ML19262A206

Abnormal Occurrence 50-289/75-11:on 750417,high Reactor Power Trip Setpoints Setting Less Conservative than Specified.Caused by Confusing Procedural Instructions & Personnel Error.Trip Setpoints Adjusted

ML19262A206
Person / Time
Site:	Three Mile Island
Issue date:	04/25/1975
From:	Arnold R METROPOLITAN EDISON CO.
To:
Shared Package
ML19262A207	List: ML19262A206 ML19262A210
References
GQL-0984, GQL-984, NUDOCS 7910260549
Download: ML19262A206 (4)

Text

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POST CFFitE 30X 542 REAOtNG, PENNSYLVANIA 19603 TELEPHONE 215 - 929-3601 GC 092L APR 2 5 1975 Director Division of Reactor Licensing U.S . Nuclear Regulatory Commission Washington, D.C. 20555

Dear Sir:

Operating License No. DPR-50 Docket No. 50-289 In accordance with the Technical Specifications for the Three Mile Island Nuclear S tation Unit 1, we are reporting the following abnormal occurrence:

(1) Report Number: A0 50-289/75-11 (2a) Report Date: April 25,1975 (2b) Occurrence Date : April 17,1975 (3) Facility: Three Mile Island Nuclear S tation Uni: 1 (4) Identification of Occurrence:

Title:

High Reactor Power Trip Setpoints Setting Less Conservative Than Specified Type: An abnormal occurrence as defined by the Technical Specifications ,

paragraph 1.8a, in that the high reactor power trip setpoints setting was less conservative than the limiting setting established in the Technical Specifications.

(5) Conditions Prior to Occurrence:

The reactor was at steady-state power with major plant parameters as follows:

Power: Core: 99.5% 9 g Elec: 852 MW (Gross) }k I RC Flow: 139 x 106 lbs/hr p

RC Pressure: 2155 psig RC Temp.: 5780F PRZR Level: 240 in.

PRZR Temp . . 6560F (6) Description of Occurrence:

While conducting routine Reactor Protection System Surveillance Testing on April 17, the high power trip point for all four channels of the Reactor Protection System was found to be set at 109.5%. The trip setpoints were i= mediately raturned to 104.75%, which is within the specification limit of 105.5%.

An investigation into the cause of the occurrence revealed that the trip setpoints had been improperly set on April 13 while being raised f rom 4.25% in preparation for unit startup.

(7) Designation of Apparent Cause of Occurrence:

The apparent cause of the occurrence is procedure , in tnat the procedure contained potentially confusing instructions as to where the digital voltmeter should be connected to read the voltage representing the trip setpoint. Personnel error contributed to the cause of the occurrence as the technician failed to obtain guidance in resolving apparent conflict prior to making adjustments and returning the channel to the normal operating status.

(8) Analysis of Occurrence:

It has been determined that the out-of-limit setpoint settings did not constitute a threat to the health and safety of the public for the following reasons :

a. The Power / Flow / Imbalance trip setpoints were set within specification limits to a value corresponding to slightly less than a maxists of 105.5% power. Had an overpower condition occurred, this feature would have performed the function of the high power trip at a value less than the hig.' power trip technical specification limit.

b. The trip setpoint setting was more conservative than that used in Chapter 14 of the IMI-l Final Safety Analysis Report.

(9) Corrective Action:

Corrective action was taken immediately to return the trip setpoints te a value within technical specification limits . Long-term corrective action has been taken through issuance and implementation of the appropriate procedure revisions to preclude misinterpretation.

In addition, the procedures have been revised to require that reactor protection system surveillance be performed by two individuals.

148224D

One individual will read the procedure and verify the activities of the other individucl, who will make the voltage measurements and se tpoint adj ustment 1.

The Plant Operations Review Committee and the S tation Superintendent reviewed and approvec these actions.

(10) Failure Data:

Not applicable.

Sincerely yours, O .

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R. C . Arnold Vice President - Generation RCA/RSB/cas cc: Of fice of Inspection and Enforcement, Region 1 U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406 File: 20.1.1/7.7.3.5.1 1482 24I