ML19210B613
| ML19210B613 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom, Maine Yankee, Crane  |
| Issue date: | 10/12/1973 |
| From: | Reinmuth G US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Thornburg H US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML19210B616 | List: |
| References | |
| RTR-REGGD-01.022, RTR-REGGD-01.047 NUDOCS 7911110092 | |
| Download: ML19210B613 (2) | |
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R. D. b rnburg, Chief, Field Support & Enforcement Branch, RO mn MILE ISLAHD UNIT 1, FAILUEE OF VOLTAGE SUPPRESSION DIODES I1 STALLED IN ENGMmFM SAFEGUARDS CIRCUIT BREArFRR - DOCKET No. 50-28 This meno is in response to your request for reviewl of the above failnres which cau.d at the subject facility and to assess the rnlated generic and safety implications, h licensee 2 reported that during testing of 480 volt AC safety related circuit breakers, numerous failures of the diodes @ IN 504) installed across the close and trip coils of the circuit breakers hava occurred. Investigation into the problem disclosed that the volt. age rating of the failed diodes is too low (400 volts) to handia Mne actual circuit breaker operation.the voltage transients occurring Based on this finding, the 14--
n has initiated a program to replace all potentially fanity diodes with a emit can=4dared more suitable for this application.
~h rep 1=e====t emit, a GE thyroctor, Model 6 RMAPIB2 has a rating of 1500 volta.
He have discussed the diode problem with the knowledgeable people from the licemese; the AE, Gilbert Associates (CAI); the breaker
====fmet=rar, Beatinghouse; and persour-1 from Region I and Licensing.
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h purpose of the voltage surge suppression circuitry is to protect
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sensitive instrumentsfrom voltage transients which can occur during f
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the opening or closing of a circuit breaker. % reason for the i
li-==='s concern of this interaction between the instrument and the circuit breakersis because the wiring for these components is installed in clase proximity of each other. It is also worthy to acta that the voltage suppression circuitry as discussed does not protect the relays nor contracts of the circuit breaker in which they are inst.11 4 In our assessment of the related generic implications concerning the failures, our discussians with West $nghouse and CAI indicated that to,4 % Control Form F0f154, h rnburg to Rain = nth, dated '
2RO Inspection Report No. 50-289/73-11 (Paragraph 7).
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M N 011110 07.q p
GwenW 1588 010 mm
H. D. Thornburg '
D12 g instru:2ent protection from voltage " spikes" using diodes in circuit breaker control circuitry has not been used at other nuclear power plants. In view of this, we conclude that the diode problem as discussed should not be generic. We have not, however, contacted all faciitties to confirm this conclusion.
Another design deficiency was noted during our investigation into the dioda problem in that the status of the "availmhility" of control power for the closing circuitry of these essential circuits breakers is not being monitored in the control room; i.e., by visual and/or audible annunciation. Additional information relating to this type of design deficiency was initially discussed in RO Report No. 71/003 dated August 31, 1971 regarding sita inspection of Pilgrim Unit 1.
With regard to the related safety implications of the diode failures, it was found that many faileres resultad in blown fuses > and subsequent loss of the control power which is needed to close the circuit breakers.
These observations sonbined with improper monitoring of control power lead us to believe that ther is a high probability a failure of a safety related circuit braskar could go sandetected.
In view of the above findings and with the oral concurrence of Licensing, it is our opinion that the licensee should perform modifications and da=a==trata adequacy through appropriata tasting. Additional changes any be desirabia to comply with Esgulatory Guide 1.22 and 1.47 with respect to control room indication of circuit breaker availability.
Since these are design changes which may require further evaluation, we are forwarding copise of this meno to Licensing for their consideration.
As follow through we recommend the regional office monitor corrective actions accordingly.
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- c. w. Rein-wh, chief Technical Assistance Branch, RO oo ec: A. Gisabusso, L
- 1. Bernero, L T. Ippolito, L B. Grier, RO
' 1IO] ] J. G. Davis, RO I3V E. J. Brunner, RO:I N0;46/C&O:123 J. P. O'Reilly, RO:I RO: TAB R0: JAB V0~ _ U $.; m w h VDTho/tmas:arj SWReinmuth 10/11/73 _ ],,1,(f f $] om a, .63-1s--suaa-44s-e7s Form AEC-Sta (Rev.9-53) AECM 0240}}