Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9403160207 LICENSEE
EVENT REPORT (LER)
FACILITY NAME: OCONEE NUCLEAR STATION, UNIT 2 PAGE: 1 OF 5
DOCKET NUMBER: 05000270
TITLE: TECHNICAL
SPECIFICATION LIMIT EXCEEDED DUE TO EQUIPMENT FAILURE
EVENT
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
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR
SECTION: 50.73(a)(2)(i)(B)
LICENSEE CONTACT FOR THIS LER:
NAME: L. V. Wilkie, TELEPHONE: (803) 885-3518 Safety Review
Manager
COMPONENT FAILURE DESCRIPTION: CAUSE: F
SYSTEM: BA COMPONENT: XIS MANUFACTURER: C753 REPORTABLE
NPRDS: Yes
SUPPLEMENTAL REPORT EXPECTED: NO
ABSTRACT:
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
ABSTRACT
TEXT PAGE 2 OF 5
BACKGROUND
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.
CONCLUSIONS
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
TEXT
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
Immediate
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.
Planned
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
available.
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
Gentlemen:
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
/ftr
Attachment
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
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