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Category:LICENSEE EVENT REPORT (SEE ALSO AO
MONTHYEARML20024J2451994-10-0606 October 1994 LER 94-006-00:on 940907,observed Receipt of Annunciator 12 Charging Pump Overload Trip.Caused by Overheated C Phase Loadside Connection at Mccb.Breaker Was Replaced & Tested. W/941006 Ltr ML20029E4701994-05-12012 May 1994 LER 94-001-00:on 940412,discovered That Total Pressure Offset Constant in Error.Caused by Technician Error. Procedure Will Be Revised to Prevent recurrence.W/940512 Ltr ML20029D7761994-05-0404 May 1994 LER 94-002-00:on 940303,noble Gas Monitor in R-35 Did Not Respond When source-checked During Surveillance.Caused by Component Failure.Corrective Actions:Monitor Repaired & Returned to svc.W/940504 Ltr ML20046C7791993-08-0505 August 1993 LER 93-009-00:on 930715,receipt of Annunciator Charging Pump 12 Overload Trip Observed by CR Operators,Resulting in Unplanned Closure of Containment Isolation Valve.Standby Charging Pump Started Immediately ML20046A9151993-07-26026 July 1993 LER 93-007-01:on 930413,discovered That Valves Required to Mitigate Consequences of Accident Not Included in Section XI ISI & Testing Program.On 930624,identified Six Addl Valve Inappropriately Ommitted from Subj Program.Valves Included ML20046A8931993-07-23023 July 1993 LER 93-008-00:on 930624,observed That Valve CV-31740, Instrument Air to Unit 1 Containment Closed Due to Failure of Coil in Solenoid Operated Pilot Valve.Valve Reopened Locally to Restore Instrument air.W/930723 Ltr ML20044D2181993-05-13013 May 1993 LER 93-002-00:on 930403,containment Isolation Valve Which Controls Reactor Makeup Water to Containment Exceeded Max Time for Closure.On 930413,lockwire & Safety Tag Removed. Caused by Communication Errors.Safety Tag Process Reviewed ML20044D2241993-05-13013 May 1993 LER 93-007-00:on 930413,discovered That Certain Feedwater Valves,Required to Mitigate Consequences of Accident,Not Included in ASME Section XI ISI & Test Program.Caused by Failure to Interpret Requirements.Valves Tested ML20024H2061991-05-23023 May 1991 LER 91-003-00:on 910423,auto-start Occurred of One Train of Auxiliary Bldg Special Ventilation Sys.Cause Unknown.Plant Mod Initiated Removing Unnecessary Wiring That Could Short Monitor module.W/910523 Ltr ML20024G7001991-04-22022 April 1991 LER 91-002-00:on 910323,auto-start of Control Room Special Ventilation Sys Occurred.Caused by Spike on Newly Installed Radiation Monitor.Wiring Changed to Provide Time Delay Feature for Remaining Four modules.W/910422 Ltr ML20028H8491991-01-28028 January 1991 LER 90-012-00:on 901229,control Room Operators Received Annunciation of Reactor Trip.Caused by Rod Control Sys Failures.Failed Cards in Rod Control Sys replaced.W/910128 Ltr ML20028H0461990-09-26026 September 1990 LER 89-018-03:on 891024,automatic Start of Auxiliary Bldg Ventilation Sys Occurred.Caused by Electronic Spike on Radiation Monitor.Radiation Monitor Modules Will Be Replaced by Upgraded Monitor module.W/900927 Ltr ML20043G1971990-06-15015 June 1990 LER 90-006-00:on 900517,electrical Spike on Radiation Monitor R-25 Caused auto-start of Spent Fuel Pool Special Ventilation Sys.Caused by Procedural Inadequacy.Request for Training Issued Re Basics of Procedure writing.W/900615 Ltr ML20043E0601990-06-0404 June 1990 LER 90-005-00:on 900504,control Room Received High Radiation Alarm & Indication of Automatic Start of Spent Fuel Pool Special Exhaust Fan 121 on Two Occasions.Caused by Electrical Spike on Monitor.Modules replaced.W/900604 Ltr ML20043B6041990-05-24024 May 1990 LER 90-004-00:on 900424,discovered That Surveillance Test SP1042, Resistance Temp Detector Bypass Flow Meter Functional Test Not Performed within Required Time Period. Caused by Personnel Error.Test performed.W/900524 Ltr ML20043E3761990-05-18018 May 1990 LER 90-007-00:on 900517,discovered That Several Relays Deenergized & Automatic Start & Loading of Diesel Generator D1 Initiated.Caused by Inadequate Design.Mod Initiated to Install Test points.W/900608 Ltr ML20042F5681990-05-0404 May 1990 LER 89-021-01:on 891212,chlorine Monitors on One Train of Control Room Ventilation Inoperable for More than 11 H. Caused by Personnel Error.Operating Procedure for Chlorine Monitoring Sys Issued & Training provided.W/900504 Ltr ML20042E6811990-04-23023 April 1990 LER 90-003-00:on 900323,automatic Start of Safeguards Cooling Water Pump Occurred Due to Inadequate Procedures. Plant Procedures Revised to Improve Guidance for Detecting Loss of prime.W/900423 Ltr ML20012D4941990-03-19019 March 1990 LER 89-004-01:on 891221,reactor Trips & Loss of Power to Reactor Coolant Pumps Occurred.Caused by Malfunctions in MG Sets,Rod Control Sys & Substation Breaker Control Sys. Voltage Regulator for MG Set replaced.W/900319 Ltr ML20006E8211990-02-20020 February 1990 LER 90-002-00:on 900117,review of Cooldown Data Showed That Cooldown Rate of Pressurizer Exceeded Tech Spec Limit.Caused by Procedure Inadequacy.Procedures Revised to Require Use of Water Space Temp to Find Cooldown rate.W/900220 Ltr ML20006E4581990-02-16016 February 1990 LER 90-001-00:on 900117,technician Mirror Contacted Bare Power Supply Terminal & Shorted Terminal to Ground,Causing Power Supply to Trip & Isolation of Outside Air to Control Room.Exposed Wire Terminal Points covered.W/900216 Ltr ML20006A9721990-01-22022 January 1990 LER 89-004-00:on 891221,unit Tripped & Reactor Coolant Pumps Lost Power.Caused by Faulty Voltage Regulation of One CRD Mechanism motor-generator Set.Regulator for Set Replaced & Tested.On 891226,identical Trip occurred.W/900122 Ltr ML20005G3731990-01-11011 January 1990 LER 89-021-00:on 891211,computer Alarmed Indicating Malfunction of Chlorine Monitors 121 & 122 & Leaving Control Room Ventilation Sys Inoperable for More than 11 H.Caused by Personnel Error.Monitor 122 Returned to normal.W/900111 Ltr ML19351A4681989-12-11011 December 1989 LER 89-020-00:on 891108,17,20,23,1201 & 08,automatic Isolation of Control Room Supply & Exhaust Occurred.Caused by Malfunctions of Chlorine Gas Detectors.Addl Monitors Installed & Actuation Logic modified.W/891211 Ltr ML20005D7071989-11-30030 November 1989 LER 89-018-01:on 891024,25,31 & 1112,control Room Received High Radiation Alarm Which Initiated Automatic Start of Auxiliary Bldg Special Ventilation Sys.Caused by Radiation Monitor Spikes.Monitor Modules replaced.W/891130 Ltr ML19332C6171989-11-22022 November 1989 LER 89-018-00:on 891024,25 & 1112,control Room Received Train a High Radiation Alarm,Initiating Automatic Start of Auxiliary Bldg Special Ventilation Sys.Caused by Spike of Radiation Monitor.Monitor replaced.W/891122 Ltr ML19332C6241989-11-22022 November 1989 LER 89-003-00:on 891023,measured Leakage Rate Exceeded Tech Specs Limit While Performing Surveillance Test Sp 2136. Caused by Wear of Grafoil Packing Due to High Frequency of Door Usage.Test Procedures modified.W/891122 Ltr ML19332C7001989-11-20020 November 1989 LER 89-019-00:on 891025,Train a of Auxiliary Bldg Special Ventilation Sys Started Automatically When Power Mistakenly Turned Off.Caused by Personnel Error.Involved Personnel Counseled.Clarifying Revs Made to procedure.W/891121 Ltr ML19325D4901989-10-16016 October 1989 LER 89-017-00:on 890914,discovered That Present Position of Transfer Switch for Power Supplying Control & Protection Relays for Diesel Generator Does Not Meet Requirements of App R.Caused by Inadequate procedures.W/891016 Ltr ML19325C7491989-10-10010 October 1989 LER 89-016-00:on 890908,control Room Received Train B High Radiation Alarm,Which Initiated Automatic Start of Auxiliary Bldg Special Ventilation Sys.Caused by Spike on Radiation Monitor 2R-30.Monitor Upgrade Being pursued.W/891010 Ltr ML19325C1991989-10-0505 October 1989 LER 89-015-00:on 890905 & 23,special Ventilation Sys of Control Rooms 122 & 121 Actuated Automatically.Caused by False High Chlorine Signal & Broken Chlorine Sensitive Paper Tape,Respectively.Detectors repaired.W/891005 Ltr ML19325C1981989-10-0505 October 1989 LER 89-014-00:on 890905,operations Personnel Recalled That SP1093.1 Performed Two Wks Previously Instead of SP1093.2. Caused by Personnel Error in Selecting Incorrect Procedure. Proper Notifications Made & SP1093.2 performed.W/891005 Ltr ML20028E3301983-01-12012 January 1983 LER 82-029/01T-0:on 821228,tiny through-wall Crack Found in heat-affected Zone of Weld on Safety Injection Supply Line from Boric Acid Storage Tanks.Cause Unknown. Fracture Mechanics Analysis Underway ML20028C2441982-12-30030 December 1982 LER 82-025/03L-0:on 821130,one Steam Flow Channel Differed from Redundant Channels During Power Reduction Due to out- of-calibr Transmitter.Cause Not Known.Transmitter Recalibr & Returned to Svc.Transmitter to Be Replaced If Drift Recurs ML20028C3681982-12-30030 December 1982 Signed LER 82-025/03L-0:on 821130,during Power Reduction,One Steam Flow Channel Differed from Redundant Channels. Transmitter Showed Out of Calibr.Cause Unknown.Transmitter Recalibr.Bistables Placed in Trip During Recalibr ML20028C1651982-12-22022 December 1982 LER 82-024/03L-0:on 821123,diesel Generator D1 Inoperable for Approx 4 Minutes After Lockout of Engine Shutdown Circuit Occurred.Probably Caused by Sticky Action of Speed Switch.Further Exam of Circuitry Will Be Performed ML20028A9761982-11-17017 November 1982 LER 82-021/03L-0:on 821027,following Use in Routine Sampling Procedure SV-33655,hot Leg Loop B Sample Inside Containment Isolation Valve Failed to Remain Closed.Caused by Malfunction of Limit Switch.Switch Replaced ML20051A9561982-05-0707 May 1982 LER 82-006/01T-0:on 820423,during Surveillance Test Sp 1104, Measured Reactor Coolant Boron Concentration Higher than Originally Predicted Value.Caused by Miscalculation of Predicted Worth.Analysis Performed to Monitor Disagreement ML20052B2731982-04-21021 April 1982 LER 82-005/03L-0:on 820322,review of Chemistry Logs Showed That Boric Acid Tank 11 Had Not Been Sampled.Caused by Communication Breakdown.Tank Sampled & Involved Personnel Will Review Rept ML20050A8331982-03-24024 March 1982 LER 82-004/03L-0:on 820226,maint Workman Accidentally Bumped Overspeed Trip Mechanism on Auxiliary Feedwater Pump, Tripping Valve & Making Pump Inoperable.Caused by Personnel Error.Valve Operator Reset ML20042A5101982-03-12012 March 1982 LER 82-003/03L-0:on 820209,during Annual Visual Insp,One Steam Exclusion Control Damper Found Inoperable.Caused by Failure of Drive Gear in Pacific Air Products Damper Model R-35-FS.Gear Replaced ML20049H6061982-02-24024 February 1982 LER 82-001/03L-0:on 820125,one Overpower Delta T Summing Unit Found Out of Spec.Caused by Foxboro Model 66RC-OL Summing Unit Instrument Drift.Device Recalibr.Evaluation Underway ML20049H6841982-02-24024 February 1982 LER 82-002/03L-0:on 820125,one Overpower Delta T Summing Unit Found Out of Spec High.Caused by Instrument Drift. Device Recalibr ML20041B4041982-02-12012 February 1982 Updated LER 81-030/03L-0:on 811211,during Testing,Degraded Voltage Relay 27A1/B25 Found W/Voltage Setpoint Outside Allowable Band.Exact Cause Unknown.Relays Recalibr & Found to Operate Correctly ML20041B3991982-02-12012 February 1982 Updated LER 81-029/03L-0:on 811210,during Surveillance Test of Bus 16 Undervoltage Relays,Error in Disconnecting Test Equipment Resulted in Blown Fuse for A-phase Relays.Fuses Replaced & Normal Power Restored to Bus ML20040A5841982-01-15015 January 1982 LER 81-029/03L-0:on 811210,during Testing of Bus 16 Undervoltage Relays,Error in Disconnecting Test Equipment Resulted in Blown Fuse for a Phase Relays.Fuses Replaced. Undervoltage Relay Tests Will Be Revised ML20040A5671982-01-15015 January 1982 LER 81-030/03L-0:on 811210,degraded Voltage Relay 27A1/B25 Found W/Voltage Setpoint Outside Allowable Band.Causes Being Considered Are Last Calibr Error & Unfamiliarity W/Time Delay Relay Characteristics ML20039E5521981-12-30030 December 1981 LER 81-031/01T-0:on 811216,during Transfer of Spent Fuel in Preparation for Reracking of Pool 2,spent Fuel Assembly Top Nozzle Separated,Causing Assembly to Tip Toward Edge of Pool.Cause Unknown.Fuel Handling Operations Suspended ML20039C2751981-12-18018 December 1981 LER 81-028/03L-0:on 811118 & 1218,bistables 2-PC-431 G & I Found Out of Tolerance.Caused by Defective Potentiometer on 811118.On 811218,leads Were Tightened,Correcting Problem ML20039C2681981-12-16016 December 1981 LER 81-027/03L-0:on 811116,discovered That Pre,Absolute & Charcoal Filter Test Not Done on 11 Shield Bldg Ventilation Sys Replacement on 811112.Caused by Procedural Inadequacies & Poor Communications 1994-05-04
[Table view] Category:RO)
MONTHYEARML20024J2451994-10-0606 October 1994 LER 94-006-00:on 940907,observed Receipt of Annunciator 12 Charging Pump Overload Trip.Caused by Overheated C Phase Loadside Connection at Mccb.Breaker Was Replaced & Tested. W/941006 Ltr ML20029E4701994-05-12012 May 1994 LER 94-001-00:on 940412,discovered That Total Pressure Offset Constant in Error.Caused by Technician Error. Procedure Will Be Revised to Prevent recurrence.W/940512 Ltr ML20029D7761994-05-0404 May 1994 LER 94-002-00:on 940303,noble Gas Monitor in R-35 Did Not Respond When source-checked During Surveillance.Caused by Component Failure.Corrective Actions:Monitor Repaired & Returned to svc.W/940504 Ltr ML20046C7791993-08-0505 August 1993 LER 93-009-00:on 930715,receipt of Annunciator Charging Pump 12 Overload Trip Observed by CR Operators,Resulting in Unplanned Closure of Containment Isolation Valve.Standby Charging Pump Started Immediately ML20046A9151993-07-26026 July 1993 LER 93-007-01:on 930413,discovered That Valves Required to Mitigate Consequences of Accident Not Included in Section XI ISI & Testing Program.On 930624,identified Six Addl Valve Inappropriately Ommitted from Subj Program.Valves Included ML20046A8931993-07-23023 July 1993 LER 93-008-00:on 930624,observed That Valve CV-31740, Instrument Air to Unit 1 Containment Closed Due to Failure of Coil in Solenoid Operated Pilot Valve.Valve Reopened Locally to Restore Instrument air.W/930723 Ltr ML20044D2181993-05-13013 May 1993 LER 93-002-00:on 930403,containment Isolation Valve Which Controls Reactor Makeup Water to Containment Exceeded Max Time for Closure.On 930413,lockwire & Safety Tag Removed. Caused by Communication Errors.Safety Tag Process Reviewed ML20044D2241993-05-13013 May 1993 LER 93-007-00:on 930413,discovered That Certain Feedwater Valves,Required to Mitigate Consequences of Accident,Not Included in ASME Section XI ISI & Test Program.Caused by Failure to Interpret Requirements.Valves Tested ML20024H2061991-05-23023 May 1991 LER 91-003-00:on 910423,auto-start Occurred of One Train of Auxiliary Bldg Special Ventilation Sys.Cause Unknown.Plant Mod Initiated Removing Unnecessary Wiring That Could Short Monitor module.W/910523 Ltr ML20024G7001991-04-22022 April 1991 LER 91-002-00:on 910323,auto-start of Control Room Special Ventilation Sys Occurred.Caused by Spike on Newly Installed Radiation Monitor.Wiring Changed to Provide Time Delay Feature for Remaining Four modules.W/910422 Ltr ML20028H8491991-01-28028 January 1991 LER 90-012-00:on 901229,control Room Operators Received Annunciation of Reactor Trip.Caused by Rod Control Sys Failures.Failed Cards in Rod Control Sys replaced.W/910128 Ltr ML20028H0461990-09-26026 September 1990 LER 89-018-03:on 891024,automatic Start of Auxiliary Bldg Ventilation Sys Occurred.Caused by Electronic Spike on Radiation Monitor.Radiation Monitor Modules Will Be Replaced by Upgraded Monitor module.W/900927 Ltr ML20043G1971990-06-15015 June 1990 LER 90-006-00:on 900517,electrical Spike on Radiation Monitor R-25 Caused auto-start of Spent Fuel Pool Special Ventilation Sys.Caused by Procedural Inadequacy.Request for Training Issued Re Basics of Procedure writing.W/900615 Ltr ML20043E0601990-06-0404 June 1990 LER 90-005-00:on 900504,control Room Received High Radiation Alarm & Indication of Automatic Start of Spent Fuel Pool Special Exhaust Fan 121 on Two Occasions.Caused by Electrical Spike on Monitor.Modules replaced.W/900604 Ltr ML20043B6041990-05-24024 May 1990 LER 90-004-00:on 900424,discovered That Surveillance Test SP1042, Resistance Temp Detector Bypass Flow Meter Functional Test Not Performed within Required Time Period. Caused by Personnel Error.Test performed.W/900524 Ltr ML20043E3761990-05-18018 May 1990 LER 90-007-00:on 900517,discovered That Several Relays Deenergized & Automatic Start & Loading of Diesel Generator D1 Initiated.Caused by Inadequate Design.Mod Initiated to Install Test points.W/900608 Ltr ML20042F5681990-05-0404 May 1990 LER 89-021-01:on 891212,chlorine Monitors on One Train of Control Room Ventilation Inoperable for More than 11 H. Caused by Personnel Error.Operating Procedure for Chlorine Monitoring Sys Issued & Training provided.W/900504 Ltr ML20042E6811990-04-23023 April 1990 LER 90-003-00:on 900323,automatic Start of Safeguards Cooling Water Pump Occurred Due to Inadequate Procedures. Plant Procedures Revised to Improve Guidance for Detecting Loss of prime.W/900423 Ltr ML20012D4941990-03-19019 March 1990 LER 89-004-01:on 891221,reactor Trips & Loss of Power to Reactor Coolant Pumps Occurred.Caused by Malfunctions in MG Sets,Rod Control Sys & Substation Breaker Control Sys. Voltage Regulator for MG Set replaced.W/900319 Ltr ML20006E8211990-02-20020 February 1990 LER 90-002-00:on 900117,review of Cooldown Data Showed That Cooldown Rate of Pressurizer Exceeded Tech Spec Limit.Caused by Procedure Inadequacy.Procedures Revised to Require Use of Water Space Temp to Find Cooldown rate.W/900220 Ltr ML20006E4581990-02-16016 February 1990 LER 90-001-00:on 900117,technician Mirror Contacted Bare Power Supply Terminal & Shorted Terminal to Ground,Causing Power Supply to Trip & Isolation of Outside Air to Control Room.Exposed Wire Terminal Points covered.W/900216 Ltr ML20006A9721990-01-22022 January 1990 LER 89-004-00:on 891221,unit Tripped & Reactor Coolant Pumps Lost Power.Caused by Faulty Voltage Regulation of One CRD Mechanism motor-generator Set.Regulator for Set Replaced & Tested.On 891226,identical Trip occurred.W/900122 Ltr ML20005G3731990-01-11011 January 1990 LER 89-021-00:on 891211,computer Alarmed Indicating Malfunction of Chlorine Monitors 121 & 122 & Leaving Control Room Ventilation Sys Inoperable for More than 11 H.Caused by Personnel Error.Monitor 122 Returned to normal.W/900111 Ltr ML19351A4681989-12-11011 December 1989 LER 89-020-00:on 891108,17,20,23,1201 & 08,automatic Isolation of Control Room Supply & Exhaust Occurred.Caused by Malfunctions of Chlorine Gas Detectors.Addl Monitors Installed & Actuation Logic modified.W/891211 Ltr ML20005D7071989-11-30030 November 1989 LER 89-018-01:on 891024,25,31 & 1112,control Room Received High Radiation Alarm Which Initiated Automatic Start of Auxiliary Bldg Special Ventilation Sys.Caused by Radiation Monitor Spikes.Monitor Modules replaced.W/891130 Ltr ML19332C6171989-11-22022 November 1989 LER 89-018-00:on 891024,25 & 1112,control Room Received Train a High Radiation Alarm,Initiating Automatic Start of Auxiliary Bldg Special Ventilation Sys.Caused by Spike of Radiation Monitor.Monitor replaced.W/891122 Ltr ML19332C6241989-11-22022 November 1989 LER 89-003-00:on 891023,measured Leakage Rate Exceeded Tech Specs Limit While Performing Surveillance Test Sp 2136. Caused by Wear of Grafoil Packing Due to High Frequency of Door Usage.Test Procedures modified.W/891122 Ltr ML19332C7001989-11-20020 November 1989 LER 89-019-00:on 891025,Train a of Auxiliary Bldg Special Ventilation Sys Started Automatically When Power Mistakenly Turned Off.Caused by Personnel Error.Involved Personnel Counseled.Clarifying Revs Made to procedure.W/891121 Ltr ML19325D4901989-10-16016 October 1989 LER 89-017-00:on 890914,discovered That Present Position of Transfer Switch for Power Supplying Control & Protection Relays for Diesel Generator Does Not Meet Requirements of App R.Caused by Inadequate procedures.W/891016 Ltr ML19325C7491989-10-10010 October 1989 LER 89-016-00:on 890908,control Room Received Train B High Radiation Alarm,Which Initiated Automatic Start of Auxiliary Bldg Special Ventilation Sys.Caused by Spike on Radiation Monitor 2R-30.Monitor Upgrade Being pursued.W/891010 Ltr ML19325C1991989-10-0505 October 1989 LER 89-015-00:on 890905 & 23,special Ventilation Sys of Control Rooms 122 & 121 Actuated Automatically.Caused by False High Chlorine Signal & Broken Chlorine Sensitive Paper Tape,Respectively.Detectors repaired.W/891005 Ltr ML19325C1981989-10-0505 October 1989 LER 89-014-00:on 890905,operations Personnel Recalled That SP1093.1 Performed Two Wks Previously Instead of SP1093.2. Caused by Personnel Error in Selecting Incorrect Procedure. Proper Notifications Made & SP1093.2 performed.W/891005 Ltr ML20028E3301983-01-12012 January 1983 LER 82-029/01T-0:on 821228,tiny through-wall Crack Found in heat-affected Zone of Weld on Safety Injection Supply Line from Boric Acid Storage Tanks.Cause Unknown. Fracture Mechanics Analysis Underway ML20028C2441982-12-30030 December 1982 LER 82-025/03L-0:on 821130,one Steam Flow Channel Differed from Redundant Channels During Power Reduction Due to out- of-calibr Transmitter.Cause Not Known.Transmitter Recalibr & Returned to Svc.Transmitter to Be Replaced If Drift Recurs ML20028C3681982-12-30030 December 1982 Signed LER 82-025/03L-0:on 821130,during Power Reduction,One Steam Flow Channel Differed from Redundant Channels. Transmitter Showed Out of Calibr.Cause Unknown.Transmitter Recalibr.Bistables Placed in Trip During Recalibr ML20028C1651982-12-22022 December 1982 LER 82-024/03L-0:on 821123,diesel Generator D1 Inoperable for Approx 4 Minutes After Lockout of Engine Shutdown Circuit Occurred.Probably Caused by Sticky Action of Speed Switch.Further Exam of Circuitry Will Be Performed ML20028A9761982-11-17017 November 1982 LER 82-021/03L-0:on 821027,following Use in Routine Sampling Procedure SV-33655,hot Leg Loop B Sample Inside Containment Isolation Valve Failed to Remain Closed.Caused by Malfunction of Limit Switch.Switch Replaced ML20051A9561982-05-0707 May 1982 LER 82-006/01T-0:on 820423,during Surveillance Test Sp 1104, Measured Reactor Coolant Boron Concentration Higher than Originally Predicted Value.Caused by Miscalculation of Predicted Worth.Analysis Performed to Monitor Disagreement ML20052B2731982-04-21021 April 1982 LER 82-005/03L-0:on 820322,review of Chemistry Logs Showed That Boric Acid Tank 11 Had Not Been Sampled.Caused by Communication Breakdown.Tank Sampled & Involved Personnel Will Review Rept ML20050A8331982-03-24024 March 1982 LER 82-004/03L-0:on 820226,maint Workman Accidentally Bumped Overspeed Trip Mechanism on Auxiliary Feedwater Pump, Tripping Valve & Making Pump Inoperable.Caused by Personnel Error.Valve Operator Reset ML20042A5101982-03-12012 March 1982 LER 82-003/03L-0:on 820209,during Annual Visual Insp,One Steam Exclusion Control Damper Found Inoperable.Caused by Failure of Drive Gear in Pacific Air Products Damper Model R-35-FS.Gear Replaced ML20049H6061982-02-24024 February 1982 LER 82-001/03L-0:on 820125,one Overpower Delta T Summing Unit Found Out of Spec.Caused by Foxboro Model 66RC-OL Summing Unit Instrument Drift.Device Recalibr.Evaluation Underway ML20049H6841982-02-24024 February 1982 LER 82-002/03L-0:on 820125,one Overpower Delta T Summing Unit Found Out of Spec High.Caused by Instrument Drift. Device Recalibr ML20041B4041982-02-12012 February 1982 Updated LER 81-030/03L-0:on 811211,during Testing,Degraded Voltage Relay 27A1/B25 Found W/Voltage Setpoint Outside Allowable Band.Exact Cause Unknown.Relays Recalibr & Found to Operate Correctly ML20041B3991982-02-12012 February 1982 Updated LER 81-029/03L-0:on 811210,during Surveillance Test of Bus 16 Undervoltage Relays,Error in Disconnecting Test Equipment Resulted in Blown Fuse for A-phase Relays.Fuses Replaced & Normal Power Restored to Bus ML20040A5841982-01-15015 January 1982 LER 81-029/03L-0:on 811210,during Testing of Bus 16 Undervoltage Relays,Error in Disconnecting Test Equipment Resulted in Blown Fuse for a Phase Relays.Fuses Replaced. Undervoltage Relay Tests Will Be Revised ML20040A5671982-01-15015 January 1982 LER 81-030/03L-0:on 811210,degraded Voltage Relay 27A1/B25 Found W/Voltage Setpoint Outside Allowable Band.Causes Being Considered Are Last Calibr Error & Unfamiliarity W/Time Delay Relay Characteristics ML20039E5521981-12-30030 December 1981 LER 81-031/01T-0:on 811216,during Transfer of Spent Fuel in Preparation for Reracking of Pool 2,spent Fuel Assembly Top Nozzle Separated,Causing Assembly to Tip Toward Edge of Pool.Cause Unknown.Fuel Handling Operations Suspended ML20039C2751981-12-18018 December 1981 LER 81-028/03L-0:on 811118 & 1218,bistables 2-PC-431 G & I Found Out of Tolerance.Caused by Defective Potentiometer on 811118.On 811218,leads Were Tightened,Correcting Problem ML20039C2681981-12-16016 December 1981 LER 81-027/03L-0:on 811116,discovered That Pre,Absolute & Charcoal Filter Test Not Done on 11 Shield Bldg Ventilation Sys Replacement on 811112.Caused by Procedural Inadequacies & Poor Communications 1994-05-04
[Table view] Category:TEXT-SAFETY REPORT
MONTHYEARML20217G4461999-09-30030 September 1999 Monthly Operating Repts for Sept 1999 for Pingp.With ML20217A9931999-09-30030 September 1999 NRC Regulatory Assessment & Oversight Pilot Program, Performance Indicator Data ML20217A1691999-09-22022 September 1999 Part 21 Rept Re Engine Sys,Inc Controllers,Manufactured Between Dec 1997 & May 1999,that May Have Questionable Soldering Workmanship.Caused by Inadequate Personnel Training.Sent Rept to All Nuclear Customers ML20216E7151999-08-31031 August 1999 Monthly Operating Repts for Aug 1999 for Pingp,Units 1 & 2. with ML20211D3981999-08-24024 August 1999 Safety Evaluation Supporting Requested Actions to Licenses DPR-42 & DPR-60,respectively ML20211C2531999-08-0404 August 1999 Unit 1 ISI Summary Rept Interval 3,Period 2 Refueling Outage Dates 990425-990526 Cycle 19 971212-990526 ML20210Q4891999-07-31031 July 1999 Monthly Operating Repts for July 1999 for Pingp,Units 1 & 2. with ML20211B5971999-07-31031 July 1999 Cycle 20 Voltage-Based Repair Criteria 90-Day Rept ML20209J1131999-07-15015 July 1999 Safety Evaluation of Topical Rept NSPNAD-8102,rev 7 Reload Safety Evaluation Methods for Application to PI Units. Rept Acceptable for Referencing in Prairie Island Licensing Actions ML20196H8621999-06-30030 June 1999 NRC Regulatory Assessment & Oversight Pilot Program, Performance Indicator Data, June 1999 Rept ML20209F9811999-06-30030 June 1999 Monthly Operating Repts for June 1999 for Prairie Island Nuclear Generating Plant,Units 1 & 2.With ML20196F4081999-06-23023 June 1999 Revised Pages 71,72 & 298 to Rev 7 of NSPNAD-8102, Prairie Island Nuclear Power Plant Reload Safety Evaluation Methods for Application to PI Units ML20195G5181999-05-31031 May 1999 Monthly Operating Repts for May 1999 for Prairie Island Nuclear Generating Plant,Units 1 & 2.With . Page 3 in Final Rept of Incoming Submittal Was Not Included ML20207B5931999-05-26026 May 1999 SER Accepting Licensee Proposed Alternative to ASME Code for Surface Exam (PT) of Seal Welds on Threaded Caps for Unit 1 Reactor Vessel Head Penetrations for part-length CRDMs ML20196L2501999-05-13013 May 1999 Rev 0 to PINGP Unit 1 COLR Cycle 20 ML20206L6191999-04-30030 April 1999 Monthly Operating Repts for Apr 1999 for Pingp,Units 1 & 2. with ML20205N1081999-03-31031 March 1999 Monthly Operating Repts for Mar 1999 for Pingp,Units 1 & 2. with ML20205Q5101999-03-15015 March 1999 Inservice Insp Summary Rept Interval 3,Period 1 & 2 Refueling Outage Dates 981109-1229 Cycle 19,970327-981229 ML20207J6951999-02-28028 February 1999 Monthly Operating Repts for Feb 1999 for Prairie Island Nuclear Generating Plant ML20202J7711999-02-0404 February 1999 Simulator Certification Rept for Prairie Island Plant Simulation Facility,1998 Annual Rept ML20202G3761999-01-31031 January 1999 Non-proprietary Rev 7 to NSPNAD-8102-NP, Prairie Island Nuclear Power Plant Reload SE Methods for Application to PI Units ML20207L2811999-01-31031 January 1999 Revised Monthly Operating Repts for Jan 1999 for Pingp,Units 1 & 2 ML20202J1731999-01-22022 January 1999 Safety Evaluation Concluding That NSP Proposed Alternative to Surface Exam Requirements of ASME BPV Code for CRD Mechanism Canopy Seal Welds Will Provide Acceptable Level of Quality & Safety ML20206P7861998-12-31031 December 1998 Monthly Operating Repts for Dec 1998 for Prairie Island Nuclear Generating Plant.With ML20205H0561998-12-31031 December 1998 Northern States Power Co 1998 Annual Rept. with ML20198J6441998-12-17017 December 1998 Rev 0 to PINGP COLR Unit 2-Cycle 19 ML20206N2731998-11-30030 November 1998 Monthly Operating Repts for Nov 1998 for Prairie Island Nuclear Generating Plant,Units 1 & 2.With ML20196D7341998-11-20020 November 1998 Third Quarter 1998 & Oct 1998 Data Rept for Prairie Island Isfsi ML20155K6301998-10-31031 October 1998 Monthly Operating Repts for Oct 1998 for Prairie Island Nuclear Generating Plant,Units 1 & 2.With ML20154H4061998-09-30030 September 1998 Monthly Operating Repts for Sept 1998 for Prairie Island Nuclear Generating Plant.With ML20202J7991998-09-30030 September 1998 Non-proprietary Version of Rev 3 to CEN-629-NP, Repair of W Series 44 & 51 SG Tubes Using Leaktight Sleeves,Final Rept ML20198P0571998-09-0303 September 1998 Rev 1 to 95T047, Back-up Compressed Air Supply for Cooling Water Strainer Backwash Valve Actuator ML20153B0761998-08-31031 August 1998 Monthly Operating Repts for Aug 1998 for Prairie Island Nuclear Generating Plant.With ML20237A3961998-08-11011 August 1998 Safety Evaluation on Westinghouse Owners Group Proposed Insp Program for part-length CRDM Housing Issue.Insp Program for Type 309 Welds Inadequate from Statistical Point of View ML20237A8171998-08-0505 August 1998 SER Related to USI A-46 Program GL 87-02 Implementation for Prairie Island Nuclear Generating Plant,Units 1 & 2 ML20236X8531998-07-31031 July 1998 Monthly Operating Repts for July 1998 for Prairie Island Nuclear Generating Plant ML20236R6481998-07-15015 July 1998 Metallurgical Investigation & Root Cause Assessment of Part Length CRDM Housing Motor Tube Cracking at PINGP Unit 2 - Preliminary Summary Rept ML20236R0771998-06-30030 June 1998 Monthly Operating Repts for June 1998 for Prairie Island Nuclear Generating Plant ML20249A5751998-05-31031 May 1998 Monthly Operating Repts for May 1998 for Prairie Island Nuclear Generating Plant ML20247G7011998-05-31031 May 1998 Metallurgical Investigation & Root Cause Assessment of Part Length CRDM Housing Motor Tube Cracking at Prairie Island Nuclear Generating Plant,Unit 2 ML20248M0561998-05-31031 May 1998 Rev 5 to CEN-620-NP, Series 44 & 51 Design SG Tube Repair Using Tube Rerolling Technique ML20247E2671998-05-0505 May 1998 Rev 0 to Pingp,Units 1 & 2,Pressure & Temp Limits Rept (Effective Until 35 Efpy) ML20247G2921998-04-30030 April 1998 Monthly Operating Repts for Apr 1998 for Prairie Island Nuclear Generating Plant ML20217M6901998-04-29029 April 1998 Safety Evaluation Accepting Methodology for Relocation of Reactor Coolant Sys P/T Limit Curves & LTOP Sys Limits Proposed by NSP for Pingp,Units 1 & 2 ML20216C6361998-03-31031 March 1998 Monthly Operating Repts for Mar 1998 for Prairie Nuclear Generating Plant Units 1 & 2 ML20216H0341998-03-31031 March 1998 Cycle-19 Voltage Based TSP Alternate Repair Criteria 90-Day Rept ML20217D2041998-03-13013 March 1998 Rev 1 to 28723-A, Intake Canal Liquefaction Analysis Rept for Pingp,Welch,Mn ML20236P9801998-03-12012 March 1998 Rev 0 to 97FP02-DOC-01, Compliance Review of 10CFR50,App R, Section Iii.O RCP Lube Oil Collection Sys ML20248L3931998-03-10010 March 1998 ISI Summary Rept Interval 3,Period 1 & 2 Refueling Outage Dates 971018-971212 Cycle 18,960303-971212 ML20216D0911998-03-0606 March 1998 Rev 0 to Prairie Island Generating Plant,Units 1 & 2, Pressure & Temp Limits Rept 1999-09-30
[Table view] |
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Northom States Power Company l 414 Nicollet Mall
- Minneapolis, Minnesota $54011927 Telephone (612) 330-5500 l- -
March 19, 1990 Report Required by 10 CFR Part 50, Section 50.73 Director of. Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission
~ Attn: Document Control Desk Washington, DC 20555
[
L PRAIRIE ISLAND NUCLEAR CENERATING PLANT Docket No. 50-282 License No. DPR-42.
50-306 DPR-60 1
l' 1
Revision 1 Unit 2 Reactor Trips and Loss of Power to Reactor Coolant Pumns ,
1 A revised Licensee Event Report is attached, l 'Please contact us if you require additional information related to these l cvents.
l 1
-Thomas M Parker
' Manager Nuclear Support Services c: Regional Administrator - III NRC Sr Resident _ Inspector, NRC NRR Project Manager, NRC MPCA
' Attn: Dr J W Ferman f Attachment
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f aTLt les Unit 2 Reactor Trips and Loss of Power to Reactor Coolant Pumps I tviatT C ATE (Si i Lim NUM64R IS) REPORT DAff17t OTHER F ACILITit8 INv0LVt0 ISI MONTM Day vtAR vtAR "(Q[,^ 4 QQ uCNTM OAv vgaR e ACnif v hauts DOCKET NWuttmist Prairie Ieland Unit 1 0 t 510 l 0 l 012; g 12
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Unit 2 tripped on December 21, 1989, from what appeared to be faulty voltage regulation by one of the control rod drive mechanism motor-generator sets. One substation circuit breaker did not operate properly and power was lost to non-safeguards 4KV buses, which supply the reactor coolant pumps. The reactor was cooled by natural circulation for about 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />. The voltage regulator for the MG set was replaced and I tested. .Since the outdoor temperature at the time of the trip was -22 F, l l the cold was blamed for the breaker malfunction. Heating was applied to r the substation breakers and testing showed proper operation. The unit i
was restarted. On December 26, 1989, a nearly identical trip and loss of non safeguards 4KV buses occurred. Extensive investigation uncovered malfunctions in the MG sets, in the rod control system, and in the
- substation breaker control system. After repairs and extensive testing, l
Unit 2 was returned to service on January 10, 1990.
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Ol 1 0l2 OF 1 l0 rixv , . w. == we u , am.mm EVFNT DESCRIPTION. CAUSE AND CORRECTIVE ACTIONS On December 21, 1989, Unit 2 was operating at 100% power.
At approximately 0223 hours0.00258 days <br />0.0619 hours <br />3.687169e-4 weeks <br />8.48515e-5 months <br /> the reactor tripped. Subsequent to the trip, power to the Unit 2 non safeguards 4KV buses (EIIS Component Identifier BU), which supply the reactor coolant pumps, was not available due to
. failure of 345KV breaker (EIIS Component Identifier BKR) 8H13 in the- 1 substation. Both emergency diesel generators (EIIS Component Identifier DG) started but did not load since the Unit 2 safeguards buses remained powered by their alternate supplies. Power was restored to the non safeguards buses, and the reactor coolant pumps, approximately three hours after the trip. Technical Specifications in effect on December 21, 1989 required one reactor coolant pump or one residual heat removal pump ].
.be. inservice at all times. Technical Specifications allowed all pumps to be shutdown for up to one hour provided the reactor was suberitical, no dilution was in progress, and at least a 10 F margin existed to saturation, ' All of the above criteria were met with the exception that the pumps were off for greater than one hour. Decay heat was being ,
removed by the steam generators with the Reactor-Coolant System in i
. natural circulation.
There was no action statement for that section of the Technical
. Specifications. At the. time of the event a revision to Technical -
Specifications had been approved, but not implemented, that added a "
section to address this issue. It states, consistent with standard Technical Specifications that when a Limiting Condition for Operation is not met and action is not specified, action must be initiated within one hour to place the unit in a condition where the equipment is not required. In this case the equipment in question was the reactor coolant pumps. The Reactor Coolant Pumps are required above 350'F so the action would be to take the unit to less than 350 F. The generic applicability statement goes on to require that for equipment required above 350 F, the unit must be in hot shutdown within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Reactor Coolant System temperature reduced below 350*F within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
Since the unit was in hot shutdown and pumps resorted prior to the 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> requirement for hot shutdown, the intent of the Technical Specifications were not exceeded.
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nxi w m a, . e. . mc w anawm Both the "first out" annunciator (EIIS Gomponent Identifier ANN) and the computer sequence of events indicated that the cause of the reactor trip was a high flux rate trip from the nuclear instrumentation system. A (negative) high flux rate trip is consistent with a dropped rod or rods.
A check of the rod drive motor-generator (MG)(EIIS Component Identifier [
MG) sets showed that the output breaker of No. 21 MG set was open. A I check of the rod control system (EIIS System Identifier AA) showed tihat ::
no fuses were blown.
Investigation of the rod drive MG set protective relaying showed that No. -
21 MG set output breaker had tripped on instantaneous reverse current.
The settings of the relays (EIIS Component Identifier RLY) were checked ;
and found to be correct. Test tripping of the relays was also !
satisfactory. Wave form observation of both MG set voltage regulators t (EIIS Identifier RG) was undertaken to determine if a defective regulator could have caused a loss of power to the rod drive system and a resulting dropping of rods. The wave forms appeared to be satisfactory. It was then decided to withdraw the shutdown bank control rods (a normal hot shutdown condition) for observation. The rods withdrew normally.
Approximately three hours later, the rods fell into the core. The output ,
breakers of both rod drive MG sets were checked and found to be open.
No. 22 MG output breaker had tripped on instantaneous reverse current. 1 It could not be determined why No. 21 MG set output breaker had tripped.
Testing was performed to attempt to duplicate the conditions. By I adjusting the voltages with the voltage regulators in manual, similar conditions could be reproduced. It was then concluded that No. 21 MG voltage regulator had failed to maintain proper voltage, resulting in degraded voltage to the rod control system and subsequent dropping of a rod or rods. This scenario coincided with information gathered concerning rod position changes at the time of the trip. This rod position indication showed that one or more rods may have started to fall into the
- core slightly before the majority of the rods. Due to unknowns about computer rod position indication (RPI) data acquisition and about RPI time response to free falling rods, this information could not be considered to be definitive. The voltage regulator for 21 MG set was replaced and tested satisfactorily. The MG set vendor concurred with the decision to replace the voltage regulator. The shutdown rods were again withdrawn and were observed for approximately five hours. It was then concluded that rod mechanism timing testing was not required and that the systems were operating correctly.
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011 01 4 OF 110 73xT c ans, ausse e #senset. ese assesnar NaC Mne JE4 W M71 Th'e response of substation 345KV breakers to the Unit-2 generator lockout (a design feature of the system) was not' normal. One of the generator output breakers, 8H13, failed to open in the required time. This resulted in substation 345KV Bus 1 being de-energized. In turn, reserve and main auxiliary power were not available for the Unit 2 non-safeguards electrical buses. Auxiliary power was restored to Unit 2, after approximately three hours. The unit was in a hot shutdown, natural circulation condition during this time. All safeguards buses were powered via their alternate sources throughout the event. Since it was very cold at the time of the trip (-22'F), it was assumed that the problem with l breaker 8H13 was related to the cold weather. " Tents" were placed around several of the breakers in the substation 'and heating was. applied.
Breaker 8H13 was trip tested several times with satisfactory opening times. Based on these actions and test results, the cause of the slow opening time was concluded to be low temperature and the breaker was now operating properly. Unit 2 was placed in service at 0009 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> on December 23, 1989.
At approximately 1232 hours0.0143 days <br />0.342 hours <br />0.00204 weeks <br />4.68776e-4 months <br /> on December 26, 1989, Unit 2 reactor tripped.
Subsequent to the trip, power to the Unit 2 non safeguards 4KV buses was
' not available due to failure of 345KV breaker 8H13 in the substation.
Both emergency diesel generators started but did not load since the Unit 2 safeguards buses remained powered by their alternate supplies. Power was' restored to the non-safeguards buses and the reactor coolant pumps approximately two hours after the trip. Technical Specifications in effect on December 26, 1989 required one reactor coolant pump or one residual heat removal pump be inservice at all times. Technical Specifications allowed all pumps to be shutdown for up to one hour provided the reactor was suberitical, no dilution was in progress, and at least a 10*F margin exists to saturation. All of the above criteria were I met with the exception that the pumps were off for greater than one hour.
Decay heat was being removed by the steam generators with the Reactor Coolant System in natural circulation.
l There was no action statement for that section of the Technical Specifications. At the time of the event a revision to Technical Specifications had been approved, but not implemented, that added a section to address-this issue. It states, consistent with standard Technical Specifications that when a Limiting Condition for Operation is L not met and action is not specified, action must be initiated within one hour to place the unit in a condition where the equipment is not
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011 OI 5 OF 1l0 i TEXT W must asses e an,nsset, we, _ _ #sC pom JEse'si(171 required. In this case the equipment in question was the reactor coolant pumps. The Reactor Goolant Pumps are re' quired above 350'F so the action would be to take the unit to less than 350'F. The generic applicability statement goes on to require that for equipment required above 350'F, the unit must be in hot shutdown within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Reactor Coolant System temperature reduced below 350'F within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
Since.the unit was in hot shutdown and pumps resorted prior to the 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> requirement for hot shutdown, the intent of the Technical Specifications l-were not exceeded.
This trip and the response of 345KV substation breaker 8H13 was nearly identical to the trip on December 21.
Both the "first out" annunciator and the computer sequence of events indicated that the cause of the reactor trip was a high flux rate trip from the nuclear instrumentation system. A (negative) high flux rate trip-is consistent with a dropped rod or rods. A check of the rod drive motor-generator (MG) sets showed that the output breakers of both MG sets were open. A check of the~ rod control system showed that no fuses were l blown.
Two task forces were formed. Task Force One was to investigate the problems with breaker 8H13. Task Force Two was to investigate the problems with the rod drive MG sets.
Task Force Two obtained on-site services of the vendor. Test programs were formulated for the MG set voltage regulators and for their protective relaying. Equipment to monitor these areas was installed.
While the MG sets were being monitored, two control rods from the shutdown banks, rod E03 and Ill, dropped into the core but an Urgent Failure alarm was not received from the rod control system. This is contrary to the design of the rod control system. As a result, Task Force Three was formed to investigate problems with the rod control system. On-site vendor assistance aas obtai.ned for this effort as well.
Testing of the MG set voltage regulators and protective relaying continued. The testing showed that the dynamic response of the voltage regulators and of the protective relaying was not adequate to maintain a reliable power supply to the rod drive system under reasonably expected upset conditions. Further investigation discovered that the neutral bus had a ground. When it was determined that the ground did not exist in
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Oil 01 6 OF } lg rm ,m .m ., Nees asm nn the MG set or the buses to the reactor trip breakers, Task Force Three was notified. It was determined that 'no'ither MG set voltage regulator was functioning adequately. Replacement regulators were obtained and
. inspected. After some discrepancies were resolved, the spare voltage regulators were bench tested satisfactorily. As-found. data and conditions of the MG set systems were obtained. A loss of prime mover test was performed to determine the response to a loss of power similar to the power conditions that existed after the trips. This test showed-that it is possible to trip one or both generator output breakers on a loss of power to the motors. Both replacement regulators were then installed.
Testing of the protective relaying showed that the settings of the relays would not maintain reliable power to the rod control system while protecting the generator even though the settings were consistent with the technical manual recommendations. The relays and their input devices were determined to be in good condition. After the replacement voltage regulators were installed, the regulator settings and the protective relay settings sete optimized to maintain a reliable power supply while '
still providing proper protection for the MG sets. As-left regulator wave forms were obtained and-long term temporary monitoring instrumentation was installed. Performance will be monitored until the next scheduled outage.
Task Force Three began a testing program to address.the problems in the rod control system. Some parts of the testing program had to wait for MG set availability, as the MG sets had been assigned the higher priority.
Rod drive mechanism timing tests were performed for rods E03 and Ill. The results of these tests disclosed " noise" in the current being monitored.
Data from past mechanism timing tests were reviewed. The ground of the neutral bus reported by Task Force Two was determined to be caused by a faulty sampling resistor for rod C09. The possible effects of a grounded neutral were analyzed. It was concluded that grounding of the sampling resistor in the power cabinet should not affect another power cabinet.
The defective resistor was replaced. Additional monitoring equipment was installed to determine the source of the noise spikes noted earlier.
Shutdown bank rods were withdrawn from the core. Again rods E03 and Ill dropped after they were withdrawn with no Urgent Failure alarm being generated. The Urgent Failure alarm circuit board was replaced after it was determined to be faulty. When "V-ref", a signal used to control current to the rod mechanisms, was noted to be intermittently low in power cabinet LAC, selected areas of the "V-ref" circuit path were
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011 J axv u . w. unc i assmim instrumented. The system was monitored and a mechanism timing test of all rods was performed. All rods were tripped from the fully withdrawn '
position in an attempt to establish the quality of the rod position indication data acquired by the computer during the previous reactor
-trips. .The trip test data generally supports the conclusion that both reactor trips were caused by the dropping of rod E03 and perhaps an, additional rod or rods. It is believed that the failure of the Urgent i Failure alarm circuit (which is designed to prevent rods from dropping in the. event of control system problems), in conjunction with an intermittent V-ref signal, caused at least rod E03 to drop, initiating the trips. Four circuit boards in the path of "V ref" in power cabinet 1AC were replaced and a mechanism timing test was performed on the rods powered by that cabinet, E03 and Ill. The Urgent Failure alarm circuits ;
in the remaining power cabinets were verified to be operable and the Unit !
- 1. rod control system neutral-to-ground potential was checked and found to be satisfactory. Long term temporary instrumentation was installed.
Performance will be monitored until the next scheduled outage. The circuit boards that were replaced have been sent to the vendor for failure' analysis. ,
Task Force One began a testing program on substation breaker 8H13.
Historical data from past unit trips during cold weather were reviewed and showed no previous problems associated with this type of breaker at temperatures as low as -10'F. Services of a consultant were obtained. :'
While preparing to perform trip time testing, clearances of the C phase.
l~ trip armature were observed to be improper. This time the testing'showed
! the opening time of C phase to be slow. Inspection of this armature showed inadequate clearances and high push-off forces. Both of these can cause'a breaker to open slowly. Wear or galling were noted when the L assembly was disassembled for inspection. No spare assemblies were -
l immediately available. Replacement parts were expedited. Breaker 8H14, L the other Unit 2 generator output breaker, was inspected, tested and l determined to be in good condition and to operate properly. Operation with only 8H14 in service was evaluated and determined to be acceptable.
Unit 2 was returned to service at 1618 hours0.0187 days <br />0.449 hours <br />0.00268 weeks <br />6.15649e-4 months <br /> on January 10, 1990.
Breaker 8H13 was later repaired, extensively tested, and returned to l- service on January 17, 1990.
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UCENSEE EVENT REPORT (LER) s/,$,etuc 'R,g","'j;gli,'*,e !"'.y ,*l.".1"'s l TEXT CONTINUATION E""/,"le'.",l"* 'M ffUi" I','e',", '/.'J" [Ts' "'HUi l W.'.^/..".'0! !"."'Et'E0,.'E"jM'Isf5E'!h e"JEi .
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'Long term corrective actiors will include review and revision of the preventive maintenance programs for the'b'reakers and the rod control system. Information gained from further monitoring will be factored into T those revisions.
ANALYSIS OF THE EVENT .
This event is reportable pursuant to 10CFR50.73(a)(2)(iv) and 10CFR50.73(a)(2)(1)(B). Plant response to the trips was as expected except for loss of power to the non safeguards 4KV buses, which supply the reactor coolant pumps. The reactor was cooled by natural circulation while power was being restored to the pumps. Safeguards buses were unaffected. These events had no effect on public health and safety.
FAILED COMPONENT IDENTIFICATION Westinghouse supplied motor-generator set:
Westinghouse Motor Rating: 150 hp, 1750 rpm, 460 VAC,
'3 ph, 60 Hz, Frame 444-TS, Starting - NEMA Code F Electric Machinery Alternator Rating: 438 Kva, 0.8 PF, 1800 rpm, 260 VAC, 3 ph, 60 Hz, Frame 727 Westinghouse "Thyrex" Voltage Regulator, Size TRX-2 Sub 1 Westinghouse Full Length Rod Control System General Electric Outdoor Air-Blast Circuit Breaker Type ATB 362-7, 362 KV PREVIOUS SIMIIAR EVENTS There have been no previous similar events at Prairie Island.
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