ML20206A548
| ML20206A548 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 11/01/1988 |
| From: | Hairston W GEORGIA POWER CO. |
| To: | Ernst M NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| HL-128, NUDOCS 8811150167 | |
| Download: ML20206A548 (3) | |
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, w ce o HL-128 50180 X7GJ17-H000 November 1,1988 U.S. Nuclear Regulatory Commission ATTN:
Mr. M. L. Einst Acting Regional Administrator - Region 11 Suite 2900 101 Marietta Street, N.W.
Atlanta, Georgia 30323 PLANT HATCH - UNIT 2 NRC DOCKET 50-366 OPERATING LICENSE NPF-5 DISCRETIONARY ENFORCEMENT AUTOMATIC OEPRESSURIZATION SYSTEM (ADS)
Gentlemen:
On October 26, 1988, in a conversation between representatives of Georgia Power Company (GPC), NRC-Region 11, ard NRC-NRR, GPC requested certain discretionary enforcement to continue operation of Plant Hatch Unit 2.
This discretion was r.eeded until a design change could be implemented to correct a
design deficiency in the automatic depressurization system ( ADS) power supply circuitry.
The NRC granted the discretionary enforcement based on the information discussed during the telephone conversation.
The discretionary enf o rc emeiit will be in place until the Unit 2 design change is implemented.
Because of the potential to ina.1vertently depressurize the vessel when making wiring changes, the prop > sed modification will not be performed while Unit 2 is on line.
- However, the change will be implemented prior to January 1, 1989.
Plant Hatch Unit 1 is presently in a refueling outage.
The design change for that unit is scheduled to be performed prior to reactor startup.
Descriptions of the design deficiency and proposed corrective action are provided in the enclosure.
The decision to grant discretionary enforcement was based on the following reasons:
- The failure mode (i.e.,
the failure of Station battery A),
coincident with a pipe break of a critical size, is extremely unlikely during the timeframe required to modify the design.
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- 1he high-pressure coolant injection (HPCI) system will still be available to mitigate a postulated loss-of-culant accident (LOCA) for small to intermediate break sizes, in the event of station battery failure.
Even without ADS, the low-pressure systems (LPCI and Core Spray) are capable of handling the large breaks, since the vessel will depressurize as a result of the LOCA.
Manual depressurization of the vessel ran still be accomplished.
Plant openators are trained on symptom-oriented emergency procedures which require the monitoring of critical parameters (e.g.,
RPV water level and pressure), and manual control when i
vessel depressurization takes place.
In
- addition, shift supervisors and plant operators have been briefed on the design l
deficiency and the potential of the single failure to disable ADS.
If you have questions, or require additional information on this subject, please contact this of fice at any time.
Sincerely, (h.,. Y W. G. Hairston, 111 I
GXM/ac i
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Enr.losure:
Description of ADS Design Deficiency and Cor ective Action.
i c:
Georgia Power Compam Mr. H. C. Nix, General Manager - Hatch j
Mr. L. T. Gucwa, Manager Licensing and Engineering - Hatch l
GO-NORMS o
U.S. Nuclear ReaV]_atory Comission. Washington. D.C.
rir. L. P. Crocker, Licensing Project Manager - Hatch U.S. Nuclear Regulatory Comission, Reaion 11 i
Mr. M. V. Sinkule, Chief Projects Section 3B Mr. J. E. Menning, Senior Resident inspector - Hatch j
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k Georgia Power h ENCLOSURL PLANT HATCH - UNIT 2 NRC DOCKET 50-366 OPERATING LICENSE NPF-5 DESCRIPTION OF ADS _ DESIGN OEFICIENCY AND COPRECTIVE ACTION Description of Design Dc-ficiency The design basis, as defined in the Plant Hatch Units 1 and 2 Final Safety Analysis Reports (FSARs) requires that the automatic depressurization system (ADS) be "single-failure proof."
Relative to that design, it hos been determined that the loss of de power from station bettery A (a single passive failure) would disable the automatic initiation of ADS.
This single-f ailure condition was not considered in the small-break loss-of-coolant accident (LOCA) analyses, which take credit for ADS under all single-failure considerations.
This design deficiency exists on both units and has existed since the analog transmittar trip system (ATTS) was installed in 1984 on Unit 2 and 1985 on Unit 1.
ihe existing ADS design has two logic trains, A and B.
Logic train A is normally powered f rom station battery A (DC-A), with an automatic backup f rom station battery B /M-8).
The sensor input in logic train A is supplied by Division I transmitters, trip units, and slave relays powered by DC-A.
ADS logic train B is energized from DC-A, with no backup power.
The sensor input in logic train B is supplied by Division II transmitters, trip units, and slave relays powered by OC-B.
A loss of DC-B disables B sensors, but has no ef fect on logic train A.
A loss of DC-A will disable logic train B and the ATTS sensor input for logic train A,
thertby disabling the automatic initiation of ADS.
Manual control functions will remain, r.orrective Action 1he proposed corrective actian involves a modification to the ADS logic to make it single-f ailure proof with regard to the power supplies.
The Division 11 backup supply (from station battery B) will be relocated from ADS logic train A to logic train B, allowing logic B to sctuate A05 even if Division I power is lost.
ADS logic A will initiate ADS if Division 11 power is lost.
All changes required by this modification are internal to control room panel 2H11 P628.
The major wiring changes involve fuses F5A and F6A, relay KlA in logic A, and relay KiB in logic 5.
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