ML19261B959
| ML19261B959 | |
| Person / Time | |
|---|---|
| Site: | Vallecitos Nuclear Center |
| Issue date: | 02/28/1979 |
| From: | Darmitzel R GENERAL ELECTRIC CO. |
| To: | Stello V Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7903090143 | |
| Download: ML19261B959 (2) | |
Text
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GEN ER AL h ELECTRIC
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ENGINEERING GENERAL ELECTRIC COMPANY. P.O. BOX 460, PLEASANTON. CALIFORNIA 94566 DIVISION N
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February 28, 1979
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Mr. Victor Stello, Director Division of Operating Reactors
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Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission VG Washington, D.
C., 20555
Reference:
License R-33, Docket 50-73
Dear Mr. Stello:
On February 20, 1979, prior to the startup of the General Electric Nuclear Test Reactor (NTR), Vallecitos Nuclear Center (VNC), high readings were noted on two recorders connected to the NTR primary coolant flow indication system. These high indications for normal flow might result in the low flow scram signal occurring at a lower flow than expected, i.e., possibly at a lower flow than required by the Technical Specifications. This is conside ed to be reportable pursuant to Section 11.(1) of License R-33.
During a startup of the NTR on February 9,1979, a high reading was noted on the primary coolant flow indicator. The reactor was immediately shut down, and an investigation was made.
As no appreciable amount of air was noted when the flow transmitter was vented, it was assumed that the problem was due to a malfunction of the recorder. Accordingly, the flow recorder indicator motor drive was replaced, and a general checkout was performed. As an added precaution, a second recorder was added to the system.
On February 20, prior to reactor startup, higher than normal flow readings were noted on both recorders. The subsequent investigation revealed a significant amount of air in the high pressure side of the transmitter.
The NTR primary coolant flow is measured by a differential pressure transmitter across an orifice. The pressure differential across the orifice plate is sensed by a bellows unit, the movement of which is linked to a transmitter. The scram signal and recorder operate from the transmitter.
Normal flow is approximately 21 gpm (95% of recorder scale); the scram trip is set at approximately 17.5 gpm (80% of scale); and the Technical Specifications require a minimum trip setting of 15 gpm (68.5% of scale).
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a GENER AL @ ELECTRIC Mr. Victor Stello February 28, 1979 the high recorder indications were apparently caused by air in the primary coolant system being trapped upstream of the orifice plate and eventually entering the high pressure sensing line.
As the transmitter is mounted at a higher elevation than the orifice section, the air would travel up into the bellows AP chamber, causing an unusually high recorder indication.
In order to prevent recurrence of this problem, the flow transmitter will be vented on a daily basis prior to reactor startup until repairs and/or modifications can be made to eliminate the air accumulation problem.
This occurrence presented no hazard to the health and safety of the general public or NTR employees.
The occurrence was reported to the NRC-Region V by telephone and telecopy on February 21, 1979.
Sincerely,
- hvhdhh, R. W. Darmitzel Manager Irradiation Processing Operation vcc cc:
Nuclear Regulatory Conmission Region V