Information Notice 1993-89, Potential Problems with BWR Level Instrumentation Backfill Modifications: Difference between revisions

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==Description of Circumstances==
==Description of Circumstances==
NRC Bulletin (NRCB) 93-03, "Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs," issued on May 28, 1993, requested thatlicensees implement hardware modifications necessary to ensure the levelinstrumentation system design is of high functional reliability for long-termoperation. In response to this bulletin, all BWR licensees with the exceptionof Big Rock Point, which does not use cold reference leg instrumentation, haveeither implemented modifications or have committed to implement modifications.The majority of these licensees have decided to install a reference legbackfill system to supply a continuous flow of water from the control roddrive (CRD) hydraulic system through the reference legs to preclude migrationof dissolved noncondensible gases down the legs. In August 1993, a potentialproblem was found at the Susquehanna nuclear power plant during the design ofthis backfill modification.DiscussionIt was postulated at Susquehanna that a manual isolation valve in one of thereference legs (see Figure 1) could be closed by operator error. Closure ofthis valve would result in pressurization of that reference leg to CRD systempressure and erroneous indication of low reactor water level and high reactorpressure on all instrumentation associated with that reference leg. Thetransient resulting from pressurization of the most limiting reference leg9311190454 1 KE-e 93-o 93Ill K.,_ IN 93-89November 26, 1993 includes reactor scram and opening of all safety relief valves (SRVs) due tothe false high reactor pressure. The SRVs would remain open and depressurizethe reactor until the valves are closed by operator action, or actual reactorpressure falls below approximately 446 kPa [50 psig] at which time the valvescan no longer stay open. Reactor depressurization and loss of inventorythrough the SRVs, in combination with the false low water level signal on theaffected reference leg, would result in closure of the main steam isolationvalves, actuation of high-pressure and low-pressure emergency core coolingsystem (ECCS) and containment isolation. Low-pressure ECCS injection wouldcommence after the low-pressure permissive is satisfied. This permissivewould be satisfied in this scenario, allowing the low pressure ECCS injectionvalves to open, because only one of the pressure transmitters is affected andthe logic would still be satisfied. A single failure could defeat this logic,however, preventing all low-pressure ECCS Injection. The low-pressurepermissive can be bypassed in the control room to open the injection valvesfor all four low pressure core spray (LPCS) pumps. The Susquehanna licenseehas informed the NRC that it has physically disabled the manual isolationvalves to prevent misoperation of these valves; in addition, the valves arenot readily accessible as they are located 6.1 meters [20 feet] above thefloor.This event was recently analyzed for the LaSalle plant by Commonwealth Edison.The analysis indicates that the low-pressure permissive for opening the low-pressure ECCS injection valve would be defeated for the LaSalle design due tothe false high pressure signal, thus preventing ECCS injection from theaffected division. If a single failure is assumed in the relay for the low-pressure permissive on the other division, no low-pressure ECCS injectionwould be available. Because the induced plant transient is potentially sosevere, LaSalle has designed its backfill modification to make the injectionpoint for the backfill system on the reactor side of the manual isolationvalve and excess flow check valve, thereby precluding the potential forpressurization of the reference leg through the backfill system.Commonwealth Edison took a different design approach for its Dresden andQuad Cities plants. The backfill system design for Dresden and Quad Citiesinjects into the reference leg on the instrument rack side of the manualisolation valve and excess flow check valve. Additional administrativecontrols were developed to ensure that the isolation valve would not beinadvertently closed. The licensee analyzed the inadvertent closure of themanual isolation valve for the Dresden and Quad Cities plants and concludedthat, while multiple SRVs would open, the resultant plant transient could bemitigated by appropriate operator actions. Without operator actions, the low-pressure ECCS would be available for event mitigation; however, a singlefailure in the instrumentation system could defeat the low-pressure permissivefor opening the low-pressure ECCS Injection valves and result in no low-pressure ECCS being available for this transient. The licensee alsodetermined that this design presented an unreviewed safety question because itwould increase the probability of a previously analyzed accident, andsubmitted an application to amend its license pursuant to 10 CFR 50.90. TheNRC is currently reviewing the licensee submitta IN 93-89November 26, 1993 Other minor problems with the backfill system have been encountered wheninstalling the system and returning the instrumentation to service afterinstallation was complete. At the Perry plant, a problem occurred when thelicensee was in the process of venting one of the instrument lines followingthe installation of the modification. The job plan directed the operation ofthe wrong valve, and instead of opening the vent valve the technician openedthe isolation valve, allowing air into the reference leg. As a result, theinstrumentation associated with the high pressure core spray system (HPCS) wasinoperable until it was re-filled and vented. Similar events have occurred atother plants due to procedural inadequacy or lack of attention to detail.Related Generic Communications* NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Causedby Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution of the Issues Related to ReactorVessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"August 19, 1992.* NRC Information Notice 93-27, 'Level Instrumentation InaccuraciesObserved During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs,' May 28, 1993.This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor RegulationTechnical contact: Amy Cubbage, NRR(301) 504-2875
NRC Bulletin (NRCB) 93-03, "Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs," issued on May 28, 1993, requested thatlicensees implement hardware modifications necessary to ensure the levelinstrumentation system design is of high functional reliability for long-termoperation. In response to this bulletin, all BWR licensees with the exceptionof Big Rock Point, which does not use cold reference leg instrumentation, haveeither implemented modifications or have committed to implement modifications.The majority of these licensees have decided to install a reference legbackfill system to supply a continuous flow of water from the control roddrive (CRD) hydraulic system through the reference legs to preclude migrationof dissolved noncondensible gases down the legs. In August 1993, a potentialproblem was found at the Susquehanna nuclear power plant during the design ofthis backfill modification.DiscussionIt was postulated at Susquehanna that a manual isolation valve in one of thereference legs (see Figure 1) could be closed by operator error. Closure ofthis valve would result in pressurization of that reference leg to CRD systempressure and erroneous indication of low reactor water level and high reactorpressure on all instrumentation associated with that reference leg. Thetransient resulting from pressurization of the most limiting reference leg9311190454 1 KE-e 93-o 93Ill


===Attachments:===
K.,_ IN 93-89November 26, 1993 includes reactor scram and opening of all safety relief valves (SRVs) due tothe false high reactor pressure. The SRVs would remain open and depressurizethe reactor until the valves are closed by operator action, or actual reactorpressure falls below approximately 446 kPa [50 psig] at which time the valvescan no longer stay open. Reactor depressurization and loss of inventorythrough the SRVs, in combination with the false low water level signal on theaffected reference leg, would result in closure of the main steam isolationvalves, actuation of high-pressure and low-pressure emergency core coolingsystem (ECCS) and containment isolation. Low-pressure ECCS injection wouldcommence after the low-pressure permissive is satisfied. This permissivewould be satisfied in this scenario, allowing the low pressure ECCS injectionvalves to open, because only one of the pressure transmitters is affected andthe logic would still be satisfied. A single failure could defeat this logic,however, preventing all low-pressure ECCS Injection. The low-pressurepermissive can be bypassed in the control room to open the injection valvesfor all four low pressure core spray (LPCS) pumps. The Susquehanna licenseehas informed the NRC that it has physically disabled the manual isolationvalves to prevent misoperation of these valves; in addition, the valves arenot readily accessible as they are located 6.1 meters [20 feet] above thefloor.This event was recently analyzed for the LaSalle plant by Commonwealth Edison.The analysis indicates that the low-pressure permissive for opening the low-pressure ECCS injection valve would be defeated for the LaSalle design due tothe false high pressure signal, thus preventing ECCS injection from theaffected division. If a single failure is assumed in the relay for the low-pressure permissive on the other division, no low-pressure ECCS injectionwould be available. Because the induced plant transient is potentially sosevere, LaSalle has designed its backfill modification to make the injectionpoint for the backfill system on the reactor side of the manual isolationvalve and excess flow check valve, thereby precluding the potential forpressurization of the reference leg through the backfill system.Commonwealth Edison took a different design approach for its Dresden andQuad Cities plants. The backfill system design for Dresden and Quad Citiesinjects into the reference leg on the instrument rack side of the manualisolation valve and excess flow check valve. Additional administrativecontrols were developed to ensure that the isolation valve would not beinadvertently closed. The licensee analyzed the inadvertent closure of themanual isolation valve for the Dresden and Quad Cities plants and concludedthat, while multiple SRVs would open, the resultant plant transient could bemitigated by appropriate operator actions. Without operator actions, the low-pressure ECCS would be available for event mitigation; however, a singlefailure in the instrumentation system could defeat the low-pressure permissivefor opening the low-pressure ECCS Injection valves and result in no low-pressure ECCS being available for this transient. The licensee alsodetermined that this design presented an unreviewed safety question because itwould increase the probability of a previously analyzed accident, andsubmitted an application to amend its license pursuant to 10 CFR 50.90. TheNRC is currently reviewing the licensee submittal.
1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information Notices rfltO CONDENSATE POTREACTOR VESSEL(QA BOUNDARY UDRYWELLREACTOR BLDG7 MANUALL ISOLATIONC EXCESS FLOW$ CHECK VALVEREFERENCE LEGCRD CHARGINGWATER HEADERINSTRtUmRACKVARIABLELEGCFIGURE 1 -SIMPLIFIED SKETCH OF BACKFILL MODIFICATIONe0 (cI-Ij3EDw, A4...achment 2IN 93-89November 26, 1993 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to93-8893-8793-8693-8593-84Status of Motor-OperatedValve Performance Pre-diction Program by theElectric Power ResearchInstituteFuse Problems withWestinghouse 7300Printed Circuit CardsIdentification of Iso-topes in the Productionand Shipment of ByproductMaterial at Non-powerReactorsProblems with X-Relaysin DB- and DHB-TypeCircuit Breakers Manu-factured by WestinghouseDetermination of Westing-house Reactor CoolantPump Seal Failure11/30/9311/04/9310/29/9310/20/9310/20/93All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor test and researchreactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor pressurized waterreactors (PWRs).93-83Potential Loss of SpentFuel Pool CoolingFollowing A Loss ofCoolant Accident (LOCA)10/07/93All holdersfor boiling(BWRs).of OLs or CPswater reactors93-8293-81Recent Fuel and CorePerformance Problems inOperating ReactorsImplementation ofEngineering Expertiseon Shift10/12/9310/12/93All holders of OLs or CPsfor nuclear power reactorsand all NRC-approved fuelsuppliers.All holders of OLs or CPsfor nuclear power reactors.OL -Operating LicenseCP -Construction Permit IN 93-89a-> November 26, 1993 Other minor problems with the backfill system have been encountered wheninstalling the system and returning the instrumentation to service afterinstallation was complete. At the Perry plant, a problem occurred when thelicensee was in the process of venting one of the instrument lines followingthe installation of the modification. The Job plan directed the operation ofthe wrong valve, and instead of opening the vent valve the technician openedthe isolation valve, allowing air into the reference leg. As a result, theinstrumentation associated with the high pressure core spray system (HPCS) wasinoperable until it was re-filled and vented. Similar events have occurred atother plants due to procedural inadequacy or lack of attention to detail.Related Generic Communications* NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Causedby Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution of the Issues Related to ReactorVessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"August 19, 1992.* NRC Information Notice 93-27, 'Level Instrumentation InaccuraciesObserved During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, 'Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs," May 28, 1993.This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.orig /s/'d by BKGrimesBrian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor RegulationTechnical contact: Amy Cubbage, NRR(301) 504-2875


===Attachments:===
IN 93-89November 26, 1993 Other minor problems with the backfill system have been encountered wheninstalling the system and returning the instrumentation to service afterinstallation was complete. At the Perry plant, a problem occurred when thelicensee was in the process of venting one of the instrument lines followingthe installation of the modification. The job plan directed the operation ofthe wrong valve, and instead of opening the vent valve the technician openedthe isolation valve, allowing air into the reference leg. As a result, theinstrumentation associated with the high pressure core spray system (HPCS) wasinoperable until it was re-filled and vented. Similar events have occurred atother plants due to procedural inadequacy or lack of attention to detail.Related Generic Communications* NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Causedby Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution of the Issues Related to ReactorVessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"August 19, 1992.* NRC Information Notice 93-27, 'Level Instrumentation InaccuraciesObserved During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs,' May 28, 1993.This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor RegulationTechnical contact: Amy Cubbage, NRR(301) 504-2875Attachments:1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information Notices
1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information Notices* SEE PREVIOUS CONCURRENCESRXB:DSSA* OGCB:DORS* TECH ED.* SRXB:DSSA* SRXB:DSSA* D:DSSA* OGCB:DORS*ACUBBAGE PWEN RSANDERS WLYON RJONES ATHADANI GMARCUS1 11/16/93 11/15/93 11/16/93 11/18/93 11/20/93 11/23/9311/2.493DOCUMENT NAME: 93-89.IN IN 93-xxNovember xx, 1993 This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor Regulation
 
rfltO CONDENSATE POTREACTOR VESSEL(QA BOUNDARY UDRYWELLREACTOR BLDG7 MANUALL ISOLATIONC EXCESS FLOW$ CHECK VALVEREFERENCE LEGCRD CHARGINGWATER HEADERINSTRtUmRACKVARIABLELEGCFIGURE 1 -SIMPLIFIED SKETCH OF BACKFILL MODIFICATIONe0 (cI-Ij3EDw, A4...achment 2IN 93-89November 26, 1993 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to93-8893-8793-8693-8593-84Status of Motor-OperatedValve Performance Pre-diction Program by theElectric Power ResearchInstituteFuse Problems withWestinghouse 7300Printed Circuit CardsIdentification of Iso-topes in the Productionand Shipment of ByproductMaterial at Non-powerReactorsProblems with X-Relaysin DB- and DHB-TypeCircuit Breakers Manu-factured by WestinghouseDetermination of Westing-house Reactor CoolantPump Seal Failure11/30/9311/04/9310/29/9310/20/9310/20/93All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor test and researchreactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor pressurized waterreactors (PWRs).93-83Potential Loss of SpentFuel Pool CoolingFollowing A Loss ofCoolant Accident (LOCA)10/07/93All holdersfor boiling(BWRs).of OLs or CPswater reactors93-8293-81Recent Fuel and CorePerformance Problems inOperating ReactorsImplementation ofEngineering Expertiseon Shift10/12/9310/12/93All holders of OLs or CPsfor nuclear power reactorsand all NRC-approved fuelsuppliers.All holders of OLs or CPsfor nuclear power reactors.OL -Operating LicenseCP -Construction Permit
 
IN 93-89a-> November 26, 1993 Other minor problems with the backfill system have been encountered wheninstalling the system and returning the instrumentation to service afterinstallation was complete. At the Perry plant, a problem occurred when thelicensee was in the process of venting one of the instrument lines followingthe installation of the modification. The Job plan directed the operation ofthe wrong valve, and instead of opening the vent valve the technician openedthe isolation valve, allowing air into the reference leg. As a result, theinstrumentation associated with the high pressure core spray system (HPCS) wasinoperable until it was re-filled and vented. Similar events have occurred atother plants due to procedural inadequacy or lack of attention to detail.Related Generic Communications* NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Causedby Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution of the Issues Related to ReactorVessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"August 19, 1992.* NRC Information Notice 93-27, 'Level Instrumentation InaccuraciesObserved During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, 'Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs," May 28, 1993.This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.orig /s/'d by BKGrimesBrian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor RegulationTechnical contact: Amy Cubbage, NRR(301) 504-2875Attachments:1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information Notices* SEE PREVIOUS CONCURRENCESRXB:DSSA* OGCB:DORS* TECH ED.* SRXB:DSSA* SRXB:DSSA* D:DSSA* OGCB:DORS*ACUBBAGE PWEN RSANDERS WLYON RJONES ATHADANI GMARCUS1 11/16/93 11/15/93 11/16/93 11/18/93 11/20/93 11/23/9311/2.493DOCUMENT NAME: 93-89.IN
 
IN 93-xxNovember xx, 1993 This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor Regulation


===Technical Contact:===
===Technical Contact:===
Amy Cubbage, NRR(301) 504-2875
Amy Cubbage, NRR(301) 504-2875Attachments:1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information Notices* SEE PREVIOUS CONCURRENCESRXB:DSSA* OGCB:DORS* TECH ED.*ACUBBAGE PWEN RSANDERS11/15/93 11/16/93 11/15/93SRXB:DSSA*WLYON11/16/93SRXB:DSSA*RJONES11/18/93D: DSSA*ATHADANI11/20/93OGCB:DORSGMARCUS At'i11/23/93D: DORSBGRIMES11/ /93DOCUMENTNAME:BWRWTLVL.WEN


===Attachments:===
instrumentation associated with the high pressure core spray system (HPCS) wasinoperable until it was re-filled and vented. Similar events have occurred atother plants due to procedural inadequacy or lack of attention to detail.Related Generic Communications* NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Causedby Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution of the Issues Related to ReactorVessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"August 19, 1992.* NRC Information Notice 93-27, "Level Instrumentation InaccuraciesObserved During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, "Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs," May 28, 1993.This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor Regulation
1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information Notices* SEE PREVIOUS CONCURRENCESRXB:DSSA* OGCB:DORS* TECH ED.*ACUBBAGE PWEN RSANDERS11/15/93 11/16/93 11/15/93SRXB:DSSA*WLYON11/16/93SRXB:DSSA*RJONES11/18/93D: DSSA*ATHADANI11/20/93OGCB:DORSGMARCUS At'i11/23/93D: DORSBGRIMES11/ /93DOCUMENTNAME:BWRWTLVL.WEN instrumentation associated with the high pressure core spray system (HPCS) wasinoperable until it was re-filled and vented. Similar events have occurred atother plants due to procedural inadequacy or lack of attention to detail.Related Generic Communications* NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Causedby Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution of the Issues Related to ReactorVessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"August 19, 1992.* NRC Information Notice 93-27, "Level Instrumentation InaccuraciesObserved During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, "Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs," May 28, 1993.This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor Regulation


===Technical Contact:===
===Technical Contact:===
Amy Cubbage, NRR(301) 504-2875
Amy Cubbage, NRR(301) 504-2875Attachments:1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information NoticesEDITED BY: R. SandersDATED: 11/15/93SRXB:DSSA* OGCB:DORS* SRXB:DSSA* SRXB:DSSA* D:DSSA OGCB:DORS D:DORSACUBBAGE PWEN WLYON RJONES ATHAqkNI GMARCUS BGRIMES11/15/93 11/16/93 11/16/93 11/18/93 11/?V/93 11/ /93 11/ /93* SEE PREVIOUS CONCURRENCE


===Attachments:===
}}
1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information NoticesEDITED BY: R. SandersDATED: 11/15/93SRXB:DSSA* OGCB:DORS* SRXB:DSSA* SRXB:DSSA* D:DSSA OGCB:DORS D:DORSACUBBAGE PWEN WLYON RJONES ATHAqkNI GMARCUS BGRIMES11/15/93 11/16/93 11/16/93 11/18/93 11/?V/93 11/ /93 11/ /93* SEE PREVIOUS CONCURRENCE}}


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Revision as of 19:20, 6 April 2018

Potential Problems with BWR Level Instrumentation Backfill Modifications
ML031070176
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  Entergy icon.png
Issue date: 11/26/1993
From: Grimes B K
Office of Nuclear Reactor Regulation
To:
References
IN-93-089, NUDOCS 9311190454
Download: ML031070176 (8)
v • d • e


UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555November 26, 1993NRC INFORMATION NOTICE 93-89: POTENTIAL PROBLEMS WITH BWR LEVELINSTRUMENTATION BACKFILL MODIFICATIONS

Addressees

All holders of operating licenses or construction permits for boiling waterreactors (BWRs).

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this informationnotice to alert addressees to potential problems that have been identified bylicensees involving hardware modification to the reactor vessel water levelinstrumentation system. It is expected that recipients will review theinformation for applicability to their facilities and consider actions, asappropriate, to avoid similar problems. However, suggestions contained inthis information notice are not NRC requirements; therefore, no specificaction or written response is required.

Description of Circumstances

NRC Bulletin (NRCB) 93-03, "Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs," issued on May 28, 1993, requested thatlicensees implement hardware modifications necessary to ensure the levelinstrumentation system design is of high functional reliability for long-termoperation. In response to this bulletin, all BWR licensees with the exceptionof Big Rock Point, which does not use cold reference leg instrumentation, haveeither implemented modifications or have committed to implement modifications.The majority of these licensees have decided to install a reference legbackfill system to supply a continuous flow of water from the control roddrive (CRD) hydraulic system through the reference legs to preclude migrationof dissolved noncondensible gases down the legs. In August 1993, a potentialproblem was found at the Susquehanna nuclear power plant during the design ofthis backfill modification.DiscussionIt was postulated at Susquehanna that a manual isolation valve in one of thereference legs (see Figure 1) could be closed by operator error. Closure ofthis valve would result in pressurization of that reference leg to CRD systempressure and erroneous indication of low reactor water level and high reactorpressure on all instrumentation associated with that reference leg. Thetransient resulting from pressurization of the most limiting reference leg9311190454 1 KE-e 93-o 93Ill

K.,_ IN 93-89November 26, 1993 includes reactor scram and opening of all safety relief valves (SRVs) due tothe false high reactor pressure. The SRVs would remain open and depressurizethe reactor until the valves are closed by operator action, or actual reactorpressure falls below approximately 446 kPa [50 psig] at which time the valvescan no longer stay open. Reactor depressurization and loss of inventorythrough the SRVs, in combination with the false low water level signal on theaffected reference leg, would result in closure of the main steam isolationvalves, actuation of high-pressure and low-pressure emergency core coolingsystem (ECCS) and containment isolation. Low-pressure ECCS injection wouldcommence after the low-pressure permissive is satisfied. This permissivewould be satisfied in this scenario, allowing the low pressure ECCS injectionvalves to open, because only one of the pressure transmitters is affected andthe logic would still be satisfied. A single failure could defeat this logic,however, preventing all low-pressure ECCS Injection. The low-pressurepermissive can be bypassed in the control room to open the injection valvesfor all four low pressure core spray (LPCS) pumps. The Susquehanna licenseehas informed the NRC that it has physically disabled the manual isolationvalves to prevent misoperation of these valves; in addition, the valves arenot readily accessible as they are located 6.1 meters [20 feet] above thefloor.This event was recently analyzed for the LaSalle plant by Commonwealth Edison.The analysis indicates that the low-pressure permissive for opening the low-pressure ECCS injection valve would be defeated for the LaSalle design due tothe false high pressure signal, thus preventing ECCS injection from theaffected division. If a single failure is assumed in the relay for the low-pressure permissive on the other division, no low-pressure ECCS injectionwould be available. Because the induced plant transient is potentially sosevere, LaSalle has designed its backfill modification to make the injectionpoint for the backfill system on the reactor side of the manual isolationvalve and excess flow check valve, thereby precluding the potential forpressurization of the reference leg through the backfill system.Commonwealth Edison took a different design approach for its Dresden andQuad Cities plants. The backfill system design for Dresden and Quad Citiesinjects into the reference leg on the instrument rack side of the manualisolation valve and excess flow check valve. Additional administrativecontrols were developed to ensure that the isolation valve would not beinadvertently closed. The licensee analyzed the inadvertent closure of themanual isolation valve for the Dresden and Quad Cities plants and concludedthat, while multiple SRVs would open, the resultant plant transient could bemitigated by appropriate operator actions. Without operator actions, the low-pressure ECCS would be available for event mitigation; however, a singlefailure in the instrumentation system could defeat the low-pressure permissivefor opening the low-pressure ECCS Injection valves and result in no low-pressure ECCS being available for this transient. The licensee alsodetermined that this design presented an unreviewed safety question because itwould increase the probability of a previously analyzed accident, andsubmitted an application to amend its license pursuant to 10 CFR 50.90. TheNRC is currently reviewing the licensee submittal.

IN 93-89November 26, 1993 Other minor problems with the backfill system have been encountered wheninstalling the system and returning the instrumentation to service afterinstallation was complete. At the Perry plant, a problem occurred when thelicensee was in the process of venting one of the instrument lines followingthe installation of the modification. The job plan directed the operation ofthe wrong valve, and instead of opening the vent valve the technician openedthe isolation valve, allowing air into the reference leg. As a result, theinstrumentation associated with the high pressure core spray system (HPCS) wasinoperable until it was re-filled and vented. Similar events have occurred atother plants due to procedural inadequacy or lack of attention to detail.Related Generic Communications* NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Causedby Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution of the Issues Related to ReactorVessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"August 19, 1992.* NRC Information Notice 93-27, 'Level Instrumentation InaccuraciesObserved During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs,' May 28, 1993.This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor RegulationTechnical contact: Amy Cubbage, NRR(301) 504-2875Attachments:1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information Notices

rfltO CONDENSATE POTREACTOR VESSEL(QA BOUNDARY UDRYWELLREACTOR BLDG7 MANUALL ISOLATIONC EXCESS FLOW$ CHECK VALVEREFERENCE LEGCRD CHARGINGWATER HEADERINSTRtUmRACKVARIABLELEGCFIGURE 1 -SIMPLIFIED SKETCH OF BACKFILL MODIFICATIONe0 (cI-Ij3EDw, A4...achment 2IN 93-89November 26, 1993 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to93-8893-8793-8693-8593-84Status of Motor-OperatedValve Performance Pre-diction Program by theElectric Power ResearchInstituteFuse Problems withWestinghouse 7300Printed Circuit CardsIdentification of Iso-topes in the Productionand Shipment of ByproductMaterial at Non-powerReactorsProblems with X-Relaysin DB- and DHB-TypeCircuit Breakers Manu-factured by WestinghouseDetermination of Westing-house Reactor CoolantPump Seal Failure11/30/9311/04/9310/29/9310/20/9310/20/93All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor test and researchreactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor pressurized waterreactors (PWRs).93-83Potential Loss of SpentFuel Pool CoolingFollowing A Loss ofCoolant Accident (LOCA)10/07/93All holdersfor boiling(BWRs).of OLs or CPswater reactors93-8293-81Recent Fuel and CorePerformance Problems inOperating ReactorsImplementation ofEngineering Expertiseon Shift10/12/9310/12/93All holders of OLs or CPsfor nuclear power reactorsand all NRC-approved fuelsuppliers.All holders of OLs or CPsfor nuclear power reactors.OL -Operating LicenseCP -Construction Permit

IN 93-89a-> November 26, 1993 Other minor problems with the backfill system have been encountered wheninstalling the system and returning the instrumentation to service afterinstallation was complete. At the Perry plant, a problem occurred when thelicensee was in the process of venting one of the instrument lines followingthe installation of the modification. The Job plan directed the operation ofthe wrong valve, and instead of opening the vent valve the technician openedthe isolation valve, allowing air into the reference leg. As a result, theinstrumentation associated with the high pressure core spray system (HPCS) wasinoperable until it was re-filled and vented. Similar events have occurred atother plants due to procedural inadequacy or lack of attention to detail.Related Generic Communications* NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Causedby Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution of the Issues Related to ReactorVessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"August 19, 1992.* NRC Information Notice 93-27, 'Level Instrumentation InaccuraciesObserved During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, 'Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs," May 28, 1993.This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.orig /s/'d by BKGrimesBrian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor RegulationTechnical contact: Amy Cubbage, NRR(301) 504-2875Attachments:1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information Notices* SEE PREVIOUS CONCURRENCESRXB:DSSA* OGCB:DORS* TECH ED.* SRXB:DSSA* SRXB:DSSA* D:DSSA* OGCB:DORS*ACUBBAGE PWEN RSANDERS WLYON RJONES ATHADANI GMARCUS1 11/16/93 11/15/93 11/16/93 11/18/93 11/20/93 11/23/9311/2.493DOCUMENT NAME: 93-89.IN

IN 93-xxNovember xx, 1993 This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor Regulation

Technical Contact:

Amy Cubbage, NRR(301) 504-2875Attachments:1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information Notices* SEE PREVIOUS CONCURRENCESRXB:DSSA* OGCB:DORS* TECH ED.*ACUBBAGE PWEN RSANDERS11/15/93 11/16/93 11/15/93SRXB:DSSA*WLYON11/16/93SRXB:DSSA*RJONES11/18/93D: DSSA*ATHADANI11/20/93OGCB:DORSGMARCUS At'i11/23/93D: DORSBGRIMES11/ /93DOCUMENTNAME:BWRWTLVL.WEN

instrumentation associated with the high pressure core spray system (HPCS) wasinoperable until it was re-filled and vented. Similar events have occurred atother plants due to procedural inadequacy or lack of attention to detail.Related Generic Communications* NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Causedby Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution of the Issues Related to ReactorVessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"August 19, 1992.* NRC Information Notice 93-27, "Level Instrumentation InaccuraciesObserved During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, "Resolution of Issues Related to Reactor VesselWater Level Instrumentation in BWRs," May 28, 1993.This information notice requires no specific action or written response. Ifyou have any questions regarding the information in this notice, pleasecontact the technical contact listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Operating Reactor SupportOffice of Nuclear Reactor Regulation

Technical Contact:

Amy Cubbage, NRR(301) 504-2875Attachments:1. Simplified Sketch of Backfill Modification2. List of Recently Issued NRC Information NoticesEDITED BY: R. SandersDATED: 11/15/93SRXB:DSSA* OGCB:DORS* SRXB:DSSA* SRXB:DSSA* D:DSSA OGCB:DORS D:DORSACUBBAGE PWEN WLYON RJONES ATHAqkNI GMARCUS BGRIMES11/15/93 11/16/93 11/16/93 11/18/93 11/?V/93 11/ /93 11/ /93* SEE PREVIOUS CONCURRENCE


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