ML20214A053
| ML20214A053 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/17/1986 |
| From: | Medford M SOUTHERN CALIFORNIA EDISON CO. |
| To: | Martin J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| IEB-86-003, IEB-86-3, NUDOCS 8611190178 | |
| Download: ML20214A053 (5) | |
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f [5 Southern California Edison Company P. O. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD CALIFORNIA 91770 B40 NAGER OF NU LEAR ENGINEERING
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18 8) 2 749 AND LJCENSING U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region V 1450 Maria Lane, Suite 210 Walnut Creek, California 94596-5368 Attention: Mr. John B. Martin, Regional Administrator
Dear Sir:
Subject:
Docket Nos. 50-206, 50-361, 50-362 San Onofre Nuclear Generating Station Units 1, 2 and 3 This letter provides the Southern California Edison response for San Onofre Units 1, 2 and 3 to IE Bulletin No. 86-03:
" Potential Failure of Multiple ECCS Pumps Due to Single Failure of Air-0perated Valve in Minimum Flow Recirculation Line". As requested, an evaluation has been conducted, and it has been determined that there is no single-failure vulnerability in the minimum flow recirculation line of any ECCS pumps that could cause a failure of more than one ECCS train.
Based on the evaluation results, no action is required.
Subscribed on this
/7* day of Mm, 1986.
Respectfully submitted, SOUTHERN CALIFORNIA EDISON COMPANY By:
DM M. O. Medford (( Engineering Manager of NucTear and Licensing Subscribed and sworn to before me this
/7 '
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U.S. Nuclear Regulatory Commission Document Control Desk Hashington, D.C. 20555 H. Rood, USNRC Senior Project Manager R. F. Dudley, USNRC Project Manager F. R. Huey, USNRC Senior Resident Inspector, San Onofre Units 1, 2&3
> s RESPONSE TO IE BULLETIN 86-03 POTENTIAL FAILURE OF MULTIPLE ECCS PUMPS DUE TO SINGLE FAILURE 0F AIR-0PERATED VALVE IN HINIMUM FLOH RECIRCULATION LINE SAN ON0FRE NUCLEAR GENERATING STATION UNITS 1, 2 AND 3 IE Bulletin 86-03 requires that for San Onofre Nuclear Generating Station Units 1, 2 and 3 a determination be made of the single-failure vulnerability of ECCS pump minimum flow recirculation lines which could result in a common cause failure of more than one ECCS train.
Provided below is a summary of the evaluation and the conclusions.
Action for Addressees 1.
Promptly determine whether or not your facility has a single-failure vulnerability in the minimum flow recirculation line of any ECCS pumps that could cause a failure of more than one ECCS train.
Resoonse Unit 1 The Unit 1 safety injection system consists of two independent, safety related trains.
Each train consists of a Safety Injection (SI) pump and a Main Feed Pump (MFP).
The SI pump provides suction pressure to the MFP, which also serves as a safety injection pump.
The SI pumps each have a miniflow recirculation line, which combine in a common header for the flow to return to the Refueling Hater Storage Tank (RHST). Since there are no valves in either SI pump miniflow line or the common header, there is no potential for a total loss of ECCS cooling due to a single failure.
The MFPs each have a miniflow recirculation line which combines in a common header for the flow to return to the RHST.
Each MFP miniflow line has an air-operated isolation valve. There are no valves in the common header. A common cause failure of the air operated valves due to a single component failure could not occur because:
o Each MFP miniflow isolation valve has a separate safety related pressurized nitrogen supply system to provide a backup to instrument air, in the event of its loss.
o Electrical power to the two solenoids that operate these valves is safety related, independent of each other, and backed up by station batteries.
Containment Spray and Containment Recirculation systems were also reviewed.
These systems are not vulnerable to a loss of miniflow because they do not contain active or train-common valves in the miniflow recirculation lines of either system.
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, It is concluded that Unit I does not have a single-failure vulnerability in the minimum flow recirculation lines of any ECCS pumps that could cause a failure of more than one ECCS train.
Units 2/3 The Unit 2/3 safety injection system consists of two safety related trains.
Each has a Low Pressure Safety Injection (LPSI) pump and a High Pressure Safety Injection (HPSI) pump. A third HPSI pump is provided as a swing pump and can provide flow to either train.
Each train has a miniflow recirculation line that can be blocked if necessary, and which combines in a common header for the flow to return to the RHST.
There is no potential for loss of all safety injection pumps due to a single failure in the miniflow lines because:
o The internals have been removed from the valve in the common header.
o There are no air-operated valves that could fail in a common mode due to loss of air. The isolation valves are motor operated, are normally open, and fail as is.
o The isolation valves in the miniflow recirculation lines of each train are powered by separate motor control centers on the respective lE safety related buses.
o Closure of the isolation valves from the control room requires operation of separate key-controlled switches.
o Automatic closure of these valves requires a Recirculation Actuation System (RAS) actuation with concurrent containment sump high level. A failure mode and effects analysis was performed as part of the design of this system which verified that neither multiple failures within the RAS circuits nor My single failure could cause unwanted closure of miniflow isolation valves in both trains.
The Containment Spray system consists of two safety related trains which share suction and miniflow piping with the respective HPSI and LPSI trains discussed above and use the same miniflow isolation valves as HPSI and LPSI.
It is concluded that Units 2/3 do not have a single-failure vulnerability in the minimum flow recirculation lines of any ECCS pumps that could cause a failure of more than one ECCS train.
No action is required.
2
, Actions for Addressees 2.
If the problem exists:
(a) promptly instruct all operating shifts of the problem and measures to recognize and mitigate the problem; (b) promptly develop and implement corrective actions which bring your facility into compliance with GDC 35.
Resoonse Units 1, 2 and 3 are not vulnerable to the type of failure described in the bulletin. Therefore, no response is required.
Actions for Addressees 3.
Within 30 days of receipt of this bulletin, (a) provide a written report to the NRC which identifies whether or not this problem exists at your facility, (b) if the problem exists (or existed),
include in the report the justification for continued operation and identify the short-term modifications to the plant operating procedures or hardware that have been or are being implemented to ensure safe plant operations.
Resoonse This response fulfills the requirements of this action.
Action for Addressees 4.
If the problem exists (or existed), provide a written report within 90 days of receipt of this bulletin informing the NRC of the schedule for long-term resolution of this and/or any other significant problems that are identified as a result of this bulletin.
Resoonse Unit 1, 2 and 3 are not vulnerable to the type of failure described in the bulletin. Therefore, no response is required.
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