ML20199H052
| ML20199H052 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/20/1997 |
| From: | Rainsberry J SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20199H054 | List: |
| References | |
| NUDOCS 9711260005 | |
| Download: ML20199H052 (4) | |
Text
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An iIHMW 1%11 R)41KhAt ** Cwgeny November 20, 1997 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlement
Subject:
Docket Nos. 50 361 and 50-362 Inter-Unit 4.16 kV Bus Cross-Tie San Onofre Nuclear Generating Station Units 2 and 3
References:
- 1) December 31, 1996 Letter frim J. L. Rainsberry (SCE) to the Document Control Desk (NRC)
Subject:
Inter-Unit 4.16 kV Bus Cross-Tie, San Onofre Nucle.r Generating Station, Units 2 and 3.
- 2) October 24, 1997 Letter from J. L. Rainsberry (SCE) to the Document Control Desk (NRC),
Subject:
Inter-Unit 4.16 kV Bus Cross-Tie, San Onofre Nuclear Generating Station, Units 2 and 3.
This letter withdraws the request in Reference 1 for NRC approval of the test methodology for the Inter-Unit 4.16 kV Bus Cross-Tie Integrated Functional Test (IFT).
This test is a niethod to demonstrate the functional ability of a g
diesel generator of an operating unit to support loads on the opposite unit.
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The I_FT would involve disconnecting a 4.16 kV bus on a Unit in Mode 1 from its 9' 0p offsite AC power source and disabling the auto sequencing of the loads in order to cross-tie to the 4.16 kV bus on the opposite unit that is in Mode 5 or 6.
In addition to demonstrat_ing the functional ability of a diesel j
generator to support loads on the opposite unit, this test would demonstrate the. ability of the diesel generator of the operating unit to operate in parallel with the diesel generator of the shutdown unit.
Because the IFT would have reautred disconnection of a 4.16 kV bus on an operating unit from
-its offsite AC power source and disabling the auto sequencing of the loads.
Southern California Edison (SCE) requested NRC approval for this test scenario.
9711260005 971120 PDR ADOCK 05000361:
P ppR San Omdre Nudcar Cxwrating station San Cicinente. CA 926740128 -
714468 7420
I i
i Document Control Desk.
t Cur rently, the Cross-Tie modification is in p'. ace, but is disabled, with leads lifted and jumpers installed, pending NRC approval of the design, testing methodology, and potential use of the modification.
l As discussed in SCE's letter dated October 24,1997(Reference 2),SCEhas q
Deen evaluating overlap testing as a method of demonstrating the functional capability of the Cross-Tie modification. SCE's evaluation has been completed, and it has been determined that overlap testing will be sufficient to demonstrate operability of the Cross-Tie without the need to disconnect a 4.16 kV bus on an operating unit from its offsite AC power source.
Testing of all circuits required to demonstrate operability of the Cross-Tie modification has been completed with the exception of testing of the diesel generator droop l
cire.?ts.
Testing of these remaining circuits will be performed before this modification it, made available for use.
Overlap testing provides an acceptable level of assurance that the Cross-Tie will perform as expected when ca)1ed upon.
This testing methodology is consistent with surveillances currently allowed by the San Onofre Units 2 and 3 Technical Specifications (1Ss),
for example, Surveillance Requirement 3.8.1.11 requires verification that upon receipt of a loss of offsite power signal that emergency buses are de-energized, loads are shed from emergency buses, and that the diesel generator auto-starts.
The Bases for this Surveillance Requirement state that "This testing may include any series of sequential, overlapping, or total steps so that the entire connection and loading sequence is verified." Therefore, overlap testing is an acceptable alternative to the ifT requested in Reference 1.
Overlap testing is considered to be sufficient to determine the functional capability of the Cross-Tie, including the ability to recover power from the offsite source of the blacked-out unit by paralleling with an operating diesel generator. However, overlap testing will not demonstrate the ability to parallel an operating diesel generator from one unit with the diesel generator of the oppot,ite unit.
paralleling the two diesel generators is beneficial because it allows recovery of the standby source of power to the blacked-out unit. However, recovery of standby power to the blacked-out unit is still possible without paralleling the diesel generator of the opposite unit through
" drop and pickup" methods, in the drop and pickup method the operator will strip the loads from the bus, open the tie breakers, then close the diesel generator breaker to connect the diesel generator to the dead bus, and then connect the desired loads manually.
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e Docyment Control Desk
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Because the. ability to parallel the diesel generator of the operating unit i
with the standby power source of the other unit will not De demonstrated through overlap testing, use of the Cioss-Tie will be procedurally controlled t
to require " drop and pickup" methods when restoring power to the blacked out l
unit using-the associated diesel generator.
Reference 1 also requested NRC review and approval of the design of the Cross-Tie and use of the Cross-Tie in a beyond-design-basis scenario. These requests are unaffected by this letter.
, to this letter contains the Failure Modes and Effects Analysis that was requested by the NRC in a phone conversation dated September 9, 1997, j
in support of review of the design of the Cross-Tie modif9ation.
If you have any questions regarding this matter, please feel free to contact me, i
Sincerely,
,s r
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Enclosure cc:
E. W. Herschoff, Regional Administrator, NRC Region IV K. E. Perkins, Jr., Director, Walnut Creek Field Office, NRC Region IV J. A. Sloan, NRC Senior Resident inspector, San Onofre Units 2 & 3 3
M. B. Fields, NRC Project Manager, San Onofre Units 2 and 3
r ENCLOSURE 1 Failure Modes and Effects Ar.aiysis Inter-Unit 4.16 kV Cross-Tie
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