ML20085G880
| ML20085G880 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 07/18/1973 |
| From: | Gilleland J TENNESSEE VALLEY AUTHORITY |
| To: | Kruesi F US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20085G875 | List: |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8308290491 | |
| Download: ML20085G880 (3) | |
Text
ENNESSEE VALLEY A HOAITY CHATTANOOGA, TENNESSEE 3740'I E W
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PARTN E AS HIP July 18, 1973 g
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Mr. F. E. Kruesi, Director Directorate of Regulatory Operations U.S. Atomic Energy Commission Washington, DC 205h5
Dear Mr. Kruesi:
On June 19, 1973, TVA r.ade an initial report to AEC-DRO Inspector W. S. Little of the failure of the level switches LS-73-56A and LS-73-56B at the Browns Ferry Nuclear Plant unit 1.
In accordance with paragraph 50 55(e) of 10 CFR 50, we submit the enclosed final report of the failure.
Very truly yours, f.E.Gilleland
" Assistant to the Manager of Power Enclosure CC (Enclosure):
Mr. Norman C. Moseley, Director Directorate of Regulatory Operations U.S. Atomic Energy Commission Region II - Suite 818 230 Peachtree Street, NW.
Atlanta, Georgia 30303 8308290491 73o73o 9
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V ENCLOSURE BROWNS FERRY NUCLEAR PLANT UNIT 1 FINAL REPORT ON FAILURE OF HPCI LEVEL SWITCHES LS-73-56A AND LS-73-563 ON CONDENSATE RING HEADER (DDN 150)
An initial report of the failure of the icvel switches LS-73-56A and LS-73-56B at the Browns Ferry Nuclear Plant unit 1 was made verbally by M. M. Price, Construction Engineer, at the plant site to W. S. Little, AEC-DRO Region II Inspector, on June 19, 1973, in compliance with 10CFR50.55(e). This letter constitutes our final written report pursuant to 10CFR50.55(e).
These two switches were reported as being defective following a scheduled test; and upon investigation, the contacts of the switches were found to be badly burned. The function of the switches is to initiate transfer of the HPCI suction from the condensate ring header to the torus. The burned contacts were stuck in a closed position which in turn transferred the HPCI suction to the torus permanently.
The switches were Robertshaw Model 83481 Levelac level switches with a 1/4-ampere rating at 250 volts DC.
A failure analysis revehled that these switches were undersized; that is, their rating should have been 1/2 cmpero at 250 volts DC.
The pertinent pieces of equipment associcted with the two redundant Icvel switches are:
(1) two valves on the torus, (2) one valve on the condensate ring header, and (3) an alarm that annunciates in the control room upon low water icvel in the condensate ring header. The power supply to the two level swit'ches, the alarm, and the three valves is 250 volts DC.
Either switch will initiate transfer of the HPCI water supply from the condensate ring header to the torus. When the transfer occurs, the' alarm is also aanunciated in the control room.
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O The safety implicaticus associated with the switches are as follows:
1
- 1..The switches are redundant such that either switch will initiate the j
transfer and actuate the alarm.
2.
The contacts on the level switches close on falling level in the condensatie ring header; thus, transfer and annunciation would occur if the switch contacts stick when closing.
3.
If the DC power fails to both switches, the transfer and annunciation will not' occur.
Failure of both switches to close or loss of the DC power will not prevent the safe shutdown of the plant because the operator can manually initiate blowdown of the reactor through the power relief valves as a backup to the HPCI. After depressurization, both low-pressure core injection and core spray can maintain water inventory in the reactor vessel.
.The corrective action taken was to replace the~ two failed switches with switches having a rating of 1/2 ampere at 250 volts DC.
This replacement was completed on June 18, 1973.
In addition to replacing the switches, it was necessary to adjust the linkage mechanism to accommodate the larger switches.
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