ML16341G729

Summary of 920923 Meeting in Rockville,Md Re Dententioning Rv Head Bolts to Serve as Vent Path During mid-loop Operation at Diablo Canyon.List of Attendees & Viewgraphs Encl

ML16341G729
Person / Time
Site:	Diablo Canyon
Issue date:	10/23/1992
From:	Hood R Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
TAC-M69740, NUDOCS 9210290286
Download: ML16341G729 (54)

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Vp UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555 October 23 1992 Docket Nos.

50-275 and 50-323 LICENSEE:

Pacific Gas and Electric Company (PG&E)

FACILITY:

Diablo Canyon Nuclear Power Plant, Units 1 and 2

SUMMARY

OF SEPTEMBER 23, 1992 PUBLIC MEETING TO DISCUSS DETENTIONING THE REACTOR VESSEL HEAD BOLTS TO SERVE AS A VENT PATH DURING MID-LOOP OPERATION AT DIABLO CANYON (TAC NO. M69740)

On September 23, 1992, the NRC staff met with the Pacific Gas and Electric Company (PG&E or the licensee) staff and a Westinghouse Electric Corporation representative in Rockville, Maryland to discuss the subject stated above.

Attendees at the meeting are given in Enclosure 1.

Slides presented by PG&E at the meeting are given in Enclosure 2.

The PG&E presentation summarized their analysis and conclusions of using the reactor vessel (RV) head as a vent path during mid-loop operation.

The licensee plans to shot-peen the steam generator tubes during the latter part of the current Diablo Canyon Unit 1 refueling outage.

To do this, it is necessary to drain the reactor coolant system (RCS) down to mid-loop to facilitate the use of temporary nozzle dams in both the hot and cold legs to seal off the steam generator.

The mid-loop operation will occur 30 to 40 days into the outage, at which time the decay heat power level will be less than 5 Mwt.

At the meeting, PG&E stated that during mid-loop operation, they plan to operate with the reactor. vessel head bolts loosened, thereby allowing the reactor vessel head to serve as a vent path in the event of loss of residual heat removal (RHR).

PG&E stated that using the pressurizer as a vent path, through either the safety valves or manways, is unsatisfactory due to the possibility of undesirable phenomena associated with flooding the pressurizer surge line.

PG&E also indicated that conducting the mid-loop operation with the reactor vessel head totally removed is also undesirable; it would add 5 or 6 days to the length of the outage.

The licensee addressed several topics regarding the use of the reactor vessel head during mid-loop operation.

These topics included:

scopes of PG&E's efforts related to shutdown and head vent issues, PG&E's approach, thermal-hydraulic and mechanical analyses conclusions, and flow vent geometry.

In

addition, PG&E discussed several issues of concern, including reactor vessel head sticking, reactor head cocking, and reactor head drag.

The licensee also addressed their steady state responses and final conclusions.

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PG&E's approach consisted of performing a thermal-hydraulic analysis of the head system to function as a vent upon a loss of RHR and of performing a

mechanical analysis of the head and the associated components to address the issues of sticking, cocking, excessive

drag, and cyclic impacting.

The licensee also discussed the effects of the head vent to avoid pressurizer surge line flooding, and whether the head vent would fulfillGeneric Letter 88-17 requirements for venting when using steam generator nozzle dams.

PG&E stated that their analysis demonstrated that the reactor pressure vessel (RPV) head could be used as a vent path without encountering mechanical damage to either the head or the RPV flange structure from cyclic impacting.

In

addition, PG&E stated that the possibility for inadequate RPV head lift due to sticking, cocking, or excessive drag as addressed in NUREG 1449 was shown to be highly unlikely if proper measures to limit lift are taken.

The licensee stated that the use of the reactor vessel head as a vent path during mid-loop operation late in the outage is acceptable because:

1.

The mid-loop operation will be undertaken when decay heat is at a

relatively low level.

2.

The "fill and spill" method will be used to cool the core in the event of a loss of RHR.

Mater will be supplied from the refueling water storage tank (RWST),

and will lift the reactor vessel head and spill over the vessel flange at 500-1200 gpm, which is sufficient to keep the core from boiling.

3.

Flow from the RMST will be throttled using a flow control valve to prevent the reactor vessel head from lifting off the vessel flange by more than 0.7 inches (equivalent to about 12 psi pressure in the vessel).

Keeping the head lift below this value will prevent it from lifting off the upper internals of the core.

This is desirable because as long as the head rests on the upper internals, the internals'lignment pins will prevent it from cocking.

The staff noted that the acceptability of using the reactor vessel head as a

vent path during mid-loop operation depends on a number of plant-specific

factors, and that all relevant factors should be thoroughly evaluated in determining acceptability.

At the conclusion of the meeting, the NRC staff indicated that the PG&E presentation was very informative.

In addition, the PG&E analysis was quite thorough and addressed a number of issues that had not previously been considered.

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POST-MEETING STAFF ACTIONS:

In the September 23 meeting, the licensee presented analyses and plans for venting the RCS during mid-loop operation late in the present outage.

The NRC staff has determined that it has no objection to use of the RV head as a

potential vent path when conducted as described by PGLE for the potential conditions that reasonably could exist at Diablo Canyon.

Specifically, this usage involves the following considerations:

(I) This evolution will be conducted late in the outage when decay heat is relatively small.

(2) Controlled flow from the refueling water storage tank (RWST) will be available even in the event of a loss of all AC electric power.

The flow rate is to be controlled at less than a value that could induce head cocking, but great enough to maintain subcooled conditions in the RCS unless safety considerations necessitate the allowance of boiling in the RCS.

(5) Incore thermocouples or their equivalent will be available to monitor upper RV temperature, should conditions occur where head lift may be used for venting the RCS.

An initial period of less than approximately I day will exist before the thermocouple connections are made following head placement, but no operations will be permitted during this time that involve reduction in RCS level or that could reasonably jeopardize residual heat removal system operation.

(6)

No significant cold leg openings will be permitted as long as the head lift capability is depended upon for venting.

(7) Suitable procedures and controls, including training in use of those procedures and controls, will be provided prior to entering a condition where head lift is used as a potential vent.

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October 23, 1992 If an event should occur in which the RV head actually operates as a vent, then a complete evaluation, including staff approval, will be required prior to a return to power operation.

Also, this finding is limited to the Diablo Canyon Power Plant because of the plant-specific nature of the analyses and operating conditions.

Original signed by Harry Rood, Senior Project Manager Project Directorate V

Division of Reactor Projects III/IV/V Office of Nuclear Reactor Regulation

Enclosures:

1. List of Attendees 2.

PG&E Viewgraphs cc w/enclosures:

See next page DISTRIBUTION

, 'Docket Fi.l.e)

.NRC 5 Local PDRs PDV Reading File TMurley/FMiraglia (12G18)

JPartl ow (12G18)

JRoe MVirgili o TQuay HRood DFoster MKhanna OGC (15B18)

EJordan (3701)

NRC Participants ACRS (10)(P315)

JMitchel1 (17G21)

KPerkins, RV OFC I PDV/LA I PDV/ INTERN j'PDV/PM

',PDV/D NAME

',DFost

',MKhanna

',HRood

,'TQuay DATE OFFICIAL RECORD COPY l /'o/pt /92 l 8 /4/92

~tO/Q'92

't /9/92 DOCUMENT NAME:

DC69740.SUM

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If an event should occur in which the RV head actually operates as a vent, then a complete evaluation, including staff approval, will be required prior to a return to power operation.

Also, this finding is limited to the Diablo Canyon Power Plant because of the plant-specific nature of the analyses and operating conditions.

Enclosures:

1. List of Attendees 2.

PG&E Viewgraphs cc w/enclosures:

See next page Harry Roo

, Senior Project Hanager Project Directorate V

Division of Reactor Projects III/IV/V Office of Nuclear Reactor Regulation

I I

Pacific Gas and Electric Company Diablo Canyon CC:

NRC Resident Inspector Diablo Canyon Nuclear Power Plant c/o U.S. Nuclear Regulatory Commission P. 0.

Box 369 Avila Beach, California 93424 Dr. Richard Ferguson, Energy Chair Sierra Club California 6715 Rocky Canyon Creston, California 93432 Ms. Sandra A. Silver Mothers for Peace 660 Granite Creek Road Santa Cruz, California 95065 Ms. Jacquelyn C. Wheeler 3303 Barranca Court San Luis Obispo, California 93401 Managing Editor The County Telegram Tribune 1321 Johnson Avenue P. 0.

Box 112 San Luis Obispo, California 93406 Chairman San Luis Obispo County Board of Supervisors Room 370 County Government Center San Luis Obispo, California 93408 Christopher J.

Warner, Esq.

Pacific Gas

& Electric Company Post Office Box 7442 San Francisco, California 94120 Mr. Hank Kocol Radiologic Health Branch State Department of Health Services Post Office Box 942732 Sacramento, California 94234 Regional Administrator, Region V

U.S. Nuclear Regulatory Commission 1450 Maria Lane, Suite 210 Walnut Creek, California 94596 Mr. Peter H. Kaufman Deputy Attorney General State of California 110 West A Street, Suite 700 San Diego, California 92101 Ms. Nancy Culver 192 Luneta Street San Luis Obispo, California 93401 Michael M. Strumwasser, Esq.

Special Assistant Attorney General State of California Department of Justice 3580 Wilshire Boulevard, Room 800 Los Angeles, California 90010 Mr. Gregory M. Rueger Nuclear Power Generation, B14A Pacific Gas and Electric Company 77 Beale Street, Room 1451 P.O.

Box 770000 San Francisco, California 94177 Diablo Canyon Independent Safety Committee ATTN:

Robert T. Wellington, Esq.

Legal Counsel 857 Cass Street, Suite D

Monterey, California 93940

ENCLOSURE 1

List of Attendees eetin Between NRC

& PG&E SEPTEMBER 23 1992 NAME Ken Bych Toby Burnett Nark Caruso John Gisclon Robert Jones Meena Khanna Arnold Lee Warren C.

Lyon Kamal Manoly Jai Rajan Harry Rood Tom de Uriarte ORIGANIZATION PG&E Westinghouse NRC/NRR/SRXB PG&E NRC/NRR/SRXB NRC/NRR/PD5 NRC/NRR/EMEB NRC/NRR/SRXB NRC/NRR/EMEB NRC/NRR/EMEB NRC/NRR/PD5 PG&E

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ENCLOSURE 2 NRC PRESENTATION SHUm0%N ISSUE:

REACTOR HEAD VENT PATH Kenneth H. Bych Thomas G. De Uriarte John M. GiscIon NUCLEARTECHNICALSERVICES PACIFIC GAS AND ELECTRIC COMPANY Toby Burnett NUCLEAR AND ADVANCEDTECHNOLOGY DIVISION WESTINGHOUSE ELECTRIC CORPORATION September 23, 1992 40dQKHBJAIS

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IV

SCOPE OF PGRE EFFORTS ON SHUYDO%N ISSUES

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PARTICIPATED IN NUMARC SEGJmOWN ISSUES WORKING GROUP

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INDUSTRY LEADER IMPLEMENTINGNUiMARC 91-06 RECOMMENDATIONS

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LEAD PLAN'I'NDCOSPONSOR FOR EPRI OIUd8 PRO GRAIVI

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DEVELOPED FOKVGG PROCEDUI&S FOR MITIGATINGLOSS OF SAFETY FUNCTIONS AT DIABLOCAR'&ON

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CONTRACTED WESTINGHOUSE TO PERFORM HEAD VENT ANALYSIS 4056KHS.MIS

1 HEAD VENT ISSUE

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CAN IT PROVIDE A FLOWPATH FOR ALTERNATE DECAY HEAT REMOVAL?

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WILLIT LIMITPRESSURE IN RCS WITHOUT FAILINGNOZZLE DAMS AND SEAL TABLELOW PRESSURE SEALS?

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ARE NRC OBJECTIONS IN NUEEG-1449 VALID?

INADEQUATELIFI'/STICKING NON-UNIFORMLIFI'COCKING)

IMPACTLOAD DAMAGETO HEAD

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HOW DOES PRESSURIZER SURGE LINEFLOODING AFFECT IT?

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DOES IT COMPLEMENT G. L. 88-17 REQUIREMENTS FOR VENT WHEN USING HOT LEG DAMS?

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APPROACH

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PERFORM A THERMALEPH)RAULIC ANALYSIS OF THE HEAD SYSTEM TO FUNCTION AS A VENT UPON A LOSS OF RKR

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PERFORM A MECHAZGCALANALYSISOF THE HEAD AM)ASSOCIATED COMPONENTS TO.

ADDRESS THE ISSUES OF STICKING, COCKING, EXCESSIVE DRAG AND CYCLIC IMPACTING 405llKHBAIIS

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l.ower Value - Unit 2

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.160 Alignment Pin (4)

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.235 Support Skirt (unit 2)

VESSEL FLANGE AND ALIGN>lZNTP1N VENT GEOilXETRY Flow (Unit.2)

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'IIIERMAL-EPQ)RAULICANALYSIS CONCLUSIONS

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. WITHTHE REACTOR HEAD IN PLACE AND NUTS LOOSENED, VENT PATHS AT THE VESSEL FLANGE ARE ADEQUATEBY A WIDE IVRVtGINTO PERMIT GRAVITYFLOW FROM THE RWST AJQ) TO PROTECT LOW PRESSURE SEALS IN THE EVENT OF LOSS OF RHR AFTER REFUELING.

I IF COLD WATER IS BEING INJECTED WITH HOT WATER AT 200 F BEING SPILLED AT THE FLANGE, RCS PRESSURE AT THE FLANGE WOULD BE WITHINTHE &kNGE OF 0.1 TO 3 PSIG, AND THE HEAD WOULD LIFTAN ADDITIONAL0 TO 0.028 INCHES (DEPENDING ON THE UNIT, DECAYHEAT, 326) UNCERTAINTIESIN FRICTION, SPRING FORCE, AND LOSS COEFFICIENTS).

IF NO COLD WATER IS BEING ADDED AM)

WATER LEVEL (OR FROTH HEIGHT) IS BELOW THE FLANGE, RCS PRESSURE AT THE FLANGE WOULD BE WIT'HINTHE EV&lGE OF 2 TO 7 PSIG, AI'G) THE HEAD WOULDLIFI'NADDITIONAL0.004 TO 0.082 INCHES 406 IKhb.MIS

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~RIIDRAULICANALYSIS CONCLUSION (Cont'1) g~4N:

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BY INJECTING COLD WAT%<&AND SPILLINGHOT WATER FROM TERY FLANGE, 40 MW CAN BE REMOVED WHHOUTEXCEEDING 10 PSIG AT TEA'LANGE.

IF NO COLD WATER IS INJECTED AND WATER LEVEL (FROTH HEIGHT) IS BELOW TEM FLANGE AND ABOVE THE TOP OF TEM CORE, 7 MW OF DECAY HEAT WOULD CAUSE LESS THAN 10 PSIG AT XKE VESSEL FLANGE. BOTH VALUES ARE WELL ABOVE 5 MW ITIIEMAXIMIMDECAY HEATAFITRREFUELING).

IIAXIMIMTRANSIENT PRESSURE, IVITEBOILING CAUSING FROTH HEIGHT ABOVE 'IHE FLANGE, CANNOTEXCEED 12 PSIG FOR 5 MWDECAYHEAT.

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EXCESSIVE LIQUIDINJECTION WILLBE CONTROLLED TO PREVENT RCS PRESSUM~B IN EXCESS OF 12 PSIG WI'IHTEK'ESSEL FLANGE VI<22K AVAILABLE.

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THECAL-FHH)RAULICANALYSIS CONCLUSION (Cont'd)....

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BECAUSE THE FLANGE VENT AREA IS SAKVL UNTILPRESSURE INCREASES, VENTINGAT THE FLANGE IS NOT A FEASIBLE MEANS OF KEEPING RCS PRESSURE BELOW 2 PSIG FOLLOWINGLOSS OF tuXR WITHCOOLANT.BOILING. THEREFORE, IF COLD LEG OPENINGS EXIST, ANOTHER HOT LEG VENT PATH IS REQUIRED; I.E., A STEAM GENERATOR MANWAYOR DISASSEMBLED HOT LEG CHECK VALVES.

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MECEGWICALANALYSIS

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FLOW VENT GEOMETRY

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VESSEL HEAD STICKING, COCKING AND DRAG 4068KHB.MIS

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T/C COLUMNS SPRAY NOZZLES IN vESSEL "INLET" INTERFACE HEAD-VESSEL ALIGNMENT PINS "OUTLET" INTERFACE OUTSID:

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HEAD VENT FLOW NETWORK 40CI.Kv8

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THE VESSEL FLANGE/HEADVENT GEOMETRY IS BASICALLYDIVIDEDINTO TWO PARTS:

A MAJOR FLOW PATH THROUGH 'IHE VESSEL FLANGE REGION, AND IN PARALLEL A RELATIVELYSIVAL FLOW PATH THROUGH THE FIVE THERMOCOUPLE COLUMNS (THE HEAD VENT LINEIS NORMALLYCLOSED AFI'ER DETENSIONING).

PART OF THE VESSEL FLANGE FLOW PATH IS ALSO DIVIDEDINTO THREE PARALLEL BW&lCHES, THROUGH THE GAP AROUI'6) THE INTERNALSHOLD DOWN SPRING, AROUI'6) THE FOUR HEAD AND VESSEL ALIGNMENTPINS, AND THROUGH THE SIXTEEN UPPER PLENUM COOLING SPRAY NOZZLES.

THESE TIBIAEPATHS IN TUINALEXITTHROUGH A COMMON PATH PAST THE 0-RINGS AT THE FLANGE MATINGSURFACE, AM)OUT PAST THE 1.5 INCH VERTICALFLANGE COUNTERBORE RECESS.

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FLO% VENT GEOMETRY (Cont'd)...

THE TOTALTHERMOCOOTLE AHMMOMAREA IS ONLY2 0 IN ~ AT THE TOP CONDUIT SEAL THE TOTALSPRAY NOZZLE AREA IS ALSO A MINORFLOW PATH AT 3.3 IN.'.

IN COMPARISON, THE FOUR ALIGNMENTPINS PROVIDE 18.5 IN.~ FOR UNIT 1.

FROM THESE VARIOUS FLOW PATHS, A MH)RAULICNETWORK ANALYSISWAS PERFORMED TO GENERATE THE OVERALL FLOW CONDUCTANCE AS A FUNCTION OF FLANGE SEPAI44TION.

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Pressure vs. Flange Separation For Unit 1 BCC 6

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Flange Separation (inches)

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VESSEL HEAD STICKING

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ONLY VERTICALCONTACTS ARE THE ALIGN-MENT PINS

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NO MECHA26SMS EXISTS FOR THE COEFFICIENT OF FRICTION TO BE GREATER TFD&lONE OR FOR GENERATION OF A HIGH LATERALFRICTIONAL FORCE

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THERE HAS BEEN NO PREVIOUS WESTINGHOUSE EXPERIENCE OF STICKING/BINDINGAFTER STUD DETENSIONING 40bbKkBPAIS

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REACTOR HEAD COCKING

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CAN NOT OCCUR AS LONG AS HEAD REMAINS ON THE UPPER SUPPORT FLANGE AND UPPER INTERNALSREMAINENGAGED ON THE ALIGNMENTPINS o

ENGAGEMENT OF UPPER SUPPORT FLANGE ON THE VESSEL/INTERNALS ALIGNMENTPINS IS MAINTAINEDFOR 3.75 INCHES OF HEAD AND INTERNALSLIFl' VENTINGREQUIREMENT IS MUCH LESS

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SEPAtMTION OF THE HEAD FROM UPPER INTERNALS CAN OCCUR BETWEEN 0.7 INCH TO 1.0 INCH OF LIFI' NEED TO LIMITLIFI'OBELOW 0.7 INCH TO PREVENT SEPAI44TION Al'6) FULFILLVENTING FUNCTION

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COCKING CAN NOT OCCUR IN THE EXPECTED IVkNGE OF MOTIONPOST-REFUELING AS THE VENTLEFl'S MUCH LESS TED'.7 INCH.

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REACTOR HEADDRAG

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DRAG CAN OCCUR FROM TWO SUAN SOURCES:

FUEL ALIGMCENTPINS UPPER INTERNALS/VESSEL HEAD ALIGNMXKI'INS

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NO DRAG OR CONTACT CAN OCCUR AT:

GUIDE SXXJDS UPPER SUPPORT FLANGE UPPER CORE PLATE FLANGE DRAG FORCES:

SPRINGS FUEL ALIGNMENTPINS UPPER IN'HHZNALS ALIGNMENTPINS 20,000 LBF 8,000 LBF 2,000 LBF

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WEIGHT OF HEAD = 431,000 LBF

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DRAG FORCES HAVEONLYASMALLEFFECT ON HEAD LIFT

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STEADY STATE RESPONSE

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POST-REFUELING:

LIQUIDINJECTION

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AT 5 MW, 272 GPM OF 70 F WATER WILLLIMITEXITTEMPERATURE AT THE FLANGE OF 200 F.

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RESULTANT SEPARATION WOULD BE 0.07 INCHES {UPWAIU)TRAVEL, OF 0.014 INCHES);

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RESULTANT PRESSURE WOULD BE 3 PSIG.

NO INJECTION - STEAMING

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RESULTANT SEPAIMTION OF 0.14 INCHES.

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RCS PRESSURE WOULD BE 2-7 PSIG.

~ Q LBS/SEC. (EQUIVALENTOFg 1UfW)

QF STEAM CAN BE RELIEVEDAT 10 PSIG.

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STEADY STATE RESPONSE (Cont'd)...

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POST-REFUELING STABILITY

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ABOUT 1 PSI DELTA P REQUIRED TO CAUSE MOTIONINNEW DIRECTION IF RCS PRESSUIM INCI&ASES, TEXE HEAD WILL RISE TO A NEW EQUILIBRIUMPOINT AND STOP WIHHOUTOSCILLATION.

VESSEL HEADL~ LESS THAN 0.12 INCH FROM CORE DECAYHEAT.

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PRESSURE INCREASES CAUSED BY CORE DECAY HEAT ARE MUCHSl&VLER THANTHE NATU1UQ PERIOD OF 'IHE HEAD-SPRING SYSTEM.

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Alai'ERTURBATIONSWILLBE XVG'IDLYDAMPED OUT.

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CONCLUSIONS THE POSSIBILITY FOR THE VESSEL HEAD TO STICK BY ALLPRACTICALCONSIDERATIONS DOESN'T EXIST. THERE HAS BEEN NO PREVIOUS WESTINGHOUSE EXPERIENCE OF HEAD STICKING.

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AI'PZ CONCEIVABLEDRAG FORCE THAT CAN BE PRODUCED TO HINDER HEADLIFl'S SMALLIN COMPARISON TO THE HEAD/LIFI'INGRIG WEIGHT, AND DOES NOT POSE Al'PZ CONCERN FOR HEAD VENTING CAPABILITY;

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COCKING OF THE VESSEL HEAD CAI'RIOT OCCUR AS LONG AS THE FLANGE SEP&VLTIONIS LIMITEDTO BELOW 0.70 INCHES. TO ASSURE THAT SEP&D.TION ABOVE 0.70 INCHES CAt'&OT OCCUR, PG8rE CONTROLS THE FLUID PATH FROM THE RWST.

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