ML19319C104
| ML19319C104 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/01/1973 |
| From: | Vaughn Thomas US ATOMIC ENERGY COMMISSION (AEC) |
| To: | James Keppler US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML19319C089 | List: |
| References | |
| NUDOCS 8001310468 | |
| Download: ML19319C104 (5) | |
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ATOMIC ENERGY COMMISSION
' *i WASHINGTON, D.C. 20545
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V3 G. Keppler, Chief, Operations Branch, RG THRU: G. W. Reinmuth, Chief, Technical Assistance Branch, R0 CRD BREAKER UNDERVOLTAGE TRIP ASSEMBLY DEFICIENCY - OCONEE UNIT NO. 1 A meeting was held at General Electric Switchgear Product Department located in Philadelphia, Pennsylvania on April 12, 1973.
The purpose of the meeting was to discuss with cognizant personnel, the problems relating to failure of their undervoltage trip assembly for the control I
rod drive trip breakers at Oconee Unit No. 1 nuclear generating station.
These undervoltage trip devices had failed to operate as designed on three separate occasions at the Oconee Unit No. 1 facility.
Mark Peranich, (RO:CB) assisted Vince Thomas (RO: TAB) in the above discussions with the GE personnel. A list of those persons contacted during the
- \\ j-visit is attached as Enclosure I.
The licensee's investigation of the subject failures identified three areas as the likely causes for failure of the undervoltage trip i
devices.
These areas-are as,follows:
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Excessive heating in the undervoltage coil and interconnecting wiring circuit.
The cause of overheating was attributed to an' underrated coil for the service intended.
F 2.
Inadequate overcurrent protection of undervoltage circuit i
components and interconnecting wiring.
The licensee's investigation disclosed that fuse' protection has not been provided for these' circuits because of a breakdown in the division of responsibility between vendors of inter-related components.
3.
Improper calibration of the undervoltage trip assembly by the GE Installation and Service (I&S) group. The set point adjustment nut of the undervoltage trip assembly was not safety wired (to prevent " set point drift") as required '
.by: approved installation and calibration procedures for the trip device.
GE considers this error a random occurrence.
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The scope of our review included examination of the appropriate-inquiry
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report and the licensee's occurrence report.
In addition to the F
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sy J. G. Keppler-MAY l hW3 above meeting with GE personnel, we also discussed the events relating to the failures with the appropriate people from the licensee and the nuclear steam system supplier Babcock & Wilcox.
In brief, the following is a summary of our findings:
Oconee Unit No. 1 CRD Trip Breaker system consists of two A/C breakers, (General Electric Model 224 A6147-200KE,,A62-25-1, 600 ampere, 600 volts) and four DC breakers, (General Electric Model 224 A3510-345KV, A62-15-2, 225 ampere, 600 volts).
The problematic undervoltage trip device, (Assembly Number 29C82G2 and Coil Number 75081G26) was installed in each of the above trip breakers.
Events relating to the three incidents above are discussed in the licensee's report to Regulatory Operations dated Feburary 23, 1973.
Our recent review of these incidents disclosed that the above mentioned
' deficiencies had been recognized and appropriate disposition has been taken to prevent recurrence of the failures.
B&W has modified the undervoltage coil circuit with suitable overcurrent protection (five y j ampere fuse) in each reactor protective undervoltage circuit of the CRD trip breaker system.
With regard to the above improper calibration problem of the undervoltage trip attachment, GE stated that this anomaly was an isolated case of field service personnel not following the approved installation and calibration instructions for the trip unit.
Specifically, following the initial undervoltage coil failure on September 13, 1972, the faulty trip breaker was sent to the GE service shop in Savannah, Georgia for-repair.
Subsequent to inspection of the breaker and prior to its shipment for return, the trip assembly spring tension was adjusted to give a drop out voltage of 60-65 volts, according to procedures.
However, the adjustment nut was not safety wired (locked) to prevent shifting of the set point.
The breaker was returned to the Oconee facility without the_ locking feature,.and installed for service. On January 23,.1973, while performing voltage " drop out" tests on this breaker, the unit failed to trip open in response to a loss of voltage.
Set point drif t of the undervoltage trip unit was identified as the cause for breaker failure.
The undervoltage trip was reset to the
. desired voltage drop.out level of 60-65 volts, the assembly adjust-ment nut was safety wired.to prevent shifting of the set point, and
-follo ing several successful low voltage drop-out testc, r.he breaker w
was returned to service.
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n J. G. Keppler MAY I tyy 4
After the above breaker failure and resolution GE also recommended that replacement undervoltage trip assemblies, more suitable for continuous (energized) operation be provided for Oconee Unit No.1 to resolve the. chronic overheating problem.
Subsequently, six replacement units with a higher coil resistance have been installed in each control rod drive breaker.
The replacement coils have a resistance of 24-26 ohms as compared to 12-15 ohms resistance for the original coils.
GE also issued a " Change Order" document dated January 31, 1973, to all appropriate departments and Field Service Offices, assigning to the replacement coil part number 75081G26.
The original coil is presently identified as, part number 75081G26S.
With regard to the corrective action taken concerning the overcurrent protection' feature for the undervoltage trip circuity, B&W has issued a Site Problem Report (SPR), with appropriate instructions regarding corrective measures to be taken, at all appropriate site facilities.
B&W stated that implementation of these measures are being coordinated by each project engineer at the engineering offices located in Lynchburg, Virginia.
Baiky Instruments and Diamond Power have been advised by B&W of these corrective measures and have established interface design responsibility concerning the overcurrent protection feature.
Both B&W and GE have taken addidonal measures to correct the above deficiencies which ;xist at other B&W facilities.
Accordingly, similar measures for resolving these deficiencies are now being incorporated in the following nuclear facilities:
1.
Arkansas Nuclear One Unit 1 2.
Davis Besse Nuclear Station 3.
. Crystal River Plant, Unit 3 4.
Three Mile Island Units 1 and 2 a
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Oconee Units 2 and 3 6.
Rancho Seco Nuclear Generating Station Unit 1 TAB Views and Recommendations In. light of the above findings, we believe that the licensee,'B&W, and GE have all been responsive to the problems as they occurred and that proper corrective action was -aken.
In our judgement the above failures do.not have serious safety i= plica'tions -in that.
" system redundancy and series trip devices assure that the plant can be safely. controlled and shutdown in the event of either an undervoltage coil failure or i _/'h failure of a breaker to trip."1 However, in order to provide rven A
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v I Licensee's ' report dated February-23, 1973, page-3.
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J. G. Keppler.
gg 7 greater confidence in the operability of the affected components and associate wiring circuits, we believe that the corrective actions as discussed are necessary.
We recommend that the responsible region inspector ascertain during future inspections of the facilities noted above, that these deficiencies have been brought to the licensee's attention and that the appropriate corrective measures have been initiated.
Follow-up should be continued until appropriate licensees have the above overcurrent protection feature and replacement trip assemblies installed in their facilities.
,butGe!Y-WWY Vincent D. Thomas Instrumentation & Control Engineer Technical Assistance Branch, RO cc: D. F. Knuth
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R. H. En3 eiken W. C. Siedle i
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~, C-ENCLOSURE I i
ATTENDEES
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h MEETING AT G. E. SWITCHGEAR PRODUCTS DEPARTMENT
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APRIL 13, 1973 i
1 Leonard Bonn GE Manager Quality Control
- J. Peter Werner GE Manager-Breaker Design l
& Development Engineering i
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A. Rice GE Manager-Electric Utility
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& Export Engineering
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- J.
Brown GE Requestion Engineer I
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- D. Morton GE Process Control Specialist k
USAEC RO:CB l-Mark Peranich i
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. Vincent Thomas-USAEC RO: TAB A
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