ML19312C179

Abnormal Occurrence Rept AO-269/75-06:on 750528,reactor Bldg High Pressure Trip Switch Setpoints Found Set Improperly. Caused by Omission from Sys Recalibr.Switches Reset & Instrument Procedures Revised

ML19312C179
Person / Time
Site:	Oconee
Issue date:	06/12/1975
From:	DUKE POWER CO.
To:
Shared Package
ML19312C176	List: ML19312C175 ML19312C179
References
NUDOCS 7912100671
Download: ML19312C179 (3)

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Report No.: A0-269/75-6 Report Date: June 12, 1975  ;

Occurrence Date: May 28, 1975 Facility: Oconee Unit 1, Seneca, South Carolina Identifica~ ion of Occurrence: Reactor Building high pressure trip switch setpoints set improperly Conditions Prior to Occurrence: Unit at power operation Description of Occurrence:

During a May 28, 1975 audit by NRC/0IE, it was determined that several Reactor Protective System (RPS) Reactor Building (RB) high pressure trip switch setpoints had exceeded the 4.0 psi limit specified in the Technical Specifications. The following is a listing of those switches which did not conform to the Technical Specification limit:

Unit 1 Unit 2 Unit 3 Channel A, 4.04 psi Channel B, 4.05 psi Channel A, 4.02 psi Channel C, 4.04 psi Channel C, 4.10 psi Designation of Apparent Cause of Occurrence:

The pressure switches were originally set to 4.0 i .1 psi in accordance with instrument procedures IP/0/A/0305/5A, B, C, and D. On June 6, 1973, the Reactor Protective System (RPS) setpoints were reduced a certain amount to allow for instrument tolerance and drift to prevent exceeding limits in Technical Specifications. The RPS Reactor Building pressure switches were inadvertently omitted from this recalibration.

Analyeds of Occurrence:

The. L .etor Protective System requires two-out-of-four channels to cause a reactor trip. In this instance, at least two of the four Reactor Building high pressure switches, for each unit, were set at or below 4.0 psi and would have functioned properly in the event of a loss of coolant accident, even in the absence of a low Reactor Coolant System pressure trip. The pressure switches in this incident were only marginally above the limit, and considering the design conservatism of this system, would also have functioned to satisfactorily limit the consequences of a postulated loss of coolant accident. It is considered that the health and safety of the public was not affected by this incident.

7912100 [7/

Corrective Action:

Instrument procedures IP/0/A/0305/5A, B, C, and D were revised to require the high Reactor Building pressure setpoint to be set at 3.8 psi to allow for instrument tolerances and drift without exceeding the Technical Specifi-cation limit. All switches have been reset to this value.

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