ML19210A194

Abnormal Occurrence 50-289/75-26:on 750724,high Reactor Coolant Pressure Trip Set Points Less Conservative than Tech Specs.Caused by Calibr Drift.Specs Will Be Changed to Account for Instrument Error

ML19210A194
Person / Time
Site:	Three Mile Island
Issue date:	08/01/1975
From:	Arnold R METROPOLITAN EDISON CO.
To:
References
GQL-1344, NUDOCS 7910240915
Download: ML19210A194 (4)

Text

NF JISTRIBUTION FOR PART 50 DOC :T MATERI AL (TEMPORARY FORM) 8339 CONTROL NO:

FILE: I!: CIDE!TT REPORT FIL'.

FROM: ::et. Edison Company DATE OF DOC DATE REC'D LTR TWX RPT OTHER Reading, Pa. 19603 R_C. Amle 8-1-75 8-5-75 XX TO: ORIG CC OTHER SENT AEC PDR G NRC 1 signed SENT LOCAL PDR XX CLASS UNCLASS PROPINFO INPUT NO CYS REC'D DOCKET NO:

. XXX 1 50-289 DESCRIPTION: Ltr advising of Abncroal Occurrer GNC LOSU RES:

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METROPOLITAN EDISON COMPANY TELEPHONE 215 - 929-2601 PCCT CFFICE BOX 542 R E A DtP3G-PENNSYLV ANI A 10CO3 Auguat 1, 1975

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Director Division of Reactor Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555 .-

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 ate reporting the following abnormal o cc urrence .

(1) Report Number: A0 50-289/75-26 (2a) Report Date: August 1, 1975 (2b) Occurrence Date: July 24, 1975 (3) Three Mile Island Nuclear Station Unit 1 (4) Identification of Occurrence:

Title:

High Reactor Coolant Pressure Trip Set Points Less Conservative Than Required by Technical Specifications Table 2.3-1 Type: An abnormal occurrence as defined by the Technical Specifications, paragraph 1.8a, in that the High Reactor Coolant pressure trip setpoints ler: conservative than required constituted a safety system setting less conservative than the limiting setting established by technical specifications table 2.3-1.

(5) Conditions Prior to Occurrence:

Power: Core:

Elect.:

1007.

777 MWe Net

}k7b 2 RC Flow: 140 x 106 lb/hr ge, u d$

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RC Press. : 2155 psig RC Temp.: 579 F PR2R Level: 240 inches PR2R Temp. : 655 F (6) Description of Occurrence:

Pressure transmitter calibration and corresponding pressure trip setpoints wure being checked as required by Surveillance Procedure 1301-1, "Sh if t and Daily Checks," due to noted dif ferences in indication oetween Reactor Protection System pressure channels.

The "as feund" setpoints (before transmitter recalibration) and the required setpoints for the channels out-of-specification were as follows:

Table 2.3-1 Actual Trip Setpoint Maximum Trip Measured at the Channel Bistable Setpoint Pressure Transmitter C High Pressure 2355 2357 D High Pressure 2355 2358 D Shutdown Bypass 1720 1722 Ismediately, the out-of-specification transmitters were recalibrated and retested and the resulting trip setpoints were verified as being within Technical Specification limits.

In addition, the pressure trip setpoints for the remaining channels were tested and verified as being within Technical Specification limita.

(7) Designation of Apparent Cause of Occurrence:

The apparent cause of this occurrence is material, in that the out of specification trip setpoints were due to minor calibration drif t in the associated reactor coolant system pressure transmitters.

(8) Analysis of Occurrence:

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

a. The maximum setpoint error (3 psi) was less than the 30 psi instrument error assumed in the accident safety analysis and, there fo re , the two effected channels were capable of performing their intended function.

b. The setpoints for the remaining 2 RPS channele were within Technical Specification limits .

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(9)* Corrective Actions :

In addition to the immediate corrective actions listed above, a proposed change to the Technical Specifications which will take into account the 30 psi instrument error assumed in the accident safety analysis is currently being prepared.

The Plant Operations Review Committee and the Station Superintendent have reviewed and approved the above listed corrective actions and have taken steps to ensure completion of the yet to be completed long term corrective actions.

(10) Failure Data:

Transmitter Application: Reactor Coolant System Narrow Range Pressure Manufacturer: Westinghouse Electric Corporation Model: 59 Pil Other Applications in Plant: NONE Similar Occurrences: A0 50-289/74-24 A0 50-289/75-15 A0 50-289/ 75-16 Sincerely, R. C. Arnold Vice President RCA:CWS:cas cc: Of fice of Inspection and Enforcement, Region 1 File: 7.7.3.5.1/20.1.1

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