ML20086B272

AO 50-267/74-18:on 740912,pin Failed in Bulk Head Electrical Connector.Caused by Galvanic Corrosion.Connectors Being Removed & Will Be Modified & Replaced & Control Rod Drive Procedures Will Be Modified

ML20086B272
Person / Time
Site:	Fort Saint Vrain
Issue date:	09/20/1974
From:	Mathie F, Swart F PUBLIC SERVICE CO. OF COLORADO
To:
References
AO-50-267-74-18, NUDOCS 8311170127
Download: ML20086B272 (9)

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. public service company a2 Cdlendo P. O. Box 361, Platteville, Colorado 80651 September 24, 1974 Mr. E. Morris Howard, Director ,,

Directorate of Regulatory Operations Revion IV, USAEC 10395 W st Colfax, Room 200 Denver, Colorado 80215 REF: Facility Operating License No. DPR-34 Docket No. 50-267

Dear Mr. Howard:

Enclosed please find a copy of Abnormal Occurrence Report No.

50-267/74/18, submitted per the requirements of the Technical Specifications.

Very truly yours, c.,[5a u O.i,..I---

Frederic E. Swart Superintendent Nuclear Production Fort St. Vrain Nuclear Generating Station FES:11 ....p...,,

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cc: Mr. Angelo Giambusso ,, , , _

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. . Date: Sept. 20, 1974 ABNOR!!AL OCCURRENCE FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 80651 REPORT NO. 50-267/74/18 FINAL IDENTIFICATION OF

• OCCURRENCE: .

5 On Septc=ber 12, 1974, upon return of the control rod drive to .

< penceration number three it was noted that a pin,had fai_ led in- .

the bulk head electrical conn _ector inside the penetration sidewall.

s Further investigation revealed that the pin had failed in such a way so as to fail the pressure seal in the connector. -

This condition is reportable as an abnormal occurrence per item 2.1C of the Technical Specifications.

CONDITIONS PRIOR TO OCCURRENCE: Steady State Power Routine Shutdown-Hot Shutdown Routine Load Change X Cold Shutdown X Other (specify)

Refueling Shutdown The reactor primary coolant circuit ,

(PCRV internal cavity) being subjects Routine Startup to a hard vacur to renove coisture from PCRV internal cavity.

The major plant parameters at the time of the event were' as follows:

Power RTR, O MWth ELECT, N/A MWe Secondary Coolant Pressure N/A psig i

Temperature N/A 'F Flow N/A #/hr.

absolute l Primary Coolant Pressure 2-50 mm Ha Temperature 120 'F Core Inlet 120 'F Core Outlet l f/hr.

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, , DESCRIPTION OF OCCURRENCE:

i All control rod drives had been removed from the PCRV for inspection and removal of corrosion products caused by moisture in the primary coolant system.

Following removal of the control rod drives, the penetration secondary closure plates were reinstalled and a vacuum drawn on the primary

• coolant system (PCRV internal cavity).

Following moisture removal by evacuation, the primary coolant system was backfilled with dry nitrogen to atmospheric pressure and preperat- -

t ions were made.to reinstall the control red drives in their respective penetrations. ,

Upon returning the control rod drive to penetration number three and ,

attempting-to connect the power cable to the penetration connector, it ,

was noted that a pin was broken off. Further investigation revealed the pin had. failed due to galvanic corrosion. The failure of the pin caused a complete f ailure of the glass to metal bond which in turn destroyed the pressure sealing capability of'the connector. (See attached figure).

Inspection of the instrumentation connector in penetration number three revealed damage of a similiar nature.

Connectors in a representattvo number of penetrations were inspected and all were found t'o have been damaged to varying degree.

At no time was the health and safety of the public compromized in sofar as the reactor was in a shutdown condition. The primary coolant circuit contained no radioactive material and was never above atmospheric pressure.

APPARENT CAUSE OF OCCURRENCE: Dcsign X Unusual Service Cond.

Including Environ.

~

Manufacture Component Failure Installation /Const. Other (specify)

Operator X P'rocedure ANALYSIS OF OCCURRENCE:

Close inspection of the failed pins indicated they had experienced galvanic

, corrosion. The end of the failed pins had the tell tail pointed configurat-ion where the galvanic action had taken place. -

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As presently constructed, there is no way to interrupt the instrument  ;

voltage applied to the connector pins except by disconnecting the air

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side of the connector on the outside of the penetration. The instru-ment systems measure control rod position, slack cable, and orifice f j

position. Voltages used are 10V and 24 V DC. Brake power to the

• penetration.comes in through the powcr cabic and can be interrupted '

by removal of the fuze in the positive lead.

A review of the electrical wiring diagrams of the penetrations indicates that all the pins except one that have experienced dcmage have a positive voltage applied. This was to be expected if galvanic action was the cause of the damage. The odd pin that indicates danage is the negative pin of the control rod drive brake circuit. Uc have measured the (-) bus voltage to ground potential and find it runs about 4.25 V+ '

above ground.

The conditions under which the galvanic action took place were as follows:

1. All control rod drives had been removed from their penetrations for inspection and cican up. Removal of the drive assembly t

also removes the primary closure. +

.2. The secondary penetration closure had been replaced and primary J

coolant circuit evacuated. '

4 The removal of the control rod drive / primary closure allowed the primary l

4 circuit atmosphere to ecce in contact with the energized connector pins.

The small quantity of moisture in the primary circuit atmosphere pro-I vided the current path.

4 Confirmation of this theory is provided by the observance by Operating

Personnel of up scale readings on both the digital and analog control rod position indicators shortly after the secondary closures were replaced and the primary circuit was being evacuated. It was not recognized at

' that time, what the cause of the up scale-reading was.

The atmosphere in the penetration at the connector prior to removal of the control rod drives was dry helium supplied from the p'urified helium j

header. No abnormal service conditions existed prior to removal of the control rod drives and no damage was noted at the connectors when they were removed.

l During normal reactor operations the atmosphere at the connectors is dry l

' helium from the purified helium header. Under these_ conditions no cathodic action can take place.

4 .

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( () Page 4 l CORRECTIVE ACTION:

I The connectors are presently being removed from the penetrations 1 and will be replaced.

i It is also intended that a modification be made in the connector to clininate the seal weld pressure seal and to replace it with an "0" ring such as that used on the penetration primary and secondary closures. This modification will greatly improve the replacability of tha connectors at some later date if pin prob 1 cms are again experienced.

In addition to replaci'ng and modifing the connectors, control rod drive removal procedures will be modified.to include disconnecting the '

instrument and power cables from the air side of the connectors to remove all voltage potentials whenever a control rod drive is re- ,

moved from the penetration and the gas side of the connector is ,

l ekposed to primary coolant.

FAILURE DATA /SIMILAR REPORTED OCCURRENCES: ,

No similiar problems have been reported.

PRO'RA$fATIC G IMPACT:

No scheduled impact should be experienced. The schedule controlling item is felt to be the pelton wheel problem reported in Abnormal Oc.currence Report No. 50-267/74/17.

CODE IMPACT:

None

• Prepared by: Approved by:

I h Es " u .$ ) 6.rev

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Frank M. Mathic ,F[ederic E. Swart Superintendent Maintenance- Superintendent Nuclear. Production 4

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