ML20063P872
| ML20063P872 | |
| Person / Time | |
|---|---|
| Site: | Zimmer |
| Issue date: | 09/30/1982 |
| From: | Borgmann E CINCINNATI GAS & ELECTRIC CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, QA-2026, NUDOCS 8210150443 | |
| Download: ML20063P872 (3) | |
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THE CINCINNATI GAS & ELECTRIC COMPANY CIN CINN AT1,OHIQ 452o1 September 30, 1982 QA 2026 E. A. BORGMAN N
$ENsom vtCE PRESIDENT U. S. Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, Illinois 60137 ATTN:
J. G. Keppler Regional Director RE:
WM. H. ZIMMER NUCLEAR POWER STATION - UNIT 1 10CFR50.55(e) - ITEM E DEFICIENCY IN DIESEL GENERATOR CONTROL LOGIC DOCKET No. 50-358, CONSTRUCTION PERMIT #CPPR-88 W.O. 57300. JOB E-5590, FILE 50.55(e) 3-R Gentlemen:
This letter constitutes an interim report concerning the subject deficiency reported under the requirements of 10CFR50.55(e). This deficiency was reported to Region III on September 9, 1982, as being potentially reportable. Our evalua-tion of the deficiency has determined that this item is reportable.
During the investigation of the loadshed and resequencing logic at 'the Wm. H.
Zimmer Nuclear Power Station, a sequence of events was discovered which could lead to the paralleling of all three (3) emergency buses on the same diesel generator, subsequent overloading of that diesel generator and possible loss of an essential bus. A brief description of the auxiliary power system for the emergency buses is provided below to aid in understanding the sequence of events.
As shown on the attached diagram, the Wm. H. Zimmer Nuclear Power Station has three (3) emergency buses. Each emergency bus may be powered from either an onsite source, one of two (2) independent offsite power sources or an emergency diesel generator. Automatic bus transfers, loadshedding and sequencing of emergency loads is controlled by a separate Essential Relay Panel (ERP) for each bus.
The ERP re-ceives intelligence from ESF actuation signals and from potential transformers located on the emergency buses and on the incoming side of the breaker connected to the offsite power sources. The sequence of events is described in the following paragraphs.
The diesel generator is assumed to be undergoing a periodic load test and is paralleled to Reserve Auxiliary Transformer (RAT) 21 or 22.
During this time a design basis event (i.e. LOCA concurrent with a loss of offsite power) is assumed to occur.
On receipt of an ESF actuation signal loadsheds will occur and sequencing will begin on all three (3) ESF buses.
In addition, the remaining diesel generators will start. Up to this point the logic occurs as designed.
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1 U. S. Nuclear Regulatory Commission Region III September 30, 1982 Page 2 QA-2026 However, since the DG under test is not tripped under this condition, the bus under test will remain energized. As a result, the DG is energizing the incoming potential transformers for the bus under test and the other 2 ESF buses. Because of this it will appear to the other 2 Essential Relay Panels that the RAT is available. The ERP's will then either transfer the bus to the RAT, or remain on the RAT if already there. The DG breaker on the 2 buses will remain open, with the DG running. When sequencing occurs, the remaining DG will attempt to pickup the loads of all ESF buses, thereby overloading the die-sei. This situation would persist until the diesel tripped. When this occurs the ERP's would function to loadshed the remaining buses, close the generator circuit breakers on the 2 buses that were not under test, and resequence all loads.
The above sequence will result in the tripping of one emergency diesel and subsequent loss of an ESF bus. It also results in unnecessary loadshedding, and resequencing of the other 2 essential buses.
Preliminary engineering evaluation of this situation reveals that it can be corrected by tripping the diesel generator with an ESF actuation signal when it is paralleled to either RAT 21 or RAT 22.
Our next report on this matter, to be submitted on November 15, 1982, will report the results of our final engineering evaluation and describe the hardware modifications required to eliminate the deficiency.
We trust that the above will be found acceptable as an interim report under 10CFR50.55(e).
Very truly yours THE CINCINNATI GAS & ELECTRIC COMPANY By E. A. BORGMANN Senior Vice President WPC/cse cc: NRC Resident Inspector ATTN:
W. F. Christianson NRC Office of Inspection & Enforcement Washington, D.C.
20555 Zimmer Project Inspector Region III
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