ML19345G117
| ML19345G117 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 11/15/1974 |
| From: | Searls F PACIFIC GAS & ELECTRIC CO. |
| To: | Goller K US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| 11769, RO-DPR-7-74-3, NUDOCS 8103020492 | |
| Download: ML19345G117 (2) | |
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PACIFIC G AS AND ELECTR,IC C O M PANY b N.lJ 77 B E A t. E S T R E E T. SAN F R A N CISCO C ALIFO R NI A 94106. (415) 781 4211 f' R E D E R I C K T. S E A R L S meet a eus.
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Docket No. 50-133 Humboldt Bay Power Plant v.s O
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Dear Mr. Goller:
This report is submitted in accordance with Section IX.H.
2.a. (1) of the Technical Specifications of License No. DPR-7.
Noti-fication of this occurrence was made via phone to office of the Director of Region V Regulatory Operations on the day of the occur-rence.
Report Number DPR-7/74-3 Report Date November 14, 1974 Occurrence Date November 5 and 6, 1974 Facility Humboldt Bay Power Plant, Unit No. 3 Eureka, California Identification of Occurrence:
A condition occurred involving the settings of two of the four reactor high pressure trip switches which were less conservative than the limiting setting established in Table VI-l of the Technical Specifications.
Description of Occurrence:
On October 30, 1974 the reactor was shut down fo.'
a regularly scheduled refueling outage.
On November 5 and 6 during the routine operational test of the reactor high pressure trip sensors required by Table IX-1 of the Technical Specifications, it was discovered that two of the trip settings were out of tolerance on the P00R ORlGlNAl.
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Mr. Karl R. Goller November 15, 1974 Assistant Director for Page 2 Operating Reactors high side; one was 1218 psig and the other was 1225 psig.
The speci-fied setting is 1200+10 psig.
Designation of Apparent Cause of Occurrence:
Inspection of the pres-sure switches revealed nothing which could have directly caused the setpoint drift.
The switch Which was found set at 1218 psig was left set at 1209 psig during the Fall 1973 refueling outage.
The contacts of the switch which was found set at 1225 psig had been mistakenly cleaned prior to the test rather than after this "as found" test.
It is believed that this maintenance contributed to the setpoint change.
Similar setpoint changes following maintenance have been observed on switches of this type in the past.
Analysis of Occurrence:
Had a higher reactor pressure condition occur-red the reactor would have tripped as designed at 1200+10 psig because only one high pressure signal in each safety channel is required to cause a trip and one reactor high pressure switch in each channel was set to operate within the specified tolerance.
Corrective Action:
In the future it will be standard practice to leave switch settings near the center of an allowed tolerance band.
Our testing and maintenance scheduling, which calls for taking "as found" data prior to any maintenance will be more strongly emphasized to all maintenance supervisors and personnel.
Failure Data:
These are the second and third instances of these particular switches drifting out of tolerance since the plant was constructed.
The sensors are Type 73 movement in a Foxboro Rotax Model M/41E pressure controller.
very truly yours, I
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Mr. R. H. Engelken, Director Directorate of Regulatory Operacions Region V U. S. Atomic Energy Commission Walnut Creek, California
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