ML20127G440

RO:730518,HPCI Isolated on High Steam Flow During Quick Start Full Flow Surveillance Test.Caused by Worn electro- Hydraulic Actuator Drive Gears.Subj Gears Repaired & HPCI Sys Tested

ML20127G440
Person / Time
Site:	Monticello
Issue date:	05/25/1973
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9211160600
Download: ML20127G440 (2)

Text

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Re'gulatory Cy.

NSIB NORTHERN 5TATES POWER COMPANY MIN N E A poli e. win N E SOTA 58401 0

May 25, 1973 p ,

E MAY291973 r Mr. J F O' Leary, Director q cMl[jWI Directorate of Licensing 88cM United States Atomic Energy Commission g DN

, Washington, D C 20545 ,

Dear Mr. O' Leary:

MONTICELLO NUCLEAR Cl3ERATING PIANT Docket No. 50-263 License No. DPR-22 lii ;h t Pressure Coolant injection System Inoperability A condition occurred at the Monticello Nuc1 car Generating Plant which we are reportinr, to your office in accordance with Section 6.7.B.1, Abnormal Occur-rence Reports, of the Technical Specifications, of Provision Operating License DPR-22.

On May 18, 1973, the liigh Pressure Coolant Injection System (HPCI) isolated on high steam flow during a " quick stcrt" full flow surveillance test. The RCIC system, LPCI system, and both Core Spray systems were framediately demonstrated to be operable in accordance with the requirements of the Technical Specifications.

Recording instruments were used to monitor llPCI system control signals and per-formance parameters. Test results indicated intermittent instability in the electrical control circuitry, slow response of the electro-hydraulic actuator, and a malfunction of the turbine speed feedback signal. These problems all contributed to excessive opening of_thn_11PCLt_ urb i _ine control valves, resulting in steamJ10ws to the llPCI'~tWUIEvhich exceeded the isolation trip set point.

Inspection and further testing disclosed a number of specific problems which were corrected as follows:

1 An intermittent circuit was discovered on the bias speed setting potentiometer which caused control system instability. The bias speed setting potentiometer was replaced with a fixed resistance of equal value.

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2. The electro-hydraulic actuator drive gears were found to be worn to the extent that they were not engaging. The excessive wear resulted from insufficient lubrication due to an improperly located oil supply passage. The gears were replaced, the lubricating and control oil system was thoroughly cleaned and flushed to remove metal fragments, and the oil passage was extended to apply an ample supply of oil directly to the gear teeth.

3. The spur gear which provides a turbine speed signal to the control system was found loose en the drive shaf t. The drive shaft was countersunk at the location of the set screws and the spur gear was reinstalled with scif-locking set screws.

4. The drive soupling for the eleccro-hydraulic actuator was also found loose on the drive shaft. Self-locking set screws were installed.

The corrective actions described under items 2, 3 and 4 above, were performed under the direction of the turbine manufacturers representative.

After completion of repair, the llPCI system was tested, control settings were adjusted to optimize performance, and satisfactory operation was demonstrated.

During the time the IIPCI system was inoperable, redundant safeguards equipment was operable and capable of providing emergency core cooling. The system was returned to operable status within the allowabic out of service time permitted by the Technical Specifications. Therefore, the llPCI system inoperability did not affect safe operation of the plant.

The only system containing components similar to the IIPCI system is the RCIC system. The actuator drive and speed pickup gear for the RCIC are mechanically different from those of the IIPCI system.

Although some difficulties have been experienced with the llPCI control system in the past, the causes of this occurrence are unrelated to any previous mal-functions. -The RCIC system has always operated very reliably. Nevertheless, a preventive maintenance inspection of both IIPCI and RC'.C turbine control systems will be conducted during the next refueling outage.

Very truly yours, h*

L 0 Mayer, P.E.

Director of Nucicar Support Services LOM/br cc: B 11 Crier G Chamof f Minnesota Pollution Control Agency Attn. Ken Dzugan t

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