ML13331A523
| ML13331A523 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/21/1990 |
| From: | Ray H SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML13331A524 | List: |
| References | |
| NUDOCS 9012270142 | |
| Download: ML13331A523 (3) | |
Text
Southern California Edison Company 23 PARKER STREET IRVINE, CALIFORNIA 92718 HAROLD B. RAY TELEPHONE SENIOR VICE PRESIDENT December 21, 1990 714-458-4400 U. S. Nuclear Regulatory Commission Attention:
Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Amendment Application No. 191 Addition of a Redundant Isolation Valve in the Volume Control Tank Outlet San Onofre Nuclear Generating Station, Unit 1 Enclosed is Amendment Application No. 191 to Provisional Operating License DPR-13 for San Onofre Nuclear Generating Station, Unit 1 (SONGS 1).
This amendment application proposes changes to the Technical Specifications to reflect certain modifications of the Volume Control and Charging System (VCCS).
The modifications are being implemented during the current Cycle 11 refueling outage to resolve single failure susceptibilities of the VCCS.
Specifically, these single failure susceptibilities concern the potential for gas binding of the charging pumps during the automatic transfer of the charging pump suction flowpath from the Volume Control Tank (VCT) to the Refueling Water Storage Tank (RWST).
Th6 potential for hydrogen gas binding of the charging pumps was identified as a result of the Emergency Core Cooling System (ECCS) Single Failure Analysis. An interim report summarizing the results of the ECCS Single Failure Analysis was submitted to the NRC on July 31, 1990. The subject VCCS modifications and proposed changes to the Technical Specifications are part of the resolution to the topic identified as Issue No. 2, "Loss of Suction to the Charging Pumps Prior to Safety Injection Signal," in Enclosure 2 of that report.
An editorial error in the Technical Specifications is also proposed to be corrected by this change.
EXISTING VCCS DESIGN The VCCS is designed such that the charging pumps can take suction from either the VCT or the RWST. During normal operation, the charging pumps are aligned to take suction from the VCT. Only one VCT outlet isolation valve is provided in the existing design configuration. The RWST is isolated by redundant 0
safety related valves during normal operation.
9012270142 901221 PDR ADOCK 05000206 P
Document Control Desk December 21, 1990 Upon receipt of a VCT low-low signal, a Safety Injection Signal (SIS), or a Safety Injection Signal with Loss of Power (SISLOP), the VCCS is designed to transfer the suction flowpath from the VCT to the RWST. This transfer is accomplished by opening the RWST safety related isolation valves (MOV-1100B and MOV-1100D), and closing the VCT isolation valve (MOV-1100C).
SINGLE FAILURE SUSCEPTIBILITY Decreasing pressurizer level results in automatically increased charging flow, and eventual isolation of letdown flow. In the event of certain single active failures, the charging pump could empty the VCT. Failure of the running charging pump could occur due to hydrogen gas entrainment, if:
a) the VCT level instrumentation fails to initiate a low-low level signal to transfer the charging pump suction from the VCT to the RWST, or b)
VCT isolation valve MOV-1100C fails to close upon receipt of a low-low signal from LT-1100, or a SIS/SISLOP.
The SIS/SISLOP, or the VCT low-low-low level pump trip signal from VCT level transmitter LT-2550, would lock-out the second pump from starting. However, hydrogen gas would potentially be trapped in the common charging pump suction line. Unless the operator notices this condition and vents the hydrogen, the second pump could also fail due to gas binding when required to start.
VCCS MODIFICATIONS To preclude the above postulated failure scenarios, SCE is implementing a design change to the VCCS. This design change involves the addition of a redundant isolation valve (MOV-1100E) in series with the existing VCT outlet isolation valve (MOV-1100C).
Additionally, the associated circuitry for the VCT and RWST safety related isolation valves is being modified. These circuit modifications will ensure that each redundant VCT or RWST isolation valve will be powered from independent power sources and actuated by independent level controls. As a result of these circuit design changes, the existing transfer switch for MOV 1100C is no longer required since both VCT isolation valves will be powered from independent electrical sources.
PROPOSED TECHNICAL SPECIFICATION CHANGES The proposed changes to the Technical Specifications are to 1) add a paragraph to Section 3.3.1.B to allow maintenance of the VCT isolation valves, 2) revise Table 4.1.2, page 4.1-7, to delete surveillance requirements for the MOV-1100C transfer switch which is being removed from the system design, and 3) correct an editorial error on page 4.1-7 of Table 4.1.2.
Document Control Desk December 21, 1990 The editorial change mentioned in item 3) above was previously proposed to be corrected in Amendment Application 176.
However, since we are correcting page 4.1-7 for the reason stated in item 2) above, we have elected to correct the editorial change at this time. A revision to Amendment Application No. 176 will be issued after SONGS 1 returns to service to delete the editorial change from that amendment.
Additional changes to Technical Specifications proposed by Proposed Change Number (PCN) 151 in Amendment Application 188 will be required by these modifications. However, the changes proposed in Amendment Application 188 are not yet part of SONGS 1 Provisional Operating License. Therefore, the Technical Specification changes related to PCN 151 will be addressed in a separate revision to PCN 151/Amendment Application 188 which will be submitted after SONGS 1 returns to service.
NRC approval of this amendment application is required before SONGS 1 can be returned to service. This system is required for mode 4 operation which is scheduled for February 20, 1991.
In order to allow sufficient time for completion of the necessary SCE internal paperwork after NRC approval of this change, we request your approval by February 13, 1991.
We are prepared to meet with the NRC staff, if necessary, to expedite approval of this proposed change.
Very truly yours, Enclosure cc:
J. B. Martin, Regional Administrator, NRC Region V C. Caldwell, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3 C. D. Townsend, NRC Resident Inspector, San Onofre Unit 1 J. H. Hickman, California Department of Health Services