ML20064B695
| ML20064B695 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 09/21/1978 |
| From: | David Williams ARKANSAS POWER & LIGHT CO. |
| To: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| 781009, NUDOCS 7810100018 | |
| Download: ML20064B695 (3) | |
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AAKANSAS POWER & LIGHT COMPANY POST OFFICE SOX 551 UTTLE ROCK. ARKANSAS 72203 (5011371-2000 September 21, 1974 4-Uv3-2 dir. K. V. Seyfrit, Director Office of Inspection and Enforcement Region IV U. S. Nuclear Regulatory Commission oil Ryan Pla:a Drive, Suite 100 Arlington, Texas 76012
Subject:
Arkansas Nuclear One - Unit 2 Docket.so.50-56S License No1.NPF-o IUCFR50.55(e) Significant Ueficiency n4 Low Pressure Safety Injection Pump blotor Failure (File:
2-0520)
Gentlemen:
The subject motor failure was originally evaluated by our organi:ation
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and determined not to be reportable as a significant deficiency. jloweyer, after consultation with tne Region IV office of Inspection and Enforcement, it was determined that it was in the best interest of all parties to report tnis item as a significant deficiency.
Sincerely,
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1 Daniel it. Williams Stanager, uicensing utiW : CSP:vb cc:
Sir. W. D..\\tacDonald, Director Office of Stanagement info rmat ion and Program Control U. S. Nuclear Regulatory Co:r.ission Washington, D. C. 20555 Or. E. Vo1 enau, Director 48 3
office of Inspection and Enforce..:ent Wasnington, J. C.
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Significant Deficiency Report Llow Pressure Safety Injection (LPSI) Pump Motor 2PM60B s
Description of Deficiency
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On August 16, 1978, while in the shutdown cooling mode, breaker trip of the vertically mounted 4000 voit, 450 H.P.
"B" LPSI pump motor was indicated.
An operator immediately investigated and upon reaching the' pump area on elevation 317' observed the motor on fire. The fire was exttuguished using both water hoses and C0 extinguishers.
The pump and motor were then removed with the motor being sent to Fagan Company in Little Rock for disassembly.
Disassembly of the pump' at the plant revealed minor damage to the impeller how-ever no damage to the pump casing was noted.
A representative of Siemens Allis (new name of motor supplier Allis-Chalmers) was requested to make a determination of the cause of failure. After noting the sig-nificant distance the rotor had to move in 'the vertical direction to cause damage to the fan, the upper bearing assembly was ins'pected.
The upper bearing assembly consists of Ldap' lex bearings mounted on a bearing thrust block.
For applications in which the pump will experience only downward thrust these two bearingh are mounted in tandem.
If,both downward and upward thrusts are experienced, as is the case here,. the bearings are mounted back-to-back to properly resist the thrusts. However, due to incorrect assembly the bearings were not in-stalled back-to-back but in tandem. Therefore, when upward thrust was experienced, the rotor was allowed to rise sufficient distance to cause the failure because greatly increased radial movement was allowed due to bearing design.
Damage to the notor was extensive. The rotor had come into centact with the stator causing irreparable damage to the rotor.
Both upper bearings showed evidence of high temperature while the lower bearing was heavily damaged.
The contact of the rotor with the stator was the probabic cause of the bearing oil fire.
Correct installation of the bearings can be assured either by the letters DB (for duplex, back-to-back) contained in the bearing number designation or by the diagrams in the instruction manual.
It has been determined that the bearing was installed incorrectly during a previous maintenance inspection.
Safety Impiteations Fuel in the core with no decay heat present tactual conditions' No safety consequences of such a failure ductng taese conditions.
Reactor at power during normal ooeration. The reactor could oe snutdown and cooled oy using emergency feedwater and steam dwap.
No danger to the public would result.
r Accident conditions (LOCA)
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The LPSI system is relied upon in safety analysis for emergency core cooling. Accommodation of a single failure was a design basis for
- his system,~so the deficiency did not result in any danger to the c 'blic or result in any adverse impact on the ~ environment.
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Corrective Action A replacement motor.was obtained to replace the destroyed LPSI motor. The replacement motor is 'slightly larger and heavier 500 li.P. machine. Since,the original ANO-2 impeller will be installed in the' pump no system characteristics will be changed. Present power cables are sufficient and breaker settings will be revised to correspond to the new motor. Seismic analysis review reveals,no support problems due to the increase in weight from 4500 pounds to 5000 pounds.
The replacement motor and the Pump Motor 2PM60A were inspected for proper bearing installation. The bearings were found to be installed properly.
As this problem was an isolated incident, we do not feci that any additional corrective action is required.
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