Information Notice 1996-41, Effects of a Decrease in Feedwater Temperature on Nuclear Instrumentation

Effects of a Decrease in Feedwater Temperature on Nuclear Instrumentation

ML031060009
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, 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:	07/26/1996
From:	Grimes B K Office of Nuclear Reactor Regulation
To:
References
IN-96-041, NUDOCS 9607220160
Download: ML031060009 (10)

K) K) July 26, 1996NRC INFORMATION NOTICE 96-41: EFFECTS OF A DECREASE IN FEEDWATER TEMPERATUREON NUCLEAR INSTRUMENTATION

Addressees

All holders of operating licenses or construction permits for pressurizedwater reactors (PWRs).

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this informationnotice to alert addressees to the potential for operation above licensed poweras a result of a decrease in feedwater temperature event affecting nuclearinstrumentation. It is expected that recipients will review the informationfor applicability to their facilities and consider actions, as appropriate, toavoid similar problems. However, suggestions contained in this informationnotice are not NRC requirements; therefore, no specific action or writtenresponse is required.

Description of Circumstances

On February 14, 1996, the licensee for the Comanche Peak Steam ElectricStation was operating Unit 2 at 95 percent rated thermal power near end-of-core life when a significant reduction in feedwater temperature occurredbecause of the loss of feedwater heaters. This reduction, in turn, caused areduction in the reactor coolant system cold-leg temperatures. The colderreactor coolant temperature, with a large negative moderator temperaturecoefficient, caused reactor power to increase to approximately 102 percentaccording to ex-core nuclear instrumentation. The nitrogen-16 (N-16)detection system reached the overpower turbine runback setpoint (109 percent)and initiated a turbine runback. The N-16 detection system measures N-16activity in the primary coolant as a measure of the total power generation.This system is a substitute for the resistance temperature detector over-temperature and over-power reactor trip functions used at other WestinghousePWRs. The plant stabil zed at an indicated power of approximately 97 percentaccording to the ex-core nuclear instrumentation.After approximately 90 minutes, a second similar turbine runback occurredwhile restoring balance-of-plant equipment. Following this runback, reactorpower was stabilized at approximately 100 percent according to nuclearinstrumentation. During the next 30 minutes, the reactor was operated atapproximately 100 percent power as indicated by nuclear instrumentation, withreactor coolant temperatures below normal. The licensee noted that the N-169607220l60ujo i 7 9,oi4(R ~IE ctG IN 96-41July 26, 1996 detection system indicated approximately 106 percent power and the computer-based plant calorimetric system indicated approximately 102 percent power.Subsequently, the reactor power was reduced to less than 100 percent by allindications.DiscussionThere are three aspects of this event which have generic implications. First,with a loss of secondary plant efficiency, programmed T e can no longerreliably represent core thermal power. Second, the venturi-based input intothe computer-based calorimetric system may not be accurate with coldfeedwater. And third, the final safety analysis report had not analyzed thistransient accurately.Following the second runback, operators noted that reactor power indicated<100 percent according to nuclear instrumentation. Although the operatorsknew that cold feedwater could cause an increase in the amount of neutronattenuation, they believed that the nuclear instrumentation indicatedconservatively (i.e., higher than actual) because they were maintaining TA"eapproximately 1.7 eC [3 OF] above TRef. The licensee could not use thecomputer-based calorimetric until some time after the second turbine runbackdue to maintenance activities. Te , based on the main turbine impulsepressure, is programmed as a functlon of turbine load and, for normalefficiency, is a good representation of thermal power. When the unit lost thefeedwater heaters, the plant efficiency decreased. Because the main turbineelectro-hydraulic control system maintained generator output, core thermalpower increased to account for the loss of efficiency, and thus, TRef nolonger accurately represented the core thermal power.The cold-leg temperature is a more appropriate indicator of the accuracy ofthe nuclear instrumentation than programmed TY.e. As the cold-leg temperaturedecreased, the amount of neutron attenuation in the downcomer area surroundingthe core increased and hence affected the amount of neutrons reaching thedetectors. The licensee analysis showed that for every 0.6 C (1 OF] of cold-leg temperature change, the nuclear instrumentation was affected by 0.6 to 0.8percent power. A review of the second transient showed that the cold-legtemperature was approximately 2.5 °C [4.5 OF] lower than when the detectorswere last calibrated. This corresponded to a 3 to 4 percent error, whichcorresponded to the difference in the actual versus the indicated power (104percent actual versus 100 percent indicated).During the review, the licensee noted that the computer-based calorimetric was4 percent lower than the actual thermal power (N-16 power monitor). Thecalorimetric was based on feedwater flow measured by venturis. Although thecalorimetric calculation used feedwater temperature as an input, temperaturessignificantly different than the normal 227 OC [440 OF] introduced errors intothe calculation.Finally, the actual events involved temperature and power levels that exceededthose in the analysis of the Decrease in Feedwater Temperature" eventpresented in Chapter 15 of the licensee final safety analysis report. In that IN 96-41July 26, 1996 analysis, the inadvertent opening of the low-pressure heater bypass valve,coupled with the trip of the heater drain pumps, resulted in a feedwatertemperature drop of less than 19 'C (35 OF], and a corresponding powerincrease of less than 10 percent. In the actual event, the feedwatertemperature dropped by approximately 111 °C (200 OF], and the licenseecalculated that reactor power would have increased by approximately 35 percentwithout operator or protective actions. The licensee determined that althoughthe initiating events were the same, the Chapter 15 analysis did not accountfor the loss of extraction steam to the high-pressure heaters, which was thecause of the temperature difference. During the event, a level imbalanceoccurred between the two heater drain tanks, which resulted in the isolationof extraction steam.The NRC staff review of analyses of feedwater temperature events at similarfacilities revealed that most of these analyses assumed similar initiatingevents as the Comanche Peak analysis and had similar conclusions concerningthe amount of feedwater temperature drop. The licensee has reanalyzed theevent to include a 119 OC [246 OF] feedwater temperature drop and concludedthat all accident analysis parameters remained within requirements.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: Harry A. Freeman, RIV(817) 897-1500E-mail: haf~nrc.govChu-Yu Liang, NRR(301) 415-2878E-mail: cylenrc.gov

Attachment:

List Of Recently Issued HRC Information NoticesA1h4 Stir A Je6tQ K> KJAttachmentIN 96-41July 26, 1996 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to96-4096-09,Supp. 196-3996-38Deficiencies in MaterialDedication and Procure-ment Practices and inAudits of VendorsDamage in Foreign SteamGenerator InternalsEstimates of Decay HeatUsing ANS 5.1 Decay HeatStandard May Vary Signi-ficantlyResults of Steam GeneratorTube ExaminationsInaccurate Reactor WaterLevel Indication and Inad-vertent Draindown DuringShutdownDegradation of CoolingWater Systems Due to IcingFailure of Safety Systemson Self-Shielded Irradia-tors Because of InadequateMaintenance and TrainingHydrogen Gas Ignitionduring Closure Weldingof a VSC-24 Multi-AssemblySealed Basket07/25/9607/10/9607/05/9606/21/9606/18/9606/12/9606/11/9605/31/96All 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 pressurized waterreactorsAll pressurized waterreactor facilities holdingan operating license or aconstruction permitAll holders of OLs or CPsfor nuclear power reactorsAll U.S. Nuclear RegulatoryCommission irradiatorlicensees and vendorsAll holders of OLs or CPsfor nuclear power reactors96-3796-3696-3596-34OL -Operating LicenseCP -Construction Permit

• ~ -K> KIN 96-41July 26, 1996 analysis, the inadvertent opening of the low-pressure heater bypass valve,coupled with the trip of the heater drain pumps, resulted in a feedwatertemperature drop of less than 19 *C [35 OF], and a corresponding powerincrease of less than 10 percent. In the actual event, the feedwatertemperature dropped by approximately 111 *C [200 OF], and the licenseecalculated that reactor power would have increased by approximately 35 percentwithout operator or protective actions. The licensee determined that althoughthe initiating events were the same, the Chapter 15 analysis did not accountfor the loss of extraction steam to the high-pressure heaters, which was thecause of the temperature difference. During the event, a level imbalanceoccurred between the two heater drain tanks, which resulted in the isolationof extraction steam.The NRC staff review of analyses of feedwater temperature events at similarfacilities revealed that most of these analyses assumed similar initiatingevents as the Comanche Peak analysis and had similar conclusions concerningthe amount of feedwater temperature drop. The licensee has reanalyzed theevent to include a 119 *C [246 OF] feedwater temperature drop and concludedthat all accident analysis parameters remained within requirements.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.Original signed by Brian K. GrimesBrian K. Grimes, Acting DirectorDivision of Reactor Program ManagementOffice of Nuclear Reactor RegulationTechnical contacts: Harry A. Freeman, RIV(817) 897-1500E-mail: haf@nrc.govChu-Yu Liang, NRR(301) 415-2878E-mail: cyl~nrc.gov

Attachment:

List of Recently Issued NRC Information NoticesDOCUMENT NAME: G:\SSK2\INFONOT.C PTo receive a copy of this docunent, tndicate in the box CO~opy So attachment/enclosure EsCopy with attachment/enctosure N

• NocopsOFFICE C BC:SRXB I BC:LPECB lI (A) DW M iNAME CYLiang* RJones* AChaffee*HAFreeman* ____ _DATE 16/ 3/96 16/21/96 17/08/96 17LI/96 IOFFILIAL MLLUM LWUF* See previous concurrence Tech Editor reviewed & concurred on 05/28/96

~1~1 -,K)IN 96-XXJuly XX, 1996 for the loss of extraction steam to ticause of the temperature difference.occurred between the two heater drainof extraction steam.he high-pressure heaters, which was theDuring the event, a level imbalancetanks, which resulted in the isolationThe NRC staff review of analyses of feedwater temperature events at similarfacilities revealed that most of these analyses assumed similar initiatingevents as the Comanche Peak analysis and had similar conclusions concerningthe amount of feedwater temperature drop. The licensee has reanalyzed theevent to include a 119 'C [246 'F] feedwater temperature drop and concludedthat all accident analysis parameters remained within requirements.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:Harry A. Freeman, RIV(817) 897-1500E-mail: haf~nrc.govChu-Yu Liang, NRR(301) 415-2878E-mail: cyl~nrc.gov

Attachment:

List of Recently Issued NRC Information NoticesDOCUMENT NAME: G:\SSK2\INFONOT.C PTo receive a copy of this document, indicate in the box CzAopy w/o attachment/enclosure E-Copy with attachment/enclosure N

• NoOFFICE l kd BC: SRXB BC:PECB )D:DRNAME CYLiang* RJones* AChaffee* BGrimesHAFreeman*DATE 6/ 3/96 6/21/96 7/08/96 7/ /96OFFICIAL RECORD COPY*See previous concurrence IN 96-XXJuly XX, 1996 for the loss of extraction steam to the high-pressure heaters, which was thecause of the temperature difference. During the event, a level imbalanceoccurred between the two heater drain tanks, which resulted in the isolationof extraction steam.The NRC staff review of analyses of feedwater temperature events at similarfacilities revealed that most of these analyses assumed similar initiatingevents as the licensee analysis and had similar conclusions concerning theamount of feedwater temperature drop. The licensee has reanalyzed the eventpursuant to Section 50.59 of Title 10 of the Code of Federal Regulations toinclude a 119 'c [246 OF] feedwater temperature drop and concluded that allaccident analysis parameters remained within requirements.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: Harry A. Freeman, RIV(817) 897-1500E-mail: haftnrc.govChu-Yu Liang, NRR(301) 415-2878E-mail: cyl~nrc.gov

Attachment:

List of Recently Issued NRC Information NoticesDOCUMENT NAME: G:\SSK2\INFONOT.C PTo receive a copy of this document, indicate in the box C-Topy u/o attachment/enclosure E=Copy with attachment/enclosure N NocopyOFFICE CONT:i kd l BC:SRXBLl BC:iPECB lI (A)iD:iDRPM I _NAME CYLiang* RJones* AChaffee* BGrimesl _ HAFreeman*DATE 6/ 3/96 6/21/96 7/08/96 7/ /96* See previous concurrenceOFFICIAL KLLUKV UV X!

IN 96-XXJuly XX, 1996 for the loss of extraction steam to the high-pressure heaters, which was thecause of the temperature difference. During the event, a level imbalanceoccurred between the two heater drain tanks, which resulted in the isolationof extraction steam.The NRC staff review of analyses of feedwater temperature events at similarfacilities revealed that most of these analyses assumed similar initiatingevents as the licensee analysis and had similar conclusions concerning theamount of feedwater temperature drop. The licensee has reanalyzed the eventpursuant to Section 50.59 of Title 10 of the Code of Federal Regulations toinclude a 119 *C [246 *F] feedwater temperature drop and concluded that allaccident analysis parameters remained within requirements.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: Harry A. Freeman, RIV(817) 897-1500Internet:haf@nrc.govChu-Yu Liang, NRR(301) 415-2878Internet:cyl nrc.gov

Attachment:

List of Recently Issued NRC Information NoticesDOCUMENT NAME: G:\SSK2\INFONOT.C PTo receive a copy of this document, Indicate in the box Conopy w/c attachment/enclosure EnCopy with attachment/enclosure N

• NoOFFICE CONT: Ekd BC: SLB BC:PECB (A)D:DRPMNAME CYLiang* RJones* ACh)f BGrimesl ~~HAFreeman*tVtDATE 6/ 3/96 6/21/96 7/7/96 7/ /96OFFICIAL RECOR COPY* See previous concurrence K-, /IN 96-XXJune XX, 1996 for the loss of extraction steam to ticause of the temperature difference.occurred between the two heater drainof extraction steam.he high-pressure heaters, which was theDuring the event, a level imbalancetanks, which resulted in the isolationThe NRC staff's review of analyses of feedwater temperature events at similarfacilities revealed that most of these analyses assumed similar initiatingevents as the licensee's analysis and had similar conclusions concerning theamount of feedwater temperature drop. The licensee has reanalyzed the eventpursuant to Section 50.59 of Title 10 of the Code of Federal Regulations toinclude a 119 'C [246 OF] feedwater temperature drop and concluded that allaccident analysis parameters remained within requirements.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:Harry A. Freeman, RIV(817) 897-1500Internet:haffnrc.govChu-Yu Liang, NRR(301) 415-2878Internet:cyl@nrc.gov

Attachment:

List of Recently Issued NRC Information NoticesDOCUMENT NAME: G:\SSK2\INFONOT.CPTo receive a copy of this document, indicate in the box Ciropy w/dattachmeft1/enctosure EnCOFFICE CONT:jkd _l BC: SRXB E C:PECB I _ A)D:DRPM INAME CYLiang* RJones AChaffee BGrimesHAFreeman* I- _DATE 6/ 3/96 6/2j /96 6/ /96 6/ /96OFFICIAL RECORD COPYIoith attachment/enclosure 1

• No copy* See previous concurrence IN 96-XXJune XX, 1996 detection system. The licensee believed that this system would probably notbe significantly affected by feedwater temperatures because of a differentmass flow rate determination method.Finally, the licensee's final safety analysis report did not accuratelyanalyze this transient. The actual events were similar to the analysis of the'Decrease in Feedwater Temperature event presented in Chapter 15. In thatanalysis, the inadvertent opening of the low-pressure heater bypass valve,coupled with the trip of the heater drain pumps, resulted in a feedwatertemperature drop of less than 35 OF, and a corresponding power increase ofless than 10 percent. In the actual event, the feedwater temperature droppedby approximately 200 OF, and the licensee calculated that reactor power wouldhave increased by approximately 35 percent without operator or protectiveactions. The licensee determined that although the initiating events were thesame, the Chapter 15 analysis did not account for the loss of extraction steamto the high-pressure heaters, which was the cause of the temperaturedifference. During the event, a level imbalance occurred between the twoheater drain tanks, which resulted in the isolation of extraction steam.The NRC staff's review of analyses of feedwater temperature events at similarfacilities revealed that most of these analyses assumed similar initiatingevents as the licensee's analysis and had similar conclusions concerning theamount of feedwater temperature drop.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: Harry A. Freeman, RIV(817) 897-1500Internet:haf@nrc.govChu-Yu Liang, NRR(301) 415-2878Internet:cyl nrc.gov

Attachment:

List of Recently Issued NRC Information NoticesDOCUMENT NAME: G:\SSK2\INFONOT.C PTo receive a copy of this docunent, indicate in the box Catopy w/o attachment/enclosure E-C with attachment/enclosure N

• No copyOFFICE lCONT:kd l BC:SRXB l BC:PECB l (A)D:DRPMNAME CYLiang 9 RJones AChaffee BGrimesHAFreema r _ _DATE /96 /96 6/ /96 6/ /96OFFICIAL RECORD COPY