ML20196E534
| ML20196E534 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 12/02/1988 |
| From: | Shelton D TOLEDO EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 1608, NUDOCS 8812120030 | |
| Download: ML20196E534 (3) | |
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TOLEDO EDISON A Cwwor Dwg Cm DONA'.D C. SHELTON
- w. %,m, Docket Number 50-346 License Number NPF-3 Serial Number 1608 December 2, 1988 United States Nuclear Regulatory Commission Document Control Desk Vashington, D. C.
20555 Subj ect:
Summary of Auxiliary Feedvater System Modification Atatus t
Gentlemen During a June 9, 1988 meeting with Nuclear Regulatory Commission (NRC) Staff, Toledo Edison (TED) representatives presented information regarding modifications being made to the Davis-Besse Nuclear Power Station (DBNPS) Unit No. 1 Auxiliary Feedvater (AFV) System.
Several questions were raised by the NRC Staff regarding inspection plans for evaluating the modifications' effectiveness.
The attachment to this letter provides the status of the corrective actions taken and planned for the AFV System components.
Specifically, status is provided for the Auxiliary Feedvater Pump Turbine (AFPT) governor valves, AFPT steam admission valves, AFPT inlet steam pressure svitches, AFPT casing drains, and the AFV Discharge Isolation Valve AF3869.
If you have any questions concerning this information, please call Mr. R. V.
Schrauder, Nuclear Licensing Manager, at (419) 249-2366.
Very truly yours, RMC/dlm Attachment cet P. H. Byron, DB-1 NRC Resident Inspector A. B. Davis, Regional Administrator, NRC Region III A. V. DeAgazio, DB-1 NRC Senior Project Manager
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THE TOLEDO ED' SON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO. CHf 0 43652
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8812120030 881202 PDR ADOCK 05000346 P
.. Dock 3t Number 50-346 i
Lic:nsa Number NPF-3 Serial. Number 1608 Allachment Page 1 DBNPS Auxiliary Feedvater System Corrective Action Status The following provides a summary of the corrective actions taken and planned for the Auxiliary Feedvater (AFV) System components which have received extensive attention due to recurring operational concerns.
Auxiliary Feedvater Pump Turbine (AFPT) Governor Valves In the past, the AFPT governor valves have not functioned consistently without exhibiting binding. The binding has been determined to have been caused by corrosion in the valves' sleeve and stem areas.
Subsequent corrosion and wear testing, conducted to determine appropriate corrective actions, determined that a new chrome plated design for the sleeves and stems should alleviate the binding concern. These new parts vere installed in both AFPT governor valves at the end of 1987.
Periodic testing during the remainder of the fuel cycle until the current refueling outage and during the refueling has not indicated a recurrence of the binding previously experienced.
Future preventive maintenance is planned to inspect / replace the governor valve parts every five years.
AFPT Steam Admission Valves The steam admission valve (HS5889A) for the No. 1 AFPT had experienced excessive steem leakage (>10 pints / hour) past the valve plug / seat consistently during Cycle 5.
The Number 2 AFPT steam admission valve (MS5889B) did not exhibit this type of leakage until approximately the middle of the fuel cycle.
The cause for leakage of MS5889A vas determined to be the installed orientation of the valve such that the valve stem moved in the horizontal direction and, therefore, caused a slight deflection of the plug such that the plug did not seat properly.
During the current refueling outage the valve was reoriented so that the stem travel is vertical and valve plug deflection is eliminated.
The cause for leakage of MS5889B appears to be vear due to excessive usage of the valve (i.e., during cycle 5, the valve was operated three times per veek versus a normal frequency of once per month). The excessive usage was a result of the increased frequency of operation of the AFPTs due to governor valve binding concerns. Vith the installation of the chrome plated governor valve parts as described previously, the testing frequency vill be greatly reduced.
The reduced exercising of the steam admission valves, the reorientation of MS5889A, and the rebuilding and restoration of both valves should eliminate the leakage concerns.
However, it should be noted that if leakage past MS5889A and MS58898 does occur, the steam traps upstream of the AFPT casings and the normally throttled AFPT casing drains vill ensure the operability of the AFPTs is not affected.
. - Dockot Nu;ber 50-346 Lic;nsa Nurber NPF-3 Serial Nu;ber 1608 Ab4achient i
Page 2 AFPT Inlet Steam Pressure Switches As reported in Licensee Event Report (LER) No.87-004, the AFPT Inlet Steam Pressure Switches PSL 106A, B, C and D and PSL 107A, B, C and D (manufactured by Static-0-Ring (SOR)) were discovered through testing not to consistently maintain their calibrated setpoint.
Investigation revealed that gases (ammonia) from the DBNPS secondary system vere diffusing between the primary and secondary diaphragm of the svitch.
As the secondary system was depressurized, the gases which had diffused between the diaphrages expanded and, therefore, prevented the svitch from actuating. TE has replaced the porous diaphragm (kapton) with a stainless steel diaphragm. This has provided improved performance and a decrease in the switches' failure rate.
In addition to the above, it has been postulated that the SOR pressure switch setpoint drift may also be caused by the calibration of the switch at the lover end of the its range. A License Amendment Request has been submitted to NRC (Serial No. 1377, dated May 4, 1987, and supplemented by Serial No. 1508, i
dated April 29, 1988) to allow raising the setpoint of the switches such that an alleviation of the setpoint drif t concern may be realized.
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AFPT Casing Drains During cycle 5, steam traps vere installed downstream of the AFPT casings to remove condensate which may be present as a result of the AFPT steam admission valve leakage. The steam traps have proven to be unreliable and have, therefore, been bypassed.
Drainage of condensate from the AFPT casings is nov accomplished via a throttled globe valve which has been demonstrated to satisfactorily resolve this concern.
AFV Discharge Isolation Valve AF3869 During testing of the AFV System in August 1988 (in Mode 5 as part of restart activities from the fifth refueling outage), AFV Discharge Isolation Valve l
AF3869 failed to open. The failure represented the third time since }085 that l
this valve had failed to perform upon demand. The failure mechanism was discovered to be a shsared pin which attaches the valve actuator torque svitch arm to the torque switch shaft.
The cause of the pin failure appears to be due to the valve disc binding in the valve seat.
Vhen the valve actuator
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attempts to open the valve, a high thrust level is developed and, upon sudden i
release of the valve disc from the valve seat, is transmitted to the actuator vorm gear. The vorm gear in turn places a high impact load on the torque switch arm and results in shearing of the cited connecting pin. The valve and actuator have been replaced and satisfactorily tested to resolve this concern.
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