PNO-II-96-071, on 961011,Unit 2 Experienced Low Seal Flow Alarm on RCP 4,seal 1 & High Standpipe Alarm on RCP 4. Controlled Shutdown Begun as Required by Procedures.Licensee Currently Investigating Cause of Equipment Malfunctions

PNO-II-96-071:on 961011,Unit 2 Experienced Low Seal Flow Alarm on RCP 4,seal 1 & High Standpipe Alarm on RCP 4. Controlled Shutdown Begun as Required by Procedures.Licensee Currently Investigating Cause of Equipment Malfunctions

ML20128M241
Person / Time
Site:	Sequoyah
Issue date:	10/11/1996
From:	Scott Sparks NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
To:
References
PNO-II-96-071, PNO-II-96-71, NUDOCS 9610160033
Download: ML20128M241 (2)

-,

~

October 11, 1996 l l '

l PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PNO-II-96-071

This preliminary notification constitutes EARLY notice of events of POSSIBLE l

safety or public interest significance. The information is as initially received without verification or evaluation, and is basically all that is known by Region II staff in Atlanta, Georgia on this date. l t

1 Facility Licensee Emeroency Classification Tennessee Valley Authority Notification of Unusual Event l Sequoyah 2 Alert l Soddy-Daisy, Tennessee Site Area Emergency Dockets: 50-328 General Emergency l X Fot Applicable l

Subject:

SHUTDOWN IN EXCESS OF 72 HOURS On October 11, 1996, at approximately 3:12 a.m., Sequoyah Unit 2 experienced a low seal flow alarm on the Reactor Coolant Pump (RCP) #4,

1. 1 seal, and a high standpipe alarm on RCP #4. At 5:22 a.m., Unit 2 began a controlled shutdown required by procedure, based on an indicated second seal flow of approximately 1.5 gpm exceeding the procedural limit l of 0.5 gpm (this is not a Technical Specification limit).

During the shutdown, at approximately 47 percent reactor power, plant operators took the first main feedwater pump off line as required by i procedure, and immediately afterwards the main turbine unexpectedly:

experienced a runback. All 12 steam dumps opened as required. The cause of the turbine runback was unknown at the time. Based on the unexpected runback, plant management directed that the reactor be manually tripped, which occurred at 8:27 a.m. All control rods fully' inserted.

Following the manual reactor trip, the No. 4 main feedwater isolation valve. failed to close for unknown reasons. In addition, operators were unable to take manual control of any auxiliary feedwater level control valves for unknown reasons. Based.on this, operators tripped the two motor driven auxiliary feedwater pumps (MDAFWPs) and placed each in Pull-to-Lock (PTL), and isolated the turbine driven auxiliary feedwater pump (TDAFWP) isolation valves to all four steam generators. This action was taken to control the cooldown of the plant. However, the Reactor Coolant System (RCS) experienced a cooldown to approximately 538 Fahrenheit, requiring that operators emergency borate the RCS (emergency i boration is required by procedure at less than 540 Fahrenheit). At that l

time, decay heat was being removed via steam dumps to the condenser. .The TDAFWP isolation valves were periodically opened to supply TDAFWP flow to the steam generators. Steam generator water levels were maintained

.within procedural limits at all times during this evolution.

l Unit 2 is presently in hot standby (MODE 3). At 10:44 a.m., electrical I leads were lifted such that the AFW controllers could be operated in l

manual. Decay heat is currently being removed by manual control of the MDAFWPs, and steam dumps to the condenser. The licensee is currently l investigating the causes of the equipment malfunctions. Preliminary information is that 3 of 4 pressure switches for turbine impulse pressure contained water. This would cause the switches to fail and rffect only the turbine runback logic to cause a turbine runback after one main 9610160033 961011 PDR I&E PNO-II-96-071 PDR

\E g 160050 ott

PNO-II-96-071 '

O I

feedwater pump was taken off line. It would also result in an AFW signal !

to the MDAFWPs and TDAFWPs being sealed in, thereby preventing manual l control. Unit 2 is not expected to restart for 14 days.  ;

l The NRC Senior Resident Inspector responded to the site at approximately l 5:00 a.m., to observe the shutdown.

The State of Tennessee was notified.

The licensee issued a press release on October 11, 1996.

This information is current as of 3:00 p.m., on October 11, 1996. I

Contact:

Scott E. Sparks ,

(404)331-5619 '

l l

i l

i l

l 1

i l

.