ML20149M140
| ML20149M140 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 02/28/1988 |
| From: | HOUSTON LIGHTING & POWER CO. |
| To: | |
| Shared Package | |
| ML20149M136 | List: |
| References | |
| NUDOCS 8802250351 | |
| Download: ML20149M140 (15) | |
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SUPPLEMENTAL REPORT ON THE INVESTIGATION OF HYDRAULIC TRANSIENT EVENTS IN THE AUXILIARY FEEDWATER SYSTEM SOUTH TEXAS PROJECT DOCKET Nos. STN 50-498, STN 50-499 HOUSTON LIGHTING & POWER COMPANY-FEBRUARY, 1988 l
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8802250351 880219 PDR ADOCK 05000498 O$ DCD ,
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South Texas Project Supplemental Report on Auxiliary Feedwater System Table of Contents Executive Summary Introduction I. Summary of Confirmatory Test Results A. Crossover Isolation Valve Static Stroke Tests B. Crossover Isolation Valve Full Flow Testing C. Motor Driven Auxiliary Feedwater Pump Performance Test D. System Testing
- 1. Mode 4 Single-Train
- 2. Mode 4 Multi-Feed
- 3. Mode 3-Single-Train
- 4. Mode 3 Multi-Feed E. Turbine Driven Pump-Mods 3 Multi-Feed I F. Auxiliary Feedwater System Safety Performance Test II. Conclusion III. Recurrence Control Attachment A - Clarifications to Original Report Attachment B - Clarifications Provided to the Original Report as Provided in Licensee Event Report 87-016 (ST-HL-AE-2420)
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South . Texas Proj ect Supplemental Report on-Auxiliary Feedwater System Executive Summary This is the supplement to the Auxiliary Feedwater System Report on Investigation of Hydraulic Transient Events, dated December, 1987. The original report, filed with the USNRC on December 24,-1987, (letter transmittal ST-HL-AE-2461) contained commitments to perform further testing and evaluation.- This supplement is submitted to document the fulfillment of those commitments and to provide clarification of information previously t submitted where additional information or examinations warrant clarification.
The testing data and analysis contained herein confirm the conclusions reached !
in the original report. The conclusion that the Auxiliary Feedwater System is ready for operation under its design basis flow conditions is shown to be valid. In addition, the testing verifies the root cause documented in the eriginal Auxiliary Feedwater Report. Houston Lighting & Power Company concludes tnat the Auxiliary Feedwater System is operable for its design basis requirements.
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South 'rexas Project Supplemental Report on Auxiliary Feedwater System Introduction The purpose of this. report is to document the additional testing and analysis on the Auxiliary Feedwater System resulting from the original commitment to verify the results of modifications made to system components. In addition, clarifications to the original report and supplemental information are provided.
Section I is the summary of data-for the system and component tests. The test performed to simulate operational conditions support the conclusions of this and the original report.
Section II contains the conclusions reached as a result of the testing and analysis and the basis for conclusions reached in the original report.
Section III aiscusses recurrence control measures taken to limit hydraulic transient events of this nature in the future.
Attachment A provides clarifications to the original Auxiliary Feedwater Report. Excerpts from that report are noted with clarification and justification.
For completeness Attachment B provides the clarifications to the original report as presented in Licensee Event Report 87-0016 (ST-HL-AE-2420) ~
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SUMMARY
OF CONFIRMATORY TEST RESULTS I.A. Crossover Isolation Valve Static Stroke Test Upon completion of the installation of new air operators on Trains A, B,.and C and internal valve work, the auxiliary feedwater system valve operability test IPSP03-AF-0010 was performed. This test established new baseline data for opening and closing times of the crossover isolation valves.
The results of this test were as follows:
Valve Opening Time (sec) Closing Time (sec)
Train A-FV-7517 23.2 4.9 Train B-FV-7516 19.1 4.2 Train C-TV-7515 21.7 5.7 Train D-FV-7518 10.8 3.8 '
I.B. Crossover Isolation Valve Full Flow Testing Valve operability testing under full flow conditions was conducted on Train A, B and C crossover isolation valves. This testing was performed after installation of stiffer valve spring operators. The test (ITEP07-AF-0008) consisted of opening and closing the crossover valves with a flow of 650 to 675 gpm through the associated test line and recording the closure stroke time of the crossover valve. The
. design criteria of valve closure within 10 seconds was met. This -
criteria was met without causing excessive vibration or water hammer.
The results of this test were as follows:
Valve Closure Time (seconds)
Train A-TV-7517 5.41 Train B-FV-7516 4.6 Train C-FV-7515 5.73 For the crossover valve on train D (FV-7518), a needle valve was installed upstream of the air supply solenoid. The needle valve was adjusted to slow th: opening stroke down from the previous 2 to 3 ;
second range to a new range on the order 7 to 10 seconds as noted in l test I.A. above. Af ter installation and adjustment of the needle valve, the crossover valve was cycled open and closed. During this time the Train D flow control valve was pro-set for 650 to 675 gpm flow through the test line. The design criteria of closure within 10 seconds was achieved. No excessive vibration or damaging waterhammer occurred during opening or closing.
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The result of this test was as follows:
Valse Closure Time (sec)
Train D-FV-7518 4.76 I.C. AFW Motor Driven Pump Performance Test Pump surveillances 1 PSP 03-AF-0001, 2 & 3 were performed to ensure that no degradation to the pumps had occurred. These test results were compared to the previous motor driven AFW pump surveillance test results and showed no indications of abnormal pump degradation.
I.D.1 Flow Control Valve Testing - Mode 4 - Single Train An evaluation of the generation of 24 hz pressure pulsations was conducted under test ITEP07-AF-0010. This test was conducted after machining of the valve seats of the A, C & D flow control valves, the installation of the mechanical stops, and the changing of limit switch settings. The test consisted of physically closing each train's flow control valve hard against the mechanical stop and then opening the containment isolation valve to establish flow to that train's steam generator. The magnitude of pressure pulses between 0 and 100 hz was examined with special emphasis at and around 24 hz. Test pressure data was taken from transmitters installed up and down stream of the flow control valves. Data was first analyzed for the flow control valve hard against the mechanical stop. The valve vas then incrementally opened with the handwheel and data. evaluated at each step. This process was repeated until a flow rate of 160 gpm or greater was achieved through each flow control valve.
In all instances the nodified valvo pressure pulsations at or around 24 hz were insignific nt and no dynamic response was generated.
I.D.2 Flow Control Valve Testink - Mode 4 - Multi Feed Test ITEP07-AF-0010 also examined the pressure pulse amplitudes from 0 to 100 hz for simultaneous feeding of all four steam generators. This test employed the B train auxiliary feedwater pump and the system crossover valves. Flow was established to all four steam generators with each flow control valve manually closed against its mechanical stop. Flow was then increased to each steam generator by approximately 20 gpm. This process was continued until flows of 160 gpm or greater were achieved simultaneously to alt four steam generators. At each change of steam generator auxiliary feed flow, the pressure data up stream and down stream of each flow control valve was analyzed. Pressure pulses were insignificant at or around the 24 l hz frequency and no dynamic response was generated. l NL.88.043.01 )
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I.D.3 Flow Control Valve Testing - Mode 3 - Single ~ Train The test as described under II.D.1 was repeated with the plant in Mode 3 operation.
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The peak pressure readings'obtained were insignificant, and no dynamic response was generated.
I.D.4 Flow Control Valve Testing --Mode 3 - Multi-Feed The test described under II.D 2 was repeated with the plant ~1n Mode 3 at normal operating pressure and temperature. The peak pressure pulses at or near 24 hz were insignificant, and no dynamic response was generated.
I.E. Flow Control Valve Testing - Turbine Driven Pump - Mode 3 Multi Feed The pressure pulsation between 0.and.100 hz upstream of the flow control valves of all auxiliary feedwater trains were examined with flow provided by the turbine driven D train AF pump. Again, as in the mode 4 multi feed motor driven tests, the data was analyzed at each change of flow rate. The first data point w'as for all valves against the mechanical stops. Flow was incrementally increased up to a flow rate of 160 gpm to each steam generator. -Special attention was given to pressure pulsations near the-24 hz range..
The peak pressure pulses at or near 24 hz were insignificant, and no dynamic response was generated.
I.F. Auxiliary Feedwater System Safety Performance Test Test ITEP07-AF-0009 was conducted to demonstrate that upon Engineered Safety Features (ESF) actuation, the motor driven auxiliary feedwater (AF) pumps start, and regulating valves control flow in both the automatic and manual modes without inducing anaccept. ole transients in the AF system. These test were completed while monitoring the system pressure and with observers in the Isolation Valve Cubicles. No abnormal pressure transients or abnormal vibrations were encountered for any of the motor driven pumps, and no abnormal dynamic response was generated.
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II. CONCLUSIONS The previously described tests of the auxiliary feedwater system flow control valves have shown these valves ready for operation. Required design and functional parameters of these tests have been met.
The testing of the Auxiliary Feedwater System, conducted as proof of the resolution of this problem, has covered the ranges of system operation in both normal and crossover feeding of steam generators.
In no instance was any indication of system hydraulic or structural resonance encountered.
III. RECURRENCE CONTROL Design change documents have been issued to make the mechanical stops, new limit switch settings and auxiliary feedwater system flow control valve internal expansion chambers part of the design of STP.- Vendor manuals governing disassembly and repair of-these valves have been revised to ensure these features are retained after any normal maintenance activities.
Based on the installation of stiffer operators on the crossover isolation valves, new baseline data was obtained for the valves and was incorporated into the appropriate surveillance test procedures.
In addition the vendor maintenance manual has been revised to reflect new part numbers for stellite coated plug retainer cages which were !
reinstalled. This stellite coating feature will make these valves '
less susceptible to foreign. material gouging which caused valve damage ;
in the past.
I The new crossover operators have added additional hydraulic stability margin to the auxiliary feedwater system and coupled with the above described changes make the auxiliary feedwater system more resistant of any future hydraulic transients.
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i ATTACHMENT A Clarifications to Original Report I'
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, Attachment A CLARIFICATIONS OF ORIGINAL REPORT A. Item "c" of page 2 of transmittal letter ST-HL-AE-2461 dated December 24, 1987. stated.
"The operation of the Train D crossover valve has been slowed down by the installation of a needle valve in the air operator."
Clarification Only the opening stroke time of the. crossover valve was increased with the addition of a needle valve. The closing stroke time was found to be acceptable based on test results.
B. On page 1 of the Auxiliary Feedwater System Report the Executive Sammary thould have included the following statement to clarify the resolution of this issue.
Clarification In addition to the installation of mechanical stops and changes to the limit switch setting on the flow control valves the internal flow geometries of the A, C and D flow control valves were altered by machicing. The seat rings of these valves were machined to create expansion chambers comperable to that existing in the B flow contr21 valve (Shown in Figure 8 of the original report). Since the mechanical stops positively prevent near seat operation, the Unit 2 seat rings will not be machined.
C. On page 30 of the Auxiliary Feedwater System Report the following statement is made. I
! "Additional tests, including dynamic testing (as suggested in RG 1.68), are scheduled during power ascension testing." i Clarificatior, The additional dynamic testing consists of testing the four preheater bypass lines connecting the main feedwater system to the aJxiliary feedwater system. This testing, to be conducted during power' ascension, will be both steady state and dynamic transient testing.
l D. On page 51 of the Auxiliary Feedwater System Report the following statement is made in continuation of Section III paragraph 8.4 concerning the D Train Valtek Crossover Valve (TV 7518).
"The maintenance work history of this valve shows some damage to the internals which is directly attributable to high impact forces caused during the operation of this valve. Action has been taken to slow down the valve response times."
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. Attachment A ,
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. CLARIFICATIONS OF 0RIGINAL REFORT l l
Clarification As part of the disassembly and examination conducted on tifis valve, the j I'
internals were.sent to the valve manufacturerLfor examination and ~'
3 determination of the cause of internal plug, sleeve and seat damage.
1 The valve manuf acturer established that' the damage had been caused by foreign material which became trapped between the valve plug and seat !
j- ring. Additional foreign m&terial had-been trapped between1the plug ;
seat and pressure balanced' sleeve. l.a such, slowing down the closing '
time of this valve to prevent recurrence of valve internal damage is not !
required.- ,
1 E. On page 56 of the Auxiliary Feedwater System Report the following statement is made in continuation of Section III, paragraph 8.5 .;
,. concerning the Valtok Flow Control Valves. '
"In addition, geometry modifications have been made on the Train A and D flow control valves by machining the. valve seats to create the expansion chember present on Valves B and C."
Clarification ,
a i The statement should be corrected as follows:
I In addition, geometry modifications have been made:on the Train A, !
C, and D flow control valves by machining the valve seat to create !
- the expansion chamber comparable to Train B flow control' valves. . r
! F. On page 67 of the Auxiliary Feeawater System Report the follcwing ,l
- statement is made.
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- "The Train B crossover valve was'found to have a bent shaft. Based on this'and a review of the vibration loading conditions,'the valves
, in Trains A , B and C are being rebuilt with new parts Including the j plug, stem, yoke and actuator.7 . The Train D crossover valva. '!
internals are being machined to repair damage done to the plug cage area." ,
1 Clarification l
To clarify the extent of work performed on the crossover valves the following information is provided.
WKM Auxiliary Feedwater Crossover Valves (C1/i'-TV-7515, B1AF-TV-7516 &
A'AF-TV-7517) i NL.88.043.01
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. Attachment A l CLARIFICATIONS OF ORIGINAL REPORT
- 1) Actuators were replaced with spare ~ actuators.' .This increased <the spring _ stiffness from 1900-to 2150 pounds /in. and increased the preload from 14 to 22 psi. The supply air cupply was also increased from 31 to 48 psi.
- 2) Bert or out.of tolerance stems were replaced with stems from spara valves. The stem for TV-7516 was apparently bent from excessive i handwheel fcrce. The-spare valve stems were machined and aligned with the plug centerline. Scoring on the plug and cage was rubbed out and no damage was noted on seating surfaces.
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Valtek Auxiliary Feedwater Crossover Valves (DIAF-FV-7518)
, A needle valve was' installed in the actuator supply air line in ,
order to r3ow down the valve opening stroke time. Actual opening '
time was' increased to approximately 10 seconds.
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ATTACHMENT B Clarifications Provided to the Original Report as Provided in LICENSEE EVENT REPORT 87-016 (ST-HL-AE-2420) e hL.88.043.01
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. Attachment B Clarifications Provided to the Original Report as Provided in LICENSEE EVENT REPORT-87-016 (ST-HL-AE-2420)
- 1.Section I.A. page 6, 2nd paragraph 4th line:
"An additional test (ITEP07-AF-0002) was successfully performed" Should read:
"Portions of the system operating procedure were successfully performed" a
- 2.Section I.B. page 11, 3rd paragraph, lith lines i
"The tee was cut out and replaced." l Should read: l "The tee was cut out and will be replaced."
- 3.Section III.C.2 page 36 1st paragraph 7th line "The test was then rerun." l I
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"The venting procedure was then rerun."
- 4.Section III.C. page 37, S6ction 4:
"The test was run on November 25" Should read:
"The test was run on November 26" !
- 5. beetion III.C. page 37, Section 5:
"This test was initially run on November 25" Should read:
"This test was initially run on November 27" l
- 6.Section III.C. page 38, Section 6:
"This test was run on November 29, 1987."
Should read:
"This test was run on December 1 and 5, 1987."
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, Attachment B Clarifications Provided to the Original Report as Provided in LICENSEE EVENT REPORT 87-016 (ST-HL-AE-2420)
. 7. 5,r....n IV.A. page 67, 3rd line:
"are being rebuilt with new. parts including the plug, stem, yoka and actuator."-
Should read:
"are being rebuilt with new parts including the ste:n, yoke and ae t'sator. "
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- 8.Section V.B. page 78, Section 3:
"has been installed on Trains A, B, and C" Should reads.
"will be installed on Trains A, B, and C."
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- 9.Section V.B. page 78, Section 4:
"The valve actuator has been fitted with a needle valva in the I airline to increase the stroke times."
Should read:
"The valve actuator will be fitted with a needle valve in the
- airline to increase the stroke times."
- 10.Section V.B. page 79, Section 5:
the FCV's have been I! sited. . . 7his was accomplished. . . .
- Should read:
the FCV will be limited....This will be accomplished....
Note: The work indicated in items 2, 8, 9, and 10 has for the most part been completec. Documentation verificatien is ongoing at this time.
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