ML16342C349
| ML16342C349 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 07/05/1988 |
| From: | Holahan G Office of Nuclear Reactor Regulation |
| To: | Kirsch D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| TAC-68258, TAC-68259, NUDOCS 8807130284 | |
| Download: ML16342C349 (8) | |
Text
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UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 July 5, 1988 Docket Nos.:
50-275 and 50-323 MEMORANDUM FOR:
Dennis Kirsch, Director Division of Reactor Safety and Projects Region V
FROM:
SUBJECT:
Gary Holahan, Assistant Director for Regions III and V Reactors Division of Reactor Projects - III IV, V and Special Projects TIA-RV-88-08 DIABLO CANYON REACTOR COOLANT PUMP BEARING LUBRICATION SYSTEM FAILURES (TAC NOS.
68258 AND 68259)
Pursuant to the Region V daily report of May 9, 1988 dealing with the subject failures at Diablo Canyon Unit 1, and subsequent telephone contacts between NRR, Region V, and the Diablo Canyon Resident Inspector, NRR initiated a TIA to respond to the following questions and/or evaluation requests:
Evaluate the licensee's justification for continued operation of Unit 2.
Evaluate the adequacy of the licensee's corrective action for Unit 1
repairs and adequacy for restart of Unit 1.
Determine the need for generic NRC notification of the other licensees who might have similar Westinghouse reactor coolant pumps.
Evaluate the reportability of the failures from the standpoint of Part 21 and 50.73.
Licensee actions were described in a telephone conference call with the licensee on May 12,
- 1988, and in Licensee Event Report (LER) 1-88-015-00 submitted by PGSE letter DCL-88-144 dated June 2, 1988.
The licensee assessment provides the following pertinent information:
The cause of the metal fatigue was preliminari ly assessed as vibration of the stationary oil chamber assembly.
The Unit 1
pumps are currently being repaired and the Unit 2 pumps will be examined and repaired or modified during the upcoming refueling outage in September 1988.
Contact:
Harry Rood 492-1352 8807i30284 SS0705 PDR ADOCK 05000275 P
PGSE Operations personnel have been instructed and procedures issued to trip an operating Unit upon a confirmed or multiple indications of bearing failure.
The portions of the lubrication system subject to failure are not structural in function, that is, their failure would not cause a loss of integrity to the motor bearing support structure.
Postulated continued operation with such undiscovered fatigue cracking would lead to a failure of the oil chamber to perform its function (to collect and direct the flow of the lubrication oil).
This could result in bearing failure in the form of wiping of the soft babbit surfaces.
Pertinent indications available to the operator to detect bearing degradation include thrust bearing upper and lower shoe temperature, upper radial bearing temperature, motor frame vibration, and shaft vibration.
Motor bearing temperatures are annunciated in the control room at 200 degrees F.
Westinghouse has concluded that thrust bearing failure is unlikely, primarily due to the fact the the thrust bearings are immersed in oil below the sump level.
If the thrust bearing were to fail, and if operators allowed pump operation to continue, the Ho. I reactor coolant pump seal could fail.
This would result in an annunciated high leak off flow alarm.
If operators continued to allow the pump to operate, failure of the Ho.
2 seal would be expected and a loss of coolant accident would result.
The licensee intends to inspect and repair or replace the Unit 2 motor lubrication system in the upcoming refueling outage in September
- 1988, Our evaluation of the regional concerns is as follows:
The licensee's justification for continued operation of Unit 2 appears to be acceptable on the basis of (I) the nature of the defects, (2) the possible consequences of the defects should flow chamber failure occur, and (3) the actions taken by the licensee to assure heightened operator awareness and revised procedural instruction to shut the plant down quickly.
- Further, in the unlikely event of an absence of operator
- action, the ultimate possible consequences of a bearing failure have been well studied and do not represent an unreviewed safety question.
The licensee's corrective actions for Unit 1 appear to be acceptable based on the operating history of the pumps.
Specifically, the refurbishment of the pumps by replacing and repairing the damaged parts should provide an operable system for at least one refueling cycle.
This would represent less pump operating time than the pumps had seen through their second refueling outage.
e The defects noted do not warrant generic action on the part of the NRC on the basis of the lack of safety significance of the lubrication system and absence of any other similar defects having been identified at plants with longer operating histories.
In conversation with Westinghouse representatives on June 9, 1988, they stated that Diablo Canyon was unique in several aspects.
Specifically, the mater ial used at Diablo for the flow chamber is unique high strength material and only Diablo attempted to reduce oil frothing problems by plugging and/or orificing the flow holes in the pump thrust runner while other pumps of this design have been provided with modification kits.
Consequently, Westinghouse does not believe this problem will occur at other plants and does not intend to issue a service bulletin.
- Further, Westinghouse does not consider the problem to be safety significant.
The oil pump lubrication system degradation was reviewed for reportability under 10 CFR Part 21 and 50.73.
The situation does not appear to be clearly reportable due to the fact that it is difficult to show that the equipment failure alone could prevent the fulfillment of a safety function (50.73) or that the defect could create a substantial safety hazard (Part 21). It is noted that the licensee submitted a voluntary event report on the subject (LER 1-88-015).
The above information is provided in response to your request.
This information has previously been verbally transmitted to your staff.
This completes our activities on TIA-RV-88-08. If you have any questions please feel free to contact us.
Gary N. Holahan, Assistant Director for Regions III 5 V Reactors Division of Reactor Projects - III, IV, V and Special Projects Office of Nuclear Reactor Regulation
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'P The defects noted do not warrant generic action on the part of the NRC on the basis of the lack of safety significance of the lubrication system and absence of any other similar defects having been identified at plants with longer operating histories.
In conversation with llestinghouse representatives on June 9, 1988, they stated that Diablo Canyon was unique in several aspects.
Specifically, the material used at Diablo for the flow chamber is unique high strength material and only Diablo attempted to reduce oil frothing problems by plugging and/or orificing the flow holes in the pump thrust runner while other pumps of this design have been provided with modification kits.
Consequently,
'l<estinghouse does not believe this problem will occur at other plants and does not intend to issue a service bulletin.
- Further,
'llestinghouse does not consider the problem to be safety significant.
The oil pump lubrication system degradation was reviewed for reportability under 10 CFR Part 21 and 50.73.
The situation does not appear to be clearly reportable due to the fact that it is difficult to show that the equipment failure alone could prevent the fulfillment of a safety function (50.73) or that the defect could create a substantial safety hazard (Part 21). It is noted that the licensee submitted a voluntary event report on the subject (LER 1-88-015).
The above information is provided in response to your request.
This information has previously been verbally transmitted to your staff.
This completes our activities on TIA-RV-88-08. If you have any questions please feel free to contact us.
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DISTRIBUTION NRC 8(
LPDR HRood GHolahan
- PREVIOUSLY CONCURRED I
DMCrutchfie1 d PDV Reading Jlee LMarsh Gary M. Holahan, Assistant Director for Regions III 5 V Reactors Division of Reactor Projects - III, IV, V and Special Projects Office of Nuclear Reactor Regulation OFC
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