ML20138R025
| ML20138R025 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 12/23/1985 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Harold Denton, Rubenstein L Office of Nuclear Reactor Regulation |
| References | |
| 85-750B, NUDOCS 8512300219 | |
| Download: ML20138R025 (4) | |
Text
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t VINGINIA ELECTRIC AND POWHH COMI%NY H ictix onn, V HGINIA 2112 61 w, L. sinwurr vics Panasonnt
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" fete"Inb e r 23, 1985 Mr. Harold R. Denton, Director Serial No. 85-750B Office of Nuclear Reactor Regulation N0/ ALM /vih Attn: Mr. Lester S. Rubenstein, Director Docket No.
50-338 PWR Project Directorate #2 License No. NPF-4 Division of PWR Licensing-A U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNIT NO. 1 GENERAL DESIGN CRITERION 17 MODIFICATION STATUS Virginia. Electric and Power Company has completed General Design Criterion (GDC) 17 required modifications for North Anna Unit 1 as discussed in our letters of November 28, 1984 and June 28, 1985, Serial Nos. 253F and 85-491. We have resolved the questions concerning analysis data versus plant performance data of several MOVs that were discussed in our letters to you dated October 21, 1985 and November 15, 1985, Serial Nos.85-750 and 85-750A, and determined that no additional GDC 17 required modifications are necessary.
We would like to clarify c ir position on MOV enhancements, specifically the installation of torque switch limiter plates, that is referenced in your Safety Evaluation (SE) dated November 13, 1984, and our letters of February 26, 1982 and May 15, 1984, Serial Nos. 76 and 253. As discussed below, ensuring protection of the motor after the MOV performs its intended safety function is a concern raised in our GDC 17 analysis, and installation of the torque switch limiter plates is but one method of providing this protection. However, it is now our intention to address this concern thru administrative measures that control torque switch settings.
4 Our GDC 17 analysis has shown that the 26 MOVs that are required to operate when the emergency bus voltage is at 80*. of rated voltage will perform their interded safety function. The attached diagram is intended to illustrate the relationship of this and several other MOV characteristics in order to facilitate discussion of our analysis. This diagram implies that when the motor voltage drops to 80*. the maximum developed torque output possible also decreases due to the proportional relationship between motor voltage and torque.
The GDC 17 concern for proper MOV operability is addressed by ensuring that the MOV's maximum developed torque output possible at 80*. rated voltar,e is higher than the torque required to operate the valve.
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s VamoNIA Ex.zcTarc Ano Powra CoxPaxy 70 Mr. liarold R.
Denton At reduced voltages, we had a concern that the motor may not develop sufficient torque to operate the torque switch when seating a valve or upon initiation of a mechanical overload (i.e., valve blockage, operator binding, etc.).
If this occurs, possible damage to the motor may result.
To protect the motor from damage, we verified by analysis that the n.oter's maximum developed torque output possible at 80% rated voltage is highcr than the torque switch setting range for normal and accident operation.
We had further planned to install torque switch limiter plates to prevent raising the torque switch setting above the 80% voltage capability of the motor. However, the installation of torque switch limiter plates is not required since the same measure of control is presently being achieved through administrative measures.
The administrative control is being accomplished by 1) maintaining a controlled document that specifies the maximum allowable torque switch setting (consistent with our GDC 17 analysis) and the design torque switch setting for operation of the valve, and 2) implementing a procedure that requires review of this controlled document prior to resetting any of the 26 MOV torque switches. These two administrative measures will provice adequate assurance that the MOV torque switch settings would not be altered without first performing a review to determine the acceptable range. This type of administrative control is successfully utilized for other plant equipment and systems. Therefore, it is our intention to control torque switch settings through ad.ninistrative measures rather than installing limiter plates as stated in previous correspondence.
er If you have any questions or need additional information, please contact us.
V truly yours, s
o-y W.
tewar Attachment
a VamonwsA Et.acraic awn Powan COMPANY TO Mr. IIarold R.
Denton cc:
Dr. J. Nelson Grace Regional Administrator NRC Region II Mr. Morris W. Branch NRC Resident Inspector North Anna Power Station Mr. Leon B. Engle NRC North Anna Project Manager PWR Project Directorate #2 Division of PWR Licensing-A I
I 4
k l
1 1
5 a
2
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i
o Max. developed torque possible at 100 % rated voltage Max. developed torque possible at 80 % rated voltage GDC17 max. torque switch setting A))owable torque switch setting range for normal and accident valve operating conditions Torque required to operate valve i
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ES:
bE 4R MOV CHARACTERISTICS
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