ML20086E835
| ML20086E835 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 12/27/1973 |
| From: | Riley B VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20086E839 | List: |
| References | |
| AO-73-34, VYV-3109, NUDOCS 8312070534 | |
| Download: ML20086E835 (2) | |
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VERMONT YANKEE NUCLEAR POWER CORPORATION SCVCNTY SEVEN OROVC STRCCT RUTLAND, VimetONT 03701
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REFERENCE:
Operating License DPR-28 Docket No. 50-271 M
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Abnormal Occurrence No. A0-73-34 N
pATJ1 4 Gentlemen:
As defined by Technical Specifications for the Vermont Yankee Nuclear Power Station, Section 6.7.B.1, we are reporting the following Abnormal Occurrence as AO-/3-34.
On December 17, 1973, while investigating a reported problem involving the "A" Station Service Water Pump.4 KV breaker, an electrician noted the 7j fact that the breaker stationary auxiliary switch assembiv rear mounting tie bolt had loosened and was disengaged from its mounting plate. This bolt serves to assist in maintaining proper switch contact alignment. The loosening and subsequent backing out of the tie bolt caused some misclignment of the switch auxiliary contacts which would have rendered those contacts.
inoperable had the breaker operated. This failure is not considered to be an abnormal occurrence, but is merely referenced to detail appropriate background information.
As a result of this incident, an investigation of all forty-seven (47) 4 KV breakers was initiated. This investigation, which was completed on December 19, 1973, indicated that all 4 KV breakers exhibited varying degrees of bolt loosening.
Due to the fact that some breakers are associated with safety related systems, it was determined that this condition was in violation of Technical Specifications, Section 1.A.4 in that it icould have resulted in one or more engineering safety feature failures
!which could have caused or threaten to cause that feature or component to be incapable of performing its intended function as defined in the
-Technical Specifications.
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VERMONT YAN;<EE NUCLEAR POWER CORPORATION 4
b Directorate of Licensing December 27, 1973 Page 2 Tightening of all loose switch tie bolts was initiated immediately upon discovery and completed by 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> on' December 19, 1973. The reactor was operating at approximately 687. power at the time of this incident.
Of a total of forty-seven (47) switchgear units (General Electric 4-Metal-Clad, Type FG6) at Vermont Yankee, forty-three (43) contain 1200 amp., General Electric Magne-Blast circuit breakers, style AM-4, 16-250-811B, and the remaining four (4) units contain 3000 amp., Magne-Blast circuit breakers, style AM-4, 16-350-lH.
All switchgear units are equipped with stationary auxiliary switches which are referenced in General Electric Company Instruction and Renewal Parts tbnual GEII-1802R, Metal-Clad Switchgear, Figure 45A.
The Plant Operations Review Committee (PORC) concluded that a
/ possible cause of bolt loosening could be attributed to improper bolt j tightening during factory assembly. This possibility is supported by the fact that the switch must be pre-wired prior to being mounted to the front mounting plate. At this time, the rear mounting tie bolt is somewnat altricult to see and coula possibly be overlooKea.when i
performing a final quality check. An additional possible cause could be due to breaker operation. During breaker closure, the switch is i
operated by the breaker operating plunger through mechanical linkage.
When the breaker is tripped, the switch is again operated in the reverse 4
direction by a spring which has been held under tension by the breaker operating plunger. The operation of the switch in either direction is, of course, rapid and pronounced and might possibly contribute to a problem of this nature.
PORC determined that as a result of this incident, all 4 KV jjswitchgear stationary auxiliary switches should be' inspected in three 7 iggtths (which would be coincidental with approximately three breaker
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operations).
If a similar condition is found to be developing at that time, the committee will undertake whatever further corrective i
action is required to assure resolution of the problem.
In addition, i
a complete inspection of all breaker associated devices 'should be conducted during each plant refueling outage.
Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION B.W. Riley Plant Superintendent WFC/kbd
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