ML17347B478

LER 89-006-01:on 890713,intake Cooling Water Flow to Component Cooling Water HXs Degraded to Below Design Basis Flow Rate for 15 Minutes.Caused by Flow Obstruction Near Header Isolation Valve.Valve replaced.W/891218 Ltr

ML17347B478
Person / Time
Site:	Turkey Point
Issue date:	12/18/1989
From:	Harris K, Dawn Powell FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-89-454, LER-89-006, LER-89-6, NUDOCS 8912260046
Download: ML17347B478 (10)

Text

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ACCESSION NBR: 8912260046 DOC. DATE: 89/12/18 NOTARIZED: NO DOCKET Turkey Point Plant, Unit 4, Florida Power and Light C 05000251Et'A'CIL:50-251 AUTH. NAME AUTHOR AFFILIATION POWELL, D. R. Florida Power & Light Co.

HARRIS,K.N. Florida Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 89-006-01:on 890713,degraded intake cooling water flow condition to CCW HXs & unit shutdown required by TS.

W/8 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR I ENCL I SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

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1 1 INTERNAL: ACRS MICHELSON 1 1 ACRS MOELLER 2 2 ACRS WYLIE 1 1 AEOD/DOA 1 1 AEOD/DS P/TPAB 1 1 AEOD/ROAB/DSP 2 2 DEDRO 1 1 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB9H3 1 1 NRR/DET/ESGB 8D 1 1 NRR/DLPQ/LHFB11, 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB11 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB, 8D 1 1 NRR/DST/SICB 7E 1 1 NRR/DST/SPLB8D1 1 1 /~Z/SRXB 8E 1 1 NUDOCS-ABSTRACT 1 1 REG~'ILE~ 02 1 1 RES/DSIR/EIB 1 1 GN2 FILE 01 1 1 EXTERNAL EG&G WILLIAMSI S 4 4 L ST LOBBY WARD 1 1 LPDR -1 1 NRC PDR 1 1 NSIC MAYS,G 1 1 NSIC MURPHYI G A ~ 1 1 NUDOCS FULL TXT 1 1 NOTE TO ALL "RIDS" RECIPIENrS:-

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L-89-454 10 CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: Turkey Point Un't Docket No. 50-251 Reportable Event: 89-06-01 Date of Ev~.nt: July 13, 1989 Degraded Intake Cooling Water Flow Condition to Component Cooling Water Heat Exchangers and Unit Shutdown Required b Technical S ecifica-ions due to Valve Failure The attached Licensee Event Report is being submitted pursuant to the requirements of 10 CFR 50.73 to provide supplemental information on the subject event.

Very truly yours, arras Vice resident T urkey Point Plant Nuclear KNH/DRP/DWH/rat attachment cc: Stewart D. Ebneter, Regional Administrator, Region II, USNRC Turkey Point Plant Senior Resident Inspector, USNRC, 8912260046 891218 F'DR ADQCK 05000251 S P13C an FPL Group company

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On July 13, 1989, Intake Cooling Water {ICW) flow to the Unit 4 Compon-ent Cooling Water l,'CCW) heat exchangers degraded to below the design basis flow rate for fif'teen minutes while backwashing the 4A ICW/CCW basket strainer . ICW flow was restored within five minutes of recog-nizing the degraded flow .condition. On July 15, 1989, the same condi-tion occurred but ICW flow was maintained above the design basis flow.

On July 16, 1989, the 4B ICW header was taken out of'ervioe for in-vestigation. The cause of these conditions was initially believed to be clogging of the 4B ICW/CCW basket strainer and/or a malfunction of its differential pressure gauge. Subsequent evaluation indicated flow obstruction in or around 4B ICW header isolation valve 4-50-308. Due to the frequency of cleaning ICW/CCW basket strainers, a management de-cision was made not to continue power operations with only one header of ICW operable. Unit 4 was placed in Mode 3 on July 17, 1989. Upon disassembly of valve 4-50-308, the valve disc was found to be in the partially opened position and separated from the valve stem. The fail-ure mechanism of the upper two valve taper pins was fatigue. Valve 4-50-308 was replaced and the 4B ICW header was returned to service on July 20, 1989. The initial degraded ICW flow condition did not affect any other plant equipment.

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Oi2 oFI0 5 At 1625 on July 13, 1989, with Unit 4 in Mode 1 at 25$ power, the 4A Intake Cooling Water (ICW)/Component Cooling Water (CCW) basket strainer (EIIS system BI, component: BSKT) was taken out of service for cleaning. (See simplified drawing of the ICW system attached.) At 1635 the Nuclear Operator observed a, degraded flow condition on the CCW heat exchangers (EIIS System: CC, component:

HX) and immediately notified the Control Room operator. The Nuclear Operator was instructed to valve the 4A ICW/CCW basket strainer back in service. At 1640, ICW flow was restored to the CCW heat exchangers. The Operations person-nel believed the source of reduced ICW f'low to the CCW heat exchangers to be clogging of the 4B ICW/CCW basket strainer. Between 1725 and 2125 the 4B ICM/

CCW basket strainer was out of service for cleaning. The basket strainer was found to be more clogged than normal.

At approximately 2200 o'i July 14, 1989 the onsite Technical Department was di-rected to perform an evaluation of the ICM degraded flow condition.. At 0800, on July 15, 1989, the Technical Department system engineer notified Operations De-partment personnel that an analysis of the degraded ICM flow condition on July 13, 1989 revealed that, the ICM flow to the CCM heat exchangers was below the de-sign basis flow rate from 1625 to 1640 on July 13, 1989.

At 1824 on July 15, 1989, an attempt was made to valve out the 4A ICM/CCM bask-

,et strainer for cleaning when ICW flow to the CCW heat exchangers decreased.

The strainer was returned to a normal alignment while ICM flow was maintained above 15,400 gpm. Sinoe the 4B ICW/CCW basket strainer had previously been cleaned and showed a diff'erential pressure decrease to approximately 1.0 paid, Operations personnel suspeoted the strainer to be clogged and the differential pressure gauge to be in error.

At 1425 on July 16, 1989, with Unit 4 in Mode 1 at 100'ower, the 4B ICW/CCM basket strainer was taken out oi service in accordance with Teohnioal Specifi-cation 3.4.5.b.1 for cleaning and to inspeot ior obstructions. The inspection showed no signifioant blookage. Subsequent evaluation of the degraded ICM flow condition by the System Engineer indicated probable flow r estriotion in or a-round 4B ICW header isolation valve 4-50-308.

Due to the f'requenoy of'leanihg ICM/CCM basket strainers, a management decision was made not to'ontinue operation with only one header of'CM operable. There-fore, at 0325 on July 17, 1989, a Unit 4 shutdown was initiated and at 0607 Unit 4 was placed in Mode 3 (hot standby).

Examination and repair of the 4-50-308 valve required isolation oi the 4B ICW header. Although no degraded flow conditions'ere indicated for the 4A ICM/CCM basket strainer f to ensure the maximum flow oapability, PPL determined that backwash of the 4A ICM/CCM basket strainer was prudent. However, with the B ICM header -at reduoed flow (approximately 8200 gpm) and therefore, technically inoperable, NRC approval was required to isolate the 4A ICM/CCM basket strainer.

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~'fl ISSI o 5 0 0 o 2 5 1 1989, the NRC approved a discr etionar y enforcement for a period of 0 0 6 0 g 5 time not to exceed one hour to perform the requested backwash of the 4A ICW/CCW basket strainer. This operation took place between 2000 and 2100 on July 18, 1989.

Valve 4-50-308 was replaced and the 4B ICW header was returned to service at 1900 on July 20, 1989. Technical Specification Action Statement time require-ments associated with the 4B ICW header low flow. condition were met.

Cause of the Event The cause of the degraded ICW flow to the CCW heat exchangers was due to failure of 4B ICW header isolation valve 4-50-308. Upon disassembly, the valve disc was found to be in the partially opened position and separated from the valve stem.

Two tapered pins, connect1ng the disc to the valve upper stem, failed in the threaded region. A metallurgical analysis per formed by FPL Nuclear Services concluded that the mechanism of failure was fatigue. The fatigue failure was most likely caused by cyclic loading from oscillation of the valve disc when normally open, combined with the pins working loose.

s Analysis of the Event The minimum required total flow to the CCW heat exchangers dut ing power opera-tion was less than the design basis flow from 1625 to 1640 on July 13, 1989.

During this time, the CCW heat exchanger outlet temperature reached a maximum recorded value of approximately 109 degrees F.

The limiting components in the CCW system from the perspective of operating CCW temperatures are the Reactor Coolant Pumps seals. Based on this limitation, the CCW heat exchanger outlet temperature may exceed 105 degrees F up to 125 de-grees F for a maximum period of 2 hours. Since the CCW heat exchanger outlet temperature reaohed a maximum recorded value of approximately 109 degrees F dur-ing the 15 minutes of degraded ICW flow, it may be conoluded that this condition had no signifioant affeot on plant equipment.

The degraded ICW flow to the CCW heat exchangers oocurred during the backwash>>s ing of the 4A ICW/CCW basket strainer. Within 5 m1nutes oi recognizing the de-graded ICW flow condition, total ICW flow to the CCW heat exchangers was restor-ed to above 15,400 gpm. Had a Design Basis Aooident occurred during this time, ICW flow to the CCW heat exchangers could have been restored in time to accomo-date the heat loads generated by a Large Break Loss of Coolant Accident.

During the time the 4B ICW header was out of service. to repair valve 4-50-308, ICW total flow to the CCW heat exchangers was maintained above that required to mitigate the consequences of a Design Basis Aocident.

The 1nstalled valve is a Model XR-70 36" manual butterfly valve supplied by the Henry Pratt Company. The replaoement valve is a Model R1A 36" manual butterfly valve supplied by the Henry Pratt Company. FPL Engineering has determined that the R1A valves have several design differ enoes, including a centered 1nstead of

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an offset stem, which would result in different loads on the taper pins. Based on this and many years of service without taper pin failures, the Model R1A valves in the ICW system are not suspect of being subject to the fatigue failure experienced on the Model XR-70 valve. The Model R1A 36" manual butterfly valve is used in the Unit 3 ICW system. Three Model XR-70 36" manual butterfly valves remain in the Unit 4 ICW system.

Corrective Actions

1) Caution statements have been added to procedures 3/4-0P-019, "Intake Cool-ing Water System," for operators to ensure that total ICW flow to the CCW heat exchangers does not drop below 15,400 gpm awhile valving an ICW/CCW basket strainer out of service for backwashing.

2) While valve 4-50-308 was removed from the 4B ICW head'er, a "crawl through" inspection was conducted to ensure removal of any obstructions to the 4B ICW/CCW basket strainer.

3) Valve 4-50<<308 was replaced. After ensuring valve integrity and operabi-lity, the 4B ICW header was returned to service.

4) A disc/stem tapered pin from the,4-50-308 valve was recovered from the 4B ICW header. A metallurgical analysis performed by FPL Nuclear Services concluded that the mebhanism of failure was fatigue. The fatigue failure was most likely caused by cyclic loading from oscillation of the valve disc when normally open, combined with the pins working loose.

5) A valve throttling test will be performed on valves 4-50-307, 309 and 310.

The test will determine whether or not a throttled valve position will stop the oscillations. Elimination of the oscillations is also expected to re-duce the possibility of the taper pins loosening. This test should be per-formed by January 15B 1990 If the valve throttling test is successful in reducing oscillations, FPL

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Nuclear Engineering will evaluate the effect on ICW system flow with the valves throttled. If acceptable, a Design, Equivalent Engineering Package

'This'ction should be complete by February 15, 1990.

(DEEP) will be issued.

7) FPL Nuclear Engineering is pursuing design details for modifying the Model XR-70 36" manual butterfly valves such that the taper pins would be pre-vented from working loose. (The same modification will be considered for Model XR-70 30" manual butterfly valves installed in the Units 3 and 4 ICW system.) FPL Nuclear Engineering will issue a sohedule for this task by January 10, 1990.

8) FPL Nuclear Engineering will issue a test request to inspeot the Model XR-70 30" manual. butterfly valves installed in the Unit 3 ICW system during the 1990 refueling outage for evidence of loosened taper pins. This re-quest will be issued by December 15, 1989. The need to inspect the Model XR-70 30" manual butterfly valves installed in the Unit 4 ICW system will be based on the results of the Unit 3 inspection.

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