ML20084G215
| ML20084G215 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 10/03/1972 |
| From: | Worden W COMMONWEALTH EDISON CO. |
| To: | Anthony Giambusso US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084G189 | List: |
| References | |
| 5487, NUDOCS 8304210533 | |
| Download: ML20084G215 (2) | |
Text
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POST OP PICE SOX F47
- CHICACC, IL&lNOl3 60690 Dresden Nucicar Power Station r is Illinois 60450 j
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tir. A. Giambusso W
Deputy Director for Reactor Projects
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f Directorate of Licensing
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U. S. Atomic Energy Cornission l.
Washington, D. C.
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SUBJECT:
_ LICE?dE DPR-19. DRESDEN NUCLEAR POWER STATION, U"IT #2, SECTION l
6.6.C.1 0F T!M TECliNICAL SPECIFICATIONS,
Dear Mr. Gia=busso:
This is to report a condition relating to the operation of the s ta t ion, in which, during preparations for a transformer outage, cc.crgency power bus 33-1 was ac-energized and the 2/3 dicsci auto-started, tripped, and failed to restart. This rendered the diesel generntor inoperable in conflict with sectica 3.9.B of the Technical Specifications.
INCIDEUT AND IINESTICATION On September 3,1972, with Unit 3 in cold shutdoun and Unit 2 l a t 350 1:'.?e, 2/3 dicsol' generator auto-started when emergency power bus 33-1 was de-energized for a tre.nsformer outage. An atte:npted reset of the auto-start signal to restore normal engine protective devices (which are bypassed during tha auto start condition) was made by moving the 2/3 diesel generator ccatrol switch frcm the " auto", position to the "stop" position and back to the " auto" position..The diesel tripped apprcximately six minutes later, even though the auto-start condition still existed.
A testing program was begun on the 2/3 diesel to establish ti; cause of the trip. When the condition was finally duplicated, a diesel
" fail-to-start" alt.cn came up uhen the control switch was turned to "stop" and back to " auto".
The diesel tripped six minutes and tucive seconds af ter this clam.
This time period coincides with the timed cngine shutdown scqaence for nonal diesel shutdown.
In addition, the diesel would not restart as long as the " fail-to-start " alatu was up.
s bni 8304210533 730606 PDR ADOCK 05000237 y
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Mr. 4. Gimayqo b' October 3, 1972 O
O Preliminary investigation indicates that the slow response of a time delsy relay within the electrical system energized the start failure relay when the control switch was momentarily placed in the l'stop" position.
The start failure elay initiated the shutdown sequence, which tock prece-dence over the continuing auto-start signal, and tripped the diesel.
If thws condition exists, it will be annunciated by a " fail-to-start" alarm in the control room.
The presence of this signal will also render the dicsci inoperable until reset at the engine control panel.
(f the alarm is not present, the diesel remains operabic.
Additional investigation revealed that this alarm had come up periodically following dicscl-generator surveillance testing.
The cperators had reset it during post-shutdotm inspections; and the condition had never resulted in the failure of a dicsci to start.
Further investigation is in progress to confirm the cause of the 2/3 diccel generator trip. This includes monitoring of relays during the start sequence, and tests on the Unit 2 and Unit 3 diesel generators to establish theits' susceptibility to this problem.
CORRECTIVS ACTION
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Uhen the cause of the malfunction has been determined, the defective components will be replaced and ex mined to determine the causa of failure.
The circuit will be redesigned if required.
In the interim, the diesel-generator operating and surveillance procedures have been changed to require an operator to be stationed at the^
engino control panci prior to a diesel shutdown.
If the " fail-to-start" clarm ccmes up, he will immediately reset it; and the dicsc1 will remain -
operabic.
This procedure will be followed on the Unit 2 and 3 dicscis ca wall as the 2/3 diesel until the problem is corrected.
When the investigation has been completed and final corrective action established, a letter will be sent summarising our findings.
Sincerely, 5 u.$ b. & u W. P. Worden Superintendent Dresden Nuclear Power Station WPW:do
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