United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9403160207                                                                                 LICENSEE
EVENT REPORT (LER)                                                                                                               
FACILITY NAME: OCONEE NUCLEAR STATION, UNIT 2             PAGE: 1 OF 5                  
                                                                         DOCKET NUMBER:  05000270                              
                                                                                                           TITLE:  TECHNICAL
DATE:  02/08/94   LER #:  94-01-00    REPORT DATE:  03/10/94                                                 
                                              OTHER FACILITIES INVOLVED:                          DOCKET NO: 
05000                                                                                             OPERATING MODE:  N  
POWER LEVEL:  100                                                                                                                        
SECTION:         50.73(a)(2)(i)(B)                                                                                                      
                                          LICENSEE CONTACT FOR THIS LER:                                               
   NAME:  L. V. Wilkie,                        TELEPHONE:  (803) 885-3518                  Safety Review
COMPONENT FAILURE DESCRIPTION:                                                   CAUSE:  F  
NPRDS:  Yes                                                                                                                                      
     SUPPLEMENTAL REPORT EXPECTED:  NO                                                                          
                                                                        On December 29, 1993, at 2100 hours, Operations
personnel discovered             water leaking from the 2A Motor Driven Emergency Feedwater
Pump automatic        initiation pressure switch (2PS0386).  On December 30, 1993, the switch      
   was replaced, an investigation was initiated, and an engineering                 evaluation into the
past operability was requested.  on February 8, 1994,        with Unit 2 at 100% full power, the
engineering evaluation determined            that the 2A Motor Driven Emergency Feedwater Pump
would not have                 automatically initiated on low Main Feedwater (MFDW) discharge
pressure          while the switch contacts were shorted by the water intrusion.  A DC            
ground alarm had been received on December 14, 1993 but had not been             located until the
pressure switch was replaced on December 30, 1993.             Problems with this model switch
have been identified previously and              replacements of a different design were in the
process of being                  scheduled.  The root cause of this event is equipment failure.               
   Corrective actions include replacing the defective pressure switch               and to replace other
switches of this model, used for sensing MFDW               discharge pressure, on all three Oconee
Units.                                                                                                                    END OF
          TEXT                                                          PAGE 2 OF 5                                                        
                                                       The Emergency Feedwater (EFDW) system [EIIS:BA] is
designed to start             automatically upon loss of Main Feedwater (MFDW) [EIIS:SJ] or low
level          in either Steam Generator (SG).  The EFDW system consists of two motor          
driven pumps and one turbine driven pump.  The Motor Driven Emergency            Feedwater
Pumps (MDEFDWP) have initiation circuitry which will start             the pumps automatically
when both Main Feedwater Pumps (MFDWP) have              low hydraulic oil pressure or both
MFDWP's have low discharge pressure.          Also, an initiation signal is generated on low SG
level.  An additional          system that is designed to actuate when MFDW is lost is the ATWS     
           Mitigation Safety Actuation Circuit (AMSAC).  The AMSAC system will              initiate
EFDW in the same way as the normal EFDW system and trip the             main turbine
(EIIS:TA).  The AMSAC system is intended to mitigate the            consequences of an
anticipated transient without scram event.                                                                                          
          The MDEFDWP'S start circuitry is provided by 125V DC supplied from               the Vital
Battery [EIIS:EJ] system.  The MDEFDWP's are started by two            automatic logic
conditions.  Automatic initiation logic 1 (Auto 1)               starts the pumps with a low SG level
in either of the two SG's.                  Automatic initiation logic 2 (Auto 2) starts the pumps with
low SG               level in either SG or low discharge pressure on both MFDWP's or low             
control oil pressure on both MFDWP'S.  MFDWP discharge pressure switch           (2PS0386)
monitors MFDWP 2A discharge pressure and is used to start the          2A MDEFDWP in a
coincident logic arrangement as described previously.                                                                      
                      Technical Specification (TS) 3.4 addresses the EFDW system and the bases        
which require automatic EFDW initiation circuitry.  The TS allows one            MDEFDWP to be
inoperable for a period of up to seven days.                                                                                       
                EVENT DESCRIPTION                                                                                                    
                                            On December 14, 1993, with Unit 2 at 100% full power, a DC ground
alarm          was received in the Unit 2 control room.  A work request was initiated to       
investigate the control battery ground detection system.  The                    investigation continued
from December 14, 1993 through December 29, 1993.                                                                      
                  On December 29, 1993, with Unit 2 at 100% full power, Operations                
personnel identified water leaking from the 2A Main Feedwater Pump               (MFDWP)
discharge pressure switch (PS) associated with the automatic             start circuitry for the 2A
Motor Driven Emergency Feedwater Pump                 (MDEFDWP).  A work request was issued
to Instrument and Electrical (I&E)         personnel for the investigation and repair of the leak. 
Also, a seven           day Limiting Condition for Operation was entered per Technical                  
Specification 3.4.2.a. because the automatic initiation circuit was out          of service.  When the
PS electrical leads were                                                                                                                   
TEXT                                                          PAGE 3 OF 5                                                                  
                      removed for repair/replacement, the DC ground alarm cleared.  Operations        
and I&E personnel then realized that the PS was causing the ground.  It          was noted that the
pressure switch was full of water.  The PS was                replaced with the same model spare and
the LCO was exited on December 30,        1993.                                                                               
                                                                             Engineering initiated an assessment of the
problem to determine the              past operability of the 2A MDEFDWP.  This assessment
included a review           of the start logic circuitry, the DC battery system ground fault                
detection circuitry, and the failed PS.  The relationship between the            125V DC battery
configuration and the point in the 2A MDEFDWP start logic        where the ground occurred was
examined.                                                                                                                           On
February 8, 1993 the assessment was completed and it was concluded            that the 2A
MDEFDWP would have started as required, for other initiation         signals, but would not have
started for a loss of MFDWP discharge                pressure.  This condition did not fully meet the
TS requirement for              automatic initiation.  This condition existed from December 14, 1993 
           until December 30, 1993, therefore, the seven day TS Limiting Condition          for
operation was exceeded.                                                                                                                     
                                      The root cause of this event is equipment failure.  The cause of the            
pressure switch (PS) failures has been attributed to the polyamide               diaphragm in the
switch becoming permeable, over time, in applications           for sensing Main Feedwater
discharge pressure.  This allows water                intrusion and will short the contacts within the
switch.  This model PS          had exhibited similar failures in the past, however, there were no
DC            grounds identified as occurring.  The DC ground that occurred on December        14,
1993 was a result of the switch failure.  After the electrical               connections to the switch
were removed, the ground was determined to be          related to the switch failure.  The PS was
determined to be inoperable as        a result of the water intrusion.                                                    
                                                                             A review of previous events for the last two
years, revealed that no             other reportable events associated with the PS's have been
identified.           However, there have been problems associated with this model PS in FDW         
 applications identified in the Problem Investigation Process (PIP)               reports.  PIP numbers
2-092-0229 and 2-092-0534 identified the same water        leakage problems with this model
switch.  The planned corrective action          was to replace all switches used to detect loss of
MFDW discharge                pressure with an improved replacement during the next scheduled
refueling        outage for each unit.  The replacement switch required seismic and              
environmental testing and a completed test report before the manufacturer        could begin
shipment.  The Unit 3 PS's have been replaced and Unit 1 and         2 are scheduled for the next    
                                        PAGE 4 OF 5                                                                                        
refueling outages.  It is concluded that the scope and schedule for these        planned corrective
actions were reasonable.  However, the corrective             measures could not be accomplished
before the circumstances surrounding          this event occurred.                                                       
                                                                                      This event is not considered recurring,
however, the failure of the              equipment is recurring.  The previous switch failures were
identified            during Technical Specification Surveillance testing and the repairs were        
made without exceeding Technical Specification limits.                                                                    
                                       The PS identified in this event is NPRDS reportable.  The manufacture
is         Custom Control Sensors model number 604GZ5.                                                                  
                                                    There were no personnel injuries, radiation exposures, or release
of             radioactive materials associated with this event.                                                                
                                                CORRECTIVE ACTIONS                                                                 
                                                                                           1.   The 2A Motor Driven Emergency
Feedwater Pump pressure switch was                 isolated and a Limiting condition for operation
(LCO) was entered.                                                                                           Subsequent                
                                                                                                                                       1.   The
pressure switch was replaced with the same model, the LCO was                exited, and an
investigation was initiated to determine the cause of             the problem.                                        
                                                                                                                  1.   Identify all pressure
switches of this model used in the sensing of              Main Feedwater Pump discharge pressure
applications and inspect for              water intrusion on a weekly basis until replaced.                     
                                                                                      2.   Replace the pressure switches as
identified in Planned Corrective                Action number 1 with a replacement that will not
exhibit the                     failures as described in this report.                                                                
                                                       3.   Evaluate other plant applications of this model number
pressure                  switch to ensure that critical applications of this switch are not              
exhibiting adverse trends and take appropriate action.                                                                       
                               TEXT                                                          PAGE 5 OF 5                                   
                                                     SAFETY ANALYSIS                                                                    
                                                                              Although a portion of the automatic initiation
circuit for the 2A Motor          Driven Emergency Feedwater Pump (MDEFDWP) was not
operable from December         14 through 30, 1993, other means for the 2A pump actuation were  
                         The 2A MDEFDWP could have automatically initiated on low Main Feedwater.   
     Pumps hydraulic oil pressure or on low Steam Generator Level (Dry out            Protection). 
Also, the Final Safety Analysis Report Chapter 10 credits          the start of the Emergency
Feedwater (EFDW) system on the loss of Main           Feedwater (MFDW) with no distinction
between a low discharge pressure            and low hydraulic oil pressure.  Therefore, since the
pressure switch            for low hydraulic oil pressure was operable there was no safety                 
significance associated with the EFDW system.                                                                                
                                    The ATWAS Mitigation Safety Actuation Circuit (AMSAC) could have     
           automatically initiated the EFDW system, including the 2A MDEFDWP,               since
this is separate circuitry.  During a loss of MFDW event, the              Operators are directed by
the Emergency operating Procedure (EOP) and            Abnormal Procedures (AP) to verify that
all Emergency Feedwater Pumps            (EFDWP) have started.  The operators could have
started the 2A MDEFDWP           manually from the Unit 2 control room.                                       
                                                                                    The 2B MDEFDWP and the Turbine Driven
Emergency Feedwater Pump were              not affected and would have the capability to
automatically start on             low MFDWP discharge pressures.                                                      
                                                                             In the event that none of the EFDWP's would
start, the EOP and APs               direct the Operators to align EFDW from one of the other two
Oconee              units.                                                                                                                          
                                 If all of these efforts failed, the EOP and AP's provide for use of             
High Pressure Injection [EIIS:BG] forced cooling and/or use of the               Standby Shutdown
Facility Auxiliary Service Water Pump [EIIS:BA].                Analyses have been performed to
verify that sufficient time is                   available for an operator to line up these systems before
any core               damage would occur.                                                                                              
                                                Therefore, sufficient redundancy exists to assure that, even with
the            Main Feedwater discharge pressure automatic start portion of the 2A             
MDEFDWP unavailable, the health and safety of the public was not                 compromised by
this event.                                                                                                                                       
ATTACHMENT TO 9403160207                                      PAGE 1 OF 1                                         
                                               Duke Power Company                                J. W. HAMPTON            
     Oconee Nuclear Site                               Vice President                 P.O. Box 1439                       
             (803)885-3499 Office           Seneca, SC 29679                                  (803)885-3564 Fax   
                                                                                           DUKE POWER                                       
                                                                                                                March 10, 1994                   
                                                                                                                                U. S. Nuclear
Regulatory Commission                                              Document Control Desk                                
                           Washington, DC 20555                                                                                            
                                                 Subject:  Oconee Nuclear Station                                                      
    Docket Nos. 50-269, -270, -287                                                   LER 270/94-01                          
                                                                                                                             Pursuant to 10
CFR 50.73 Sections (a)(1) and (d), attached is Licensee           Event Report (LER) 270/94-01,
concerning a Technical Specification limit         which was exceeded due to equipment failure.      
                                                                                                               This report is being
submitted in accordance with 10 CFR 50.73                   (a)(2)(i)(B).  This event is considered to
be of no significance with            respect to the health and safety of the public.                                
                                                                                  Very truly yours,                                               
                                                                                                 J. W. Hampton                                   
                                Vice President                                                                                                     
                                                                xc:  Mr. S. D. Ebneter                       INPO Records
Center                      Regional Administrator, Region II       Suite 1500                               U.S.
Nuclear Regulatory Commission      1100 Circle 75 Parkway                   101 Marietta St., NW,
Suite 2900        Atlanta, Georgia 30339                   Atlanta, Georgia 30323                                     
                                                                                                      Mr. L. A. Wiens                        
Mr. P. E. Harmon                         Office of Nuclear Reactor Regulation    NRC Resident
Inspector                   U.S. Nuclear Regulatory Commission      Oconee Nuclear Site                     
Washington, DC 20555                                                                                                                       
                 *** END OF DOCUMENT ***                                                                                        
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