On June 2,1983, with Plant Hatch Unit 2 in the Cold Shutdow'n Condition, the motorized operator on RHR inboard injection valve 2E11-F015B failed to function during a test.
The valve was not required to be operable at that time, so NRC reporting was deemed unnecessary.
On August 3,1983, during an attempt to place Hatch-2 into the Shutdown -Cooling Mode, the operator on valve 2E11-F01SA failed to function.
That event, which placed Hatch-2 in a seven day LCO per Technical Specification Section 6.9.1.9.b, was reported on September 1,1983 by Licensee Event Report (LER) 50-366/1983-076.
Evaluation of Occurrences:
The cause of these two failures has been attributed by GPC to the backing out of the the locking nut on the wom gear shaft inside och r.iotor opera tor.
This allowed a critical worm gear to back out of -its position in the bearing and bellville spring pack.
Since the threads of 'the worm gear on each motor were Eme from the scarring which results from proper tightening of the locking nut set screw, GPC has concluded that this set scmw, which secures the locking nut in position, was not tightened by the vendor for these operators before they were shipped to Plant Hatch.
The condition in each motorized operator following the slippage of the wonn gear from its intended position prevented the internal torque sensing switch fmm stopping the motor af ter the valve had fully closed.
This i
resulted in the trip of the valve motor circuit breaker (preventing motor burnup) and the resulting failure of each valve to respond to a subsequent open signal.
The failure of either of these valves to open due to this problem following a Design Basis Accident at Hatch-2 would prevent one complete loop of the Low Pressure Core Injection (LPCI) system, containing two of the four LPCI ptmps, from injecting into the reactor vessel.
Coupled with an assumed singte failure of one of the two Core Spray system pumps, the plant would be left with insufficent low pressure ECCS to ensure the integrity of the fuel cladding during a design basis accident.
Therefore, GPC concluded that these failures constituted a defect in a basic plant component necessary to assure the capability to shutdown the reactor and maintain it in a safe shutdown condition. This requires reporting to the NRC under 10 CFR 21.
Backgmund Information:
The cotorized operators in question were installed at Hatch-2 in early February 1983 as part of the GPC effort to meet the requirements of 10 CFR 50.49.
After this installation, both of these devices were functionally checked per plant procedures and found to be working properly.
A review initiated by GPC after these incidents indicated that these two motors were i
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c March 30,1984 Page Two the only Limitorque Model SMB-4 operators installed as part of the equipment qualification program upgrade.
However, SMB-4 motors are installed on several other critical valves at Plant Hatch including the fc11oving:
E11-F015A6B 2E11-F048A6B E11-F016A6B 2N21-F110 E11-F048A6B 2E41-F008 E41-F008 Similar types of problems have previously been reported by I 6 E Information Notice 83-70 and I 6 E Circular 79-04 as well as a recent Institute of Nuclear Power Operations (INPO) significant event report which included details of causes and prevention for these types of events.
Corrective Actions and Preventive Measures:
Based on corrective measures recommended by Lisiitorque and also the above mentioned INP0 report, GPC has performed modifications on the two failed valve motors to prevent future occurrences of this type of problem.
In addition GPC.will conduct an engineering review of Liritorque ' motors at Plant Hatch to detemine if the recommended preventive maintenance is necessary for any of the SMB Model operators installed cn any valves at Hatch, including those listed above.
GPC will' then make a detemination on a valve-by-valve basis as to whether or not any modifications or repairs are necessary to prevent valve malfunction due to lock nut ~ slippage.
In the cases where a modification has been or is found to be necessary, the repair has been or will be the staking of the threads en the wom gear set screw as described in INPO Procedure No. PMP2-ZG-25, rev. 03.
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