PNO-IV-99-040, on 990924,licensee Was Replacing Motor Operator for Suction Valve on B Recirculation Loop.After Completing Repairs,Operators Plan to Restart Reactor.Info Has Been Discussed with Licensee

PNO-IV-99-040:on 990924,licensee Was Replacing Motor Operator for Suction Valve on B Recirculation Loop.After Completing Repairs,Operators Plan to Restart Reactor.Info Has Been Discussed with Licensee

ML20212G355
Person / Time
Site:	Cooper
Issue date:	09/24/1999
From:	Clark J, Marschall C NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
To:
References
PNO-IV-99-040, NUDOCS 9909290202
Download: ML20212G355 (1)

L SeptImber 24,1999 L

PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCJ_

L* V PNO-IV-99-040 ,.

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 Region IV staff in Arlington, Texas on this date.

Ensigy. Licensee Emernency Classification

. Nebraska Public Power District X Notification of Unusual Event Cooper 1 . . Alert l s Brownville, Nebraska Site Area Emergency Dockets: 50-298 General Emergency 1 p Not Applicable

Subject:

PLANT STARTUP FROM SHUTDOWN GREATER THAN 72 HOURS Operators manually shut down the Cooper Nuclear Station unit on September 17 at 8:40

, p.m. (CDT); additionally the licensee declared an Unusual Event at 8:56p.m. (C0T) because of a hydrogen detonation in the Z-sump. Operators exited the Unusual Event at 1:07 a.m.

(CDT) on September 18 after venting the hydrogen through the offgas system to ensure no hydrogen remained. Because the Z-sump supports operability of the standby gas treatment system, operators shut down the plant.

The Z-sump collects condensate from the offgas and standby gas treatment systems via drain piping. The drain piping contains liquid " loop seals" designed to minimize gases entering the sump. The licensee stated that a procedure problem caused hydrogen to back up past the loop seals as operators throttled a valve in the augmented offgas system. The hydrogen migrated into conduit connected to the sump, and a spark caused by contacts in the starting controls for a sump pump provided the ignition source. The resultant hydrogen L detonation caused minor damage to equipment connected to the Z-sump, including conduit, i floats and level switches. No damage occurred to any other equipment. After a purging the

- offgas system, the licensee repaired the damaged Z-sump equipment and installed seals in l the conduit to prevent the hydrogen from reaching an ignition source. In addition, they  !

changed procedures for throttling a valve in the offgas system to minimize the migration of 1 hydrogen past the loop seals in the drain piping.

As of 10 a.m. on September 24, the licensee was replacing a motor operator for the suction

. valve on the "B" recirculation loop. After completing these repairs, operators plan to restart l the reactor.  !

The state of Nebraska will be informed.

. . Region IV received notification of this occurrence by telephone from the SRI at 10 a.m. on September 17,1999. Region IV has informed the EDO, NRR, and PA. This information has been discussed with the licensee and is current as of 9 a.m. on September 24,1999.

Contact:

Charles S. Marschall (817)860-8185 Jeff Clark (402)825-3371 9909290202 990924 E M ,-0 0 aa ) oQ 180092