ML19339B180
| ML19339B180 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 10/31/1980 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| IEB-79-27, IEC-79-02, NUDOCS 8011060464 | |
| Download: ML19339B180 (2) | |
Text
.
s' SOUTH CAROLINA ELECTRIC & GAS.COMPAM cost ornce.oi s.($4 M CotuHa:A, south CAROLIN 29218 T. c. HicHots, Ja.
October 31, 1980 pg A 26 Vgg Patssotwt amo Gaoup (asconvg Nvetran Orgnationes W
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@g gMICH Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Subject:
Virgil C. Suumer Nuclear Station Docket No. 50/395 I&C Questions - IEB-79-27
Dear Mr. Denton:
As requested by Mr. Hubert Li of the I&C branch, South Carolina Electric and Gas Company (SCE&G), acting for itself and agent for South Carolina Public Service Authority, provides forty-five (45) copies of the SCE6G position on IEB-79-27, " Loss of Non-Class lE Instrumentation and Control Power System Bus During Operation".
Item numbers in this letter correspond to item numbers in the bulletin.
la.
Each class lE and non class 11 bus supplyir.g power to safety and non safety related instrumentation and control system is supplied power from a particular source through an inverter. Upon loss of a.c. power to each of these inverters, an alarm is provided in the control room.
lb.
Loads connected to these buses which are necessary for the plant to achieve cold shutdown are the auxiliary safeguard cabinets, the reactor protection relay panels, the process racks, the auxiliary relay racks and the solid state protection cabinets.
During normal shu'.down, several non safety related systems or portions of safety systems with non safety controls are utilized and there-fore, lack redundancy.
Examples are the feedwater system, the condenser steam dump system, the CVCS letdown system and the normal charging path of the CVCS system.
Inverter failure may prevent the operator from utilizing several of these systems.
However, an alternate means to achieve cold shutdown utilizes only safety related systems as de-scribed in the response to FSAR question 211.86.
The inverter loads of these safety related systems are the same as listed above except the auxiliary relay racks.
Since these systems are redundant and powered from separate inverters, loss of a single inverter does not prevent the plant from achieving cold shutdown condition 3.
I 8011060464
a J'
Mr. Harold R. Denton October 31, 1980 Page Two Ic.
No modifications are proposed as a result of this review.
2.
Plant procedures required to achieve cold shutdown upon loss of power to each class lE and non class lE bus supply-ing power to safety and non safety related instrument and control systems have been reviewed.
These procedures cover the concerns addressed in items 2a, b and e of this bulletin.
3.
IE Circular 79-02, " Failure of 120 Volt Vital A.C. Power Supplies", has been re-reviewed to include both class lE and non class 1E safety related power supply inverters.
The class lE inverters are dual input inverters which provide continuous power to 120 volt vital a.c. buses.
Transfer from one input to the or.her is accomplished with-out interruption of the output. There are two non class lE inverters, one of which is a dual input inverter which operates in the same manner as the class lE inverters.
The other is a single input inverter. The output from this inverter is paralleled with a supply from a 480-120 volt transformer which is connected through a static transfer switch. Upon loss of inverter output, automatic transfer is initiated to the backup source.
Operation of the transfer switch is alarmed in the control room. No design modifications are proposed as a result of this re-review.
If you have any questions, please let us know.
Very truly yours, 1
A 9
T. C. Nichols, Jr.
RBC:TCN:rh cc:
V. C. Summer G. H. Fischer T. C. Nichols, Jr.
E. H. Crews, Jr.
D. A. Nauman O. S. Bradham O. W. Dixon, Jr.
R. B. Clary W. A. Williams, Jr.
B. A. Bursey J. B. Knotts J. L. Skolds NPCF/Whitaker File b