ML20084D154

AO 50-237/75-38A Supplementing AO-50-237/75-38 Re Failure of MO-2-1301-2 Valve to Operate.Apparently Caused by Excessive Cycling of Valve.Valve Stem Probably Experienced Metal Fatigue Due to Multiple Actuations

ML20084D154
Person / Time
Site:	Dresden
Issue date:	01/14/1976
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084D157	List: ML20084D154 ML20084D177
References
32-76, 785, AO-50-237-75-38, NUDOCS 8304080482
Download: ML20084D154 (2)

Text

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Comm nith Edison

,gCON Dresden N..;;r P,:w;r Station f ("

13 R.R. # 1 Morris, Illinois 60450 Telephone 815/942-2920 Yy

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BBS LTR. #32-76 January 14, 19 Nf.{f $ j ;*),Ni

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Mr. James G. Keppler, Regional Director p

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y Directorate of Regulatory Operation-Region lil

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(;g*g er U. S. Nuclear Regulatory Coramission W

M c' 799 Roosevelt Road Glen Ellyn, Illinois 60137 etYY

SUBJECT:

SUPPLEMENTAL REPORT TO LETTER DATED JUNE 25.-1975, ENTITLED

" FAILURE OF VALVE M0-2-1301-2 TO OPERATE" (REPORT NO. 50-237/

75-38)

References:

1)

Report No. 50-237/75-38 2)

Drawing 12E2507A Report Number: 50-237/75-38A Report Date: January 14, 1976 Facility:

Dresden Nuclear Power Station, Morris, Illinois INTRODUCTION As reported in abnormal occurrence report 50-237/75-38, investigation continued on the operational failure of isolation condenser outboard steam supply valve M0 2-1301-2.

Valve 1301-2 had been discovered with a bent stem during a high flow isolation valve surveillance.

DESIGNATION OF APPARENT CAUSE OF OCCURRENCE The valve stem distortion was apparently caused by excessive cycling of the valve as described in the original report. The valve operator motor has been determined to be slightly oversized for the application (see corrective action).

Given the motor size as well as the valve's relatively high speed of operation, it is considered probable ~that the valve stem experienced metal fatigue as a result of the multiple actuations.

CORRECTIVE ACTION The valve operator and the torque and limit switches were disassembled and inspected by the maintenance department.

No problems were indicated which could have caused failure of the valve stem.

A vendor representative was called in to examine the operator, valve, and

,785 torque switch assembly.

He determined that an extra belleville spring washer had been installed in the torque switch assembly at the factory.

Subsequent communication with the Limitorque Co. revealed that extra

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8304080482 760114 1 stalled in tor'que gwi.tch assemblics to accommodate '[

PDR ADOCK 05000237 Jr. 4 1Jto COPY EENT REGION

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Mr. J:mes G. K':ppler J;nunry 14,,,

1976 4

varying valve dimensions and torque requirements. The belleville washer would have had no effect on valve operation.

New Limitorque valves use a spacer instead of the belleville spring washer to compensate for differing applications.

Station personnel and the vendor representative noticed that the operator motor appeared to be oversized for the application.

The Station Nuclear Engineering Department reviewed the problem and concurred with this observation.

In the past, Limitorque apparently sized D.C. motors for valve operators on the assumption that torque varied with the square of the voltage. The correct approach is to use a more linear relationship which results in a smaller motor.

A modification has been issued to reduce the motor size on valve M0 1301-2 from 100 f t -lb to 80 f t -lb for both Units 2 and 3 This modification should prevent similar problems from recurring on these valves.

Sincerely,

,,,/hY fb,YlW

. B. Stephenson Superintendent BBS:JSK:smp File /NRC l

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