ML13331A527
| ML13331A527 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 01/14/1991 |
| From: | Ray H SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML13331A528 | List: |
| References | |
| NUDOCS 9101150348 | |
| Download: ML13331A527 (3) | |
Text
Southern California Edison Company 23 PARKER STREET IRVINE, CALIFORNIA 92718 HAROLD B. RAY TELEPHONE SENIOR VICE PRESIDENT 714-458-4400 January 14, 1991 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 Amendment Application No. 189, Supplement 1 ECCS Actuation Logic and Vital Bus Transfer San Onofre Nuclear Generating Station, Unit 1 Enclosed is Supplement 1 to Amendment Application No. 189 for the San Onofre Nuclear Generation Station, Unit 1 (SONGS 1).
This supplement consists of Proposed Change No. 233, Revision 1, and proposes Technical Specification changes to resolve single failure susceptibilities of the 4160 volt electrical distribution system and the Safeguards Load Sequencing System (SLSS).
The supplement also proposes a license condition to require installation of a plant modification prior to Cycle 12 operation. The modification will resolve a single failure susceptibility concerning automatic transfer between the power sources for the electrical distribution system vital buses.
NRC COMMENTS ON AMENDMENT APPLICATION 189 This supplement is necessary to address comments received during the currently ongoing NRC review of Amendment Application 189, dated September 28, 1990.
Specifically, responses to the following NRC comments are included in this supplement:
- 1.
The setpoint and response time for the 4160 volt bus undervoltage reactor trip instrumentation channels should be included in the Technical Specifications.
- 2.
The modes of applicability for the 4160 volt bus undervoltage reactor trip instrumentation should be specified in a manner consistent with the Standard Technical Specifications for Pressurized Water Reactors, NUREG-0452.
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Document Control Desk January 14, 1991
- 3.
A monthly surveillance frequency should be considered for the 4160 volt bus undervoltage reactor trip channels in lieu of the once a refueling outage interval originally proposed by Amendment Application 189.
- 4.
Additional explanation of the assumptions made in the vital bus transfer probabilistic risk assessment (PRA) should be provided to demonstrate the assumptions are realistic.
This supplement is a complete resubmittal of Amendment Application 189.
Change bars are provided in the left margin throughout the supplement, to denote the text revisions that were necessary to address the above NRC comments.
RESOLUTION OF NRC COMMENTS The setpoint and response time for the 4160 volt bus undervoltage reactor trip instrumentation channels were not included in our original amendment application since the SONGS 1 Technical Specifications do not specify either of these two parameters for other reactor trip instrumentation. However, the NRC requested that these two parameters be included in the Technical Specifications for these reactor trip channels to be consistent with the Standard Technical Specifications. Therefore, two new Technical Specification tables are proposed by this supplement for reactor trip instrumentation setpoints and response times. Those tables refer to a setpoint/response time curve (Figure 3.5.1-1) that is typical for the type of relays used in the 4160 volt bus undervoltage reactor trip circuitry. We are now developing the specific curve for the bus undervoltage reactor trip channels based upon testing of all the associated relays. The specific setpoint/response time curve for these reactor trip channels will be submitted as a second supplement to this amendment application by January 25, 1991.
This supplement proposes that the 4160 volt bus undervoltage reactor trip instrumentation be applicable to Modes 1, 2, 3, and 4. These modes of applicability are proposed to be consistent with those specified for loss of 4160 volt bus voltage in Table 3.3-3 of NUREG-0452 for Engineered Safety Feature actuation system instrumentation.
Amendment Application 189 proposed that the 4160 volt bus undervoltage reactor trip instrumentation channels be tested every refueling outage. This surveillance interval was selected since surveilling this instrumentation during power operation risks spurious reactor trips. The SONGS 1 electrical distribution system is designed to automatically trip the reactor if 1 out of 2 channels for each 4160 volt bus IC and 2C sense undervoltage. However, as discussed in the NRC safety evaluation report on degraded grid voltage dated June 23, 1982, and in the Order dated January 2, 1990, we are committed to change this reactor trip logic during Cycle 12 to 2 out of 3 from each of the two 4160 volt buses. We plan to implement monthly surveillance of the instrumentation when the 2 out of 3 trip logic is installed during Cycle 12.
Document Control Desk January 14, 1991 Delaying the monthly surveillance requirement until that time will minimize the potential for surveillance testing to cause spurious reactor trips.
We have revised the PRA concerning the vital bus transfer single failure susceptibility. The revised analysis was necessary to provide additional explanation of the PRA assumptions and to more accurately reflect the design of the SONGS 1 electrical distribution system as it will be configured upon return to service. The revised PRA results continue to demonstrate that the risk of scheduling the resolution of the vital bus single failure issue for the Cycle 12 refueling outage is negligible (i.e., the risk of core damage is less than 2 x 10' per year of plant operation).
Since this supplemental amendment application affects mode 4 plant operation, NRC approval is needed prior to entering mode 4 (currently scheduled for February 20, 1991).
Therefore, we request your approval by February 13, 1991, to allow sufficient time for completion of our administrative process after NRC approval of this change. 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