ML19263B616
| ML19263B616 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 01/16/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | John Miller GEORGIA POWER CO. |
| References | |
| NUDOCS 7901220210 | |
| Download: ML19263B616 (2) | |
Text
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[,p ** '8%qjo, NUCLEAR REGULATORY COMMISSION
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UNITED STATES
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REGloN il
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<dh (, g 101 M ARIETT A STREET.N.W.
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ATLANTA, GEORGI A 30303 o,
JAN 161979 In Reply Refer To:
RII:JP0 50-321, 50-366 50-424, 50-425 Georgia Power Company Attn:
Mr. J. H. Miller, Jr.
Executive Vice President 270 Peachtree Street, N. k'.
Atlanta, Georgia 30303 Gentlemen:
The enclosed Circular 79-02 is forwarded to you for information.
If there are any questions related to your understanding of the suggested actions, please contact this office.
Sincerely, Ib am ces P. O'Reilly D ector
Enclosures:
1.
List of IE Curculars Issued in the last 12 months 790122cytg
JAN 161979 e
. Georgia Power Company cc w/ encl:
K. M. Gillespie Construction Project Manager Plant E. 1. Hatch P. O. Box 439 Baxley, Georgia 31513 M. Manry, Plant Manager Plant E. 1. Hatch P. O. Box 442 Baxley, Georgia 31513 W. M. Johnston Project Construction Manager Vogtle Nuclear Plant P. O. Box 282
. Waynesboro, Georgia 30830
i UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 January 16, 1979 IE Circular No. 79-02 FAILURE OF 120 VOLT VITAL AC POWER SUPPLIES Description of Circumstances:
On September 16, 1978, Arkansas Nuclear One - Unit 2, while in hot functional testing preceding initial criticality, suffered a degrada-tion of both of the independent off-site power sources. This produced an undervoltage condition on the Engineering Safety Features (ESF) Buses and caused an inadvertent ESF actuation.
The licensee determined that the ESF actuation occurred on a loss of at least two of the uninter-ruptable 120 volt vital AC power sources.
Immediate investigation revealed that all four of the Solidstate Controls, Inc., (SCI) inverter static switches had automatically transferred to the alternate power supply (the 120 volt AC being supplied by transformers directly off the ESF buses rather than from the inverter output.)
Figure 1 (attached) shows the functional interconnection of the 120 volt AC power supply system.
A single conclusive cause of the undesired SCI inverter static switch transfer could not be identified. However, the following problems were discovered during subsequent investigation.
(a) The SCI inverters have circuitry to monitor the incoming DC voltage level which, on sensing a low voltage (nominally 104 DC volts for these inverters) will trip both input breakers to the inverter component after an adjustable time delay.
The setting of these time delay relays were not verified during either preoperational testing or subsequent maintenance. The time delay is necessary in order to accommodate transient loading conditions which may be encountered.
(b) On one SCI inverter, a DC fuse within the inverter component was found blown.
The vendor indicated that this fuse will blow due to an excessive DC voltage to the inverter component caused b a
transient on the 480 AC inp the taps on the 480V to 120 limit the DC voltage to the 8
maximum rating in the event DUPLICATE DOCUMENT
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