Information Notice 1990-06, Potential for Loss of Shutdown Cooling While at Low Reactor Coolant Levels
UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555January 29, 1990NRC INFORMATION NOTICE NO. 90-06: POTENTIAL FOR LOSS OF SHUTDOWN COOLINGWHILE AT LOW REACTOR COOLANT LEVELS
Addressees
- All holders of operating licenses or construction permits for nuclear powerreactors.
Purpose
- This information notice is intended to alert addressees to a potential problemaffecting the operability of the residual heat removal (RHR) system duringoperating conditions involving mid-loop operation. It is expected that re--cipients will review the information for applicability to their facilitiesand consider actions, as appropriate, to avoid similar problems. However,suggestions contained in this information notice do not constitute NRCrequirements; therefore, no specific action or written response is required.
Description of Circumstances
- On July 18, 1989, at Comanche Peak Unit 1, train 'Al of the residual heatremoval system was in operation prior to initial fuel loading. The airoperated RHR heat exchanger flow control valve (FCV) was being used tomaintain system flow below 2000 gpm. The reactor vessel water level wasbeing maintained slightly abpve the center line of the hot legs.The inverter supplying power to the controller for the FCV failed. The lossof power to the controller resulted in the FCV failing to its emergency corecooling system (ECCS) position of being fully open. The open valve causedan increase in system flow to 4400 gpm. This sudden, increased flow causedconditions where vortexing was expected at the suction of the RHR pipe con-nection to the RCS.The power supply for the controllers was manually transferred to an alternatesource and the FCV was throttled, thus terminating the event.Discussion:The FCV is manually throttled to maintain a desired rate of flow through theRHR heat exchanger. The heat exchanger flow rate is adjusted to control thetemperature of the water being returned to the vessel. Total system flow isregulated by throttling the heat exchanger bypass valve coincident with theadjustment of the FCV.001230175 Z ( (' D*1 IC,eo uachr
IN 90-06January 29, 1990 During this event, there were no indications of pump air ingestion. However,the increased system flow corresponded to the rate at which vortexing hadbeen calculated to occur based on the existing RCS level. The licensee hadpreviously determined maximum permitted flow rates for various reduced levelsof the RCS to prevent the possibility of vortexing and air entrainment intothe RHR pump.Although RHR pump operation was never actually impaired, the potential existedfor air to be introduced to the pump's suction. This concern is exacerbated by* the fact that the heat exchanger FCVs for both trains of RHR are powered fromthe same inverter. Since the FCVs open fully on a loss of power, both trainsof RHR could become inoperable on a loss of power during mid-loop operation.(A loss of instrument air would also cause the FCVs to fail to the full openposition and could also result in the loss of both trains of the RHR system).During most modes of operation, having the FCVs go -fully open on loss ofpower or instrument air is not a safety concern because having the valvesfully open does not normally prevent the system from performing its safetyfunction. However, having the valves go fully open while at mid-loop couldresult in the loss of decay heat removal capability. This loss could persistuntil electrical power or instrument air is restored and air is vented fromthe RHR system.The licensee has revised procedures for mid-loop operation to require manuallypositioning the cold leg injection isolation valves to limit the maximum flowthrough the system, even with the FCVs fully open. This lineup will be usedwhenever the unit is at mid-loop and protects against the consequences offailure of either electrical power or instrument air.Several generic communications have been issued informing licensees of theconsequences of the loss of residual (decay) heat removal and the operatingconditions under which the probability of a loss increases; i.e., reducedinventory conditions. The most recent publications include Generic Letter(GL) No. 87-12, "Loss of Decay Heat Removal While the Reactor Coolant Systemis Partially Filled;" GL No. 88-17, *Loss of Decay Heat Removal;" NRC In-formation Notice (IN) 87-23, "Loss of Decay Heat Removal During Low ReactorCoolant Level Operation;" IN 88-36, 'Possible Sudden Loss of RCS InventoryDuring Low Coolant Level Operation;" and IN 89-67, "Loss of Residual HeatRemoval Caused by Accumulator Nitrogen Injection." The event describedabove introduces a subtle failure scenario which licensees may not haveconsidered.
IN 90-06January 29, 1990 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 NRR project manager.Charles E. Rossi, irectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: Nick Fields, NRR(301) 492-1173Steve Bitter, RIV(817) 897-1500Attachment:List of Recently Issued NRC Information Notices
IIN 90-06January 29, 1990 During this event, there were no indications of pump air ingestion Howeverthe increased system flow enrraenan~nA n~ -~ neto. HwvrAttachment ~q ) sx 90-06Jasmary 2§ 1990Page I of ILIST OF RECEITLT ISSUEDNIR INFORtAT1011 OTICESJCW --lnfonationNotice No.90-0590-04SubJectInter-System Discharge ofReactor CoelantIssuance1/26/9OCracking of the Upper Shall- 1/26/90to-Transition Cone GirthMelds Is Steam GeneratorsIssued teAll holders of ULsor Ch for nuclearpower reactors.All holders of OLsor CPs.for Westinghouse.designed and CombustionEngineering-disignednuclear power reactors.All holders of OLsor CPs for uclewrpower reactors.All holders of OLsor CPs for Slis.All holders of NRCmaterials licenses.90-03 malfunction of Borg-VarnerSBlted Sonnet Check ValvesCausd by Failure of theSwing Arm90-02 Potential Degradation ofSecondary Contaient90-01 lIportace of ProperResponse to Self-IdentiftedViolations by Licensees89-90 Pressurizer Safety ValvLift Setpoint Shift89-8 Event NotificattonWorkshents89-88 Recent XRC-SponsoredTesting of motor-OperatedValves8647 Disablilg of EmergencyDiesel Generators byTheir Neutral Ground-FaultProtection Circuitry8945. etalclad. Lou-VoltageSupp. 2 Power Circuit DreakarsRefurbished withSubstandard Parts1/23/901/29D1/12/9012/28/84 All holder of OMsor Ch for Pilb.12/26/89 All holders of CLsor en for nuclearpower reactors.12/26189 All holders of Otsor CPs for nutlearpoer reactors.12/19189 All helders of OLsor CVs for nuclearpower reactors.12/IS/1 9 All holders of OLsor CPs for nuclearpower reactors.OL*OpitunceS -_CV s Construction PermitUNITED STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON, D.C. 20555OFFICIAL BUSINESSPENALTY FOR PRIVATE USE. 8300IPOSTAGE & FEES PAOIDISNiRC1 IN 90-06January 29, 1990 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 NRR project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:Nick Fields, NRR(301) 492-1173Steve Bitter, RIV(817) 897-1500Attachment:List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEEAB:NRR*NFields: db1/12/90TECH:EDITOR*BCalure1/13/90EAB:NRR C:EAB:NRR*DCFischer *CJHaughney1/16/90 1/16/90C:OGCB:NRR*CHBerlinger1/17/90NRR:SRXB*RJones1/23/901 /Z3'90
K)jV%2IN 90-January , 1990 No specific action or written response is required by this informationIf you have any questions about this matter, please contact one of thecontacts listed below or the Regional Administrator of the appropriateoffice.notice.technicalregionalCharles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:Nick Fields (301) 492-1173Steve Bitter (817) 897-1500Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEEAB:NRR*NFields:db/ /90D:DOEA:NRRCERossi/ /90TECH:EDITOR*BCalure/ /90EAB:NRR*DCFischer/ /90C:EAB:NRR*CJHaughney*/ /90C:OGCB:NRR*CHBerlinger/ /90N R BRJV esI j:/90
IN 90-January , 1990%...Z'age 3 of 3No specific action or written response is required by thisinfornation notice. If you have any questions about this matter,please contact the technical contact listed below or the RegionalAdministrator of the appropriate regional office.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts:Nick Fields (301) 492-1173Steve Bitter (817) 897-1500List of Recently Issued NRC Information NoticesAttachment:AJFEAB:NRRNFields:dbJr //,/90C0Wvtn Au tVIU46x1 4fhire0rAtU rAITECH:EDITOR EAB:NRRDCFischerI /11/SQ , /14/90C:EAB:NRRCJHaughneyI /14/90CVC:OGCB:NRRCHBerlinger/ 117/90D:DOEA:NRRCERossi/ /90