Information Notice 1997-27, Effect of Incorrect Strainer Pressure Drop on Available Net Positive Suction Head

Effect of Incorrect Strainer Pressure Drop on Available Net Positive Suction Head

ML031060005
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Crane
Issue date:	05/16/1997
From:	Slosson M M Office of Nuclear Reactor Regulation
To:
References
IN-97-027, NUDOCS 9705150337
Download: ML031060005 (8)

May 16, 1997

NRC INFORMATION NOTICE 97-27: EFFECT OF INCORRECT STRAINER PRESSUREDROP ON AVAILABLE NET POSITIVE SUCTIONHEAD

Addressees

All holders of operating licenses or construction permits for light-water power reactors, exceptthose licensees who have permanently ceased operations and have certified that fuel hasbeen permanently removed from the reactor vessel.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alertaddressees that two licensees of boiling-water reactors (BWR) have recently identifiedinaccurate assumptions in licensing-basis calculations for net positive suction head (NPSH).One of the licensees has decided to immediately shut down the reactor to replace suctionstrainers in the emergency core cooling system (ECCS) before the next refueling outage. Itis expected that recipients will review the information for applicability to their facilities andconsider actions, as appropriate, to detect or avoid similar problems. However, suggestionscontained in this information notice are not NRC requirements; therefore, no specific action orwritten response is required.

Description of Circumstances

MonticelloOn April 15, 1997, Northem States Power, the licensee for the Monticello Nuclear PowerPlant, notified the NRC staff that the NPSH available to the core spray pumps may not meetthe required NPSH under all accident conditions. During a review of the ECCS pump NPSHrequirements, the licensee calculated a new higher head loss, approximately 3.6 meters(11.7 feet) per 630 Us (10,000 gpm) rather than 0.3 meter (1 foot) per 630 Us (10,000 gpm),for clean ECCS suction strainers. The specific scenario of concern involved a failure of thelow-pressure coolant-injection loop select logic to select the intact reactor recirculation loop.As a result, the licensee determined that the core spray pumps may not have adequateNPSH available during the first 10 minutes following a design-basis loss-of-coolant accident(LOCA).4or/& qq.0.~ qqo~r/(\C4;PDA OtOI7p; ,9 0 E 5 K>-IN 97-27May 16, 1997 Dresden Units 2 and 3On December 20, 1996, Commonwealth Edison, the licensee for the Dresden Nuclear PowerStation Units 2 and 3, notified the NRC staff that the ECCS may be susceptible to NPSHproblems since the suction strainer design was based on an incorrect head loss value. Whileconducting a plant-specific analysis in support of its response to NRC Bulletin 96-03, thelicensee discovered that the new value for the head loss across clean suction strainers was1.8 meters (5.8 feet) per 630 Us (10,000 gpm) versus 0.3 meter (1 foot) per 630 Us(10,000 gpm) as described in the Updated Final Safety Analysis Report. With the calculatedhead loss, no credit taken for containment overpressure, and the accident conditionsdescribed above, the licensee determined that the ECCS may fail to operate as intended.DiscussionDuring its review of the Monticello operability evaluation, the NRC staff questioned whetherthe licensee would be able to reflood the reactor core following a LOCA and preventexceeding the 1204 OC (2200 'F) peak cladding temperature limit as required by 10 CFR50.46. Monticello has large quantities of fibrous insulation in its drywell. The MonticelloECCS suction strainers have a very small surface area and very high approach velocities.Even a small quantity of insulation reaching the suction strainers, which are located in thetorus, can cause sufficient head losses across the strainer to cause a loss of NPSH. Thisscenario is outside the original licensing basis of the plant, but it could occur, given thecurrent knowledge available.On May 9, 1997, the licensee for Monticello decided to shut down the reactor and replace theECCS suction strainers. The existing strainer on each of the four suction lines is a truncatedcone design about 43 cm (17 inches) in diameter and 25 cm (10 inches) long. Each strainerwill be replaced with two larger strainers, each of which is about 102 cm (40 inches) indiameter and 213 cm (84 inches) long. The plant will remain shut down until the strainerscan be procured and installed, currently estimated to be 3 to 4 months.The Dresden units have large quantities of reflective metallic insulation (RMI) in their drywell.The Dresden Units 2 and 3 strainers are also very small with very high approach velocities.However, the head loss associated with debris beds composed mostly of RMI is typically lesssevere than head loss associated with debris beds composed of fibrous materials. Theexisting strainers are being replaced with larger strainers at Dresden Unit 3 during the currentrefueling outage and the licensee plans to replace them at Unit 2 during the next outage. Asan interim corrective action the licensee submitted on January 13, 1997, an emergencytechnical specification amendment requesting that the staff evaluate an Unreviewed SafetyQuestion (USQ) associated with the operation of Dresden Units 2 and 3 with the existingstrainers. The licensee's submittal sought staff approval of operation of both units with theincreased head loss across the clean ECCS strainers; revised Technical Specifications (TS)values for a lower allowable water temperature in the suppression chamber and the ultimateheat sink; and a revised TS bases that states credit was taken for 13.8 kilopascals (2 psig) ofcontainment pressure (this compensates for a slight increase in the amount of NPSHdeficiency during the first 10 minutes following a LOCA). The NRC staff issued theamendments on January 28, 199 ti,/IN 97-27May 16, 1997 The staff notes that continued operation by BWR licensees during the development of theresolution of the BWR ECCS strainer clogging issue is based on the premise that licenseeswill be able to reflood the reactor core immediately following a design-basis LOCA. Inresponse to NRC Bulletin 93-02, Supplement 1, BWR licensees implemented interimmeasures to ensure that they could mitigate a design-basis LOCA should the ECCS strainersclog. The acceptability of the licensees' interim measures depended upon (1) adequate timefor operators to respond to clogged strainers to align alternate water sources (both safety-related and nonsafety-related sources), (2) emergency operating procedures (EOPs) whichprovide adequate guidance on mitigating a strainer clogging event, (3) operator training tomitigate a strainer clogging event, (4) recent cleaning of suppression pools, and (5) theremoval of loose and temporary fibrous materials stored in the containment.This information notice requires no specific action or written response. If you have anyquestions about the information in this notice, please contact one of the technical contactslisted below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager./`Marylee M. Slosson, Acting DirectorDivision of Reactor Program ManagementOffice of Nuclear Reactor RegulationTechnical contacts: Robert Elliott, NRR301-415-1397E-mail: rbe@nrc.govKerri Kavanagh, NRR301-415-3743E-mail: kak~nrc.gov

Attachment:

List of Recently Issued NRC Information NoticesV37i1

i TI>AttachmentIN 97-27May 16,'1997 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to97-26Degradation in Small-Radius U-Bend Regionsof Steam Generator Tubes05/19/97All holders of OLs or CPsfor pressurized-waterreactors87-10,Sup. 1Potential for WaterHammer During Restart ofResidual Heat RemovalPumps05/15/97All holders of OLs or CPsfor boiling-water reactors97-2597-24Dynamic Range Uncertain-ties in the Reactor VesselLevel InstrumentationFailure of Packing Nutson One-Inch UraniumHexafluoride CylinderValves05/09/9705/08/97All holders of OLs or CPsfor Westinghouse pressurized-water reactorsAll U.S. Nuclear RegulatoryCommission licensees andcertificatees authorizedto handle uranium hexa-fluoride in 30- and 48-inchdiameter cylinders97-23Evaluation and Reportingof Fires and UnplannedChemical Reactor Eventsat Fuel Cycle Facilities05/07/97All fuel cycle conversion,enrichment, and fabricationfacilities97-2297-21Failure of Welded-SteelMoment-Resisting FramesDuring the NorthridgeEarthquakeAvailability of AlternateAC Power Source Designedfor Station Blackout Event04/25/9704/18/97All holders of OLs orCPs for nuclear powerreactorsAll holders of OLsfor nuclear powerreactorsOL = Operating LicenseCP = Construction Permit IN 97-27May 16, 1997 The staff notes that continued operation by BWR licensees during the development of theresolution of the BWR ECCS strainer clogging issue is based on the premise that licenseeswill be able to reflood the reactor core immediately following a design-basis LOCA. Inresponse to NRC Bulletin 93-02, Supplement 1, BWR licensees implemented interimmeasures to ensure that they could mitigate a design-basis LOCA should the ECCS strainersclog. The acceptability of the licensees' interim measures depended upon (1) adequate timefor operators to respond to clogged strainers to align alternate water sources (both safety-related and nonsafety-related sources), (2) emergency operating procedures (EOPs) whichprovide adequate guidance on mitigating a strainer dogging event, (3) operator training tomitigate a strainer clogging event, (4) recent cdeaning of suppression pools, and (5) theremoval of loose and temporary fibrous materials stored in the containment.This information notice requires no specific action or written response. If you have anyquestions about the information in this notice, please contact one of the technical contactslisted below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.original signed by S.H. Weiss forMarylee M. Slosson, Acting DirectorDivision of Reactor Program ManagementOffice of Nuclear Reactor RegulationTechnical contacts: Robert Elliott, NRR301-415-1397E-mail: rbeenrc.govKerri Kavanagh, NRR301-415-3743E-mail: kak@nrc.gov

Attachment:

List of Recently Issued NRC Information NoticesTech Editor reviewed and concurred on 05/14197*SEE PREVIOUS CONCURRENCEDOCUMENT NAME: G:\TJC\MONTICEL.IN1To recelve a copy of this document, Indicate In the box: AC" a Copy without enclosures "E" Copy with enclosures N _ No copyOFFICE TECH I C:PECB* AD: DRPM I

CONTACT

S* E ¶ l 1 1NAME JCarter 5/14/97 AChaffee MSlosspqRElliott 5/14/97._ _ KKavanagh 5/14/97 _ {V u__DATE 05/14/97 05/15/97 05/_5 l97OFFICIAL RECORD COPY

-YIN 97-xxMay xx, 1997 measures to ensure that they could mitigate a design-basis LOCA should the ECCS strainersclog. The acceptability of the licensees' interim measures depended upon (1) adequate timefor-operators to respond to clogged strainers to align alternate water sources (both safety-related and nonsafety-related sources), (2) emergency operating procedures (EOPs) whichprovide adequate guidance on mitigating a strainer clogging event, (3) operator training tomitigate a strainer clogging event, (4) recent cleaning of suppression pools, and (5) theremoval of loose and temporary fibrous materials stored in the containment.This information notice requires no specific action or written response. If you have anyquestions about the information in this notice, please contact one of the technical contactslisted below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.Marylee M. Slosson, Acting DirectorDivision of Reactor Program ManagementOffice of Nuclear Reactor RegulationTechnical contacts:Robert Elliott, NRR301-415-1397E-mail: rbe@nrc.govKerri Kavanagh, NRR301-415-3743E-mail: kak@nrc.gov

Attachment:

List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEDOCUMENT NAME: G:%TJCUWONTICEL.lN1To receive a copy of hius document indicate In the box: "C" a Copy without enclosuresE- Copy with enclosures "N -No copyOFFICE TECHC:SCSB* C:SRXB* C:PECB D:(A)DRPM

CONTACT

S* lNAME JCarter 5/14/97 CBerlinger JLyons AChaffee MS1oRElliott 5/14/97KKavanagh 5/14/97 ___IJDATE 05/14/97 05/14/97 05/14/97 05/1(197 1051y197~~.,fl ncT Aron~nrn l l IWUILAL KtLUKU LUOT44%U -tWi7 IN 97-xxMay xx, 1997 clog. The acceptability of the licensees' interim measures depended upon (1) adequate timefor operators to respond to clogged strainers to align alternate water sources (both safety-related and non-safety-related sources), (2) emergency operating procedures (EOPs) whichprovide adequate guidance on mitigating a strainer clogging event, (3) operator training tomitigate a strainer clogging event, (4) recent cleaning of suppression pools, and (5) theremoval of loose and temporary fibrous materials stored in the containment.This information notice requires no specific action or written response. If you have anyquestions about the information in this notice, please contact one of the technical contactslisted below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.Marylee M. Slosson, Acting DirectorDivision of Reactor Program ManagementOffice of Nuclear Reactor RegulationTechnical contacts:Robert Elliott, NRR301-415-1397E-mail: rbe@nrc.govKerri Kavanagh, NRR301-415-3743E-mail: kak@nrc.gov

Attachment:

List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEDOCUMENT NAME: G:ITJCWMONTICEL.lN1Tn rmehro a etmv of this docwnent. Indicate In the box: wC" w Copy without enclosures"EF U Copy with enclosures "N" w No copyOFFICE ITECH C: I C: SRXB* IC:PECB ID:(A) DRPM

CONTACT

S* I l I l IlNAME JCarter 5/14/97 CBerlinger JLyons AChaffee MSlossonRElliott 5/14/97KKavanagh 5/14/97 .-DATE 05/14/97 05/14/97 05/14/97 05/ /97 05/ /97OFFICIAL RECORD COPY IC%/

IN 97-xxMay xx, 1997 This information notice requires no specific action or written response. If you h anyquestions about the information in this notice, please contact one of the tech Ical contactslisted below or the appropriate Office of Nuclear Reactor Regulation (NR project manager.Marylee M. Slosson cting DirectorDivision of React Program ManagementOffice of NueI Reactor RegulationTechnical contacts: Robert Elliott, NRR K Kavanagh, NRR301-415-1397 153743E-mail: rbe@nrc.gov E-mail: kak@nrc.gov

Attachment:

List of Recently Issued NRC Inf mation NoticesDOCUMENT NAME: G:ITJC\MONTl L.IN1To receive a copy of this document, Indicate the box: "C" u Copy without enclosures "E" -Copy wfth enclosures W' m No copyOFFICE TECH l : -SCSB l C: SUB l .C: PECB l D: (A) DRPMlCONIDCTS I I I I INAME Rl /.a9 er Jy i "aAChaffee MSlossonDATE 05/iy/97 / 05//4/97 M 05/97 105/ /97 05/ /97EFCIAL RECORD COPY