Part 21 Report - 1997-610
ACCESSION #: 9705210044
LICENSEE EVENT REPORT (LER)
FACILITY NAME: COMANCHE PEAK STEAM ELECTRIC
STATION UNIT 2 PAGE: 1 OF 6
DOCKET NUMBER: 05000446
TITLE: AUXILIARY FEEDWATER STEAM ADMISSION VALVE FAILED OPEN DUE
TO A RUPTURED DIAPHRAHM
EVENT DATE: 04/15/97 LER #: 97-001-00 REPORT DATE: 05/15/97
OTHER FACILITIES INVOLVED: CPSES UNIT 1 DOCKET NO: 05000445
OPERATING MODE: 1 POWER LEVEL: 100
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR
SECTION:
50.73(a)(2)(iv) & OTHER
LICENSEE CONTACT FOR THIS LER:
NAME: RAFAEL FLORES - SYSTEM ENGINEERING
MANAGER TELEPHONE: (817) 897-5590
COMPONENT FAILURE DESCRIPTION:
CAUSE: SYSTEM: COMPONENT: MANUFACTURER:
REPORTABLE NPRDS: N
SUPPLEMENTAL REPORT EXPECTED: NO
ABSTRACT:
On April 15, 1997, at approximately 12:37 a.m., while CPSES Unit 2 was in
Mode 1 at 100% reactor power, the auxiliary feedwater turbine steam
admission valve, 2-HV-2452-2, failed open due to leakage through the
valve diaphragm, starting the Turbine Driven Auxiliary Feedwater Pump
(TDAFWP) 2-01. Water flowed from the TDAFWP to all four steam generators
for approximately 30 - 40 seconds until the flow control valves were
closed. On April 20, 1997, at approximately 12:03 p.m., 2-HV-2452-2 came
off its closed seat due to leakage through a newly replaced diaphragm.
No water flowed into the steam generators. The TDAFWP speed control
annunciator alerted the Control Room Staff to a start of the TDAFWP for
both the events.
TU Electric believes that the cause of this condition was that new
"thick" replacement diaphragms developed by the valve vendor were
susceptible to under torquing (pullout) and over torquing (crush). The
auxiliary feedwater system remained capable of performing its intended
safety function throughout the event. A replacement "thin" diaphragm
(original design) has been obtained and installed in the auxiliary
feedwater turbine steam admission valve, 2-HV-2452-2.
This report also includes reporting data pursuant to the requirements of
10CFR21.
END OF ABSTRACT
TEXT PAGE 2 OF 6
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
Any event or condition that results in a manual or automatic
actuation of any Engineered Safety Feature (ESF), including the
Reactor Protection System (RPS)(EIIS:(JC)). Additionally, this
report satisfies the reporting criteria of 10CFR21.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
a) On April 15, 1997, at 0037, Comanche Peak Steam Electric
Station (CPSES) Unit 1 and Unit 2 were in Mode 1 at 100%
reactor power.
b) On April 20, 1997, at 1203, Comanche Peak Steam Electric
Station (CPSES) Unit 1 and Unit 2 were in Mode 1 at 100%
reactor power.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE
INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED TO
THE EVENT
There were no inoperable structures, systems or components that
contributed to these events. Additionally, there were no
related activities in progress which contributed to this event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE
TIMES
a) At approximately 12:37 a.m., on April 15, 1997, auxiliary
feedwater turbine steam admission valve 2-HV-2452-2 failed
open, starting Turbine Driven Auxiliary Feedwater Pump
(TDAFWP) 2-01. Water flowed from the TDAFWP to all four
steam generators for approximately 30 - 40 seconds until
the flow control valves were closed. Steam supply manual
isolation valve 2MS-0128 was closed manually to stop the
turbine. The system was placed in a 7 day Limiting
Condition of Operations (LCO) due to one of the steam
supplies to the CPSES Unit 2 TDAFWP being isolated.
b) On April 20, 1997, CPSES Unit 2 was in Mode 1 at 100%
reactor power. At approximately 12:03 p.m., 2-HV-2452-2
came off its closed seat due to leakage through the newly
replaced diaphragm.
TEXT PAGE 3 OF 6
This caused TDAFWP 2-01 to accelerate to 490 rpm. No
water was injected into the steam generators. The TDAFWP
was tripped, the number 2 steam supply was manually
isolated and the TDAFWP was manually reset. The system
was placed in a 7 day LCO due to one of the steam supplies
to the Unit 2 TDAFWP being isolated.
An event or condition that results in an automatic or manual
actuation of any ESF, including the RPS, is reportable within 4
hours under 10CFR50.72(b)(2)(ii). At 1:12 a.m., on April
15,1997, the Nuclear Regulatory Commission Operations Center
was notified of the event via the Emergency Notification System
for event a). For the event b), the Nuclear Regulatory
Commission Operations Center was notified of the event via the
Emergency Notification System on April 20, 1997 at
approximately 1:35 p.m.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE
OR
PROCEDURAL ERROR
TDAFWP speed control annunciator alerted the Control Room Staff
to a start of the TDAFWP for both the events.
II. COMPONENT OR SYSTEM FAILURES
A. FAILURE MODE, MECHANISM, AND EFFECT OF EACH FAILED COMPONENT
A ruptured "thick" diaphragm was determined to be the cause of
the valve failing open.
B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
On April 11, 1997, the original "thin" diaphragm installed in
2-HV-2452-2 was replaced because the diaphragm developed a
leak. The original diaphragm had been in service for
approximately five years.
The new "thick" replacement diaphragms were developed by the
valve vendor to withstand higher pressures. However, the
thicker diaphragm appears to be susceptible to under torquing
(pullout) and over torquing (crush).
TEXT PAGE 4 OF 6
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE
OF
COMPONENTS WITH MULTIPLE FUNCTIONS
Not applicable - No failures of components with multiple
functions have been identified.
D. FAILED COMPONENT INFORMATION
Manufactured by: Fisher Valve
Part Name: Valve Diaphragm
Part No.: 1R6375X0022
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Not Applicable- No Safety System responses occurred.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Not Applicable- No safety system trains were inoperable during
this event.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT
The inadvertent delivery of cold auxiliary feedwater to the
steam generators will result in a slight increase in the heat
removal by the secondary system, such as described in FSAR
Section 15.1. This event is bounded in severity by the
"decrease in feedwater temperature" event presented in FSAR
Section 15.1.1 and the "increase in feedwater temperature"
event presented in FSAR Section 15.1.2; both transients are
significantly more severe than the actual event. In any case,
all relevant event acceptance criteria continue to be
satisfied. Based on this discussion it is concluded that this
event did not adversely affect the safe operation of CPSES Unit
2 or the health and safety of the public.
TEXT PAGE 5 OF 6
IV. CAUSE OF THE EVENT
On April 11, 1997, the original "thin" diaphragm installed in
2-HV-2452-2 was replaced because the diaphragm developed a leak.
The original diaphragm had been in service for approximately five
years.
The new "thick" replacement diaphragms were developed by the valve
vendor to withstand higher pressures. However, the thicker
diaphragm appears to be susceptible to under torquing (pullout) and
over torquing (crush).
EVENT a)
On April 15, 1997, auxiliary feedwater turbine steam admission
valve 2-HV-2452-2 failed open, starting TDAFWP 2-01. The
turbine driven auxiliary feedwater pump flowed water to all
four steam generators, for approximately 30 - 40 seconds, until
the flow control valves were closed.
The investigation indicated a ruptured diaphragm as the cause of the
valve failing open.
EVENT b)
On April 20, 1997, CPSES Unit 2 was in Mode 1 at 100% reactor
power. On April 20, 1997, at approximately 12:03 p.m.,
2-HV-2452-2 came off its closed seat due to leakage through the
newly replaced diaphragm. This caused TDAFWP 2-01 to
accelerate to 490 rpm. No water was injected into the steam
generators.
The investigation indicated that the newly installed diaphragm had
ruptured and caused the valve to fail open.
V. CORRECTIVE ACTIONS
The actuator for 2-HV-2452-2 has been disassembled and the
individual components examined. Fisher Valve representatives have
examined the installation process, and have determined that
installation was in accordance with their methodologies used in the
laboratory while developing the thicker
TEXT PAGE 6 OF 6
diaphragms. A replacement "thin" diaphragm (original design) has
been obtained and installed in 2-HV-2452-2.
There are four of these model valve actuators in service in safety
related applications at CPSES. All four of these valves were
monitored for leakage after installation. The remaining valves of
this model are installed in nonsafety applications.
The Unit 1 "thick", valve diaphragms have been in service for
several months. The early failure rate on these diaphragms is
indicated as being less than three weeks. Therefore, these valves
can continue in service until replacement of the thick diaphragms
with newly manufactured "thin" diaphragms can be scheduled.
VI. PREVIOUS SIMILAR EVENTS
There have been no other previous LERs, which had similar causes
that resulted in TDAFW Pump operation. Previous failures are being
reviewed by the Task Team, which has been established to evaluate
this event.
VII. ADDITIONAL INFORMATION
All times noted are Central Day light Times.
Additionally, this report satisfies the reporting criteria of
10CFR21.
*** END OF DOCUMENT ***
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