ML19210A177

Abnormal Occurrence 50-289/75-16:on 750605,variable Low Reactor Coolant Sys Pressure Trip Setpoints Less Conservative than Tech Specs.Specific Cause Not Established. Setpoints Will Be Checked to Assure Proper Calibr

ML19210A177
Person / Time
Site:	Three Mile Island
Issue date:	06/16/1975
From:	Arnold R METROPOLITAN EDISON CO.
To:
Shared Package
ML19210A178	List: ML19210A177 ML19210A180 ML19210A185
References
NUDOCS 7910240901
Download: ML19210A177 (4)

Text

NRC OlbTRIBUTION FOR PART 50 ']OCK" ATERIAL (TEMPORARY FORM)

CONTROL NO: 05/N FILE: INCIDW" EEPC'T TIE FROM: Metropolitan Edison Co I DATE OF DOC DATE REC'D LTR TWX RPT OTHER Reading, Pa R C Arnold 6-16-75 6-19-75 XXX ORIG CC OTHER SENT AEC POR YY TO:

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CLASS UNCLASS PROPINFO INPUT NO CYS REC'D DOCKET NO:

XXXXXX 1 50-289 DESCRIPTION: ENCLOSURES:

Ltr reporting abnormal occurrance #75-16 on 6-5-75. . . .concerning out o f limit settir gs , ,

for the reactor coolant pressure trip -

setpoints.....

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rJ. c Director hpi ti1'"0,.iJD. . , . -

Division of Reactor Licensing . .

U. S . Nuclear Regulatory Commission .: , ,

Washington, D.C. 20555 ~! . ,3,,, . -

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Dear Sir:

Docket No. 50-289 Operating License No. DPR-50 In accordance with the Technical Specifications of our Three Mile Island Nuclear Station Unit 1 (TMI-1), we are reporting the followin b rmal oc curren ce. U t/,

A >g, , \ t (1) Report Number: A0 50-289/75-16 .g (2a) Report Date: June 16,1975

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(3) Three Mile Island Nuclear Station Unit 1 ,','.

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N, (4) Identification of Occurrence: ' ' \ if

Title:

Out of Limit Settings for the Reactor Coolant Pressure Trip Setpoints.

Type: An abnormal occurrence as defined by the Technical Specifications, paragraph 1.8a, in that the out of limit settings for the reactor protection system (RPS) were less conservative then the limiting settings established in the Technical Specifications.

(5) conditions Prior to Occurrence:

The reactor was in a cold shutdown condition with major plant parameters as follows:

Power: Core: 0'll Elec.: 0 .We }kfh kb 6G14

. . RC Flow: 0 lbs/hr.

RC Press: 0 psig RC Temp: 122 F PRZR Level: 270 in.

PRZR Temp . : 122 F (6) Description of Occurrence:

On June 5,1975, Surveillance Procedure 1303-4.1, " Reactor Protection System Surveillance", was being performed in preparation for a reactor s ta rt up . Test results showed that the variable low reactor coolant system pressure trip setpoints for three RPS channels were less con-servative than required by the Technical Specifications.

The out-of-specification channels were recalibrated and retested, and the resulting trip setpoints were verified as being within Technical Specification limits. In addition, complete electronic checks of the Reactor Protection System and Engineered Safeguards System were performed using a voltmeter which was known to be in calibration. All checks were s a tisf acto ry .

The "as-found" setpoint (before recalibration) and the required setpoint for the ibannels out of specification were Table 2.3-1 Trip Setpoint Actual Trip Point at 590oF (16.257 out -7755) Skasured at the Bistable A 1831.5 psig 1827.4 psig B 1831.5 1828.9 D 1831.5 1827.5 (7) Designation of Apparent Cause of Occurrence:

The apparent cause of the occurrence is not known for sure, although it is suspected that it may be either

a. material, in that the RPS tempi Tature-to-pressure signal converters were out of calibration, which in turn may have been the result of converter instrument drif t being gree ter than it should be,

b. procedural, in that a voltmeter utilized at one point of the follow-up checks was found to be out of calibration, and it is possible that it may have been utilized in previous calibrations of the converters , or

c. personnel, in that work done in nearby sections of kPS cabinets could have possibly adversely effected calibration of the converters.

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. (8) Analysis of Occurrence:

It has been determined that the out-of-limit trip point settings did not constitute a threat to the health and safety of the public, since the maximum setpoint error (4.1 psig low) was more conservative than the 30 psig naasurement error assumed in the accident safety analysis.

(9) Corrective Ac' lon:

Short-term corrective action was taken as described above to recalibrate and retest the affected channels .

Long-term corrective action is planned as follows :

a. The variable low pressure trip feature for all four RPS channels will be tested each week for the next month to determine instrument drift.

b. The out-of-calibration voltmeter will be returned to the calibration laboratory for inspection and repair. Further, a report detailing the extent of and reasons for the problem will be generated and appropriate corrective actions taken.

c. Surveillance procedure data sheets will be amended to show test equipment serial numbers which will in turn help identify potential problems involving calibration equipment.

d. An investigation will be conducted to determine if any other work in the RPS cabinets could have effected calibration of the signal converter, and if so, appropriate corrective actions will then be taken.

The Plant Operations Review Committee and Station Superintendent reviewed and approved the above actions.

(10) Failure Data:

a. Previous Failures: None

b. Equipment Identification:

1. Bailey System 880 Reactor Protection System

2. Hewlett-Packard Digital Voltmeter Model 3460 B Since raly ,

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R. C.rn. %oldL RCA: RSB: tas File: 20.1.1 / 7.7.3.5.1 cc: Office of Inspection and Enforcement, Region I

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