United States Nuclear Regulatory Commission - Protecting People and the Environment

Morning Report for January 4, 1999

                       Headquarters Daily Report

                         JANUARY 04, 1999

***************************************************************************
                    REPORT             NEGATIVE            NO INPUT
                    ATTACHED           INPUT RECEIVED      RECEIVED

HEADQUARTERS                           X
REGION I                               X
REGION II                              X
REGION III                             X
REGION IV           X
PRIORITY ATTENTION REQUIRED  MORNING REPORT - REGION IV  JANUARY  4, 1999

Licensee/Facility:                     Notification:

Texas Utilities Electric Co.           MR Number: 4-99-0001
Comanche Peak 2                        Date: 01/04/99
Glen Rose,Texas                        Resident Inspector
Dockets: 50-446
PWR/W-4-LP

Subject: MANUAL TRIP OF UNIT 2 FOLLOWING A MAIN TURBINE CONTROL FAILURE

Discussion:

This morning report provides additional information not contained in the
January 3, 1999, Event Notification (EN#35213).  At approximately
11:14a.m. (CST) on January 3,1999, the Comanche Peak Steam Electric
Station, Unit 2, main turbine generator control valves suddenly and
unexpectedly closed while at 100 percent rated power.  As designed, all
steam dumps immediately opened and rods automatically stepped in to
control the reactor coolant system temperature transient.  The reactor
plant, designed to withstand a 50 percent load rejection, experienced an
equivalent 80 percent load rejection event.  Shortly after the control
valves had closed (approximately 5 seconds), the main turbine control
system began operating as if it had been transferred to the speed control
mode by controlling main generator output to 200 MWe.  The main turbine
generator speed control mode resulted in the control valves cycling
between the fully closed position to 3 percent open every few seconds.
About 9 seconds into the event, one pressurizer power-operated relief
valve opened for approximately 5 seconds to control the resultant reactor
coolant system pressure increase.  The pressurizer relief tank blowout
disc remained intact.  As pressurizer level oscillated from the cyclic
operation of the control valves, reactor coolant system pressure
continued to slowly decrease.  Pressurizer heaters, Groups B and D,
failed to automatically energize as designed.

After approximately one minute, operators manually tripped Unit 2.  The
auxiliary feedwater system automatically started when steam generator
levels dropped following the manual trip.  Other than one redundant
auxiliary feedwater flow instrument failure, everything operated as
expected during the trip.  The unit was stabilized in Mode 3, Hot
Standby.

Prior to defining the restart schedule, the licensee plans to determine
the cause of the main turbine control system failure; implement
commitments made to the NRC regarding issues found during their review of
NRC Generic Letter 96-01, "Testing of Safety-Related Logic Circuits;" and
complete repairs to the pressurizer backup heaters, the auxiliary
feedwater flow instrument, and several other minor failures which
occurred during the transients.

Regional Action:

The resident inspectors are monitoring the licensee's troubleshooting and
recovery efforts.

Contact:  Joe Tapia                  (817)860-8243
          Anthony T. Gody            (254)891-1500
_
Page Last Reviewed/Updated Thursday, March 29, 2012