ML20217N928

Special Rept:On 991003,PZR PORV Actuation Mitigated RCS low- Temp Overpressure Transient.Caused by a RCP Facilitating Sweeping of Entrained Air Out of RCS Loops.Operating Procedure 2-OP-5.1 Will Be Revised

ML20217N928
Person / Time
Site:	North Anna
Issue date:	10/20/1999
From:	Matthews W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
99-513, NUDOCS 9910290164
Download: ML20217N928 (2)

Text

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VIRGINIA hLECTRIC AND POWER COMI*ANY Ricituoxu,VinorwIA canot g . .

October 20,1999 United States Nuclear Regulatory Commission Serial No.99-513 Attention: locument Control Desk NAPS: MPW Washington, D.C. 20555 Docket Nos. 50-339 License Nos. NPF-7 Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER GTATION UNIT 2 PRESSURIZER PORV SPECIAL REPORT Pursuant to North Anna Technical Specification (TS) Section 3.4.9.3.e and 6.9.2.f, a Special Report is hereby submitted for a condition that resulted in a pressurizer (PZR) power operated relief valve (PORV) actuation to mitigate a reactor coolant system (RCS) low-temperature overpressure transient.

With Unit 2 in Mode 5, cold shutdown, the RCS loops were filled to solid water conditions using a loop vacuum fill method during a recent refueling outage. On October 3,1999, the "A" reactor coolant pump (RCP) was started to facilitate sweeping of entrained air cut of the RCS loops. At the time, RCS temperature in two of three loops was slightly higher than 130 degrees F with one loop slightly below and RCS pressure at approximately 325 psig. With RCS temperature less than 130 degrees F f.he PORV lift setpoint is 375 pounds and increases to 415 pounds when temperature is greater than 130 degrees F. Upon start of the RCP, an expected increase in RCS pressure was indicated and control room personnel initiated actions to control pressure.

The letdown pressure control valve (PCV) potentiometer was adjusted to decrease pressure. Within 12 seconds of the RCP start, the PZR PORV (2-RC-PCV-2455C) cycled open. After the PORV opened, RCS temperature increased to 131 degrees F, the PORV setpoint limit automatically shifted to 415 psig and the PORV closed. The RCS pressure was stabilized and the RCP secured to support a ccntainment Type A leakage test.

1 A similar incident occurred on April 28, 1998, during a refueling outage, with RCS temperature at approximately 127 degrees F and pressure at approximately 330 psig, when the "C" RCP was started to facilitate heat-up of the RCS and sweep entrained air out of the loops. The letdown PCV exhibited a slow response, and within 16 seconds of the RCP start, the PZR PORV (2-RC-PCV-2456) cycled open. Following this incident an evaluation of the sluggish operation of the letdown PCV and procedure reviews were performed. Guidance associated with starting an RCP was placed in the procedure for Unit Startup from Mode 5 at less than 140 degrees F to Mode 5 at less than 200 f degrees F (2-OP-1.1). o 9910290164 991020 PDR S ADOCK 05000339 pg

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During the time of the October 3,~ 1999 incident, Operations personnel were performing 2-OP-5.1, a vent and drain procedure, and were aware that an RCS temperature of

130 degrees F was optimal to prevent actuating the PORV. However, the amount of Component Cooling (CC) flow hindered the heat-up process. In additional, the amount of charging flow,60 gallons per minute, provided a smaller margin with which to control pressure via the letdown PCV. As a result, the PORV actuated upon the start of the RCP. Following the Type "A" test, CC was isolated from the residual heat removal heat exchangers thereby increasing the.RCS temperature to approximately 143 degrees F between the 3 loops. A subsequent start of an RCP did not result in lifting the PZR PORV.

Operating procedure,2-OP-5.1, will be revised to provide guidance for starting an RCP with the loops unisolated. Enhancements are being reviewed concerning letdown PCV operating margin. The Station Nuclear Safety and Operating Committee has reviewed this report and it will be provided to the Management Safety Review Committee.

Should you have any questions regarding this report, please contact us.

Very truly yours, 3

kJ0f W. R. Matthews Site Vice President

' Commitments made in this letter: Operating procedure 2-OP-5.1 will be revised.

cc: U.- S. Nuclear Regulatory Commission  !

Region 11 '

Atlanta Federal Center -

61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. M. J. Morgan NRC Senior Resident inspector North Anna Power Station 1

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