ML20209B232

Forwards AEOD/C602, Operational Experience Involving Turbine Overspeed Trips, Case Study Rept. NRR Should Address Listed Recommendations to Improve Auxiliary Feedwater Sys Reliability

ML20209B232
Person / Time
Site:	Davis Besse
Issue date:	08/20/1986
From:	Heltemes C NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
To:	Harold Denton, Taylor J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE), Office of Nuclear Reactor Regulation
Shared Package
ML20209B180	List: ML20209B175 ML20209B232 ML20209B275 ML20209B342 ML20209B412 ML20212Q421
References
AEOD-C602, IEIN-86-014, IEIN-86-14, NUDOCS 8609080194
Download: ML20209B232 (3)

Text

i August 20, 1986 b

02 MEMORANDUM FOR: Harold R. Denton, Director Office of Nuclear Reactor Regulation James M. Taylor, Director Office of Inspection and Enforcement FROM: C. J. Heltemes, Jr., Director Office for Analysis and Evaluation of Operational Data

SUBJECT:

CASE STUDY REPORT - OPERATIONAL EXPERIENCE INVOLVING TURBINE OVERSPEED TRIPS Following the resolution of all peer review comments, we have finalized and enclosed our case study report on operating experience involving auxiliary feedwater (AFW) system turbine cverspeed trips in PWR plants. The study also includes a review of BWR high pressure coolant injection HPCI system turbine and reactor core isolation cooling (RCIC) system turbine overspeed trip events. The events studied occurred during the period from early 1972 to September 1985 and were identified primarily from Licensee Event Reports (LERs). Each event involved a steam turbine designed and built by the Terry Corporation and a governor supplied by the Woodward Governor Company. This study was performed in response to action item 8(f) of_the actions directed by the EDO to respond to the NRC staff investigations of the June 9, 198b event at Davis-Besse. A total of 128 turbine overspeed trip events involving AFW, HPCI and RCIC systems were reviewed. Overspeed trips of AFW turbines were found to be relatively widespread and one of the major causes for loss of operability or unavailability of AFW systems.

Our study concludes that the dominant attributed causes of AFW turbine overspeed trips are speed control problems associated with the governor, and trip and reset problems associated with the trip valve and overspeed trip mechanism. The governor speed control problems involve: (1) slow response of the governor during quick startup, (2) entrapped oil in the Woodward Model PG-PL governcr speed setting cylinder, (3) incorrect governor setting, and (4) water induction into the turbine. The trip and reset problems sten from the complexity of reset operations and a lack of trip position indication, lhese problems are primarily the result of inadequate performance by plant personnel, inadequate procedures, and insufficient design considerations.

lhe study contains several recommendations to prevent or reduce the overspeed trip problems. Implementation of the recommended actions should significantly improve AFW system reliability and availability. The principal recommendations are as follows:

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I Harold R. Danton James M. Taylor

1. Alleviate the effect of slow response of the governor valve during the turbine startup transient by implementing a steam bypass modification for turbines equipped with a Woodward Model EG governor.

I 2. Avoid entrapped oil in the speed. setting cylinder by establishing

. administrative controls for bleeding off the entrapped oil, installing a

controllable dump valve, or providing indication in the control room ,

for a spinning turbine.

l 3. Ensure the adequacy of the existing vendor-supplied calibration procedures for governor speed setting.

f

4. Prevent water induction into the turbine by providing adequate provisions for condensate removal from the steam supply line to the AFW turbine.

5. Minimize trip and reset problems by assessing the adequacy of the existing procedural instruction, upgrading the training program, and providing local indication as well as control room indication for trip and reset. conditions.

It is requested that NRR address our recommendations in their programs to

,- improve' AFW system reliability (particularly in response to action items by i the ED0 in connection with the NRC staff investigations of the June 9, 1985 i eventatDavis-Besse).

Finally, the enclosed report recognizes that IE has already issued Information Notice 86-14 "PWR. Auxiliary Feedwater Turbine Control Preblems" which addresses j some aspects of the overspeed problems related to entrapped oil and water induction. However, it is- also requested that IE issue another information i notice to draw attention to the other AFW turbine overspeed trip cause

, categories identified in the. case-study.

< If you have any question regarding this study, please feel free to contact l Chuck Hsu of my staff. Mr. Hsu can be reached at X_24443.

or p ud sip od bF C. J. Moltomes, Jr.

C. J. Heltemes, Jr., Director l Office for Analysis and Evaluation

of Operational Data

Enclosure:

As Stated cc: See next page 1 DISTRIBUTION: o PDR CHsu WLanning AE0D SF EBrown KBlack

AEOD CF MChiramal MWilliams ROAB SF Plam FHebdon i ROAB CF SRubin CJHeltemes

• See next sheet for previous concurrence I 0FC : ROAB.  : SC:ROAB  : BC:ROAB  : DD:AE D  : D:AE0D  :  :

!NAME: CHsu:nc  : MChiramal : SRubin  : FH  : CH emes  :  :

DATE : 8/15/86*  : 8/15/86*  : 8/15/86*  : 8/w /86  : 8/40/86  :  :

OFFICIAL RECORD COPY

.. g Harold R. Denton 2. Avoid entrapped oil in the speed setting cylinder by establishing administrative controls for bleeding off the entrapped oil, installing a controllable dump valve, or providing indication in the control room for a spinning turbine.

3. Ensure the adequacy of the existing vendor-supplied calibration procedures for governor speed setting.

4. Prevent water induction into the turbine by providing adequate provisions for condensate removal from the steam supply line to the AFW turbine.

5. Minimize trip and reset problems by assessing the adequacy of the existing procedural instruction, upgrading the training program, and providing local indication as well as control room indication for trip and reset conditions.

It is requested that NRR address our recommendations in their programs to improve AFW system reliability (particularly in response to action items by the ED0 in connection with the NRC staff investigations of the June 9,1985 event at Davis-Besse).

Finally, the enclosed report recognizes that IE has already issued Information Notice 86-14 "PWR Auxiliary Feedwater Turbine Control Problems" which addresses some aspects of the overspeed problems related to entrapped oil and water induction. By separate memorandum, we have requested that IE issue another information rotice to draw attentior to the other AFW turbine overspeed trip cause categories identified in the case study.

If you have any question regarding this study, please feel free to contact Chuck Hsu of my staff. Mr. Psu can be reached at X_24443.

l C. J. Heltemes, Jr., Director Office for Analysis and Evaluation of Operational Data

Enclosure:

As Stated cc: See next page DISTRIBUTION:

PDR CHsu WLanning l AEOD SF EBrown KBlack AE0D CF MChiramal MWilliams R0AB SF Plam FHebdon ROAB CF SRubin CJHeltemes OFC : 8 AB  : SC:ROAB  : BC:ROAB  : DD:AEOD  : D:AEOD  :  :

_____:f,..G.[dk___:_f.pf..pa_:-___________:-___________:-___________:____________:___________

'NAME : C su:nc  : MChiramal : SRubin  : FHebdon  : CHeltemes :  :

!DATE : 8//f /86  : 8//[/86  : 8/6/86  : 8/ /86  : 8/ /86  :  :

l OFFICIAL RECORD COPY

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