PNO-II-93-063, on 931116,Unit 2 Shut Down Due to Concerns Re Potential Operability of Eight CCS Check Valves.Caused by Failure in Open Position of Seven & Eight Had Internal Piston Incorrectly Installed.Unit 2 Placed in Cold Shutdown

PNO-II-93-063:on 931116,Unit 2 Shut Down Due to Concerns Re Potential Operability of Eight CCS Check Valves.Caused by Failure in Open Position of Seven & Eight Had Internal Piston Incorrectly Installed.Unit 2 Placed in Cold Shutdown

ML20058J762
Person / Time
Site:	Sequoyah
Issue date:	11/17/1993
From:	Scott Sparks NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
To:
References
PNO-II-93-063, PNO-II-93-63, NUDOCS 9312140229
Download: ML20058J762 (2)

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• Please use this copy, instead of previous one. Thank You.

l' l November 17, 1993 P_REMMFARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PNO-II-93-063 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information is as initially received without verification or evaluation, and is basically all that is known by the Region II staff on this date. ,

Facility Licensee Emeroency Classification l Tennessee Valley Authority Notification of Unusual Event l Sequoyah 2 Alert

Soddy-Daisy, Tennessee Site Area Emergency [

l Dockets: 50-328 General Emergency I

X Not Applicable

Subject:

SEQUOYAH UNIT 2 SHUTDOWN i On November 16, 1993, Sequoyah plant management shut down Unit 2 from rated power due to concerns associated with the potential operability of l eight component cooling water system (CCS) check valves located in the i l supply lines to the reactor coolant pump (RCP) thermal barrier heat  ;

exchangers.

Radiography of the eight Unit 1 CCS check valves revealed that seven were ,

l failed in the open position and the eighth had an internal piston '

I installed incorrectly. Removal and inspection of one of the Unit 1 check l valves indicated that they could not be relied on to close on reverse l 1 flow. The safety function of the valves is to prevent a potential l intersystem LOCA in the event of a coincident failure of one of the RCP l thermal barrier heat exchangers. Unit 1 was in cold shutdown during the  :

! inspection activities.

l Based on the results of the Unit 1 inspections, the licensee concluded i that inspections of the Unit 2 CCS check valves should be performed. At 9:13 a.m. on November 16, Unit 2 began a power decrease from approximately 100% reactor power and at 11:30 p.m., the unit entered hot standby (MODE 3) operation.

The licensee plans on placing Unit 2 in cold shutdown to allow for inspection / repair of the subject check valves. The root cause of the check valve failures has not yet been determined. Other repair ,

activities are also being planned for the outage.

The licensee estimates that the Unit 2 outage will last approximately one week if no additional problems are encountered. Unit 1 will remain in cold shutdown with work activities continuing to support the refueling outage.

The resident inspectors were onsite, and bill conitor the licensee's activities.

The NRC received initial notification of this event from the licensee at 8:30 a.m., (EDT) on November 16, 1993.

The State of Tennessee has been informed.

9312140229 931117 PDR I&E PNO-II-93-063 PDR Oh l 13tR b A, 1 LIO ,

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'PHO-II-93-063 1 j

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l This information as current as of 9:00 a.m., on Nove.rber 17, 1993, i~

Contact:

Scott Sparks (404)331-5619 j i

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