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LER 94-011-00:on 941001,magnesium Alloy Rotor Motor on Reactor Water Recirculation Sys Pump Discharge Isolation Valve Failed,Placing Facility in Lco.New Operator Motor Installed & Associated Breaker Replaced
	ML18038B184
Person / Time
Site:	Browns Ferry
Issue date:	03/09/1995
From:	Austin S; TENNESSEE VALLEY AUTHORITY
To:	;
Shared Package
ML18038B183	List: ML18038B182; ML18038B184;
References
	LER-94-011-01, LER-94-11-1, NUDOCS 9503140140
	Download: ML18038B184 (16)
	v • d • e

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/y NRC F(XN 366A. U.S IN)CLEAR REGULATIXIY CUBIISSI(HI APPROVED BY (HNI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIHATED BURDEN,PER RESPONSE TO COHPLY 1JITH THIS INFORHATIOH COLLECTION REQUEST: 50.0 HRS. FORIIARD C(HIENTS REGARDING BURDEN EST I NATE TO THE INFORHAT ION AND RECORDS HANAGEHEHT BRANCH (HHBB 771C), U.S. NUCLEAR REGULATORY COHHISSIOH, LICENSEE EVENT REPORT NASHINGTOH, DC 20555-0001, AND TO THE PAPERIJORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104) ~ OFFICE OF HANAGEHEHT AND BIA)GET, llASHINGTOH DC 20503 FACILITY NNK (1) DOCKET IRMKR (2) LER IRHNKR (6) PAGE (3)

YEAR SEQUENTIAL REVISION NQIBER NUHBER Browne Ferry Unit 2 05000260 94 011 00 2 of 8 TEXT If more s ce is r ired use edditionsl c ies of NRC Form 366A (17)

I ~ PLANT CONDITIONS On October 1, 1994, Unit 2 commenced shutdown for the Cycle 7 refueling outage. At approximately 0100 hours0.00116 days 0.0278 hours 1.653439e-4 weeks 3.805e-5 months the Unit 2 Reactor was manually scrammed. The mode switch was placed in the shutdown position. Operations was in the process of aligning the Residual Heat Removal (RHR)[BO] system to the shutdown cool'ing mode.

Units 1 and 3 were shutdown and defueled.

ZZ. DESCRIPTION OF EVENT Event:

On October 1, 1994, at approximately 1245 hours0.0144 days 0.346 hours 0.00206 weeks 4.737225e-4 months , the control room operator [utility, 1'icensed]'ttempted to close Reactor Water Recirculation System (RWRS) [AD] pump B discharge isolation valve

[ISV](79 valve). See the figure at the end of this report. The valve failed to close. Additionally, the associated breaker

[BKR] and thermal overloads tripped.

The breaker and, thermal overloads were reset. A second attempt to close the valve was made. On this attempt, the breaker did not trip, however no valve motion was detected. Consequentlyr Loop I of RHR was declared inoperable. Thus, as required by Unit 2 Technical Specifications (TSs), TVA entered a Limiting Condition for Operation (LCO) for the RHR (Low Pressure Coolant Injection (LPCI) and Containment Cooling [BE]) system. These TSs require that if any 2 RHR,pumps (LPCI mode) become inoperable, the reactor shall be placed in Cold Shutdown mode within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months .

An entry into the drywell [NH] was made and, by 1423 hours0.0165 days 0.395 hours 0.00235 weeks 5.414515e-4 months , RWRS pump B discharge isolation valve was manually closed.

Accordingly, the LCO for the RHR system was exited. By 1448

'hours, shutdown cooling was established.

This event is not reportable per 10 CFR 50.73 for the following reasons.

~ The physical evidence indicates that when the motor was energized to close RWRS pump B discharge isolation valve, the motor rotor partially disintegrated, particularly along the joint between the rotor bars and the end ring on one end of the rotor. The valve was opened on May 31, 1993 at the onset of Cycle 7 operation,. and was not operated again until October 1, 1994. Therefore, there is no conclusive evidence that the valve operator motor failed prior to October 1, 1994.

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NRC - F(XDI 366A U.S. IN)CLEAR REGULATORY CLNSII SS ION APPROVED BY LNHI NO 3150-0104 (5-92) EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE TO COHPLY LIITH THIS IHFORHATIOH COLLECTION REDUEST: 50.0 HRS. FORHARD CQBIENTS REGARDIHG BURDEN ESTIHATE TO THE INFORNATION AND RECORDS NANAGENENT BRANCH (HNBB 7714), U.S. NUCLEAR REGULATORY COIBIISSIOH, LICENSEE EVENT REPORT MASHIHGTOH, DC 20555-0001, AHD TO THE PAPERNORK REDUCTION

'TEXT CONTINUATZON PROJECT (3150-0104), OFFICE OF HANAGENEHT AND 20503 BLA)GET,'ASHINGTON DC FACILITY MAIR (1) DOCKET IRBNLER (2) LER mHHLER (6) PAGE (3)

YEAR SEOUENTIAL REVISLOH NLIIBER NLNIBER Browns Ferry Unit 2 05000260 94 011 00 3 of 8 TEXT If morc s cc is r ircd usc cdditionsL c ics of NRC Form 366A (17)

~ TVA also evaluated whether this event was reportable as a condition that had been found while the reactor was in operation would have resulted in the nuclear power plant including its principle safety barriers being seriously degraded. In this event, RWRS pump A discharge valve did close when required. Thus, it is reasonable to assume the RWRS pump A discharge valve would have performed its safety function. Therefore, one division of RHR (LPCI) would have performed its safety function.

Additionally, the BFN Updated Final Safety Analysis Report (UFSAR) states that the pumps, piping, controls, and instrumentation of LPCI are separated and protected so that no single failure or any single physical event can make both divisions of LPCI inoperable.

If RWRS pump B discharge isolation valve failed to close during a design basis accident, this condition would have been bound by the UFSAR. Either the Core Spray (CS) System (BU] or the, LPCI system can independently supply sufficient cooling water to meet the safety objective for any rupture of the nuclear system up to and including a Design Basis Accident.

As previously noted, this, e rent is not reportable in accordance with 10 CFR 50.73. However, the circumstances surrounding this event are similar to those described by IE Information Notice 86-02: "Failure of Valve Operator Motor During Environmental Qualification Testing," 'in that a Reliance brand AC motor with a magnesium alloy rotor failed after being exposed to a steam environment. It has been documented that motors with magnesium alloy rotors are susceptible to failure under high humidity conditions. Therefore, TVA is submitting this voluntary report due to the generic safety significance.

B~ Ino erable Structures Com nents or S stems that Contributed to the Event:

None.

C Dates and A roximate Times of Ma or Occurrences:

October 1, 1994 at 1245 CST The RWRS pump B discharge isolation valve fails to close. A 24 hour2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months LCO for RHR is entered.

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NRC FORN 366A. U.S. JRJCLEAR REGULATORY CJHSIISSION APPROVHJ BY (HHI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIHATEO BURDEN PER RESPONSE TO CQIPLY illTH THIS INFORHATIOH COLLECT ION REOUEST: '50.0 HRS. FORIIARD COJHIENTS REGARDING BURDEN EST IHATE TO THE IHFORHAT I OH ANO RECORDS WNAGEHEHT BRANCH (HHBB 7714), U.S. NUCLEAR REGULATORY COWIISSIOH ~

LICENSEE EVENT REPORT llASHIHGTON, DC 20555-0001, AHD TO THE PAPERIJORK REDUCTION TEXT CONTINUATZON PROJECT (3150-0104), OFFICE OF HANAGEHENT ANO BUDGET, HASHINGTOH DC 20503 FACILITY NJUE (1) DOCKET JRNKR (2) LER RMGt (6) PAGE (3)

YEAR SEQUENTIAL REVISION NWBER NINBER Browns Ferry Uni.t 2 05000260 94 011 00 4of 8 TEXT tf more s ce is r ired use additional co ies of HRC Form 366A (17)

October 1, 1994 at 1423 CST The RWRS pump B discharge isolation valve i.s manually closed. The 24 hour2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months LCO for RHR is subsequently exited.

D. Other S stems or Seconda Functions Affected:

None.

E. Nathod of Discove t After the first attempt to close the valve, the Unit 2 Control Room Operator received indication that the 480V Reactor Motor Operated Valve breaker associated with the valve tripped. After the second attempt to close the valve, the operator had indication no valve motion had taken place.

F. 0 erator Actionst Operator actions taken during this event were as expected. At the onset of the event Operati.ons reset the tri.pped breaker and thermal overloads. A second attempt to close the valve from the control room was made. When that failed, operati.ons personnel were dispatched to the drywell to manually close the valve.

G. Safet S stem Res nses:

None.

ZIZ ~ CAUSE OF THE EVENT Ao Immediate Cause:

The immediate cause of the event was the failure of the RWRS discharge valve to close.

B. Root Cause:

This event resulted from a failure of the valve operator motor.

TVA's investigation has determined that upon energizing the motor for the closing of the RWRS discharge isolation valve, the motor's rotor partially disintegrated, particularly along the joint between the rotor bars and the end had ring on one end of the rotor. Zt is postulated that the rotor degraded over time in the high humidity environment. This in addition to the fragments from the failed rotor effectively locked the rotor and prohibited any motion when energized. This resulted in damage in the stator winding insulation. Repeated starting of the valve motor u.n a second attempt to close the valve, with winding damage and the

HRC FOHN 366A U.S. IN)CLEAR REGUULTORY CQIIISS ION APPROVED BY HR NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE TO COHPLY lJITH THIS IHFORKATIOH COLLECTIOH REQUEST: 50.0 HRS. FORMARD CONlENTS REGARDING BURDEN ESTINATE TO THE INFORHATIOH AHD RECORDS HANAGENENT, BRANCH (HHBB 7714), U.S. NUCLEAR REGULATORY CQOIISSIOHg LICENSEE EVENT REPORT NASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104), OFFICE OF NANAGEHENT AND BUDGET, HASHINGTOH DC 20503 FACILITY IQ% (1) DOCKET IRHSER (2) LER IRHRKR (6) PAGE (3)

TEAR SEQUEHT IAL REVISION NWBER HUNGER Browns Ferry Unit 2 05000260 94 Oll 00 5 of 8 TEXT If more s ce is r ired Use additional co les of HRC Form 366A (17) locked rotor condition caused the motor to draw, excessive current that resulted in significant damage to the motor internals before the breaker could open. For further details of the failure analysis performed on the motor, see Section V.C .of this report.

C. Contributin Factors:

None.

IV ANALYSIS OF THE EVENT BFN is analyzed in the Updated Final Safety Analysis Report for a Loss of Coolant Accident (LOCA) assuming a double-ended break on one of the recirculation system pump discharge lines with a single failure of the LPCI injection valve in the unbroken line.

A double-ended line break will result in a rapid depressurization of the reactor vessel and loss of reactor coolant inventory. Either a low-low-low water level or a high drywell pressure plus a low reactor

.pressure would initiate Emergency Core Cooling Systems (i.e., CS system and LPCI mode of RHR system). The CS or 'LPCI system can independently supply sufficient coolant to meet the safety objective for any rupture in the nuclear system up to and including the Design Basi.s Accident. Thus this event did not affect the safety of the plant, its,personnel, or the public.

V. CORRECTIVE ACTIONS A. Immediate Corrective Actionst TVA issued a work order to investigate the failure of the RWRS pump B discharge valve to close. This investigation identified a possible phase to ground short in the motor circuit, and thus, the valve was manually closed. A new operator motor was installed pri.or to returning Unit 2 to power operation following cycle .7 refueling outage. The breaker associated with the valve power circuit was also replaced.

B. Corrective Actions to Prevent Recurrence:

Parts of the motor rotor were shipped to the vendor and TVA Central Labs for a further failure analysis. To determine if enhanced testing methods are necessary to ensure valve operability, TVA will evaluate tne surveillance requirements for similar type valves. Additionally, TVA will develop administrative controls to document occurrences of thermal overload actuations of magnesium rotor motors.

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NRC FQUI 366A U.S IRICLEAR 'EQJLATNIY C(NBIISSIQI APPROVED BY DR NO. 3150-0104 (5.P2) EXPIRES 5/31/95

'STIHATED BURDEN PER RESPONSE TO COHPLY llITN THIS INFORHATION COLLECTION REOUEST: 50.0 HRS. FORMARD C(N%ENTS REGARDING BURDEN ESTIHATE TO TNE INFORHATION AND RECORDS HANAGEHENT BRANCH (HNBB 7714) ~ U.S. NUCLEAR REGULATORY CONIISS ION, LICENSEE EVBNT RBPORT MASNINGTON, DC 20555-0001 ~ AND TO THE PAPERlJORK REDUCTION TBXT CONTINUATION PROJECT (3150-0104) ~ OFFICE OF HANAGEHENT AND BINGET ~

MASNINGTON DC'0503 FACILITY NA% (1) DOCKET IRBSER (2) LER IRBSER (6) PAGE (3)

YEAR SEQUENTIAL REVISION NQlBER NUHBER Browns Ferry Unit 2 05000260 94. 011 00 6 of 8 TEXT tf more s ce is r ired use edditionst c ies of NRC Form 366A (17)

C. Add tional Actions Taken The valve operators for the RWRS pump A (3 valve) discharge valve, the RHR shutdown cooling suction inboard isolation valve, and the High Pressure Coolant Injection [BJ) (HPCI) system steam line inboard isolation valve also contain magnesium alloy rotors.

They, are also located in the drywell'. Because the RWRS pump A discharge valve operator. motor was located in a steam environment, it was also removed for inspection.

found evidence of corrosion on the rotor. Accordingly, the motor This inspection was replaced. The 'HPCI and RHR valve operator motors with magnesium alloy, rotors were inspected utilizing a borescope.

However, no corrosion or other abnormalities were identified.

Four other valves in the RHR system .have operator motors with magnesium alloy rotors. These valves are located outside the drywell. The operator motors were also inspected, with no abnormalities observed.

The RWRS Pump B discharge valve motor was dissembled and the following preliminary observations were made:

~ The stator winding was shorted to ground in all three phases.

~ The stator windings did not have any indications of a catastrophic failure.

~ The motor bearings turned freely with no indications of binding.

~ A large section of one rotor end ring and two fan blades (a single piece casting) had overheated and separated from the rotor bars.

Additionally, TVA performed a detailed failure analysis on both the RWRS pumps A and B discharge valve operator motors. The findings from the analysis are summarized below:

Pum A Dischar e Valve Motor Corrosion Products were observed on the rotor and some small portions of the rotor fan blade material were .missing.

The rotor material'ad not recrystallized, indicating temperatures approaching 400 degrees had not been attained.

The rotor paint was missing in some areas and thinned in others.

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NRC F(NN 366A U.S. IRICLEAR REGULATORY CCNIISSION APPROVED BY (NNI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTINATED BURDEN PER RESPONSE TO CONPLY UITH THIS INFORHATION COLLECTION REQUEST: 50.0 HRS. FORllARD CQI(ENTS REGARDING

,, BURDEN ESTINATE TO THE INFORHATION AND RECORDS NANAGEHENT BRANCH (HNBB 7714), U.S. NUCLEAR REGULATORY CQBIISSION, LICENSEE EVENT REPORT llASHINGTON, DC 20555-0001, 'AND TO THE PAPERIJORK REDUCTION TEXT CONT ZNUATION PROJECT (3150-0104), OFFICE OF NANAGEKENT AND BISGET, IIASHINGTON DC 20503 FACILITY NA% (1) DOCKET IRBBIER (2) LER IRBBIER (6) PAGE (3)

YEAR SEQUENTIAL REVISION NUNBER NUHBER Browns Ferry Unit 2 05000260 94 Oll 00 7'of 8 TEXT If more s ce is r ired use additional co ies of NRC Form 366A (17)

Pum B Dischar e Valve Motor Overheating of the entire rotor was identified.

The: rotor material exhibited'ultidirectional cracking and shrinking.

The rotor temperature as a whole is estimated to have exceeded 400 degrees, while portions of the rotor attained an estimated 800-1,100 degrees and melted.

Casting quality was not unusual.

No evidence of corrosion .products were identified on the rotor.

VZ ~ ADDITIONAL INFORMATION A, Failed Com nents:

The motor, a Reliance Brand 13 horse power, 3 phase 460 volt Frame 256TY failed while attempting to close the RWRS pump B discharge valve.

B, Previous LERs an Similar Events!

There have been no previous LERs c ncerning the failure of a RWRS pump discharge valve to close due to a motor failure.

VII. Cammitment s The actions described in Section V of this report are not Regulatory Commitments. That is, they are not actions required to restore compliance with obligations. Obligation means an action that is a legally binding requirement imposed through applicable rules, regulations, orders, and licenses. potential These for actions being taken are to attempt to minimize the further failures of motors with magnesium alloy rotors.

Energy Industry Identification System (EIIS) system and component codes are identified in the text with brackets (e.g., [XX)).

NRC FORN 366A U.S M)CLEAR, REGULATORY CCSIIISSION APPROVED BY $$ NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTINATED BURDEN PER:RESPONSE TO COHPLY WITH THIS INFORHATION COLLECTION REQUEST: 50.0 HRS. FORWARD COOIENTS REGARDING BURDEN ESTINATE TO THE INFORNATION AND RECORDS HANAGENENT BRANCH (HNBB 7714), U.ST NUCLEAR REGULATOR'Y CNIIISSION, LICENSEE EVENT REPORT WASHINGTON, DC 20555-0001, AND TO THE PAPERlJDRK REDUCTION TEZT CONTZNUATZON PROJECT (3150-0104), OFFICE OF NANAGENENT AND BIA)GET,,

'ASHINGTON DC 20503 FACILITY NAIK (1) DOCKET NINIBER'2) LER IRMGI (6) PAGE (3)

TEAR SEQUENTIAL REVISION'UNBER NNIBER Browns Ferry Unit 2 05000260 94 011 , 00 8 of 8 TEXT If more s ce is r ired use additional co ies of MRC Form 366A (17)

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ML18038B184

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