Information Notice 1992-39, Unplanned Return to Criticality During Reactor Shutdown: Difference between revisions

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==Description of Circumstances==
==Description of Circumstances==
The licensees for the following plants recently experienced unplannedcriticalities during reactor shutdowns: the Monticello Nuclear GeneratingPlant, the Big Rock Point Nuclear Plant, and the Grand Gulf Nuclear Station.MonticelloOn June 6, 1991, an unplanned criticality occurred at the Monticello NuclearGenerating Plant during a reactor shutdown when an unanticipated cooldownoccurred in conjunction with rod insertion. The licensee initiated thisshutdown to repair a leaking safety-relief valve shortly after the plant wasreturning to power following a refueling outage.Since this shutdown occurred shortly after the cycle startup, the reactor didnot generate sufficient decay heat to produce the steam needed to supply thenormal steam system loads and still maintain pressure in the reactor. Ascontrol rods were being inserted using notch insertion, the reactor coolantsystem pressure and temperature began to decrease. As long as the operatorcontinued to insert control rods, the reactor remained subcritical.However, when the operator stopped inserting control rods to review andevaluate plant conditions, the cooldown continued, adding sufficientreactivity to overcome the negative reactivity from the insertion of controlrods and causing the reactor power to increase. The reactor power continued to92050_*,, C j'Ai / 1 ( / /CDQc K)IN 92-39May 13, 1992 increase until an intermediate-range monitor (IRM) tripped on a high-high fluxsetpoint, causing a reactor scram.Further details of the event may be found in Licensee Event Report50-263/91-15 or NRC Inspection Report 50-263/91-13.Big Rock PointOn November 30, 1991, an unplanned criticality occurred at the Big Rock PointNuclear Plant during a reactor shutdown when a cooldown occurred in conjunctionwith a rod insertion. The event occurred during a scheduled shutdown for arefueling outage.After taking the main turbine off line and bringing the reactor to asubcritical condition, the licensee delayed actions to continue insertingcontrol rods while changing shifts. However, the reactor coolant systemcontinued to cool down because the normal steam system loads were removingheat. The cooldown added sufficient reactivity to eventually overcome theeffects of the control rods, and the reactor returned critical. The operatorsnoticed the condition in approximately 2 minutes and took the appropriateactions to return the reactor subcritical.Further details of the event may be found in Licensee Event Report50-155/91-OO9-orJNRC-Inspection-Report 50-155/91-25. _ _ _Grand GulfOn December 30, 1991, an unplanned criticality occurred at the Grand GulfNuclear Station during a reactor shutdown when a cooldown occurred inconjunction with a rod insertion. The event occurred during a scheduledshutdown for a maintenance outage to replace a recirculation pump shaft. Tominimize the release of plated-out radioactive material from the fuel claddingand channels to the reactor coolant system, a slow power reduction and a slowcooldown were prescribed for this shutdown.The slow power reduction and the effects of an earlier outage minimized reactordecay heat and xenon peaking. The operators were driving rods into the coreindividually because gang drive for the control rods was unavailable. Thismade the reactivity insertion slower than normal. The operators insertedrods to reduce flux to range 3 on the IRMs and stopped rod insertion in orderto perform a source range monitor surveillance. Indicated power reached IRMrange 1. However, the reactor coolant system continued to cool down becausethe normal steam system loads were removing heat. In order not to affect thesource range monitor surveillance, the shift supervisor elected to not insertcontrol rods and alerted the operators to the possibility of a return tocriticality as the cooldown continued. The reactivity added by the cooldowneventually overcame the effects of the control rods. The reactor returned to acritical condition, and reactor power increased on a reactor period between 300to 800 seconds. The operators, having been trained on a similar event atanother BWR, were monitoring the condition and expected the power to increaseto the point of adding heat, where the fuel and moderator temperature coeffi-cients would halt the reactor power increase. As the power increased, the IN 92-39May 13, 1992 reactor operator ranged the IRMs to prevent a reactor scram. Power levelremained on scale. The power increase was terminated with the IRMs reading onrange 7 and 8. The operators completed the source range monitor surveillance,then resumed inserting rods and successfully completed the shutdown.Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. The experience at Monticello, Big RockPoint, and Grand Gulf indicates that shutdowns in situations with low decayheat present a unique challenge to reactivity control if inadvertent recritica-lity is to be prevented. These events emphasize the importance of the operatorgiving continuous attention to plant parameters during a shutdown. Further,accepting recriticality without prior management approval and procedures, i.e.,an ad-hoc approach, raises concerns due to the lack of opportunity for contin-gency planning.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 (NRR) project manager.Va&res'E.Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307
The licensees for the following plants recently experienced unplannedcriticalities during reactor shutdowns: the Monticello Nuclear GeneratingPlant, the Big Rock Point Nuclear Plant, and the Grand Gulf Nuclear Station.MonticelloOn June 6, 1991, an unplanned criticality occurred at the Monticello NuclearGenerating Plant during a reactor shutdown when an unanticipated cooldownoccurred in conjunction with rod insertion. The licensee initiated thisshutdown to repair a leaking safety-relief valve shortly after the plant wasreturning to power following a refueling outage.Since this shutdown occurred shortly after the cycle startup, the reactor didnot generate sufficient decay heat to produce the steam needed to supply thenormal steam system loads and still maintain pressure in the reactor. Ascontrol rods were being inserted using notch insertion, the reactor coolantsystem pressure and temperature began to decrease. As long as the operatorcontinued to insert control rods, the reactor remained subcritical.However, when the operator stopped inserting control rods to review andevaluate plant conditions, the cooldown continued, adding sufficientreactivity to overcome the negative reactivity from the insertion of controlrods and causing the reactor power to increase. The reactor power continued to92050_*,, C j'Ai / 1 ( / /CDQc


===Attachment:===
K)IN 92-39May 13, 1992 increase until an intermediate-range monitor (IRM) tripped on a high-high fluxsetpoint, causing a reactor scram.Further details of the event may be found in Licensee Event Report50-263/91-15 or NRC Inspection Report 50-263/91-13.Big Rock PointOn November 30, 1991, an unplanned criticality occurred at the Big Rock PointNuclear Plant during a reactor shutdown when a cooldown occurred in conjunctionwith a rod insertion. The event occurred during a scheduled shutdown for arefueling outage.After taking the main turbine off line and bringing the reactor to asubcritical condition, the licensee delayed actions to continue insertingcontrol rods while changing shifts. However, the reactor coolant systemcontinued to cool down because the normal steam system loads were removingheat. The cooldown added sufficient reactivity to eventually overcome theeffects of the control rods, and the reactor returned critical. The operatorsnoticed the condition in approximately 2 minutes and took the appropriateactions to return the reactor subcritical.Further details of the event may be found in Licensee Event Report50-155/91-OO9-orJNRC-Inspection-Report 50-155/91-25. _ _ _Grand GulfOn December 30, 1991, an unplanned criticality occurred at the Grand GulfNuclear Station during a reactor shutdown when a cooldown occurred inconjunction with a rod insertion. The event occurred during a scheduledshutdown for a maintenance outage to replace a recirculation pump shaft. Tominimize the release of plated-out radioactive material from the fuel claddingand channels to the reactor coolant system, a slow power reduction and a slowcooldown were prescribed for this shutdown.The slow power reduction and the effects of an earlier outage minimized reactordecay heat and xenon peaking. The operators were driving rods into the coreindividually because gang drive for the control rods was unavailable. Thismade the reactivity insertion slower than normal. The operators insertedrods to reduce flux to range 3 on the IRMs and stopped rod insertion in orderto perform a source range monitor surveillance. Indicated power reached IRMrange 1. However, the reactor coolant system continued to cool down becausethe normal steam system loads were removing heat. In order not to affect thesource range monitor surveillance, the shift supervisor elected to not insertcontrol rods and alerted the operators to the possibility of a return tocriticality as the cooldown continued. The reactivity added by the cooldowneventually overcame the effects of the control rods. The reactor returned to acritical condition, and reactor power increased on a reactor period between 300to 800 seconds. The operators, having been trained on a similar event atanother BWR, were monitoring the condition and expected the power to increaseto the point of adding heat, where the fuel and moderator temperature coeffi-cients would halt the reactor power increase. As the power increased, the
List of Recently Issued NRC Information Notices zI-0.<OD n; co> 0m Z.4-mrno00zZ G2-cnaEn z* omo) Zen q-n M0n a0 na -h <-Attachment 1IN 92-39May 13, 1992Page I of 1LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESDate ofInformationinformationNotice No.92-381 92-3792-16,Supp. 1I 92-36' 92-35SubjectImplementation Date forthe Revision to the EPAManual of ProtectiveAction Guides and Pro-tective Actions forNuclear IncidentsImplementation of theDeliberate Nisconduct RuleLoss of Flow from the Re-sidual Heat Removal Pumpduring Refueling CavityDraindownIntersystem LOCA OutsideContainmentHigher Than Predicted Ero-sion/Corrosion in Unisol-able Reactor Coolant Pres-sure Boundary Piping InsideContainment at A BoilingWater ReactorNew Exposure Limits forAirborne Uranium andThoriumIncreased InstrumentResponse Time WhenPressure DampeningDevices are InstalledIssuance05/12/9205/08/9205/07/9205/07/9205/06/92Issued toAll holders of OLs or CPsfor nuclear power reactors,non-power reactors andmaterials licensees auth-orized to possess largequantities of radioactivematerial.All Nuclear RegulatoryCommission Licensees.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.-u0rn>mD-C > 0u) D-D2zzz>092-3492-33I CP -'05/06/92 All licensees whose opera-tions can cause airborneconcentrations of uraniumand thorium.04/30/92 All holders of OLs or CPsfor nuclear power reactors.(Operating LicenseConstruction Permit IN 92-39May 13, 1992 reactor operator ranged the IRMs to prevent a reactor scram. Power levelremained on scale. The power increase was terminated with the IRMs reading onrange 7 and 8. The operators completed the source range monitor surveillance,then resumed inserting rods and successfully completed the shutdown.Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. The experience at Monticello, Big RockPoint, and Grand Gulf indicates that shutdowns in situations with low decayheat present a unique challenge to reactivity control if inadvertent recritica-lity is to be prevented. These events emphasize the importance of the operatorgiving continuous attention to plant parameters during a shutdown. Further,accepting recriticality without prior management approval and procedures, i.e.,an ad-hoc approach, raises concerns due to the lack of opportunity for contin-gency planning.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 (NRR) project manager. Original Signed byNhedes E, RossiCharles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307


===Attachment:===
IN 92-39May 13, 1992 reactor operator ranged the IRMs to prevent a reactor scram. Power levelremained on scale. The power increase was terminated with the IRMs reading onrange 7 and 8. The operators completed the source range monitor surveillance,then resumed inserting rods and successfully completed the shutdown.Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. The experience at Monticello, Big RockPoint, and Grand Gulf indicates that shutdowns in situations with low decayheat present a unique challenge to reactivity control if inadvertent recritica-lity is to be prevented. These events emphasize the importance of the operatorgiving continuous attention to plant parameters during a shutdown. Further,accepting recriticality without prior management approval and procedures, i.e.,an ad-hoc approach, raises concerns due to the lack of opportunity for contin-gency planning.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 (NRR) project manager.Va&res'E.Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment:List of Recently Issued NRC Information Notices
List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEABNAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee*DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92OFC C:DOEA:OGCB D X,NAME CBerlinger*DATE 04/21/92 05/ 7/92DOCUMENT NAME: IN 92-39 IN 92-XXApril xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. The experience at Big Rock Point, GrandGulf, and Monticello indicates that shutdowns in situations with low decay heatpresent a unique challenge to reactivity control if inadvertent recriticalityis to be prevented. These events emphasize the importance of the operatorgiving continuous attention to plant parameters during a shutdown. Further,accepting recriticality without prior management approval and procedures, i.e.,an ad-hoc approach, raises concerns due to the lack of opportunity for contin-gency planning.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307


===Attachment:===
zI-0.<OD n; co> 0m Z.4-mrno00zZ G2-cnaEn z* omo) Zen q-n M0n a0 na -h <-Attachment 1IN 92-39May 13, 1992Page I of 1LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESDate ofInformationinformationNotice No.92-381 92-3792-16,Supp. 1I 92-36' 92-35SubjectImplementation Date forthe Revision to the EPAManual of ProtectiveAction Guides and Pro-tective Actions forNuclear IncidentsImplementation of theDeliberate Nisconduct RuleLoss of Flow from the Re-sidual Heat Removal Pumpduring Refueling CavityDraindownIntersystem LOCA OutsideContainmentHigher Than Predicted Ero-sion/Corrosion in Unisol-able Reactor Coolant Pres-sure Boundary Piping InsideContainment at A BoilingWater ReactorNew Exposure Limits forAirborne Uranium andThoriumIncreased InstrumentResponse Time WhenPressure DampeningDevices are InstalledIssuance05/12/9205/08/9205/07/9205/07/9205/06/92Issued toAll holders of OLs or CPsfor nuclear power reactors,non-power reactors andmaterials licensees auth-orized to possess largequantities of radioactivematerial.All Nuclear RegulatoryCommission Licensees.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.-u0rn>mD-C > 0u) D-D2zzz>092-3492-33I CP -'05/06/92 All licensees whose opera-tions can cause airborneconcentrations of uraniumand thorium.04/30/92 All holders of OLs or CPsfor nuclear power reactors.(Operating LicenseConstruction Permit
List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEABNAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee*DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92OFC C:DOEA:OGCB D:DOEANAME CBerlinger* CRoss tDDATE 04/21/92 /9OFFICIAL RECORD COPYDOCUMENT NAME:IN DENKIG IN 92-XXApril xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Raising therange of the IRMs in the event of recriticality can be inappropriate if thelicensed operators do not have management's oversight, training, and specificprocedures for this.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307


===Attachment:===
IN 92-39May 13, 1992 reactor operator ranged the IRMs to prevent a reactor scram. Power levelremained on scale. The power increase was terminated with the IRMs reading onrange 7 and 8. The operators completed the source range monitor surveillance,then resumed inserting rods and successfully completed the shutdown.Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. The experience at Monticello, Big RockPoint, and Grand Gulf indicates that shutdowns in situations with low decayheat present a unique challenge to reactivity control if inadvertent recritica-lity is to be prevented. These events emphasize the importance of the operatorgiving continuous attention to plant parameters during a shutdown. Further,accepting recriticality without prior management approval and procedures, i.e.,an ad-hoc approach, raises concerns due to the lack of opportunity for contin-gency planning.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 (NRR) project manager. Original Signed byNhedes E, RossiCharles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEABNAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee*DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92OFC C:DOEA:OGCB D X,NAME CBerlinger*DATE 04/21/92 05/ 7/92DOCUMENT NAME: IN 92-39 IN 92-XXApril xx, 1992 DOCUMENT NAME:IN DENKIG
List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEABNAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee*DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92OFC C:DO J f D:DOEANAME CBerlinger CRosswa'yDATE f/;11/92/ 92OFFICIAL RECORD COPYDOCUMENT NAME: IN DENNIG IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. In the event ofrecriticality, promptly inserting control rods and terminating the cooldown aremore conservative actions than raising the range of the IRMs to prevent scramwhile waiting on the changing temperature to reverse the direction of thepower. Raising the range of the IRMs in the event of recriticality can beinappropriate if the licensed operators do not have management's oversight,training, and specific procedures.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR IV t'/ ' f'(301) 504-1307 4.f,


===Attachment:===
IN 92-XXApril xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Raising therange of the IRMs in the event of recriticality can be inappropriate if thelicensed operators do not have management's oversight, training, and specificprocedures for this.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEABNAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee*DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92OFC C:DO J f D:DOEANAME CBerlinger CRosswa'yDATE f/;11/92/ 92OFFICIAL RECORD COPYDOCUMENT NAME: IN DENNIG
List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCECOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:D0EA:OEABNAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffeeDATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 q1/t3/92OFC C:DOEA:OGCB D:DOEANAME CBerlinger CRossiDATE / /92 / /92OFFICIAL RECORD COPYDOCUMENT NAME: IN DENNIG IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. In the event ofrecriticality, promptly inserting control rods and terminating the cooldown aremore conservative actions than raising the range of the IRMs to prevent scramwhile waiting on the changing temperature to reverse the direction of thepower. Raising the range of the IRMs in the event of recriticality can beinappropriate if the licensed operators do not have management's oversight,training, and specific procedures.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, 'RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307


===Attachment:===
IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. In the event ofrecriticality, promptly inserting control rods and terminating the cooldown aremore conservative actions than raising the range of the IRMs to prevent scramwhile waiting on the changing temperature to reverse the direction of thepower. Raising the range of the IRMs in the event of recriticality can beinappropriate if the licensed operators do not have management's oversight,training, and specific procedures.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR IV t'/ ' f'(301) 504-1307 4.f,Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCECOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:D0EA:OEABNAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffeeDATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 q1/t3/92OFC C:DOEA:OGCB D:DOEANAME CBerlinger CRossiDATE / /92 / /92OFFICIAL RECORD COPYDOCUMENT NAME: IN DENNIG
List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEABNAME GWright* PO'Connor (OK RDennig* JMain* RJones* AChaffeeDATE 03/11/92 3 /17/92 Xis 192 03/11/92 03/13/92 / /92OFC C:DOEA:OGCB D:DOEANAME CBerlinger CRossiDATE / /92 / /92 IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Since recriti-cality has not been avoided, promptly inserting control rods and terminatingthe cooldown are more conservative actions than raising the range of the IRMsto prevent scram while waiting on the changing temperature to reverse thedirection of the power. Raising the range of the IRMs in the event of recriti-cality can be inappropriate if the licensed operators do not have management'soversight, training, and specific procedures.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RII(708) 790-5695Paul O'Connor, NRR(301) 504-1307


===Attachment:===
IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. In the event ofrecriticality, promptly inserting control rods and terminating the cooldown aremore conservative actions than raising the range of the IRMs to prevent scramwhile waiting on the changing temperature to reverse the direction of thepower. Raising the range of the IRMs in the event of recriticality can beinappropriate if the licensed operators do not have management's oversight,training, and specific procedures.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, 'RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEABNAME GWright* PO'Connor (OK RDennig* JMain* RJones* AChaffeeDATE 03/11/92 3 /17/92 Xis 192 03/11/92 03/13/92 / /92OFC C:DOEA:OGCB D:DOEANAME CBerlinger CRossiDATE / /92 / /92 IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Since recriti-cality has not been avoided, promptly inserting control rods and terminatingthe cooldown are more conservative actions than raising the range of the IRMsto prevent scram while waiting on the changing temperature to reverse thedirection of the power. Raising the range of the IRMs in the event of recriti-cality can be inappropriate if the licensed operators do not have management'soversight, training, and specific procedures.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC :RIII :S Oq;:EfAB:ADM:RPB :C:D B :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEA-____ _ _________---- _ --____________ ----_ -:---------------NAME :GWright* :Rbennig :JMain* j Jones :AChaffee :CBerlinger :CRossiDATE :03/11/92 :3 /11/92 :03/11/92 : /13/92 : / /92 : / /92 : / /92OFFICIAL RECORD COPYDocument Name: IN DENNIG
List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC :RIII :S Oq;:EfAB:ADM:RPB :C:D B :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEA-____ _ _________---- _ --____________ ----_ -:---------------NAME :GWright* :Rbennig :JMain* j Jones :AChaffee :CBerlinger :CRossiDATE :03/11/92 :3 /11/92 :03/11/92 : /13/92 : / /92 : / /92 : / /92OFFICIAL RECORD COPYDocument Name: IN DENNIG Further details of the event may be found in NRC Inspection Report 50-416/92-04and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactor inthe desired condition by properly anticipating, controlling, and responding tothe plant's changing parameters. Once a reactor has been placed in asubcritical condition, as part of a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Given thatrecriticality has not been avoided, prompt insertion of control rods andtermination of the cooldown are more conservative actions than upranging IRMsto prevent scram while waiting on temperature coefficients to turn power.Upranging IRMs in the event of recriticality can be inappropriate if managementoversight, prior training, and specific procedures are absent.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a particular challenge to reactivitycontrol, and require heightened operator and management awareness to avoidrecriticality. In addition, the events at Monticello and Big Rock Pointhighlight the importance of continuous operator attention to plant parametersin the course of a shutdown.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact oneof the technical contacts listed below or the appropriate Office of NuclearReactor Regulation (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307


===Attachment:===
Further details of the event may be found in NRC Inspection Report 50-416/92-04and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactor inthe desired condition by properly anticipating, controlling, and responding tothe plant's changing parameters. Once a reactor has been placed in asubcritical condition, as part of a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Given thatrecriticality has not been avoided, prompt insertion of control rods andtermination of the cooldown are more conservative actions than upranging IRMsto prevent scram while waiting on temperature coefficients to turn power.Upranging IRMs in the event of recriticality can be inappropriate if managementoversight, prior training, and specific procedures are absent.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a particular challenge to reactivitycontrol, and require heightened operator and management awareness to avoidrecriticality. In addition, the events at Monticello and Big Rock Pointhighlight the importance of continuous operator attention to plant parametersin the course of a shutdown.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact oneof the technical contacts listed below or the appropriate Office of NuclearReactor Regulation (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information NoticesOFC :RIII :SC:DOEA:OEAB:ADM:RPB :C:DST:SRXB :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEANAME :GWright :RDennig :JMain_ w :RJones :AChaffee :CBerlinger :CRossiDATE ://92 :1/92 :3/11 /92 :1/92 ://92 :1 /92 :/ /92OFFICIAL RECORD COPYDocument Name: IN DENNIG/DUP
List of Recently Issued NRC Information NoticesOFC :RIII :SC:DOEA:OEAB:ADM:RPB :C:DST:SRXB :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEANAME :GWright :RDennig :JMain_ w :RJones :AChaffee :CBerlinger :CRossiDATE ://92 :1/92 :3/11 /92 :1/92 ://92 :1 /92 :/ /92OFFICIAL RECORD COPYDocument Name: IN DENNIG/DUP IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition, as part of a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Given thatrecriticality has not been avoided, prompt insertion of control rods andtermination of the cooldown are more conservative actions than uprangingIRMs to prevent scram while waiting on temperature coefficients to turn power.Upranging IRMs in the event of recriticality can be inappropriate if managementoversight, prior training, and specific procedures are absent.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a particular challenge to reactivitycontrol, and require heightened operator and management awareness to avoidrecriticality. In addition, the events at Monticello and Big Rock Pointhighlight the importance of continuous operator attention to plant parametersin the course of a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307


===Attachment:===
IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition, as part of a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Given thatrecriticality has not been avoided, prompt insertion of control rods andtermination of the cooldown are more conservative actions than uprangingIRMs to prevent scram while waiting on temperature coefficients to turn power.Upranging IRMs in the event of recriticality can be inappropriate if managementoversight, prior training, and specific procedures are absent.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a particular challenge to reactivitycontrol, and require heightened operator and management awareness to avoidrecriticality. In addition, the events at Monticello and Big Rock Pointhighlight the importance of continuous operator attention to plant parametersin the course of a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information NoticesOFC :R111 bC:DOEA:OEAB:ADM:RPB :C:DST:SRXB :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEANAME :GWrightV' :RDennig :JMain :RJones :AChaffee :CBerlinger :CRossiDATE :3 /II/92 ://92 :/ /92 :/ /92 :/ /92 :/ /92 :/ /92OFFICIAL RECORD COPYDocument Name: IN DENNIG
List of Recently Issued NRC Information NoticesOFC :R111 bC:DOEA:OEAB:ADM:RPB :C:DST:SRXB :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEANAME :GWrightV' :RDennig :JMain :RJones :AChaffee :CBerlinger :CRossiDATE :3 /II/92 ://92 :/ /92 :/ /92 :/ /92 :/ /92 :/ /92OFFICIAL RECORD COPYDocument Name: IN DENNIG}}
 
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Revision as of 18:50, 6 April 2018

Unplanned Return to Criticality During Reactor Shutdown
ML031200314
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: 05/13/1992
From: Rossi C E
Office of Nuclear Reactor Regulation
To:
References
IN-92-039, NUDOCS 9205060036
Download: ML031200314 (12)
v • d • e


UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555May 13, 1992NRC INFORMATION NOTICE 92-39: UNPLANNED RETURN TO CRITICALITY DURINGREACTOR SHUTDOWN

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 recent events involving unplanned returns tocriticality caused by the cooldown of the reactor coolant system during reactorshutdowns. It is expected that recipients will review the information forapplicability 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

The licensees for the following plants recently experienced unplannedcriticalities during reactor shutdowns: the Monticello Nuclear GeneratingPlant, the Big Rock Point Nuclear Plant, and the Grand Gulf Nuclear Station.MonticelloOn June 6, 1991, an unplanned criticality occurred at the Monticello NuclearGenerating Plant during a reactor shutdown when an unanticipated cooldownoccurred in conjunction with rod insertion. The licensee initiated thisshutdown to repair a leaking safety-relief valve shortly after the plant wasreturning to power following a refueling outage.Since this shutdown occurred shortly after the cycle startup, the reactor didnot generate sufficient decay heat to produce the steam needed to supply thenormal steam system loads and still maintain pressure in the reactor. Ascontrol rods were being inserted using notch insertion, the reactor coolantsystem pressure and temperature began to decrease. As long as the operatorcontinued to insert control rods, the reactor remained subcritical.However, when the operator stopped inserting control rods to review andevaluate plant conditions, the cooldown continued, adding sufficientreactivity to overcome the negative reactivity from the insertion of controlrods and causing the reactor power to increase. The reactor power continued to92050_*,, C j'Ai / 1 ( / /CDQc

K)IN 92-39May 13, 1992 increase until an intermediate-range monitor (IRM) tripped on a high-high fluxsetpoint, causing a reactor scram.Further details of the event may be found in Licensee Event Report50-263/91-15 or NRC Inspection Report 50-263/91-13.Big Rock PointOn November 30, 1991, an unplanned criticality occurred at the Big Rock PointNuclear Plant during a reactor shutdown when a cooldown occurred in conjunctionwith a rod insertion. The event occurred during a scheduled shutdown for arefueling outage.After taking the main turbine off line and bringing the reactor to asubcritical condition, the licensee delayed actions to continue insertingcontrol rods while changing shifts. However, the reactor coolant systemcontinued to cool down because the normal steam system loads were removingheat. The cooldown added sufficient reactivity to eventually overcome theeffects of the control rods, and the reactor returned critical. The operatorsnoticed the condition in approximately 2 minutes and took the appropriateactions to return the reactor subcritical.Further details of the event may be found in Licensee Event Report50-155/91-OO9-orJNRC-Inspection-Report 50-155/91-25. _ _ _Grand GulfOn December 30, 1991, an unplanned criticality occurred at the Grand GulfNuclear Station during a reactor shutdown when a cooldown occurred inconjunction with a rod insertion. The event occurred during a scheduledshutdown for a maintenance outage to replace a recirculation pump shaft. Tominimize the release of plated-out radioactive material from the fuel claddingand channels to the reactor coolant system, a slow power reduction and a slowcooldown were prescribed for this shutdown.The slow power reduction and the effects of an earlier outage minimized reactordecay heat and xenon peaking. The operators were driving rods into the coreindividually because gang drive for the control rods was unavailable. Thismade the reactivity insertion slower than normal. The operators insertedrods to reduce flux to range 3 on the IRMs and stopped rod insertion in orderto perform a source range monitor surveillance. Indicated power reached IRMrange 1. However, the reactor coolant system continued to cool down becausethe normal steam system loads were removing heat. In order not to affect thesource range monitor surveillance, the shift supervisor elected to not insertcontrol rods and alerted the operators to the possibility of a return tocriticality as the cooldown continued. The reactivity added by the cooldowneventually overcame the effects of the control rods. The reactor returned to acritical condition, and reactor power increased on a reactor period between 300to 800 seconds. The operators, having been trained on a similar event atanother BWR, were monitoring the condition and expected the power to increaseto the point of adding heat, where the fuel and moderator temperature coeffi-cients would halt the reactor power increase. As the power increased, the

IN 92-39May 13, 1992 reactor operator ranged the IRMs to prevent a reactor scram. Power levelremained on scale. The power increase was terminated with the IRMs reading onrange 7 and 8. The operators completed the source range monitor surveillance,then resumed inserting rods and successfully completed the shutdown.Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. The experience at Monticello, Big RockPoint, and Grand Gulf indicates that shutdowns in situations with low decayheat present a unique challenge to reactivity control if inadvertent recritica-lity is to be prevented. These events emphasize the importance of the operatorgiving continuous attention to plant parameters during a shutdown. Further,accepting recriticality without prior management approval and procedures, i.e.,an ad-hoc approach, raises concerns due to the lack of opportunity for contin-gency planning.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 (NRR) project manager.Va&res'E.Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment:List of Recently Issued NRC Information Notices

zI-0.<OD n; co> 0m Z.4-mrno00zZ G2-cnaEn z* omo) Zen q-n M0n a0 na -h <-Attachment 1IN 92-39May 13, 1992Page I of 1LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESDate ofInformationinformationNotice No.92-381 92-3792-16,Supp. 1I 92-36' 92-35SubjectImplementation Date forthe Revision to the EPAManual of ProtectiveAction Guides and Pro-tective Actions forNuclear IncidentsImplementation of theDeliberate Nisconduct RuleLoss of Flow from the Re-sidual Heat Removal Pumpduring Refueling CavityDraindownIntersystem LOCA OutsideContainmentHigher Than Predicted Ero-sion/Corrosion in Unisol-able Reactor Coolant Pres-sure Boundary Piping InsideContainment at A BoilingWater ReactorNew Exposure Limits forAirborne Uranium andThoriumIncreased InstrumentResponse Time WhenPressure DampeningDevices are InstalledIssuance05/12/9205/08/9205/07/9205/07/9205/06/92Issued toAll holders of OLs or CPsfor nuclear power reactors,non-power reactors andmaterials licensees auth-orized to possess largequantities of radioactivematerial.All Nuclear RegulatoryCommission Licensees.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.-u0rn>mD-C > 0u) D-D2zzz>092-3492-33I CP -'05/06/92 All licensees whose opera-tions can cause airborneconcentrations of uraniumand thorium.04/30/92 All holders of OLs or CPsfor nuclear power reactors.(Operating LicenseConstruction Permit

IN 92-39May 13, 1992 reactor operator ranged the IRMs to prevent a reactor scram. Power levelremained on scale. The power increase was terminated with the IRMs reading onrange 7 and 8. The operators completed the source range monitor surveillance,then resumed inserting rods and successfully completed the shutdown.Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. The experience at Monticello, Big RockPoint, and Grand Gulf indicates that shutdowns in situations with low decayheat present a unique challenge to reactivity control if inadvertent recritica-lity is to be prevented. These events emphasize the importance of the operatorgiving continuous attention to plant parameters during a shutdown. Further,accepting recriticality without prior management approval and procedures, i.e.,an ad-hoc approach, raises concerns due to the lack of opportunity for contin-gency planning.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 (NRR) project manager. Original Signed byNhedes E, RossiCharles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEABNAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee*DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92OFC C:DOEA:OGCB D X,NAME CBerlinger*DATE 04/21/92 05/ 7/92DOCUMENT NAME: IN 92-39 IN 92-XXApril xx, 1992 DOCUMENT NAME:IN DENKIG

IN 92-XXApril xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Raising therange of the IRMs in the event of recriticality can be inappropriate if thelicensed operators do not have management's oversight, training, and specificprocedures for this.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEABNAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee*DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92OFC C:DO J f D:DOEANAME CBerlinger CRosswa'yDATE f/;11/92/ 92OFFICIAL RECORD COPYDOCUMENT NAME: IN DENNIG

IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. In the event ofrecriticality, promptly inserting control rods and terminating the cooldown aremore conservative actions than raising the range of the IRMs to prevent scramwhile waiting on the changing temperature to reverse the direction of thepower. Raising the range of the IRMs in the event of recriticality can beinappropriate if the licensed operators do not have management's oversight,training, and specific procedures.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR IV t'/ ' f'(301) 504-1307 4.f,Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCECOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:D0EA:OEABNAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffeeDATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 q1/t3/92OFC C:DOEA:OGCB D:DOEANAME CBerlinger CRossiDATE / /92 / /92OFFICIAL RECORD COPYDOCUMENT NAME: IN DENNIG

IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. In the event ofrecriticality, promptly inserting control rods and terminating the cooldown aremore conservative actions than raising the range of the IRMs to prevent scramwhile waiting on the changing temperature to reverse the direction of thepower. Raising the range of the IRMs in the event of recriticality can beinappropriate if the licensed operators do not have management's oversight,training, and specific procedures.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, 'RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEABNAME GWright* PO'Connor (OK RDennig* JMain* RJones* AChaffeeDATE 03/11/92 3 /17/92 Xis 192 03/11/92 03/13/92 / /92OFC C:DOEA:OGCB D:DOEANAME CBerlinger CRossiDATE / /92 / /92 IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition during a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Since recriti-cality has not been avoided, promptly inserting control rods and terminatingthe cooldown are more conservative actions than raising the range of the IRMsto prevent scram while waiting on the changing temperature to reverse thedirection of the power. Raising the range of the IRMs in the event of recriti-cality can be inappropriate if the licensed operators do not have management'soversight, training, and specific procedures.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a unique challenge to reactivitycontrol and require the operator and management to give careful attention toavoid recriticality. The events at Monticello and Big Rock Point also highlightthe importance of the operator giving continuous attention to plant parametersduring a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS CONCURRENCEOFC :RIII :S Oq;:EfAB:ADM:RPB :C:D B :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEA-____ _ _________---- _ --____________ ----_ -:---------------NAME :GWright* :Rbennig :JMain* j Jones :AChaffee :CBerlinger :CRossiDATE :03/11/92 :3 /11/92 :03/11/92 : /13/92 : / /92 : / /92 : / /92OFFICIAL RECORD COPYDocument Name: IN DENNIG

Further details of the event may be found in NRC Inspection Report 50-416/92-04and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactor inthe desired condition by properly anticipating, controlling, and responding tothe plant's changing parameters. Once a reactor has been placed in asubcritical condition, as part of a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Given thatrecriticality has not been avoided, prompt insertion of control rods andtermination of the cooldown are more conservative actions than upranging IRMsto prevent scram while waiting on temperature coefficients to turn power.Upranging IRMs in the event of recriticality can be inappropriate if managementoversight, prior training, and specific procedures are absent.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a particular challenge to reactivitycontrol, and require heightened operator and management awareness to avoidrecriticality. In addition, the events at Monticello and Big Rock Pointhighlight the importance of continuous operator attention to plant parametersin the course of a shutdown.This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contact oneof the technical contacts listed below or the appropriate Office of NuclearReactor Regulation (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information NoticesOFC :RIII :SC:DOEA:OEAB:ADM:RPB :C:DST:SRXB :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEANAME :GWright :RDennig :JMain_ w :RJones :AChaffee :CBerlinger :CRossiDATE ://92 :1/92 :3/11 /92 :1/92 ://92 :1 /92 :/ /92OFFICIAL RECORD COPYDocument Name: IN DENNIG/DUP

IN 92-XXMarch xx, 1992 Further details of the event may be found in NRC Inspection Report50-416/92-04 and Licensee Event Report 50-416/91-16.DiscussionThe underlying principle of reactivity management is to maintain the reactorin the desired condition by properly anticipating, controlling, and respondingto the plant's changing parameters. Once a reactor has been placed in asubcritical condition, as part of a plant shutdown, it is of primary importancethat the reactor be maintained in that subcritical condition. Given thatrecriticality has not been avoided, prompt insertion of control rods andtermination of the cooldown are more conservative actions than uprangingIRMs to prevent scram while waiting on temperature coefficients to turn power.Upranging IRMs in the event of recriticality can be inappropriate if managementoversight, prior training, and specific procedures are absent.The experience at Grand Gulf and Monticello indicate that slow shutdowns insituations with low decay heat present a particular challenge to reactivitycontrol, and require heightened operator and management awareness to avoidrecriticality. In addition, the events at Monticello and Big Rock Pointhighlight the importance of continuous operator attention to plant parametersin the course of a shutdown.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 (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Melvyn Leach, RIII(708) 790-5559Geoffrey Wright, RIII(708) 790-5695Paul O'Connor, NRR(301) 504-1307Attachment: List of Recently Issued NRC Information NoticesOFC :R111 bC:DOEA:OEAB:ADM:RPB :C:DST:SRXB :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEANAME :GWrightV' :RDennig :JMain :RJones :AChaffee :CBerlinger :CRossiDATE :3 /II/92 ://92 :/ /92 :/ /92 :/ /92 :/ /92 :/ /92OFFICIAL RECORD COPYDocument Name: IN DENNIG


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