ML052550490
| ML052550490 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 09/08/2005 |
| From: | Scherer A Southern California Edison Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BL-03-001 | |
| Download: ML052550490 (5) | |
Text
SOUTIERN CALIFORNIA EDISON An EDISON I\\TERNA TIONA I Conlpans A. Edward Scherer Manager of Nuclear Regulatory Affairs September 8, 2005 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
Subject:
San Onofre Nuclear Generating Station Units 2 and 3 Docket Nos.60-361 and 50-362 NRC Bulletin 2003-01 Response To Third NRC Request For Additional Information
Reference:
Letter from A. E. Scherer (SCE) to the Document Control Desk (NRC) dated August 1, 2003;
Subject:
San Onofre Nuclear Generating Station Units 2 and 3, Docket Nos. 50-361 and 50-362, 60-Day Response to NRC Bulletin 2003-01, 'Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors"
Dear Sir or Madam:
By the referenced letter, Southern California Edison (SCE) submitted a 60-day response to Bulletin 2003-01, "Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors."
The U. S. Nuclear Regulatory Commission staff has requested additional information in order for the staff to continue its review. The information request was discussed during a telephone call on August 10, 2005, wherein SCE agreed to provide a written response. Enclosed is the SCE response to the request for additional information.
If you have any questions or require any additional information, please contact Mr. Jack Rainsberry at (949) 368-7420.
Sincerely, Enclosure cc:
B. S. Mallett, NRC Region IV, Regional Administrator J. N. Donohew, NRC Project Manager, San Onofre Units 2 and 3 C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 and 3 P.O. Box 128 San Clemente, CA 92672 949-368-7501 Fax 949-368-7575
to)
ENCLOSURE SCE RESPONSE TO THIRD REQUEST FOR ADDITIONAL INFORMATION SAN ONOFRE NUCLEAR GENERATING STATION (SONGS). UNITS 2 AND 3 SOUTHERN CALIFORNIA EDISON COMPANY NRC BULLETIN 2003-01 DOCKET NOS. 50-361 AND 50-362 NRC staff has requested that Southern California Edison (SCE) summarize the SONGS actions with respect to the Candidate Operator Actions (COAs) listed in WCAP-16204, "Evaluation of Potential ERG and EPG Changes to Address NRC Bulletin 2003-01 Recommendations (PA-SEE-0085),"
identifying for each COA whether or not SONGS has adopted the action. For each action adopted, staff has requested the affected procedure identification. For each action not adopted, staff has requested a brief justification.
WCAP-16204 Revision I Assessment Southern California Edison (SCE) has reviewed the Candidate Operator Actions (COAs) addressed by the Westinghouse Owners Group (WOG) in WCAP-16204, Evaluation of Potential ERG and EPG Changes to Address NRC Bulletin 2003-01 Recommendations (PA-SEE-0085)," Revision 1, March, 2004 and incorporated in Revision 5.3 to CEN-152. SCE used qualitative risk assessments to compare the potential risk increase aspects to the potential risk decrease aspects of procedural modifications in implementing COAs recommended by the WOG. The potential risk increase aspects include the increase in the likelihood of operator error in responding to a Loss Of Coolant Accident (LOCA) and the increase in the likelihood of failure of secured equipment should redundant operating equipment experience a random single failure. Potential risk decrease aspects generally include increasing the time to automatic switchover to recirculation, and/or reducing the velocity of recirculation through one or both of the sumps. Assessments of the COAs are provided on an item-by-item basis below.
COA la-CE - Operator Action to Secure One Spray Pump This COA was not adopted. Implementing this recommended operator action would require an additional action to manually stop (secure) one operating Containment Spray (CS) pump. Securing one of the two operating CS pumps increases risk, because should the operating pump subsequently fail randomly or become disabled due to loss of a vital bus, total interruption of spray flow would occur. Should the operating pump fail, operator action would be required to restart the secured pump, and the pump being restarted would be subjected to the potential for another demand failure (subsequent to the initial demand in response to an engineered safety feature actuation signal). Additionally, manual operator actions to secure a CS pump and then to restart a CS pump (given failure of the operating pump) would introduce a distraction. Hence, the operator Page 1 of 4
failure probability in responding to a LOCA event could increase, given the short time available for operator intervention and performing additional manual actions.
The analyses of record for dose and for containment pressure and temperature credit uninterrupted spray flow. Should the operating pump fail, a loss of spray flow would result. Since there is no assurance that successful re-start of the secured pump would be achieved, then there is an increase in risk that the resultant radiological dose and containment pressure and temperature limits would be exceeded.
In summary, it has been determined that the net effect of the procedural modification in response to an unlikely event (i.e., emergency sump failure) would be an increase in risk since the adverse effects on the equipment, operators, and containment systems in mitigating a LOCA event outweigh any minimal benefit.
COA lb - Operator Action to Secure Both Spray Pumps This COA was not adopted. Implementing this recommended operator action would require an additional action to perform the necessary verifications, and manually stop (secure) both operating CS pumps. Securing the two operating CS pumps increases risk, because should a containment fan cooler subsequently fail randomly or become disabled due to loss of a vital bus, operator action would be required to restart a secured pump, and the pump being restarted would be subjected to the potential for another demand failure (subsequent to the initial demand in response to an engineered safety feature actuation signal). Additionally, manual operator actions to secure CS pumps and then to restart a CS pump (given failure of a containment fan cooler) would introduce a distraction. Hence, the operator failure probability in responding to a LOCA event could increase, given the short time available for operator intervention and performing additional manual actions.
More importantly, the analyses of record for dose and for containment pressure and temperature credit uninterrupted spray flow. Securing both containment spray pumps could result in radiological dose and containment pressure and temperature limits being exceeded.
In summary, it has been determined that the net effect of the procedural modification in response to an unlikely event (i.e., emergency sump failure) would be an increase in risk since the adverse effects on the equipment, operators, and containment systems in mitigating a LOCA event outweigh any minimal benefit.
COA 2 - Manually Establish One Train of Containment Sump Recirculation Prior to Automatic Actuation This COA was not adopted. Establishing one train of Containment Sump recirculation prior to automatic actuation requires manual operator action to override an automatic safety function.
During normal operation, the Low Pressure Safety Injection pumps are in standby mode and aligned for emergency operation. The pumps automatically start upon receipt of a Safety Injection Actuation Signal (SIAS) to supply borated water to the Reactor Coolant System from the Refueling Water Storage Tanks (RWSTs). The proposed COA would require that the operators take manual action to open and close valves realigning the suction of one train from the RWST to the containment sump, and manually stopping the pumps on the train continuing to take suction from the RWST. Risks associated with stopping these pumps, and potential subsequent required restarts are addressed in the justifications for COAs 1, 3, and 4.
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Establishing one train of containment sump recirculation prior to automatic actuation would result in a lower available net positive suction head (NPSH) because the water level in containment would be lower than at the point of automatic actuation, due to the inventory remaining in the RWST. The WCAP recognizes that plants must have sufficient existing margin, or be able to demonstrate that operating one train will improve the margin such that it compensates for the lower water level.
Running only one recirculation train would reduce the debris transport slightly, but would then result in all of that debris being drawn into one sump, resulting in an increase in pressure drop, as compared to the pressure drop that would exist while running two trains in the recirculation mode.
This, coupled with the lower water level, would have a detrimental effect on pump NPSH margin.
Additionally, containment spray with RWST inventory has a greater cooling effect than with higher temperature sump inventory. It is concluded that the potential risks incurred by commencing recirculation with lower NPSH margin, and containment spray with higher temperature fluid than available from the RWST, outweigh the potential benefits.
COA 3-CE - Terminate One Train of HPSIIHiah Head Iniection After Recirculation Alianment This COA was not adopted. Securing a High Pressure Safety Injection (HPSI) pump requires manual operator action to override an automatic safety function. During normal operation, the pumps are in standby mode and aligned for emergency operation. The pumps automatically start upon receipt of a SIAS to supply borated water to the Reactor Coolant System from the RWSTs.
The operators would be required to manually stop one pump. Shutting down a HPSI Pump increases risk because, in the case of a failure of an operating pump, operator action would be required to restart the shut-down pump, and the pump being restarted would be subject to the potential for another demand failure (subsequent to the initial demand in response to an engineered safeguards actuation). Additionally, manual operator action to secure a HPSI pump and restart a HPSI pump (given failure of the operating pump) would introduce a distraction. Hence, the operator failure probability in responding to a LOCA event could increase, given the demands for operator intervention and performance of additional manual actions.
In summary, since the proposed procedural modification would benefit an unlikely event (i.e.,
emergency sump failure), and would adversely affect the equipment and the operators in mitigating a LOCA event, it has been determined that the net effect would be an increase in risk.
COA 4 - Early Termination of One LPSIIRHR Pump Prior to Recirculation Alignment This COA was not adopted. Securing a Low Pressure Safety Injection (LPSI) pump requires manual operator action to override an automatic safety function as in the COA 2 assessment.
Shutting down a LPSI Pump increases risk because, in the case of a failure of an operating pump, operator action would be required to restart the shut-down pump, and the pump being restarted would be subject to the potential for another demand failure (subsequent to the initial demand in response to an engineered safeguards actuation). Additionally, manual operator action to secure a LPSI pump and restart a LPSI pump (given failure of the operating pump) would introduce a distraction. Hence, the operator failure probability in responding to a LOCA event could increase, given the short time available for operator intervention and performance of additional manual actions.
In summary, since the proposed procedural modification would benefit an unlikely event (i.e.,
emergency sump failure), and would adversely affect the equipment and the operators in mitigating a LOCA event, it has been determined that the net effect would be an increase in risk.
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COA 5-Refill of Refuellna Water Storaue Tank COA 5 was incorporated into S023-12-11, "EOI Supporting Attachments", Attachment 2, "Floating Steps [FS]", FS-20, uMONITOR RWST Level."
COA 6 - Inlect More Than One RWST Volume From a Refilled RWST or by Bvpassina the RWST The portion of COA 6 relating to Injecting More Than One RWST Volume From a Refilled RWST was incorporated into S023-12-11, *EOI Supporting Attachments," Attachment 14, ORecirculation Actuation Signal (RAS) Operation," Step 4a.
The portion of COA 6 relating to Bypassing the RWST was not adopted. Bypassing the RWST for alternate reactor coolant system injection would involve a complex valve lineup during a LOCA event. The human failure probability in carrying out this complex task during a LOCA event would be high. Additionally, the distraction this activity represents during a LOCA would represent an error likely situation and should be avoided. The high human failure probability in performing this complex task and its negative impact on operators' timely response to a LOCA event, together with the unlikelihood of emergency sump failure, would make RWST bypass a net risk increase.
COA 7-Provide More Aggressive Cooldown and Depressurization Following A Small Break LOCA This COA was incorporated into S023-12-11, "E0I Supporting Attachments," Attachment 14, "Recirculation Actuation Signal (RAS) Operation," Step 8.
COA 8-CE - Provide Guidance on Symptoms and Identification of Containment Sump Blockage This COA was incorporated into S023-12-11, "EOI Supporting Attachments3, Attachment 2, OFloating Steps [FS]*, FS-22, OMONITOR ECCS Pump(s) Suction After RAS.".
COA 9-CE - Develop Contingency Actions In Response to: Containment Sump Blockage.
Loss of Suction, and Cavitation This COA was incorporated into S023-12-11, PEOI Supporting Attachments", Attachment 2, uFloating Steps [FS]', FS-22, 'MONITOR ECCS Pump(s) Suction After RAS.' A continuously applicable step was added to the EQ1s to provide guidance to the operators on expected ECCS pump performance while on containment sump recirculation and actions to take should these pumps show unstable flow, discharge pressure, or motor amperage. The containment sump recirculation attachment was also enhanced to address this issue.
COA 10 - Early Termination of One Train of HPSI Infection Prior to Recirculation Alignment This COA was not adopted for the same reasons stated in COA 3.
COA 11 - Prevent or Delay Containment Spray for Small Break LOCAs (<1.0 Inch Diameter) In Ice Condenser Plants This COA is not applicable to San Onofre Nuclear Generating Station.
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