Information Notice 1996-36, Degradation of Cooling Water Systems Due to Icing

Degradation of Cooling Water Systems Due to Icing

ML031060039
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, 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, Three Mile Island, 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
Issue date:	06/12/1996
From:	Grimes B K Office of Nuclear Reactor Regulation
To:
References
IN-96-036, NUDOCS 9606070097
Download: ML031060039 (11)

"JUNITED STATESNUCLEAR REGULATORY COMMISSIONOFYFICE OF NUCLEAR REACTOR REGULATION-WASHINGTON, DC 20555-0001June 12, 1996NRC INFORMATION NOTICE 96-36: DEGRADATION OF COOLING WATER SYSTEMS DUE TOICING

Addressees

All holders of operating licenses or construction permits for nuclear powerreactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this informationnotice to alert addressees to potential degradation of facility water intakesystems (circulating, service, and fire water) due to icing conditions.It is expected that recipients will review the information for applicabilityto their facilities and consider actions, as appropriate, to avoid similarproblems. However, suggestions contained in this information notice are notNRC requirements; therefore, no specific action or written response isrequired.

Description of Circumstances

Wolf CreekBetween 1:45 a.m. and 2:45 a.m. (all times central standard time) onJanuary 30, 1996, operators at Wolf Creek received alarms indicating that thecirculating water system traveling screens were becoming blocked. A visualinspection showed that the traveling screens for bays 1 and 3 were frozen andthat water levels in these bays were approximately 2.5 m [8 ft] below normal.The emergency service water system was started with the intent to separatethis system from the service water system. However, the emergency servicewater system was incorrectly aligned; flow was directed to the service watersystem and warming flow to the emergency service water system suction bays wasrestricted. Operators also shifted to circulating water pump B. At approxi-mately 3:30 a.m., operators received a service water pressure alarm and anelectric fire pump started on low service water pressure. The shift super-visor then directed a manual reactor/turbine trip. Circulating water systembays were subsequently determined to be at 3.5 m [12 feet] below normal. Thelevel loss was caused by water from the spray wash system freezing and block-ing the traveling screens.The Train A emergency service water system pump was tripped and declaredinoperable at 7:47 a.m. because of low discharge pressure and high strainerdifferential pressure. At about 8:00 a.m., the supervising operator coming onshift noted the incorrect alignment of the emergency service water system andtook action to correct it. At about 5:45 p.m., the operators declared Train A'~P) C-FW 0f bla .pDR :t:-E moric6 6'sVOU 160612 '

1.'K)IN 96-36June 12, 1996 operable on the basis of an engineering evaluation and placed it in service.However, the pump was again stopped 1-1/2 hours later at approximately7:30 p.m. when the pump exhibited further oscillations in flow and pressure.At approximately 8:00 p.m., operators noted that emergency service watersystem Train B suction bay level was 4.5 m [15 ft] below normal and decreasingslowly. Operators placed additional heat loads on Train B and the suction baylevels subsequently recovered. At 10:14 p.m., the operators again startedTrain A emergency service water system and secured it at 10:27 p.m. due todecreasing flow and pressure.At about 10:00 a.m. on January 31, divers inspected the suction bay of Train Aand noted complete blockage of the trash racks by frazil ice. Train B was notinspected because the pump was running. The ice blockage was cleared by4:00 p.m. by sparging the trash racks with air. The emergency service watersystem was designed to have warming flow injected in front of trash racks toincrease bulk water temperature and prevent the formation of frazil ice. Dueto calculational errors by the architect-engineer and the as-built systemconfiguration, the emergency service water system warming flow wasinsufficient to prevent frazil ice from forming at the Train A trash racks.FitzPatrickOn February 25, 1993, at 1:25 a.m., the electric fire pump started on low fireheader pressure. After verifying normal fire header pressure, operatorssecured the electric fire pump, and the diesel fire pumps subsequently startedon low header pressure. It was later determined that the fire jockey pump hadlost suction because of the decreasing screenwell level.Over the next several minutes, operators noted an increase in circulatingwater system motor amperage (which is consistent with decreased suctionpressure). Reactor power was also reduced and one circulating water pump wassecured. At 1:40 a.m., an operator reported that the screenwell level wasapproximately 3 m [10 ft] below normal and the reactor was manually scrammed.After a second circulating water pump was subsequently secured, the screenwellwater level quickly recovered. The licensee concluded that the reducedscreenwell level had been caused by ice partially blocking the lake intakestructure. Either frazil ice formed around or in front of the heated intakebar racks, or slush ice was present in front of the bar racks.FermiOn February 5, 1996, at approximately 2:30 p.m., diesel generator servicewater pump C failed to develop normal discharge pressure, flow, and motorcurrent during a surveillance. This made Division I emergency dieselgenerator (EDG) 12 inoperable. After several unsuccessful attempts to startthe pump, an air purge of the pump column on the discharge of the pump wasinitiated in an attempt to clear any obstruction in the column or the pumpinlet. The licensee detected blockage when it tried to blow air through thepipe. At 8:21 p.m., the pump was started and after 3 to 5 seconds an erraticdischarge pressure was noted. In a short time, pump flow, discharge pressure,and motor amps were normal. The following day, on February 6, dieselgenerator service water pump B was started. The pump, which cools Division II

K> < IN 96-36June 12, 1996 EDG 13, showed no flow, no pressure, and low amperage for the first30 seconds. After approximately 90 seconds, normal flow discharge pressureand motor current were achieved. The remaining safety-related pumps weretested satisfactorily.The diesel generator service water pumps are all deep-draft pumps and takesuction from the ultimate heat sink reservoir which is a segregated pool. Thelicensee evaluation concluded that although the reservoir temperatures aremaintained above 5 eC [41 OF], part of the pump column and two of the linearguide bearings are located above the water level and are exposed to ambientair temperature conditions. The failure of the diesel generator service waterpump C was attributed to ice buildup around the shaft and spider bearing fromleakage past the discharge check valve and the cold weather. The licenseealso concluded that under some credible meteorological conditions, thefunctions of both divisions could have been affected.DiscussionFrazil icing is a phenomenon that affects the operation of intake structuresin regions that experience cold weather. The accumulation of frazil ice onintake trash racks can completely block the flow of water into the intake.The process starts when the water flowing into the intake is supercooled (acondition where the water is below the freezing point). The supercooling maybe very small, on the order of a few hundredths of a degree.The supercooling occurs with a loss of heat from a large surface area such asa lake with open water and clear nights. High winds contribute to the problemby providing mixing of the supercooled water to depths as great as 6 to 9 m[20 to 30 ft]. The frazil ice, which is composed of very small crystals(1-15 mm) with little buoyancy because of their size, is carried along in thewater and mixed all through the supercooled water.The suction of the supercooled water and the suspended frazil ice crystalsthrough an intake structure brings the frazil ice crystals in contact with thetrash rack bars. Frazil ice crystals easily adhere to any object with whichthey collide. The ice collects first on the upstream side of the trash racks,then steadily grows until the space between the trash racks is bridged. Thisbridging rapidly blocks the trash racks. The accumulation of ice can with-stand high differential pressures; effectively damming the intake suction.Facility vulnerability to icing events is a function of plant design. Fraziland other ice formation is dependent on specific environmental conditions andrepresents a potential common-mode failure that can cause the loss or degrada-tion of multiple cooling water systems, including the potential loss of theultimate heat sink.

IN 96-36June 12, 1996 Related InformationNUREG/CR-0548, "Ice Blockage of Water Intakes."This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation project manager.Ii -..--.....-.Brian K. Grimes, Acting DirectorDivision of Reactor Program ManagementOffice of Nuclear Reactor RegulationTechnical Contacts:John R. Tappert, NRR(301) 415-1167Internet:jrtlnrc.govBruce Jorgensen, RIII(708) 829-9615Internet:blj@nrc.govAttachment:List of Recently Issued NRC Information NoticesIk W (0%0%J4-c- -dI

K>AttachmentIN 96-36June 12, 1996 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to96-35Failure of Safety Systemson Self-Shielded Irradia-tors Because of InadequateMaintenance and TrainingHydrogen Gas Ignitionduring Closure Weldingof a VSC-24 Multi-AssemblySealed Basket06/11/9605/31/96All U.S. Nuclear RegulatoryCommission irradiatorlicensees and vendorsAll holders of OLs or CPsfor nuclear power reactors96-3496-33ErroneousDefectiveResults iiData FromThermocouplei a Fire05/24/96All material and fuel cyclelicensees that monitor tem-perature with thermocouples96-3296-3196-30Implementation of 10 CFR50.55a(g)(6)(ii)(A),"Augmented Examinationof Reactor Vessel"Cross-Tied Safety Injec-tion AccumulatorsInaccuracy of DiagnosticEquipment for Motor-Operated Butterfly ValvesRequirements in 10 CFRPart 21 for Reporting andEvaluating Software ErrorsSuggested Guidance Relatingto Development and Imple-mentation of CorrectiveActionPotential Clogging of HighPressure Safety InjectionThrottle Valves DuringRecirculation06/05/9605/22/9605/21/9605/20/9605/01/9605/01/96All holders of OLs or CPsfor nuclear power reactorsAll holders of OLs or CPsfor pressurized waterreactorsAll holders of OLs or CPsfor nuclear power reactorsAll holders of OLs or CPsfor nuclear power reactorsAll material and fuel cyclelicenseesAll holders of OLs or CPsfor pressurized waterreactors96-2996-2896-27OL -Operating LicenseCP = Construction Permit

.IIN 96-36June 12, 1996 IN 96-XXJune XX, 1996 Related informationNUREG/CR-0548, *Ice Blockage of Water Intakes"This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation project manager.Brian K. Grimes, Acting DirectorDivision of Reactor Program ManagementOffice of Nuclear Reactor RegulationTechnical Contacts:John R. Tappert, NRR(301) 415-1167Internet:Jrt@nrc.govBruce Jorgensen, RIII(708) 829-9615Internet:bl Jnrc.govAttachment:List of Recently Issued NRC Information NoticesDOCUMENT NAME:G:\JRT\WOLFICE.INTech Editor reviewed 5/1/96To receive a copy of this document, indicate in the box: ACTattachment/enclosure 'El -Copy with attachment/enclosure* see orevious concurrences-Copy withoutON" -No copyOFFICE

CONTACT

S C C/SRXB:DSSA I C/PECB:DRPM I D/DRPMNAME JTappert

• LMarsh

• AChaffeer,(, IBGrimesBJorgensen *DATE 5 /2/96 5/14/96 6 _ _ _6/ _/96UrIU-lAL KLLUKU WO/WY-,*-)

-IN 96 dMay XX, 1995 IN 96-XXMay XX, 1995 This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation project manager.Brian K. Grimes, Acting DirectorDivision of Reactor Program ManagementOffice of Nuclear Reactor RegulationTechnical Contacts:John R. Tappert, NRR(301) 415-1167Internet:jrt~nrc.govBruce Jorgensen, RIII(708) 829-9615Internet:bl Jnrc.govAttachment:List of Recently Issued NRC Information NoticesDOCUMENT NAME:G:\JRT\WOLFICE.INTech Editor reviewed 5/1/96To receive a copy of this document, Indicate in the box: "C'attachment/enclosure HEN -Copy with attachment/enclosure* see nrevinus concurrences-Copy withoutON" -No copy--r-V. ---*OFFICE

CONTACT

S IC C/SRXB:DSSA [_ C/PECB:DRPM I D/DRPMNAME JTappert

• LMarsh

• AChaffee BGrimesBJorgensen *DATE 5 12/96 5/14/96 5 / /96 5 / /96.- -----------. bOFFICIAL KLLRCD COPY so§S

IN 96-XXMay XX, 1995 This information notice requires no specific action or writtenyou have any questions about the information In this notice, plone of the technical contacts listed below or the appropriate 0Nuclear Reactor Regulation project manager..actofTechnical Contacts:John R. Tappert,(301) 415-1167Internet :Jrt~nrcBrian K. Grimes Acting DirectorDivision of Resctor Program ManagementOffice of Nu ear Reactor RegulationNRR uce Jorgensen, RGN III(708) 829-9615:.gov Internet:blj@nrc.govNRC I iormation NoticesAttachment:List of Recently IssuedDOCUMENT NAME:G:\JRT\WO 4ICE.INTech Editor reviewed /1/96To receive a copy p this documiattachment/enclosyre "E -Coiseep nrpvinu!ent, indicate in the box: IC'py with attachment/enclosureI concurrences= Copy withoutON, -No copyOFFICE CONTSCTS IC C/SRXB:DSSA _ C/PECB:DRPM l/DRPMNAME JT pert

• LMarsh

• AChaffee BGrimesAB4rgensen *DATE /2/96 5/14/96 5 / /96 5 / /967 ArTTA I £'LFIL rIILvrv -'WI I AULOISI.WWI 5 JP4\

IN 96-XXMay XX, 1995