05000446/LER-1997-001, :on 970415,auxiliary Feedwater Steam Admission Valve Failed to Open Due to Ruptured Diaphragm.Actuator for 2-HV-2452-2 Has Been Disassembled & Individual Components Examined
| ML20141E585 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 05/15/1997 |
| From: | Flores R TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| To: | |
| Shared Package | |
| ML20141E574 | List: |
| References | |
| REF-PT21-97 LER-97-001, LER-97-1, NUDOCS 9705210044 | |
| Download: ML20141E585 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| 4461997001R00 - NRC Website | |
text
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AUXILIARY FEEDWATER STEAM ADMISSION VALVE FAILED OFEN DUE TO A RUFTURED DIAPHRAHM evorn o. n3, a s~umo a, a on osie g,
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i ABSTRACT (Limit to 1400 spaces, i e, approximately 15 single-sptCed typewntten lines) (16)
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 N:uage 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 TDAFMP for both the events.
TV 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.
9705210044 970515 PDR MDP.K 05000446 S
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SUMMARY OF THE EVENT, li4CLUDING 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 l
power. At approximately 12:03 p.m., 2 HV-2452-2 came off its l
closed seat due to leakage through the newly replaced diaphragm.
1 Enclosura to TXX-97110 N C ronM 366A U S NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
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b0 03 06 Tant (d more space a requwed une additorial copees of NRC Form 366A) (1D 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 i
of any ESF, including the RPS, is reportable within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> under 10CFR50.72(b)(2)(ii). At 1:12 a.m.. on April 15,1997, the Nuclear Regulatory Comission Operations Center was notified of the event via the Emergency Notification System for event a). For the event b), the Nuclear Regulatory Commission Operations Certer was notified of the event via the Emergency Notification System on April 20, 1997 at approximately 1:35 p.m.
E.
THE HETHOD 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 H0DE, HECHANISH, 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).
Enclosura to TXX-97110
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U S NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
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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
Manufact'ured by:
Fisher Valve Part Name:
Valve Diaphragn 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 CONSE0VENCES AND IMPLICATIMS 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, ali 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.
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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 feeowater turbine steam admission valve 2 HV 2452 2 failed open, starting TDAFWP 2 01. The turbine driven i
auxiliary feedwater pump flosed 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 I
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 thickbr j
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Enclosura to TXX-97110 N,NC109tM X4A U S NUCLEAR REGULATORY COMMISSION
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UCENSEE EVENT REPORT (LER)
TEXT CONTINUATION i
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.N.C,_ _ u,n 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 non-safety applications.
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The Unit 1 " thick", valve diaphragms have been in service for several months.
i The early failure rate on these diaphragms is indicated as being ' ass than i
three weeks. Therefore, these valves can continue in service until replacement of the thick diaphragms with newly manufactured " thin" diaphragms can be scheouted.
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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.
3 VII.
ADDITIONAL INFORMATION
All times noted are Central Day light Times.
Additionally, this report satisfies the reporting criteria of 10CFR21.
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