ML20246H533

Part 21 Rept Re Defect in Motor Mounting Bolts on Limitorque Operators & Reliance Motors.Caused by Loosening of Motor End Bell Bolts.All Normally Inaccessible Operators W/Susceptible Bolting Will Be Inspected

ML20246H533
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	02/14/1989
From:	Murphy W VERMONT YANKEE NUCLEAR POWER CORP.
To:	Russell W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
REF-PT21-89, REF-PT21-89-049-000 BVY-89-15, PT21-89-049-000, PT21-89-49, NUDOCS 8903200256
Download: ML20246H533 (3)

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VERMONT YANKEE I NUCLEAR POWER CORPORATIO'N

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RD 5, Box 169, Ferry Road. Brattleboro, VT 05301 ENGINEERING OFFICE 580 MAIN STREET BoLToN MA01740 (508) 779-6711 February 14, 1989 U.S. Nuclear Regulatory Commission Office of Inspection & Enforcement Region I 475 Allendale Road King of Prussia, PA 19406 Attn: Mr. W. Russell Regional Administrator

Reference:

a) License No. DPR-28 (Docket No. 50-271) 1

Subject:

Notification of Potential Existence of a Defect in Accordance with 10CFR21.21 In accordance with the provisions of 10CFR Part 21, Section 21, we are hereby notifying you that we have obtained information indicating that a defect may exist with respect to motor mounting bolts on Limitorque Operators.

l Enclosure I to this letter documents the details of this notification.

Should you have any questions regarding this matter, please contact us.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION I

l Warren P. Murphy y

l Vice President and Manager of Operations

/dm cc: USNRC Director, Office of Nuclear Material Safety and Safeguards USNRC Document Control Desk, NRR <

USNRC Office of Nuclear Reactor Regulation, Project Manager, VYNPS USNRC Resident Inspector, VYNPS C '\

8903200256 890214 I i PDR ADOCK 05000271 t 8 PNU

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ENCLOSURE I l

.- l PART 21 REPORT l COMPANY INFORMING Vermont Yankee Nuclear Power Corporation THE' COMMISSION RD 5, Box-169 Ferry Road ,

Brattleboro, Vermont 05301 )

I FACILITY Vermont Yankee Nuclear Power Station l PO Box 157 l l Governor Hunt Road j l

Vernon, Vermont 05301-  !

FIRM SUPPLYING Name: Limitorque Corporation f COMPONENT Address: 5114 Woodall Road l l Lynchburg, VA 24506 l -

l l

C7 NATURE OF DEFECT During surveillance testing on November 30, 1988, when the Core Spray test ,

valve (V14-26A) was actuated from the control room to open, it failed to operate I properly. The valve was then manually unseated and' stroked open but failed to close and tripped the MCC circuit breaker. Investigation of this matter revealed that the four (#10-32) motor end bell bolts had failed. The stator had )

rotated 180 degrees and a short circuit developed.

This most recent occurrence was similar to a failure on December 15, 1987.

The earlier experience was on the RHR containment spray outboard injection i valve (V10-26A) on which the (#10-32) motor end bell bolts failed. The first event was previously dispositioned as an isolated occurrence but the.second failure raised further concern as it was of similar nature. The potential Part i 21 reportable evaluation process was initiated when the failure occurred on the V14-26A.

During the subject evaluation, a limited scope industry survey was per-formed and it was determined that other utilities have experienced similar These other utilities concluded that their failures were isolated

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failures.

occurrences. This determination is valid for the single incident but when viewed collectively, it appears to be a common mode of failure.

Vermont Yankee contacted the motor manufacturer, Reliance, who stated that~

the motor case design was proprietary information to Limitorque Corporation.

This information was sought because Reliance changed its design several years ago to replace these #10-32 bolts. The bolts were replaced with 3"-20 studs nutted on each end. Vermont Yankee is currently working with Limitorque to determine the failure mechanism of the #10-32 bolts. Limitorque is performing this failure analysis and its completion is expected by March 15, 1989.

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' Enclosure I

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Vermont Yankee preliminary evaluations identify the apparent cause of the s two failures to be loosening of the motor end bell bolt (s). Following this loosening, all motor support loads are transferred to the bolts which become overstressed and potentially fail. The vendors (Reliance and Limitorque) were both contacted for recommended torque specifications, however, neither company has any recommended torque values for these bolts.

DATE ON WHICH DEFECT WAS DETECTED 1 i

A potential Part 21 Report Evaluation was initiated on December 6, 1988.

NUMBER OF COMPONENTS AT FACILITY Vermont Yankee has thirty-five (35) safety-related valves utilizing the Reliance motor frames with the #10-32 internal end bell bolts.

I CORRECTIVE ACTIONS Vermont Yankee has taken the following corrective actions:

Following the first occurrence (1987), 43 operators of various bolting designs were inspected for loose bolts, however, no loose or broken bolts were found.

As a result of the second failure, an inspection of all accessible safety related valve actuators (58 of 83) was performed, of which 27 are of the suscep- t tible design (#10-32). This inspection identified three #10-32 bolts which were l slightly loose (1/8 to 1 turn tightening required).

During the current outage, Vermont Yankee will:

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1. inspect all 8 normally inaccessible operators with the susceptible bolting

(#10-32):

2. reinspect the 27 normally accessible operators with the susceptible bolting; and

3. on all normally inaccessible operators and those safety-related operators with the #10-32 bolting scheduled to be overhauled, the susceptible bolting will be replaced with known high strength material.

Vermont Yankee will continue to evaluate the failure mode and failure ana-lysis being performed by Limitorque. Any corrective action resultant of these evaluations will be implemented as appropriate. In addition, VY will provide any necessary supplements to this report as a result of our continuing analysis of the situation.

/dm

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