ML19317D984
| ML19317D984 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 04/27/1976 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19317D979 | List: |
| References | |
| RO-269-76-05, RO-269-76-5, NUDOCS 7912100661 | |
| Download: ML19317D984 (2) | |
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DUKE POWER COMPANY OCONEE UNIT 1 S
Report No.: R0-269/76-5 Report Date: April 27, 1976 Occurrence Date: April 13, 1976 Facility: Oconee Unit 1, Seneca, South Carolina Identification of Occurrence: Overpressurization of Core Flood Tank "1A" resulting from valve failure.
Conditions Prior to Occurrence: Unit at 86% full power.
Description of Occurrence:
On April 13, 1976, routine addition of nitrogen to Core Flood Tank "lA" was being performed to maintain the nitrogen overpressure in the tank at 600 1 25 psig as required by Oconee Technical Specification 3.3.3.a.
During this operation, nitrogen manual addition valve N-128 failed in an open position al. lowing the tank pressure to increase above the Technical Specification limit.
Valve N-137 upstream of valve N-128 was closed to terminate the pressure increase, and a reactor shutdown was immediately initiated when the pressure increased above the 625 psig limit. The pressure reached a maximum of 649 psig, but within 30 minutes was reduced to the Technical Specification limits by venting to the Quench Tank. At this time reactor shutdown was terminated.
Apparent Cause of Occurrence:
This incident was caused by mechanical failure of valve N-128.
The valve stem had separated from the valve disc and had not allowed the valve to seat properly when closure was attempted.
Additionally, the pressure regulator,
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normally controlling the nitrogen header pressure delivered to the core flood
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tanks had been allowed to drift above the normal 625 psig setpoint. This allowed the pressure to increase above 625 psig when valve N-128 failed open.
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Analysis of Occurrence:
This incident resulted in a maximum pressure of 649 psig in Core Flood Tank "1A" for a short period of time. This tank is designed for 700 psig and has been hydro-tested to 1050 psig during pre-operational testing. Also, there is a relief valve on the tank which would have limited the pressure to 660 psig.
Had a loss-of-coolant accident occurred while the tank was at its maximum pressure of 649 psig, core flooding would still have occurred from the core flood tanks; however, the rate of flooding would have been slightly increased.
It is concluded that this incident did not affect the health and safety of :he public.
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,RO-269/76-5 April 27, 1976 Page 2 e
Corrective Action:
A work request was issued, and the failed valve, N-128, has been repaired.
Also, administrative actions have been taken to assure that, prior to use, the setpoint for the high pressure header regulator will be checked to make sure that it is properly limiting the nitrogen pressure in the core flood tank to 625 psig.
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