ML19317E067
| ML19317E067 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 03/05/1974 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19317E066 | List: |
| References | |
| NUDOCS 7912120832 | |
| Download: ML19317E067 (2) | |
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O DUKE POWER COMPANY OCONEE NUCLEAR STATION Report No.:
A0-269/74-4 Report Date:
March 5, 1974 Occurrence Date:
February 22, 1974 1
Facility:
Oconee Unit 1 Identification of Occurrence:
Overpressurization of B Core Flood Tank Conditions Prior to Occurrence:
Steady-State Power Oconee Unit 1 was operating at 100 percent full power Description of Occurrence:
On February 22, 1974, the Oconee Unit 1 B core flood tank pressure was in-advertently increased to approximately 660 psig.
Technical Specification 3.3 requires that the core flood tank pressure be maintained at 600 1 25 psig.
The folleving describes the sequence of events:
1545 Control room operator received computer alarm for B core flood tank low pressure (592 psig).
Operator received B core flood tank low pressure alarm on statalarm board. Nitrogen header pressure was not sufficient for makeup to the core flood tanks; therefore, the utility operator was dispatched to increase header pressure by cutting in another nitrogen bottle. At the same time, another utility operator opened the B core flood tank makeup valve.
1546 The operator received a call to investigate the radiation monitor panel and left the core flood tank pressure gage.
1547 The operator received a computer alarm indicating B core flood tank high pressure (616 psig).
1548 The utility operator closed the B core flood tank makeup valve.
1600 Pressure in the B core flood tank peaked at about 660 psig, and then decreased to 630 psig.
1646 After venting to the reactor building atmosphere, B core flood tank pressure was reduced to below 625 psig.
Designation of Apparent Cause of Occurrence:
The apparent cause of this incident was deficiencies in the operating procedure for the core flooding system.
The present procedure does not preclude opening
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, the core flood tank nitrogen makeup valves while the nitrogen header pressure is being increased by cutting in additional nitrogen supplies at relatively high pressure.
Operator error also contributed to this incident. The operator should not have permitted himself to be distracted from monitoring the core flood tank pressure while the nitrogen makeup supply valve was open.
l Analysis of Occurrence:
There was no structural damage to the tank or associated piping. The core flood tanks have a design pressure of 700 psi and were successfully hydro tested at 1050 psi during preoperational structural testing. The pressure increase was limited to 660 psig by core flood tank relief valve actuation.
If the core flood tank pressure had equalized with the nitrogen header pressure, the pressure in the core flood tanks would not have exceeded 700 psig.
If a loss of coolant accident were postulated to occur while the B core flood tank was at its maximum pressure of 600 psig, core flooding would occur slightly sooner, but the present LOCA analyses would be insensitive to such a small time difference.
It is concluded that this incident did not affect the safe operation of the plant or the health and safety of the public.
Corrective Action:
Immediate corrective action was to reduce the core flood tank pressure below 625 psig by venting the nitrogen to the reactor building atmosphere.
To prevent recurrence of a similar incident, operating procedures for the l
core flooding system will be modified to prevent makeup to the core flood tanks while nitrogen header pressure is being increased. The operating i
procedure will also be modified to require verification that sufficient nitrogen header pressure exists prior to makeup to the core flood tanks.
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