05000254/LER-1979-004-01, /01T-0 on 790122:piece of Control Rod Drive Return Nozzle Thermal Sleeve Retaining Ring Was Missing.Cause Unknown

/01T-0 on 790122:piece of Control Rod Drive Return Nozzle Thermal Sleeve Retaining Ring Was Missing.Cause Unknown

ML19261B484
Person / Time
Site:	Quad Cities
Issue date:	02/01/1979
From:	Dunesia Clark COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19261B483	List: 05000254/LER-1979-004, Forwards LER 79-004/01T-0 05000254/LER-1979-004-01, /01T-0 on 790122:piece of Control Rod Drive Return Nozzle Thermal Sleeve Retaining Ring Was Missing.Cause Unknown
References
LER-79-004-01T, LER-79-4-1T, NUDOCS 7902260326
Download: ML19261B484 (3)

LER-1979-004, /01T-0 on 790122:piece of Control Rod Drive Return Nozzle Thermal Sleeve Retaining Ring Was Missing.Cause Unknown

Event date:
Report date:
2541979004R01 - NRC Website

text

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69 EVEr. T D ATE 14 75 hEPORT DAT E 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h lo l2l An inspection of the reactor vessel internals revealed that a piece of the Control l

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Additional inspections performed on l o,, l the CRD return nozzle included an ultrasonic examination of the nozzle inner radius,

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LER NUMBER:

LER/R0 79-04/01T-0 11.

LICENSEE NAME: Commonwealth Edison Company Quad-Cities Nuclear Power Station Ill.

FACILITY NAME: Unit One IV.

DOCKET NUMBER: 050-254 V.

EVENT DESCRIPTION

On January 22, 1979, a visual inspection of the Unit One reactor vessel internals was performed.

The inspection revealed that a piece of the Control Rod Drive nozzle thermal sleeve retaining ring was missing.

The missing section of the ring was approximately 1-1/4 inch long, 1/4 inch thick, and 29/32 inch wide.

The inspection was performed using a remote operated TV camera and video moni tor.

The remainder of the retaining ring and weld was found intact.

Additional inspections performed on the CRD return nozzle included an ultrasonic examination of the nozzle inner radius nozzle to safe end weld and the safe end to pipe weld.

All examinations were satisfactory.

The CRD return line has been isolated since December, 1977 VI.

PROBABLE CONSEQUENCES OF THE OCCURRENCE The thermal sleeve was installed in the CRD return nozzle to reduce the thermal cycling ef fects of the relatively cold CRD water entering the reactor vessel. The thermal sleeve is held in place by the retaining ring, which is welded to a spacer ring. The retaining ring restricts movement of the thermal sleeve. Additional tension is placed on the thermal sleeve by a Bellville washer located between the thermal sleeve flange and the reactor vessel wall.

Since only a small piece of the retaining ring was found missing, no abnormal movement or vibration of the thermal sleeve should be experienced.

The retaining ring and thermal sleeve provide no structural strength to the reactor vessel; therefore, the structura l integrity of the nozzle and reactor vessel was not affected by the broken retaining ring.

By isolating the CRD return water to the reactor, thermal cycling in the nozzle area should be reduced significantly. All safety questions were answered when a lost parts analysis of the missing piece was performed.

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CAUSE

The cause of this occurrence is not known at this time.

Approximately 1-1/4 inch of the ring was broken of f; the outside diameter was broken off at the fillet weld.

Further investigation of the missing piece was not possible with the type of inspection that was performed.

9 The retaining ring was manufactured by the Babcock and Wilcox Co., material spec. SA-312, Type 304 stainless steel.

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CORRECTIVE ACTION

A search will be made to locate the missing piece. A 1cose parts analysis was performed for the missing piece and for any additional pieces of the retaining ring.

An ultrasonic examinat.on of the nozzle area verified that the nozzle was structurally intact.

A modification will be initiated to remove the thermal sleeve during the next Unit One refueling outage.

The Unit Two thermal sleeve was removed during the spring 1978 refuel outage.

The CRD return line will normally be kept isolated.