ML20206S736

Summary of ACRS Subcommittee on Westinghouse Reactor Plants 860730 Meeting in Washington,Dc Re Review of Loss of All in- Plant Ac Power & 851121 Water Hammer Event.Presentation Schedule & Sequence of Events Encl

ML20206S736
Person / Time
Site:	San Onofre
Issue date:	08/13/1986
From:	Advisory Committee on Reactor Safeguards
To:	Advisory Committee on Reactor Safeguards
References
ACRS-2446, NUDOCS 8609220361
Download: ML20206S736 (30)

Text

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?\G 96 ACRS Subcommittee Meeting Sumary/ Minutes -

for Westinghouse Reactor Plants July 30, 1986 Washington, DC Purpose The ACRS Subcommittee on Westinghouse Reactor Plants met on July 30, 1986 (half-day) at Wshington, DC. The purpose of this meeting was to complete the review of the loss of all in-plant AC power and water hammer event at San Onofre, Unit 1 (SONGS-1), on November 21, 1985. The Subcommittee had met on February 12, 1986 to discuss the event with the Incident Investigation Team (IIT). For the current meeting, discussion was focused on root cause analyses and corrective actions taken at SONGS-1 prior to restart and on the generic implications of the event.

On July 30, 1986, the Subcommittee heard presentations from Staff representatives of NRR, I&E and Region V. Copies of the agenda and selected viewgraphs from the presentation are attached. The meeting began at 1:00 p.m. and adjourned at 6:00 p.m., and was held entirely in open session. The principal attendees were as follows:

Attendees:

ACRS NRR G. Reed, Chairman R. Dudley J. Ebersole, Member A. Serkiz W. Kerr, Member P. Gill C. Michelson, Member C. Wylie, Member I&E I. Catton, Consultant E. Merschoff l D. Houston, Staff

-- Region V S'CE A. Chaffee R. Ornelas RES N. Zuber DESIC:iATE3 031GIliAL Ccetified By _

Westinghouse Meeting Minutes July 30, 1986 Discussion On November 21, 1985, SONGS-1 experienced loss of all in-plant AC power and a severe incidence of water hammer in the feedwater system which caused a leak, damaged plant equipment, and challenged the integrity of the plant's heat sink. An Incident Investigation Team (IIT) was formed to pursue the event and their findings and conclusions were documented in NUREG-1190, " Loss of Power and Water Hammer Event at San Onofre, Unit 1, on November 21, 1985," January 1986.

The Westinghouse Reactor Plants Subcommittee met on February 12, 1986 to review the IIT findings with the Staff and Utility (SCE). This meeting

-(July 30,1986) was held to complete the review of the event and its consequences and focused on: (1) the check valve failures (root causes, correctiveactionsandgenericaspects),(2)waterhammerissues(plant ,

specific and generic), and (3) plant modifications made to prevent a reoccurrence of this event. The Staff had completed their evaluation of these issues and had authorized restart of SONGS-1 on July 13, 1986.

In opening remarks, G. Reed discussed four lessons learned from the event to consider for on-going programs and studies. The scope of these lessons are related to the following: (1) the major or sole system (auxiliary feedwater) for decay heat removal was seriously challenged and had it failed, the plant would have lost its heat sink, (2) the quality of maintenance and engineering judgment in doing maintenance should be reviewed, (3) water hammer issues need some further review, l and (4) the SONGS-1 event was complicated by the lack of power operated valves and non-return valves on the individual steam line leads from the

steam generators.

Highlights from the Staff presentations and Subcommittee concerns are given in the following paragraphs:

l (1) The initiator of this event was a ground on a 4KV cable. The j root cause of the failure was due to an inadequate maintenance I

(

• Westinghouse Meeting Minutes July 30, 1986 action which left a hot feedwater line uninsulated. At the location, the FW line crossed over the cable tray which contained the 4KV cable. The degradation of the cable insu-lation was caused by the high temperature (400 F) and aging.

A survey of the plant revealed 142 areas of high ambient temperature (> 140 F). Of 55 total 4KV circuits, 6 were determined as failed due to the temperature effects or aging on insulation or terminals.

The Subcommittee expressed concerns about the structure of the SCE maintenance organization, i.e., the interaction between mechanical and electrical groups, and the quality of the maintenance personnel, whether or not they are aptitude tested for the position.

(2) The water hammer as SONGS-1 was due primarily to check valve failure in conjunction with: (a) imbalanced flow in the main FW line, and (b) a condensation-induced event in a steam generator line with AFW flow. The Staff discussed a review of reported water hammer events (40 total) from 1981 through 1985 and the underlying causes. Since the SONGS-1 event did not involve any new mechanism, the Staff felt that water hammer issues considered in USI A-1 (resolved in 1981) should not be reopened.

The results of a similar water hammer study by'EPRI was summarized by I. Catton. For the same time frame, 58 events were reported but no different mechanisms were found. N.

~~

. Zuber reported that RES was funding a project at MIT and that I two mechanisms were being studied: (a) leakage through check valves, and (b) slug formation due to condensation in a low point. He indicated that the purpose of the study was toward prevention of such occurrences.

4

• Westinghouse Meeting Minutes July 30, 1986 The Subcommittee expressed concerns as to whether water hammer analyses have properly considered failure of the check valves.

Another concern was the current trend of removing pipe snubbers and supports believed to be based solely on seismic considerations.

(3) The check valve failures were attributed to location, sizing and design application. Prior failure of these valves had occurred at SONGS-1 and corrective actions had subsequently evolved. Three main factors were identified as contributing to valve failure: (a) continuous reduced flow conditions that failed to keep the valve fully open, (b) stream turbulence caused by nearby flow regulating valves, and (c) poor valve design. The Staff discussed their generic review of all check valves (6 manufactures), failure data, and resolution. The resolution of the issue appears to be a document innder development by the industry due to be issued in August 1986, which addresses maintenance and testing of check valves.

Also, industry plans to issue a design and application guide for the valves.

The Subcommittee expressed concerns regarding the lack of design criteria for check valves. It was felt that check valves would fail their function as part of the pressure l boundary in case of an up-stream line break.

(4) The plant modifications made to prevent reoccurrence of this event were discussed. These included but were not limited to

~~

the following: replacement of MCC Pacific check valves with l

better designed and properly sized Atwood-Morrill valves (also l relocated), addition of check valves inside containment, automatic closure of FW regulating valves for certain upset conditions, sloping of the "B" feedline away from steam

1 Westinghouse Meeting Minutes July 30, 1986 generator, improvements to enhance reliability of electrical system, improved maintenance and surveillance schedules and revisions to the procedures for abnormal condition response.

(5) At the conclusion of the meeting, the Subcommittee agreed upon an agenda for a presentation to the Canmittee on August 8, 1986 which included a chronological summary of the event, a brief description of the maintenance organization and selection of personnel, a review of check valve failures, a review of water hammer issues, and a summary of the plant modifications.

NOTE: Additional meeting details can be obtained from a transcript of this meeting available in the NRC Public Document Room, 1717 H Street, N.W., Washington, D.C., or can be purchased from ACE-Federal Reporters, 444 North Capitol Street, Wash-ington, DC 20001, (202) 347-3700.

Is. .

Revised: 7/25/86 ACRS Subcommittee Meeting On Westinghouse Reactor Plants July 30, 1986 Washington, DC

- Tentative Presentation Schedule -

1. Subcomittee Chairman's Report G. Reed 1:00 pm

2. Brief Sumary of November 21, A. Chaffee, 1:10 pm 1985 Event at SONGS-1 Region V

3. Discussion of Check Valve Failures E. Merschoff, 1:30 pm IE

- Root Cause Analysis and Test Results

- Corrective Action and Evaluation

- Generic Aspects

4. Discussion of Water Hamer Issues R. Dudley, 2:15 pm NRR

- Additional Check Valves Inside Containment

- FW Reg Valve Auto-Closure

- Sloped "B" FW Line

- Review of Water Hamer Generic A. Serkiz, Issue (USI A-1) NRR

• • • BREAK *** 2:45 pm

5. Electric Power Issues P. Gill, 3:00 pm NRR

- Cable Failure

- DG Loading /4KV Reliability

- Vital Bus 4

- Other

+ .

4 W Reactor Plants July 30, 1986

- Tentative Presentation Schedule -

6. Systems Review Issues C. Tinkler, 3:30 pm NRR

- Reanalysis of Limiting Cases for Manual Actions

- Steam Generator' Blowdown

- Main Steam System Design

7. Inspection of Unit 1 Restart A. Chaffee, 4:00 pm Program Region V

- Material Condition Review Program

- Plant Modifications

- Procedures

- Training,

8. General Discussion and Concluding G. Reed 4:30 pm Remarks

• • • ADJOURN *** 5:00 pm

o .

NOVEMBER 21, 1985 SAN ONOFRE UNIT 1 SEQUENCE OF EVENTS -

SUMMARY

Initial Conditions Reactor Power 60%

South Circulating Water Pump secured S.G. continuous blowdown in progress Troubleshooting ground indication on 4ky Fox 3 critical function monitor system disabled Five check valves in feedwater/AFW have undetected seat failures at this time Transient Initiator 0451 Aux Transformer C phase to phase fault 4ky bus 2C automatically deenergized System Response 0451

• Loss of 4kv bus 2C deenergized :

East Feedwater Pump NE and SE Condensate Pumps East Heater Drain Pump Vital 120 VAC bus 4 ENS phone rings spuriously on loss of power Diesel Generator 2 starts automatically but does not load per design East feedwhter pump discharge check valve fails to seat as pump coasts down Running west feedwater pump pressurizes the east condensate train.

East flash evaporator ruptures l

0451 Reactor manually tripped per procedure

. Turbine trip All inplant power lost except for 120 VAC vital buses (battery / invertor)

Electric and steam driven AFW pumps receive automatic initiation signals Steam pump begins 31 minute warm up period Electric pump at rest As west feedwater pump stops, all steam generators begin to empty their feedwater lines to the ruptured flash evaporator i

Spurious annunciation of safety injection Operators begin attempts to restore offsite power Diesel Generator 1 starts automatically but does not load per design

0455 Steam driven AFW pump begins to deliver 130 gpm flow. Flow is lost to the ruptured flash evaportor ,

Operators determine that the Loss of Voltage Sequencer did not complete sequence. Attempt closing breakers from control room with numerous difficulties 0455 Station power restored -

Electric AFW pump starts Operators shut feedwater isolation valves per procedure, unknowingly stopping further voiding of steam generators AFW flow starts filling feedwater lines RCS pressurizer level noted low RCS pressure noted low 0458 South charging pump started 0501 Started RCP B to provide pressurizer spray 0502 Terminated AFW flow to minimize RCS cooldown. Resumed AFW flow at 40 gpm 0506 Licensee declared an Unusual Event onsite 0507 A loud bang was heard in turbine building mezzanine. The water hammer 11ad occurred in the feedwater line. Steam / water leak occurs in a check valve bonnet 0527 Wide range level indication dropped offscale low in all three steam generators 0528 Increased'AFW to S;G. A and C to 70 gpm 0530 Blowdown from S.G. 's secured Wide range level returned on scale on'S.G.'s A and C 0630 Started emergency boration for cold shutdown 0800 Entered Mode 4 0835 Secured steam driven AFW pump due to low steam pressure 0910 Attempted to open RHR suction valves; but pressure interlock did not clear although pressure was below 400 psig 0918 RHR interlock overriden, RHR valves opened 0935 West RHR pump started 0936 East RHR pump started 0940 Unusual Event terminated

O 3.. . .

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, .1045 Feedwater leak through check valve manually isolated 1508 The plant entered Mode 5 November 22. 1985 0100 Operators entered containment sphere and identified damaged pipe,

- supports, and insulation on the B S.G. feedwater line 9

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IE REVIEW 0F PLANT SPECIFIC ASPECTS I, APPROACH

1. INSPECTI0ftS SONGS-1 MCC PACIFIC ATWOOD MORRILL UTAH TEST FACILITY OTHER CHECK VALVE vet! DORS -

OTHER tlVCLEAR POWER PLAf!TS ,

2. MEETINGS WITH LICEllSEE

- FEBRUARY 19, 1986

- MARCH 5, 1986

- MARCH 19, 1986

3. REVIEWED LICENSEE SUBMITTALS DATED

- MARCH 2, 1986

- APRIL 8, 1986

- MAY 1, 1986

- MAY 5, 1986 II, RESULTS

1. ROOT CAUSE AtIALYSIS

• LICENSEE'S SUEMITTAL PROPERLY ATTRIBUTES FAILURES TO IMPROPER SIZIf!G IMPROPER LOCAT10fl IMPROPER DESIGt! APPLICATI0f!

2. ADEQUACY. OF CHECK VALVE DESIGil

• POOR CHOICE FOR THIS APPLICATION HIGH FLOW-LOW DP FLUTTER / WOBBLE

- MARGIllAL FLOW RATES TURBULEf!CE ,

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3. CORRECTIVE ACTI0fl

• REPLACE-FEEDWATER CHECK VALVES WITH VALVES OF PROPER SIZE PROPER DESIGN

• MOVE IMPROPERLY PLACED VALVES

' PERFORM FULL SCALE TESTItlG

• REVIEW FAILURE DATA

• LOOK AT ALL OTHER CHECK VALVES

4. IST PROGRAM

• REVIEWED AllD FOUND ACCEPTABLE

• EllHANCEMEt!TS M0filTOR FEEDWATER VALVES OPEll 8 It!SPECT QUAtlTITATIVE LEAK RATE CRITERIA FULL SCALE TESTIliG

5. ADEQUACY OF CHECK VALVES Ill OTHER SYSTEMS

' DISASSEMBLE ALL MCC-PACIFIC CHECK VALVES (29)

• DISASSEMBLE Ally WITH PREVIOUS PROBLEMS (5)

• DISASSEMBLE Ally WITH MARGINAL SIZItiG, LOCATION, OR

) DESIGil APPLICATI0tl (15) 5 1

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IE REVIEW 0F GEllERIC ASPECTS t

I. APPROACH

1. I N S P liC T V EfID O R S MCC PACIFIC

- ATWOOD & MORRILL VELAN .

- CRAtlE AtlCHOR DARLIllG

2. VISIT LICEf! SEES SONGS-1 Il0RTH AtlMA MILI.ST0tlE HOPE CREEK LIMERICK PEACH BOTTOM

3. REVIEW FAILURE DATA IlPRDS LER 50.55(E)

PART 21 Pfl0

- VE!! DOR RECORDS LICENSEE RECORDS

4. REVIEW Ill SERVICE TESTit!G COMMITMENTS - SAMPLED 5 SYSTEMS AT 16 PLAtlTS IMPLEMEllTATI0tl - LOOKEP AT TESTING PROCEDURES II. PESULTS

. 1. IDEtITIFIED POTE!!TI ALLY GEtlERIC ISSUES LICEtlSEE/VEllDOR INTERFACE WITH CHECK VALVE SUPPLIERS LARGELY INEFFECTIVE CHECK VALVES CFALLEllGED BY fl0f!-0PTIMAL:

'SIZIt'G 1 *LOCATI0tl 4 *DESIGt! APPLICATI0fl IST IllEFFECTIVE AT DETECItlG DEGRADED C0llDITIONS 1

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III..RESOLUTI0fl .

1. MEET WITH OWilERS GROUPS S INP0 APRIL 7 MAY 21

2. IflDUSTRY PLAi!

ISSUE-SCER

- MAIllTEllANCE TESTIllG ISSUE DESIGN AflD APPLICATION GUIDE SIZIflG LOCATI0flS APPLICATI0f!S

3. NRC STAFF WILL C0flTINUE TO WORK WITH INDUSTRY T0. RESOLVE ISSUES F

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SAN ONOFRE UNIT 1 CABLE FAILURE O FAILURE - TRANSFORMER "C" CABLE PHASE TO PHASE FAULT 0 CABLE-TYPE.- SUPLEX, 3/C 750 MCM COPPER, BUTYL RUBBER, NEOPRENE JACKET ALUMINUMARMOUPED, MANUFACTURED'65 n ROOT CAUSE - OVERHEATING DUE TO LONG TERM EXPOSURE TO LOCALIZED HEAT SOURCE O FAILURE ECHANISM - SPLITTING OF TE INSULATION SURFACE FROM EXCESSIVE TEMPERATURES AND PRESSURES 0 LICENSEE CONCLUDED - PROBLEM LOCALIZED. REMAINING CABLES NOT SUBJECT TO SAME HOSTILE ENVIRONENT.

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CABLE RELIABILITY ASSESSE NT 0 LICENSEE INSPECTED AND TESTED ALL "SIPFLEX" CABLE (BOTH 4KV AND 600V)

To ASSESS ITS INTEGRITY.

O WALKDM1 INSPECTIONS PERFORMED AND DOCUfENTED TO IDENTIFY POTENTIAL HEAT SOURCES AFFECTING CABLES.

O LICENSEE ESTABLISHED CABLE EVALUATION TASK FORCE FOR ASSESSING MATEP.IAL CONDITION OF CABLES.

O CABLES FROM TRANSFORMERS "C",'"A" & "B" REPLACED. OTHER 4KV CABLES NOT PASSING TEST ALSO REPLACED.

O LICENSEE INTEf0S TO TEST ALL 4KV CABLES EVERY 5 YEARS.

O EXISTING ENVIRONFENTAL QUALIFICATION CONDITION MONITORING PROGRN1 EXPANDED TO MONITOR PLANT AMBIENT TENERATURES IN TURBINE BUILDING.

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SIMPLEX 5KV CABLE CONSTRUCTION

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LICENSEE MODIFICATIONS TO PREVENT

~FEECLINE WATER HAMMER 0 PRIMARY PROTECTION - PREVENT FEEDLINE V0IDING BY FIXING CHECK VALVES

- NEW DESIGN, IMPROVED IN-SERVICE TESTING, PERIODIC INSPECTION O FURTHER MODIFICATIONS TO PREVENT WATER HAMMER:

ADDITION OF CHECK VALVES INSIDE CONTAINMENT

' PREVENT VOIDING

'AFW RELIABILITY

'FEEDLINE BREAK PROTECTION

- AUT0-CLOSURE OF FW REG. VALVES (LOMFW, T. TRIP, AFW INIT.)

REPLACE "B" FEEDLINE WIfH PIPING SLOPED AWAY FROM STEAM GENERATOR 1

= - - - - .--.- m- - - ,w--- g--t- ,---,e -y-- - . - -- - ,.w-- -- -+-+----ey -y-- - -- rw-

! FINAL 'B' FEEDWATER LINE SLOPE TO REDUCE WATER HAMMER SUSCEPTIBIL STEAM

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WATER HAMMERS 1969 to 1980

. 14 8 OCCURREXCES' REPORTED

. FREQUEXCY = 0.29 / RX-YR i . UXDERLYIXG CAUSES WERE DESIGX & OPERATIOXS RELATED

! . REVIEW OFDAMAGE IXCURRED

& SAFETY SIGXIFICANCE WAS BASIS FOR A-1 RESOLUTIOX. ,

. XO BACKFIT REQUIREMENTS WATER HAMMERS li 1981 to 1985

. 40 OCCURRENCES REPORTED

. FREQUEXCY = 0.13 / RX-YR i . SIMILAR UXDERLYIXG CAUSES '

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L N UC L EA R POWER 3 _AN T 0 3 E RA- I N G -1 S- O RY l .

CUMMULATIVE YEARS 600 LEGEND E/d BWRs MA- PWRs 500-- -

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! 69 71 73 75 77 79 81 83 CALENDAR YEAR i - - . . - . _ - . - .

WA-~ER -IAVV R - IS- O RY .

ANNUAL OCCURENCE 20 LEGEND 18--

EM BWRs

- E PWRs i

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6970717273747576777879808182838485 CALENDAR YEAR

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.o WATER HAMMER HISTO RY .

FREQUENCY OF OCCURENCE

• LEGEND z -

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1981 to 1985

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. 22 PWR OCCURREXCES

. UNDERLYIXG CAUSES:

.. VOIDED LIXES

.. STEAM -

WATER EXTRAIXMENT

.. SYSTEM SWITCH-OVERS

.. OPERATIOXAL ERRORS I

CQNCLUSIONS -

. SONGS-1 11/21/85 WATER HA M MER WAS THE RESULT OF GROSS CHECK VALVE FAILURES

. REVIEW OF CY 81 -

85 EVEXTS HAS XOT REVEALED XEW PHEXOMEXA

. FREQUEXCY OF OCCUREXCE HAS HAS DECREASED

. LEVELS OF DAMAGE SIMILAR

. XEW PLANTS WERE XOT MAJOR COXTRIBUTORS

. GEXERIC BASIS FOR RE-OPEXIXG USI A-1 DOES XOT EXIST l

4 SYSTEM REVIEW ISSUES MANUAL ACTIONS REQUIRED FOR OPERATION OF THE AFW SYSTEM (ITEM 3 A.1 - LACK 0F AUTOMATIC LOADING 0F THE DIESEL GENERATORS FOLLOWING A LOSS OF POWER EVENT)

LACK 0F REMOTE CONTROL OF STEAM LINE ISOLA 7 ION VALVES (ITEM 3.A.2)

LACK OF STEAM GENERATOR BLOWDOWN STATUS IN CONTROL ROOM (ITEM 3.A,3) 4

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MODS

• FEEDWATER SYSTEM o NEW CHECK VALVES INSIDE CONTAINMENT o NEW B FEEDWATER LINE o NEW CHECK VALVES OUTSIDE CONTAINMENT

- 4" BYPASS

- 10" S/G FEED CHECK VALVE

- 12" MFP DISCH CHECK VALVES o AUTO ISOLATION OF MAIN FEEDWATER REG VALVES

• STEAM GENERATOR BLOWDOWN o AUTO ISOLATION ON AFW ACTUATION o REMOTE MANUAL CONTROL IN CONTROL ROOM o POSITION INDICATION IN CONTROL ROOM h

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• ELECTRICAL SYSTEM (AUX) o OVERCURRENT LOCK 0UT PROTECTION FOR DIESEL GENERATOR o

DELETION OF AUX C TRANSFORMER BYPASS REACTANCE INTERL o

BUS 1C AND 2 C TIE BKRS TO 1A AND IB INTERLOCK CHANGED TO-60 OPEN ON LOSS OF POWER o

LOCK 0UT RESET REMOVED TO ALLOW BRINGING ON OFFSITE POW THROUGH MAIN TRANSFORMER MORE QUICKLY o 4KV BUS PARALLEL ALARM ADDED o DIESEL GENERATOR SHIFT TO AUTO DROOP ON PARALLEL WITH OFFSITE POWER o ENVIRONMENTAL PROTECTION OF 4KV CABLE

• OTHER o IMPROVED COMPONENT RELIABILITY BY PROVIDING POWER FROM UPS

- SAFETY INJECTION ANNUNCIATION

- EVENT COMPUTER

, - VITAL BUS 4 (POST STARTUP) o VITAL BUS LABELING (POST STARTUP)

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o ABNORMAL CONDITION RESPONSE

• POST TRIP REVIEW

~

o ONSITE REVIEW COMMITTEE MEETS REQUIREMENTS o OVERSITE BY CONTRACTOR (MAC) ADDED o ONSITE HAD FAILED TO RECOGNIZE POTENTIAL FOR NOISE IN FEED LINE YIELDING CHECK VALVE FAILURE -

• POST TRIP REVIEW o PROCEDURALIZED o REQUIRES ONSITE REVIEW COMMITTEE INPUT UNDER CERTAIN CONDITIONS EMERGENCY NOTIFICATION o ENSSPURIOUSRINGINGFIXEDBYADDINGMORERELIABLEPOW/ER o POLICY ISSUED ON USE OF ENS (IE MEMO)

- RESIDENTS WILL NOT ASSUME PHONE WATCH o REPORT OF UE NOT VIOLATION o EVENT PROPERLY CLASSIFIED

.