ML19256F400
| ML19256F400 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 11/30/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Tallman W PUBLIC SERVICE CO. OF NEW HAMPSHIRE |
| References | |
| NUDOCS 7912190087 | |
| Download: ML19256F400 (1) | |
Text
TA UNITED STATES g
g NUCLEAR REGULATORY COMMISSION 3
,~>E REGION I U"
[
631 PARK AVENUE KING OF PRUSSIA, PENNSYLVANIA 19406 November 30, 1979 Docket Nos. 50-443 50-444 Public Service Company of New Hampshire ATTN:
Mr. W. C. Tallman President 1000 Elm Street Mancheste., New Hampshire 03105 Gentlemen:
The enclosed IE Bulletin No. 79-27 is forwarded to you for information.
Although no written response is required at this time, these concerns will be addressed as part of the licensing process for your plant.
If you desire additional information regarding this matter, please contact this office.
Sincerely, n
Boyce H. Grier Director
Enclosures:
1.
List of Recently Issued IE Bulletins CONTACT:
D. L. Caphton (215-337/5308) cc w/encls:
John D. Haseltine, Project Manager J774 35O r um ooc 8.7
ENCLOSURE 1 UNITED STATES SSINS No.:
6820 NUCLEAR REGULATORY COMMISSION Accession No.:
0FFICE OF INSPECTION AND ENFORCEMENT 7910250499 WASHINGTON, D.C.
20555 IE Bulletin No. 79-27 Date: November 30, 1979 Page 1 of 3 LOSS OF NON-CLASS-1-E INSTRUMENTATION AND CONTROL POWER SYSTEM BUS DURING OPERATION Description of Circumstances:
On November 10, 1979, an event occurred at the Oconee Power Station, Unit 3, that resulted in loss of power to a non-class-1-E 120 Vac single phase power panel that supplied power to the Integrated Control System (ICS) and the Non-Nuclear Instrumentation (NNI) System.
This losc of power resulted in control system malfunctions and ignificant loss of information to the control room operator.
Specifically, at 3:16 p.m., with Unit 3 at 100 percent power, the main condensate pumps tripped, apparently as a result of a technician performing maintenance on the hotwell level control system.
This led to reduced feedwater flow to the steam generators, which resulted in a reactor trip due to high coolant system pressure and simultaneous turbine trip at 3:16:57 p.m.
At 3:17:15 p.m., the non-class-1-E inverter power supply feeding all power to the integrated control system (which provides proper coordination cf the reactc,r, steam generator feedwater control, and turbine) and to one NNI channel tripped and failed to automatically transfer its loads from the CC power source to the regulated AC power source.
The inverter tripped due to blown fuses.
Loss of power to the NNI rendered control room indicators and recorders for the reactor coolant system (except for one wide-range RCS pressure recorder) and most of the secondary plant systems inoperable, causing loss of indication for systems used for decay heat removal and water addition to the reactor vessel and steam generators.
Upon loss of power, all valves controlled by the ICS assumed their respective failure positions.
The loss of power existed for approximately three minutes, until an operator could reach the equipment coom and man =lly switch the inverter to the regulated AC source.
The above event was discussed in IE I
~
16, 1979.
NUREG 0600 " Investigation into the Ma TMI LER 78-021-03L whereby the RCS de Entire document previously on loss of a vital bus due to inverte entered into system under:
ANO 1774 551 si No. of pages:
7