ML19224A451
| ML19224A451 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 01/16/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Herbein J METROPOLITAN EDISON CO. |
| References | |
| NUDOCS 7902010282 | |
| Download: ML19224A451 (8) | |
Text
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>S "EGut UNITED STATES t-NUCLEAR REGULATORY COMMISSION f Yp k
7 ~g 'b,ej -f REGION I 631 PARK AVENUE g*
g KING OF PRUS$1 A, PENNSYLV ANI A 19406 January 16, 1979 Docket Nos. 50-289 50-320 Metropolitan Edison Company ATTN:
Mr. J. G. Herbein Vice President - Generation P. 0. Box 542 Reading, Pennsylvania 19640 Gentlemen:
The enclosed IE 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, h
Ibw Boyce H. Grier Director
Enclosures:
1.
IE Circular No. 79-02 2.
List of IE Circulars Issued in the last 12 months cc w/encls:
E. G. Wallace, Licensing Manager J. J. Barton, Project Manager R. C. Arnold, Vice President - Generation L. L. Lawyer, Manager - Generation Operations - Nuclear G. P. Miller, Superintendent J. L. Seelinger, Unit 1 Superintendent J. B. Logan, Unit 2 Superintendent G. A. Kunder, Unit 2 Superintendent - Technical Support I. R. Finfrock, Jr.
Mr. R. Conrad G. F. Trowbridge, Esquire Miss Mary V. Southard, Chairman, Citizens for a Safe Environment
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 IE Circular fic. 79-02 Date:
January 16, 1979 Page 1 of 3 FAILURE OF 120 V0LT 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 degradation 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 s ta t!
switches had automatically transferred to the alternate power supp, (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 settings 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 by a transient on the 480 AC input.
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the taps on the 480V to 120V t limit the DC voltage to the in DUPLICATE DOCUMENT maximum rating in the event of Entire document previously entered gqt into system under:
ANO 79 0ll 9 MN 790119025"I y,
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