United States Nuclear Regulatory Commission - Protecting People and the Environment


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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