ML20126B823

Special Rept 92-007:on 921121,Train a RHR Pump Suction Relief Valve Lifted to Mitigate RCS Pressure Transient in Response to Pressure Increase.Operations Procedures Revised & Westinghouse Provided Lower RCS Pressure Operating Band

ML20126B823
Person / Time
Site:	Farley
Issue date:	12/17/1992
From:	Woodard J SOUTHERN NUCLEAR OPERATING CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
92-007, 92-7, NUDOCS 9212220222
Download: ML20126B823 (3)

Text

. ~ -,~._.,~.. - ~ .. ..- . ~ ~ . . . - . . . . . ~ _ - . . . - . . - . - . . . - . . . . ~ - . _ . - ~ - . . .

. *' , Soutnern Nuclear Operabng Company Post Offico Box 1295 Birntngham, Mabama 35201 Teleptone 205 868-5086 o

, , ,,,,,,, Southern Nuclear Operating Company l

December 17, 1992 vie swtNm el etne sstem

$((N[e"c"t i '

\

i I

Docket No. 50-348 I

U. S. Nuclear Regulatory Commission i

ATTN: Document Control Desk-Washington, D. C. 20555 s

Joseph M. Farley Nuclear Plant - Unit 1 Special Report No.92-007. RHR Relief Valve lift l

Gentlemen:

! In accordance with the requirements of Technical Specification 3.4.10.3, the enclosed Special Report No.92-007, Unit 1,- is submitted.

Respectfully submitted, D

. Woodard MM i BHW: map 0101

-Enclosure cc: Mr. S. D. Ebneter Mr. S. T. Hoffman Mr. G. F. Maxwell I

. . a .

Jo:eph M. Farley Nuclear Plant Special Report No.92-007 RHR Relief Valve lift This Special Report is being submitted in accordance with Technical Specification 3.4.10.3 due to the lifting of the A train Residual Heat Removal (RHR) pump suction relief valve to mitigate a Reactor Coolant System (RCS) pressure transient. At the time of this event the 8 train RHR pump suction relief valve was isolated for maintenance.

[jrcumstances Initiatina the Transient On 11-21-92 Unit I was operating in Mode 5 (Cold Shutdown), with RCS temperature at 184 degrees and RCS pressure at 400 psig (read from the A loop wide range pressure instrumentation) controlled by a pressurizer bubble. The B and C Reactor Coolant Pumps (RCPs) were running. Operations procedures provided an operating RCS pressure range under these conditions of 350-425 psig.

At 0616 on 11-21-92, the C RCP was secured for maintenance on the pump's resistance temperature detectors (RTDs). Due to normal thermal-hydraulic characteristics of the reactor coolant system, RCS pressure at the C loop hot leg increased when the C RCP was secured. The operators were monitoring and controlling RCS pressure using the C loop wide range pressure instrumentation.

This pressure was near the high end of the allowable operating pressure band.

The pressure increase which occurred due to securing the C RCP was sufficient te cause the A train RHR relief valve off the C loop to lift. The setpoint for the relief was verified to be 445 psig on October 15, 1992 during the Unit 1 eleventh refueling outage. The 445 psig setpoint is within the allowable tolerance for RHR suction relief valves of 450 psig plus O psig minus 10 psig.

For the transient, pressure did not exceed 450 psig.

Effect of RHR Pelief Valves on the Transient The A train RHR relief valve off the C RCS loop lifted in response to the pressure increase. Approximately 1700 gallons of RCS inventory were relieved to the Pressurizer Relief Tank (PRT). The relief valve reseated approximately 4 minutes into the event limiting the RCS pressure drop to 376 psig. The subsequent addition of the colder makeup water caused RCS pressure to be further reduced, however, RCS. pressure did not drop below 330 psig for the event. Pressurizer level dropped to approximately 0, however the core remained covered at all times. Pressurizer level was regained approximately 6 minutes into the event after the operators opened a flowpath from the-Refueling Water Storage Tank (RWST) to the RCS. Normal system status was restored at 0630.

J.,-

L l

Special Report 92-007 j Page 2 i

i i Corrective Action Necessary to Prevent Recurrence

An investigative team consisting of engineering personnel from the design organizations, the FNP staff and the corporate staff, was assembled and

, performed a detailed investigation of the event.

A test procedure was written and the sequence of events was simulated on Unit I at a lower system pressure. Following a review of the test results and

l. evaluation of the conditions at the time of the event, the team concluded that

the initial RCS pressure and resulting pressure increase from the C RCP trip caused the A train RHR relief valve to lift. The cause of the event was

' determined to be procedural deficiency in that the allowable operating RCS pressure range was too high for the prescribed plant conditions.

! All snubbers and hangers supporting the RHR relief valve discharge piping were i examined. No problems were found.

l l To provide additional operating margin, Westinghouse, based on docume_nted engineering calculations, provided a lower RCS pressure operating band of 325-

, 375 psig for RCP operation in the plant configuration where RHR is in service.

Operations procedures have been revised accordingly.

i Additional Information Farley Nuclear Plant Unit 1 is a three loop Westinghouse pressurized water

reactor. There are 2 RCS wide range pressure indicators, one on the A loop i

and one on the C loop. These pressure indicators are used when the RHR system is aligned to the RCS. The pressure seen by these two loops is dependent on

! whether or not the RCP. on that loop is running. If the loop's RCP is running, j the pressure seen in that loop can be approximately 20-25 psig lower than if the pump were not running.

l P

4 4

i i

i

, - . , - - - , - - . . . .. . . . -