ML20217Q556
| ML20217Q556 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 04/07/1998 |
| From: | Nunn D SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20217Q561 | List: |
| References | |
| 50-361-98-05, 50-361-98-5, 50-362-98-05, 50-362-98-5, NUDOCS 9804130020 | |
| Download: ML20217Q556 (18) | |
Text
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Vice President An LDISON INTERNATIONAL Company April 7,1998 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket Numbers 50-361 and 50-362 Linestarter and AFW Supplementa' information San Onofre Nuclear Generating Station, Units 2 and 3
References:
1)
LER 1998-003, dated March 9,1998 2)
LER 1998-001, dated February 12,1998 Southern Caiifornia Edison (SCE), in its continuing review of the events documented in the referenced Licensee Event Reports (LERs), has developed additional information which SCE believes is pertinent to the inspection currently being conducted by the Senior Resident inspector, which will be documented in inspection Report 50-361/98-05; 50-362/98-05.
Reference 1 documents an occurrence of an inoperabia containment emergency sump outlet valve due to equipment failure. The valve was last cycled open/ closed on January 6,1998. SCE believes the valve's reversing linestarter failed during the last close cycle such that the valve would not open when called upon. On January 27, 1998 plant conditions were such that operability of the valve was no longer required.
SCE has evaluated certain realistic recovery actions which would have been pursued if an event requirin0 Recirculation Actuation System (RAS) actuation had occurred, the emergency sump iso;stion valve had not operated, and the redundant train's recirculation ccpability was not immediately available. These recovery actions are not modeled in the Probabilistic Risk Assecsment (PRA) beceuse NRC guidance does not permit credit for actions which are not procedurslized. Therefore, the benefits of the recovery actions are conservatively not reflected in the risk increase value stated in j
Reference 1. SCE estimates that the resultant core damage risk increase from the inoperability of the containment emergency sump outlet valve, crediting the evaluated recovery actions, is 6E-6 for the period, January 6,1998 to January 24,1998. This increase in risk is characterized es small.
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Document Control Desk April 7,1998
- Attachment 1, " Recovery Sequence Diagram,2HV9305 Failure," illustrates the evaluated recovery action sequence of events and includes a verbal description of each of the actions. Attachments 2 through 4 include information which supports the Recovery Sequence Diagram (RSD).
SCE has completed the Failure Analysis Report associated with the inoperability of the containment emergency sump outlet valve due to equipment failure. This report is included as Attachment 5. In summary, the conclusion is that the inoperability of 2HV9305 was due to a single, isolated, undetectable failure of the reversing linestarter.
The failure mechanism is attributed to soil stabilization activities outside the Protected Area circa 1980, which generated a fine (10-100 micron) aerosol grit. The presence of the grit, which looks like common dust to the naked eye, could not have been identified or prevented by accepted industry Quality Assurance (QA) inspection techniques. Due to the passage of time, how and when ths grit was deposited cannot be conclusively determined., "Linestarter Chronology of Events," provides the chronology of SCE activities relative to the identification and subsequent investigation of the inoperable containment emergency sump outlet valve. It should be noted that SCE promptly replaced the linestarters that may have been affected by the grit in both Units 2 and 3.
Reference 2 documents an inoperability of the Turbine Driven Auxiliary Feedwater (TDAFW) pump due to a loose threaded collar in the speed sensing circuitry (speed probe). The pump would have been able to perform its function if called upon for all conditions except a seismic event. SCE has evaluated certain realistic actions to recover the TDAFW pump in the event it was required following a seismic event. In particular, the ability to locally start and manually control the TDAFW pump f c proceduralized and the operators are specifically trained on this action. However, this recovery action was not conservatively reflected in the core damage risk increase value stated in Reference 2. The revised estimated increase in core damage risk reeulting from the loose speed probe threaded collar, with credit for the recovery action, is 3E-8 for the period December 11,1997 to December 29,1997, and less than 7E-7 per year in prior years had the condition existed at that time. These increases are characterized as very small. Attachments 7 and 8 present the RSD and PRA for the evaluated recovery scenario.
1
Document Control Desk April 7,1998 This information is being provided to support the Region IV review and an April 9,1998 intemal NRC staff meeting. Therefore, be advised, SCE's Nuclear Oversight Division is performing a routine eeview of the information presented in the attachments. SCE will advise the Region when the review is complete. In addition, SCE will revise the referenced LERs to include the appropriate information from these evaluations in a j
separate submittal.
If there is any additional information you require, of if you have any questions, please contact me.
Sincerel cN Attachments:
- 1. Recovery Sequence Diagram,2HV9305 Linestarter Failure
- 2. LOCA Evaluation of Safety Significance of Failure of Emergency Sump Valve Linestarter (LER 1998-003)
- 3. Small Break Loss-of-Coolant Accident (SBLOCA) with incomplete Recirculation Actuation Signal (RAS)- A Simulator Case Study
- 4. Probabilistic Risk Assessment - 2HV9305 Linestarter Failure
- 5. Failure Analysis Report 98-005, Failure Analysis of the 2HV9305 Motor Starter
- 6. Linestarter Chronology of Events
- 7. Recovery Sequence Diagram, Auxiliary Feedwater Speed Probe
- 8. Probabilistic Risk Assessment - 2P140 Speed Probe Sensor Connection Vulnerability cc:
J. Lieberman, Director, Office of Enforcement E. W. Merschoff, Regional Administrator, NRC Region IV T. Pat Gwynn, Director, Division of Reactor Projects, NRC Region IV J. A. Sloan, NRC Senior Resident inspector, San Onofre Units 2 and 3 G. M. Vasquez, Enforcement Officer, NRC Region IV
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ATTACHMENT 1 1
Recovery Sequence Diagram,2HV9305 Linestarter Failure i
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RECOVERY SEQUENCE DIAGRAM w,
2HV9308 UNESTARTER FAILURE LOCA LEGEND r
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E lNITIATING EVENT OR g
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9 SUCCESS CRITERION l
j RCS Pressure l
Reaches SIT injection Point r
3 SS Dirocta Mairt 10 OSC/TSC l
m Reetare a-CCW Menned
' RWST Level ACTION Reaches RAS BLUE. OPERATOR f
I Satpoint RED. MAINTENANCE Reeseemble SW
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r Sacle of OSC/TSC CCW/Natify CR Activated 2HV9305 Felis
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Reetore "B" Recognize Failure f
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Rutme Secure HPSI Diegnose
& CS Pumps Ophons 3g g
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Train B Recirc Estetsehed Restae Cross tie Run 'tP019 w/o
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Troutneshoatrg Notify CR 28 21 y
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L J 19 Restert 2P018
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I LONG TERM CORE COVERY 4e a CD AM
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RECOVERY SEQUENCE DIAGRAM 2HV9305 Linestarter Failure Notes PREFACE In LER 2-98-003 SCE identified that 2HV9305 was considered inoperable due to the mechanical interlock on the valve's reversing linestarter failing such that the valve would not open when called upon during an event. The duration of the inoperability is considered to be from January 6,1998 to January 24,1998. The Probabilistic Risk Assessment (PRA) model does not include any potential recovery actions if both recirculation flow paths are failed. This Recovery Sequence Diagram (RSD) addresses the ability to successfully recover a recirculation flow path and establish long term core covery for the period of time when the Train B Component Cooling Water (CCW) heat exchanger had been declared inoperable to repair a tube leak ( and 2HV9305 was inoperable). For the purposes of this RSD establishment of long term core covery is considered success., "LOCA Evaluation of Safety Significance of Failure of Emergency Sump Valve Linestarter (LER 98-003)," is the basis for the timing of event progression in the RSD. Attachment 3, "Small Break Loss-of-Coolant Accident (SBLOCA) with incomplete Recirculation Actuation Signal (RAS)- A Simulator Case Study," provides an input to the judgements of operator response times discussed in the RSD. Attachment 4, "A1 -
Recovery of HV9305," provides the basis for the final estimate of risk increase. Other bases for values are discussed in the RSD notes. includes details of assumptions made for the analysis. Because of the timing for breaks > 2", SCE has conservatively assumed no success in recovering a recirculation flow path prior to core damage. Any other pertinent information about plant conditions are included in the individual notes. The Attachment 2 analysis utilizes ABB's CENTS code. While the CENTS code is not approved for use in LOCA
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analyses, ABB has determined utilization of this code for this application is appropriate.
SCE has compared the Attachment 2 analysis results to MAAP runs performed for the Individual Plant Examination and the results from the CENTS code and the MAAP runs are consistent.
During the inoperable 2HV9305 period, two heat treats were performed. Thc PRA models heat treats by making the Train B CCW unavailable. SCE has concluded that non-recovery from the effectr of heat treats on event progression is incredible, if a heat treat occurring on Unit 2 was in progress at the time of the event, the subsequent turbine trip and loss of condenser load by themselves would terminate the heat treat, and restore the circulating water temperaure quickly. Based on Operations' judgement, this would be sufficient such ihat Train B CCW would be able to provide the required cooling (motor, containment spray etc.). In the case of a heat treat occurring 2
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RECOVERY SEQUENCE DIAGRAM 2HV9305 Linestarter Failure Notes on Unit 3, the SS would direct termination of the heat treat by normalizing gate position.
The SS would evaluate swapping SWC pumps to the unaffected (Unit 2) intake based on the cool off rate of the Unit 3 intake. This transfer involves overriding and stopping the running Salt Water Cooling (SWC) pump, racking out its breaker, and racking in the opposite pump breaker (located adjacent to each other on the 50 foot elevation of the Control Building). The risk increases stated in this RSD reflect recovery from the heat treats. (inclusion of recovery from the heat treats would affect the reported risk increases by less than 4%.)
It should be ncied that evaluations similar to that presented in this RSD could be performed for other time periods and additional refinements of the overall risk increase from the 2HV9305 linestarter failure could be made.
CONCLUSIONS The evaluation of recovery actions indicate that 90% of the time at least one recovery action would be successful prior to core uncovery. A best estimate of the risk increase for the period between January 6,1998 and January 24,1998, considering recovery actions which were not modeled in the PRA, is 6E-06. This is based on an evaluation of the potential recovery action subsequent to the failure of 2HV9305 to open (based on the linestarter failure) during the time period when the CCW heat exchanger was inoperable as well. The evaluation conservatively assumes that recovery would only be potentially successful for small (< 2") breaks.
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l RECOVERY SEQUENCE DIAGRAM 2HV9305 Linestar'.er Failure Notes The follow:ng table summarizes the results of the evaluation.
RECOVERY ACTIONS HPSI CCW TRAIN 8 2HV9305
) RUN HPSI ANALYSIS O
CROSS TIE RESTORATION RESTORATION COOLING
~
TIME TO 154 MIN.
245 MIN.
170 MIN.
. AIN.
264 MIN. TO COMPLETION U
RY (AFTER EVENT INITIATION)
SUCCESS 0.8 0.6 0.5 NO CREDIT N/A PROBABluTY TOTAL RISK INCREASE 6E-6 CONsIDERING RECOVERY ACTIONS 1.
SS DECLARES EVENT in accordance with procedure SO123-Vill-1 " Recognition and Classification of Emergencies," the Shift Superintendent (SS) would declare a Site Area Emergency. This initial declaration would start the activation of the Operations Support Center (OSC) and the manning r4 the Technical Support Center (TSC),
which is where the Station Emergency firector (SED) will assume control of the event progress. Further declarations /uscalation of the event classification would be made in accordance with procedure SO123-Vill-1.
2.
OSCUSC MANNED 3.
OSC/TSC ACTIVATED The OSC is initially staffed by onshift Maintenance and Health Physics (HP) personnel. Minimum staffing of Maintenance personnelincludes; 1 mechanical l
craft,1 electrical craft and 1 Emergency Group Leader (EGL). The procedural l
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RECOVERY SEQUENCE DIAGRAM 2HV9305 Linestarter Failure Notes i
maximum time for staffing the OSC is 60 minutes from the declaration of an Alert or higher emergency class. SCE experience is that the OSC is operational within 27 minutes of emergency declaration, based on average dayshift and i
backshift drill performance.
The TSC is staffed by representatives from Operations, Engineering, Maintenance, Chemistry, Health Physics and plant management. The TSC is considered activated when minimum staffing requirements are met, including the Station Emergency Director (SED). The procedural maximum time for staffing the TSC is 60 minutes from the declaration of an Alert or higher. SCE experience is that the TSC is activated within 33 minutes (average) for dayshift drills, and within 50 minutes (average) for backshift drills.
Emergency coordinator responsibilities may be turned over from the Shift Superintendent to the SED anytime following TSC activation. This is usually timed to avoid interference with emergency notifications and plant activities. SCE experience is that SED turnover occurs within 14 minutes of TSC activation, based on average drill performance.
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4.
SS DIRECTS MAINT. TO RESTORE "B" CCW Due to the number of components affected, the impact of the work on the Salt Water (SW) side of the Train B CCW heat exchanger is included in the Shift turnover and Shift briefings. Based on Emergency Drill performance and Operations experience, SCE concludes the benefits of Train B CCW heat exchanger restoration would be recognized and pursued early in the event, but no later than activation of the TSC. The SS would direct equipment restoration and release of the clearance promptly. This type of CCW worked is performed on an around the clock basis. Therefore, in addition to the minimum OSC personnel which are on site, the personnel which were performing the work prior to the event would be available.
S.
REASSEMBLE SW SIDE OF CCW/ NOTIFY CR The work being performed on the SW side of the CCW heat exchanger was tube leak repair. Therefore, restoration of the Train B CCW function would simply involve removal of equipment, restoration of the manways 5
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RECOVERY SEQUENCE DIAGRAM 2HV9305 Linestarter Failure Notes and release of the clearance. The leakage which prompted the repair was minor and the heat exchanger satisfied operability criteria even with the tube les.k. Upon declaration of the Site Area Emergency, maintenance personnel performing the repair would have stopped work l
and been directed to an assembly area. These personnel would then be l
directed back to the work area to restore the Train B CCW. Upon completion of the work, the Control Room (CR) would be notified. The HP impacts in this area are such that access would not be a concern, it is l
estimated that it would take < 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> (from the time the direction was given) to reassemble the SW side of the heat exchanger and notify the l
CR.
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S.
Restoration of Train B CCW and SW flow would be accomplished by i
Equipment Operators removing clearances and positioning 8 valves, and l
the CR operators racking in the appropriate breakers. The start of 2P026, l
and SWC 2P113 or 2P114 would be automatic based on the Safety l
Injection Actuation Signal (SlAS). Given other potential CR activities, it is l
estimated that it would take < 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to restore CCW flow.
7.
RESTORE DC/ START 2P019 l
The CR Operators would restore control power (DC) to High Pressure Safety injection (HPSI) pump 2P019. The start of 2P019 would be automatic based on the SIAS. This is estimated to take < 5 minutes.
l 8.
TRAIN B RECIRC ESTABLISHED A Train B recirculation (recirc) pathway from the containment sump to the l
core and back to the sump is established with the flow passing through sump valves 2HV9304 and 2HV9302. HPSI 2P019 would provide the motive force. The total estimated maximum time for this recovery action from event initiation is four hours. The Attachment 2 analysis indicates for the 2" break scenario core uncovery occurs at 264 minutes after event initiation. For purposes of estimating the overall risk increase from the 6
l RECOVERY SEQUENCE DIAGRAM 2HV9305 Linestarter Failure Notes 2HV9305 inoperability, SCE has assigned a conservative success probability of 0.6 for this recovery action. That is,60% of the time for a break size < 2" equivalent (note, for PRA purposes breaks < 3/8"in size do not require recirculation), the CCW heat exchanger would be restored prior to core damage.
9.
INJECTION BEGINS Shortly efter the event, injection from the charging pumps and HPSI begins. In the January time period, three charging pumps were available.
However, the Attachment 2 analysis assumes that only two charging pumps, taking suction from the Boric Acid Makeup (BAMU) Tank, are in operation at the time of the event and continue operating for the event duration. The assumption is conservative with respect to time to core uncovery. The swing HPSI pump (2P018), which was aligned to Train A automatically starts, and in accordance with procedure SO23-12-3, " Loss of Coolant," the operators would start the Train A HPSI pump (2P017) to maximize SI flow. To maximize Refueling Water Storage Tank (RWST)
J water demand, the Attachment 2 analysis assumes the swing and Train A HPSI pumps both start at 2.3 minutes. The Train B HPSI pump would not start due to the maintenance on the Train B CCW heat exchanger and the
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attendant removal of control power from the associated Emergency Core Cooling System (ECCS) pumps.
10.
RCS PRESSURE REACHES SIT INJECTION POINT The point at which the RCS pressure reaches 615 psig, the volume of water from the Safety injection Tanks (SITS) would begin to inject into the RCS. Dependent on the RCS pressure the SITS would continue to provide a source of water until the SITS were empty. The Attachment 2 analysis estimates the time of SIT volume injection starts at 57 minutes and ends at 162 minutes from event initiation for the 2" break case.
11.
RWST LEVEL REACHES RAS SETPOINT When the RWST level reaches the RAS setpoint, a signal is sent to stop 7
RECOVERY SEQUENCE DIAGRAM 2HV9305 Linestarter Failure Notes the Low Pressure Safety injection (LPSI) pumps, close the miniflow valves, and open the emergency sump isolation valves (2HV9302/4, Train A and 2HV9303/5, Train B). The Attachment 2 analysis indicates for the 2" break scenario at 120 minutes from event initiation, the RAS setpoint is j
reached.
It is reasonable to assume that RAS would actuate at 18.5% of actual level in the RWST, since RAS is initiated by the two lowest indicating loops of the four RWST level channels. In addition, the time of RAS actuation is only relevant to the recovery plans which start after RAS initiation and a small change in RAS timing would not change the i
conclusions relative to completion of those recovery actions.
12.
2HV9305 FAILS TO OPEN Upon receipt of the RAS signal,2HV9305 would not open, due to the failed linestarter. The valve position indication lights would show the valve still in the closed position. In addition, based on past experience, shortly after the receipt of the signal, the control power fuse associated with 2HV9305 would blow. This would result in loss of remote position indication in the control room. The loss of control power for the valve would result in visual indication on the "ESF Bypass Status Panel" and an audible alarm.
13.
RECOGNIZE FAILURE OF 2HV9'305 TO OPEN Based on Operator training and annunciator response, the Operators I
would verify proper RAS initiation, which includes emergency sump isolation valves position indication. In addition, the LOCA procedure includes valve position verification. Based on the Attachment 3, Simulator Case Study and Operations experience it is estimated that recognition of 2HV9305 failure to open wpuld occur in < 1 minute from the RAS signal.
14.
SECURE HPSI & CS PUMPS The RWST valves do not automatically close on a RAS signal. Thus, the HPSI pumps (2P017 and 2P018) and the Containment Spray (CS) pump 8
RECOVERY SEQUENCE DIAGRAM 2HV9305 Linestarter Failure Notes would continua to draw on the RWST. (Note, the charging pumps are drawing off the BAMU Tank and will function throughout the event.)
Based on the Attachment 3, Simulator Case Study and Operations experience, it is estimated that the Operators would allow the HPSI and CS pump to continue to draw on the RWST until approximately the 5%
level is reached, if required. At that point the Operators would override the SlAS signal and stop the pumps. The Operators would be watching RWST level as well as pump discharge pressure and flow.
15.
DIAGNOSE OPTIONS i
Upon recognition of the failure of 2HV9305 to open and the unavailability of Train B due to the CCW heat exchanger work, the Operations /TSC team would evaluate potential means to obtain RCS inventory control and establish long term core covery. The viability of options pursued are i
dependent on break size and perceived complexiP, of the tasks. Three options are presented in this RSD: 1) cross-tie the t. PSI suction, such j
that a flow path via the Train B sump isolation valves and the Train A HPSI pump is available; 2) rostore the availability of 2HV9305, such that a flow path via the Train A sump isolation valves and the Train A HPSI pump is available, and 3) run the Train B HPSI pump without cooling. At this point in the event the operator actions are not specifically addressed by procedures but would be guided by judgement and experience. This diagnosis is estimated to take < 15 minutes. The Simulator Case Study (Attachment 3) documents the ability of the crews to do this type of diagnosis.
16.-
DISPATCH PEO TO OPEN 2MUO11 Based on' direction from the CR/TSC, a Plant Equipment Operator (PEO) would be dispatched to manually open 2MUO11, HPSI pump 2P018 Train B Suction isolation Valve (direction may also be given to close 2MUO10). The 8" valve (s) is located on the -15 foot elevation of the Equipment Safety Building. Because recirculation has not begun, this area would be accessible.
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l RECOVERY SEQUENCE DIAGRAM 2HV9305 Linestarter Failure Notes 17.
PEO OPEN 2MUO11/ NOTIFY CR The PEO would proceed to the Engineered Safety Features (ESF) pump rooms, unlock and manually open the valve (if diredion was given to close 2MUO10, this would also be performed), and notify the CR. Based on related SCE experience, it is estimated that it would take < 15 minutes from direction to open the valve to the notification to the CR that the valve was open.
18.
RESTART 2P018 The Operator would restart the swing HPSI pump,2P018 from the control room. This is estimated to take < 3 minutes from the notification that valve 2MUO11 is open.
19.
TRAIN B/ TRAIN A RECIRC ESTABLISHED A Train B/ Train A recirc pathway from the containment sump to the core and back to the sump is established with the flow passing through sump valves 2HV9304, and 2HV9302. HPSI pump 2P018 would be supplied through valve 2MUO11 and would provide the motive force. The total estimated maximum time for this recovery action from event initiation is
< 152 minutes. The Attachment 2 analysis indicates for the 2" break j
scenario, core uncovery occurs at 264 minutes. For purposes of estimating the overall risk increase from the 2HV9305 inoperability, SCE has assigned a conservative success probability of 0.80 for this recovery action.
20.
DIRECT MAINT. TO TROUBLESHOOT 2HV9305 Based on direction from the CR/TSC, Electrical Maintenance would be dispatched from the OSC to Motor Control Center (MCC) 2BE on the 50 foot elevation of the Coritrol Building to troubleshoot the failure of 2HV9305 to open (and the subsequent blown fuse).
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RECOVERY SEQUENCE DIAGRAM l
2HV9305 Linestarter Failure Notes 21.
TRANSIT TO MCC & PERFORM TROUBLESHOOTING Electrical Maintenance would go from the OSC on the 70 foot elevation in the Control Building to the MCC on the 50 foot elevation. Access to the Control Building is in no way prohibited.
Initial troubleshooting of the valve failure would include; visual inspection of the circuit, replacing the blown fuse and attempting to stroke the valve (which is assumed to fail), meggering the control circuit (which would be i
satisfactory), and visually inspecting / attempting to manually actuate the mechanical interlock (which is assumed to fail). Based on related i
experience, it is estimated that this would take < 21 minutes. At this point, it would be observed that the mechanical interlock was not allowing the linestarter to operate. Options, to correct this would be evaluated. Three options are available: 1) disable the mechanical interlock,2) rewire the linestarter, or 3) replace the mechanical interlock (interlocks were in stock in the warehouse, due to the ongoing linestarter replacement activities).
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SCE has been replacing this type of interlock since 1995 and the Maintenance staff is familiar with the configuration. Therefore it is SCE's judgement that the first option would be pursued.
22.
PERFORM WORK TO OPEN in order to disable the mechanical interlock, the power breaker would be opened, the operating coils would have to be removed, the mechanical interlock would be disabled by; removal of the plastic rod that restricts contact movement, the operating coils would be replaced, the breaker i
shut and the valve stroked. Based on SCE experience this would take <
10 minutes. The second option described in Note 21 (rewire the linestarter) is estimated to take < 15 minutes, and the third option (replace the linestarter) is estimated to take < 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
23.
2HV9305 Open i
Once the mechanical interlock had been disabled and the breaker closed, the valve would open due to the existence of a RAS actuation l
signal. Position of the valve is indicated in the control room.
11 RECOVERY SEQUENCE DIAGRAM 2HV9305 Unestarter Failure Notes 24.
RESTART 2P018 The swing HPSI pump,2P018 would be restarted from the control room.
This is estimated to take < 3 minutes.
25.
TRAIN A RECIRC ESTABLISHED 3
A Train A recirculation pathway from the containment sump to the core and back to the sump is established with the flow passing through sump valves 2HV9305 and 2HV9303. HPSI 2P018 would provide the motive l
force. The total estimated maximum time for this recovery action (disable the mechanical interlock) from event initiation to completion is 170 minutes. The Attachment 2 analysis indicates for the 2" break scenario, core uncovery occurs at 264 minutes after event initiation it should be noted that complete replacement of the interlock could be accomplished j
only slightly after core uncovery. There is some time between core l
uncovery and core damage. For purposes of estimating the overall risk j
increase from the 2HV9305 inoperability, SCE has assigned a l
conservative success probability of 0.5 for this recovery action. That is, that 5 out of 10 times 2HV9305 would be restored and recirculation established prior to core damage.
i 26.
RUN 2P019 W/O SW COOLING
]
While establishment of a recirculation pathway utilizing 2P019 without cooling water is viable, and can be accomplished from the CR, the need to minimize heat load on the CCW system is present, the potential for long term pump damage exists, and HP considerations in the ESF pump rooms affecting the ability to pursue the cross-tie option, make this recovery action less likely to be chosen.
l 27.
SECURE TRAIN B ECUS in order to prevent heat input to the CCW System, the Operators would need to override and close the ECU valves from the CR (such that the 12 1o
RECOVERY SEQUENCE DIAGRAM 2HV9305 Linestarter Failure Notes CCW pump motor and the HPSI motor and seal cooling were the only loads.) If they did not, they would quickly receive a CCW High Temperature alarm, secure the CCW pump and then take action to isolate the Emergency Cooling Units (ECUS). Because the work on the CCW heat exchanger was on the tube side and not the shell side of the heat exchanger, the sheer volume of CCW system water would provide a heat sink for operation. This is estimated to take < 5 minutes.
28.
RESTORE DC TO 2P026 The CR Operators would restore control power (DC) to CCW pump 2P026. The start of 2P026 would be automatic based on the SIAS. This is estimated to take < 5 minutes.
29.
RESTORE DC/ START 2P019 The CR Operators would restore control power (DC) to HPSI pump 2P019. The start of 2P019 would be automatic based on the SIAS. This is estimated to take < 5 minutes.
30.
TRAIN B RECIRC ESTABLISHED A Train B recirculation pathway from the containment sump to the core and back to the sump is established with the flow passing through sump valves 2HV9304, and 2HV9302. HPSI 2P019 would provide the motive force. The total estimated maximum time for this recovery action from event initiation is < 149 minutes. The Attachment 2 analysis indicates for the 2" break scenario, core uncovery occurs at 264 minutes after event.
For purposes of estimating the overall risk increase from the 2HV9305 inoperability, SCE has not credited this recovery action.
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ATTACHMENT 2 LOCA Evaluation of Safety Significance of Failure of Emergency Sump Valve Linestarter (LER 1998-003ll
.