ML20246E038
| ML20246E038 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 05/01/1989 |
| From: | Hairston W ALABAMA POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-011, IEB-88-11, NUDOCS 8905110121 | |
| Download: ML20246E038 (15) | |
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' Alabama Power Company 40 inverness Center Parkway Post Office Box 1295 Birmingham, Alabama 35201 Telephone 205 868-5581 W. G. Hairston, lit Senior Vice President Nuclear Operations AlabamaPower tre southem electic system Docket No. 50-364 May 1, 1989 U.:S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D. C.
20555 Gentlemen:
Joseph H. Farley Nuclear Plant - Unit 2 NRC Bulletin No. 88-11 Pressurizer Surge Line Thermal Stratification On December 20, 1988 the NRC issued Bulletin No. 88-11, Pressurizer I
Surge Line Thernal Stratification. The purpose of this bulletin was to request that licensees establish and implement a program to confirm pressurizer surge line integrity in view of the occurrence of thermal stratification and to inform the staff.of actions taken to resolve this issue.
Item 1.a'of NRC Bulletin 88-11 requires licensees to conduct a visual inspection (ASME,.Section XI, VT-3) of the pressurizer surge line at the first available cold shutdown which exceeds seven days. This inspection should determine any gross discernible distress or structural damage in the entire pressurizer surge line including piping, pipe supports, pipe whip restraints and anchor bolts. The bulletin also requested under Item 1 of reporting requirements that any discernible distress and damage be reported to the NRC, including corrective actions taken or plans and schedules for repair, before restart of the unit.
Alabama Power Company has performed an inspection of the Farley Nuclear j
Plant, Unit 2, pressurizer surge line.
This inspection was conducted on Harch 29 and 30 and April 1, 1989 by an ASME Code Section XI, VT-3 certified examiner. The inspection was first performed with the iissulation installed on the surge line and no vater in the line.
Small gaps were observed in the insulation at several locations and the insulation was noted to be coming apart between pipe whip restraints 2PSR-1 and 2 PSP-2, and 2PSR-3 and 2PSh-4 on the pressurizer side (see sketch included in the attachment).
Several areas of damaged insulation were noted where the insulation appears to have been hit or dented.
An inspection was then conducted with the insulation removed from the surge line and the line full of water.
Gaps at the pipe whip restraints hhh w_-.-_____-______--_-_-_------
U. S. Nuclear Regulatory Commission ATTN:
Document Control Desk Page 2 were measured and recorded. The surge line was inspected for any indications of contact with the pipe whip restraints and any evidence of insulation rubbing.
Rub marks were noted on the piping and the pipe whip restraints at 2 PRS-3 and 2 PRS-8.
Rub marks were noted on the piping only at' pipe whip restraints 2 PRS-4 and 2 PRS-5.
At pipe whip restraints 2 PRS-4 and 2 PRS-5, the surge line was in contact with the whip restraints. Rub marks were also noted on pipe whip restraints 2 PRS-1 and 2 PRS-2; however, no evidence of pipe markings was found at these locations.
Spring supports 2RC-R1 and 2RC-R3 and snubber 2RC-R2 vere also examined for any evidence of damage.
Spring support 2RC-R3, which is a trapeze-type support, was found to be bottomed out (i.e., unloaded) and one of the base plates of the hanger has pulled away from the concrete approximately one inch on one side of the plate. The other side of this plate has pulled from the concrete slightly. The other spring hanger of support 2RC-R3 was also pulled slightly away from the concrete and bottomed out.
On snubber 2RC-R2, the pin at the top of the snubber was not fully engaged and a lockring was missing.
As a result of the findings observed in the visual inspection, Westinghouse performed an assessment of the Unit 2 surge line including the effects of stratification loading in accordance with Section III of the ASME Code, which is the design code of record for Farley Nuclear Plant, Unit 2.
This review included an evaluation of the failed spring hanger condition, as well as the maximum assumed flow stratification condition.
Although complete fatigue usage for the entire line has not been calculated in this assessment, an estimate of the fatigue usage has been made at the hot leg nozzle, which is the critical location, to justify continued safe operation. As a result of this assessment, considering that the highest usage factor occurs at the hot leg nozzle, it has been conservatively determined that the hot leg nozzle is acceptable for a total of 15 years of plant operation or 75 heatups and cooldowns.
Since Farley Nuclear Plant, Unit 2, has experienced 15 heatup and cooldown cycles and has been operating for less than eight years, it has been determined that continued power operation is acceptable for an additional seven years or 60 heatup and cooldown cycles.
In addition to the assessroent performed on the Unit 2 surge line, surface and volumetric nondestructive examinations (NDE) were performed at critical locetions on the surge 'ine.
These examinations include a dye penetrant examination on the four surface markings at pipe whip restraints 2 PRS-3, 2 PRS-4, 2 PRS-5 and 2 PRS-8, and all surge line velds.
Ultrasonic examination was alto performed on all rurge line velds.
No indications from these NDEs were found. ite failed spring hanger 2hC~R3 has also been redesigned based on the maximum assumed stratification loading.
Before restart of Unit 2, the new design for spring hanger 2RC-R3 vill be installed and the missing lockring on the top pin of snubber 2RC-R2 vill be replaced.
In addition to the corrective actions stated above, Alabama Power Company plans to install monitoring instrumentation on the Unit 2 surge line in order to more effectively evaluate the thermal stratification issue. This instrumentation is being installed for monitoring of the pipe outside vall temperatures and pipe displacements
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for one cycle of operation.
U.' S. Nuclear Regulatory Commission
. Document Control Desk Page 3 ATTN:
In concert with NRC Bulletin No. 88-11, Item 1.b., Alabama Power Company hereby submits the attached Justification for Continued Operation (JCO),
which has been reviewed by the Plant Operations Review Committee.
Upon completion of the monitoring program, which meets Item 1.c of NRC Bulletin No. 88-11, Alabama Power Company vill update stress and fatigue analyses for Unit 2 as required by Item 1.d of NRC Bulletin No. 88-11.
The schedule for completion of this effort is in accordance with.the existing Westinghouse Ovners Group program as denoted by Alabama Power-Company letter to the NRC dated March 3, 1989.
If thera are any questions, please advise.
Respectfully submitted, ALABAMA POWER COMPANY l().).$4 W
V. G. Hairston, III VGH,III/RGV:mV.6.45 Attachment SVORN TO AND SUBSCRIBED BEFORE ME cc:
Mr. S. D. Ebneter Mr. E. A. Reeves THIS
/JT DAY OF M6
. 1989 Mr. G. F. Maxwell
@tary Public My Commission Expires:
WWEC.!S,1992 i
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JUSTIFICATION FOR CONTINUE 0 OPERATION REGARDING PRESSURIZER SURGE LINE STRATIFICATION JOSEPH M. FARLEY UNIT 2
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1.
INTRODUCTION First reported in INP0 SER 25 87, pressurizer surge line temperature measurements at a German PWR indicated thermal transients different than design.
Recent' measurements at several domestic PWR's have indicated that the temperature difference between the pressurizer and the hot leg results in stratified flow in the surge line, with the top of the flow stream being hot (pressurizer temperature) and the bottom being colder (hot leg temperature). The top-to bottom temperature differe' ce can reach 250 F n
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to 300 F in certain modes of operation, particularly Modes 3, 4, or 5 during hettup and cooldown.
Surge line stratification causes two effects:
Global bending of the pipe different than that predicted in the o
original design.
Fatigue 1tfe of the piping can be reduced due to the global and local o
stresses from stratification.
Westinghouse has performed an assessment of the Farley Unit 2 pressurizer surge line, with regard to stratification loading conditions and the j
acceptability of continued operation. The results of our assessment are j
discussed in the following sections.
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2.
EVALUATION OF THE FARLEY UNIT 2 SURGE LINE Bulletin 88-11 Visual Insnaction A visual inspection of Farley Unit 2 was performed per the requirements of NRC Bulletin 88-11 and ASME Section XI, VT-3 on March ?g, 30, and April 1, 198g. No structural damage to the surge line piping was observed.
An as found inspection was first performed with the insulation installed and no water in the pipe. Several instances of gaps in insulation and insulation coming apart were found, especially between whip restraints 2PSR-1 and 2PSR-2, and between 2PSR-3 and 2PSR 4 on the pressurizer side.
(SeeattachedsketchAPR14503.) Also, several areas of damaged insulation were found where it appears to have been hit or dented. These instances of insulation damage have no impact on the stratification issue.
The inspection was continued with the insulation removed and the pipe filled with water.
Gaps at the pipe whip restraints were recorded. Rub marks were noted on the piping and on the restraint at restraints 2 PRS-3 and 2 PRS 8.
Rub marks were also found on the piping at restraints 2 PRS-4 and 2PR$-51 the piping is currently in contact with the restraints at these locations. Rub marks were found on restraints 2 PRS 1 and 2 PRS-2, but none were found on the pipe.
Inspection of the supports revealed that trapeze type spring support 2RC-R3 had been damaged.
For one of the spring hangers, the base plate had pulled away from the concrete about one inch; the spring hanger was bottomed out, i.e. fully extended. The other spring hanger of spring support 2RC-R3 was pulled away from the concrete slightly and was also bottomed out. The pin at the top of the snubber (2RC R2) was not fully j
engage'd and a snapring was missing. The pin has been reinserted and the proper locking hardware reinstalled; however, the lack of full pin engagement on the snubber has no impact on the stratification issue.
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s Mon-Destructive Examination Subsequent to the Bulletin 88-11 visual inspection, surface and volumetric l
nondestructiveexaminations(NDE)wereperformedatcriticallocationson the surge line. The four areas where surface markings were identified on j
the pipe during the visual inspection (at whip restraints 2 PRS-3, 2 PRS-4, 2 PRS 5, and 2PR$-8) were examined using dye penetrant examination (PT).
No indications were found.
l Ultrasonic examination (UT), as well as PT, have been performed on all surge line welds, including the surge line to hot leg nozzle weld, and the surge line to pressurizer nozzle weld. The UT examinations utilized the i
enhanced methodology discussed in NRC Bulletin 88 08. No indications were found. Two'stirface indications were noted from the PT examination, but t
neither were reportable.
Itcreal Stratification Assessment Analysis Westinghouse has performed an assessment of the surge line, including the effects of stratification loading, in accordance with Section III of the ASME Code, which is the design code of record for Farley Unit 2.
The review included an evaluation of the failed spring hanger condition, as well as the maximum assumed flow stratification condition. Although complete fatigue usage for the entire line has not been calculated in this assessment, an' estimate of the fatigue usagt, has been made at the critical location (hot jeg nozzle) in order to justify continued safe operation.
I As indicated above, spring hanger 2RC R3 was pulled away from the concre.te. To. assure that this condition has not imposed excessive stresses on the surge line, a deadweight analysis was performed assuming 2RC-R3 inactive. The results indicate that the primary stresses in the 4
surge line remained within the ASME Code allowable limits.
In addition, the results of the thermal analysis discussed below, including the maximum assumed stratification loading, were used to redesign hanger 2RC-R3 to 6
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accommodate the thermal growth of the surge line. The modified design includes a new spring hanger with increased travel limits, and new base i
plate and anchor bolts.
In order to evaluate the potential of meeting the ASME Section !!! Code limits including the effects of stratification, a structural model of the i
Farley Unit 2 surge line was developed using the ANSYS general purpose finite element computer code. The case of maximum assumed stratification transient and step temperature profile has been analyzed for Farley Unit 2, and is based on bounding Farley system temperatures and measured flow stratification profiles at several plants. The ANSYS model reflects the redasign of spring support 2RC-R3 and gaps at the pipe whip restraints to represent the actual surge line configuration, including pipe contact with the restraints when the gaps are closed.
The maximum assumed thermal stratification, which may occur in Mode 3 (hot standby), Mode 4(hotshutdown),orMode5(coldshutdown),showsa vertical downward movement of the line which is larger than that predicted by the original design analysis, and confirms the observations mada during the walkdown.
The results of the ANSYS analysis show the piping loads to be maximum at the hot leg nozzle. The expansion stress range between the stratification case and normal operating conditions, while higher than the thermal expansion strest range from the original design analysis, was found to be within the ASME Code allowable stress.
Westinghouse has performed complete, detailed analyses for several plants in which ASME fatigue usage factors have been calculated. These calculations considered both thermal stratification and thermal striping at various locations ir the surge line. Total stresses include the combined effects of pressure, operating basis earthquake (OBE), global thermal expansion moments from ANSYS analyses, local stratification, and local striping stresses in the pipe wall. Of these stresses, the pressure, local stratification, and striping effects in the pipe wall will be applicable to Farley Unit 2 and have been used in the assessment of a
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' total stress for Farley Unit 2. -The maximum global thermal expansion stresses have been obtained from the case of maximum assumed stratification as noted previously OBE stresses from the previous design analysis are still valid.
l The results of the fatigue assessment indicate the highest usage factor occurs at the hot leg nozzle. The controlling hot leg nozzle weld has i
been conservatively determined to be acceptable for a total, of 15 years of plant operation or 75 heatups and cooldowns.
Since Farley' Unit 2 has been operating for less than eight years and has experienced 15 heatup and cooldown cycles during that time, continued power operation is acceptable for at least an additional seven years or 60 more heatup and cooldown cycles.
It is judged, however, that the actual stratification temperature profile for Farley Unit 2 is significantly lower than the maximum assumed stratification profile used in this assessment. Thisjudgement.is supported by a number of surge line monitoring programs that have been conducted at other plants, and also by the geometry of the Farley Unit 2 surge line, which has a somewhat larger slope than most plants.
Based on data which will be obtained from instrumentation currently being installed on the Farley Unit 2 surge line, it is judged that a detailed analysis will demonstrate a fatigue life consistent with the 40-year design life of the plant.
Succe Line Monitorina Procram In order to more effectively evaluate the thermal stratification phenomenon at Farley Unit 2, instrumentation is being installed on the surge line that will provide the capability for continuous monitoring of pipe outside wall temperatures and pipe displacements.
It is intended that the instrumentation is temporary and will remain in place on the o
surge line throQh the course of the next fuel cycle, at which time it will be removed.
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Resistancetemperaturedetectors(RTD's)willbeplacedatsixlocations along the surge line. The RTD's will be clamped to the outside of the pipe with a stainless steel band at each location. The' surge line insulation will be replaced over the RTD's. Eight linear position transducers (lanyards) will be attached to the surge line at four locations, measuring both horizontal and vertical pipe movement at each t
location. The lanyards will be attached to the surge line via stainless steel (1/16inchdiameter) cable. The cabling will be run Yrom the RTD's and transducers, via a multiplexer inside containment, to a ' data logger located outside containment.
It is expected that the data obtained from this program will not only demonstrate the conservatism of the stratification loading used in the current assessment, but will support the use of a lower, more realistic profile in the detailed stratification analysis required by Bulletin 88-11.
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'3.
OVERALL SAFETY ASSESSMENT I
Sumary of the Status of the Farlav Unit 2 Surae Lina Alabama Power has conducted the walkdown of the Farley Unit 2 surge l ine as required by Bulle'in 8811. Extensive nondestructive examinations have also been performed, including a visual examination of the complete 1-ne for signs of physical distress, UT and PT of all welds, and PT of i
scratches and markings believed to be the result of contact..with whip' restraints. The results are discussed in Section 2 of this d00.
Westinghouse has performed an assessment of the surge line, including!the effects of stratification loading, in accordance with the ASME Code Section III, which is the design code of record for Farley Unit 2.
The assessment included an evaluation of the failed spring hanger conditio,n, as well as the maximum assumed stratification condition. Theresults(of this assessment, which include the conditions observed during the walk ldown
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and the redesigned spring hanger, indicate that continued safe operation of Farley Unit 2 is justified.
The design of the Farley Unit 2 surge line is timilar to the surge lines of other Westinghouse plants. The layout includes three bands and one' long radius elbow to allow for thermal expansion of the line. The material is Type 304 stainless steel. Operation of the plant relative to parameters affecting the surge line (primarily the maximum temperature' difference between the pressurizer and the reactor coolant loops) is also sim.ilar to many other plants.
Therefore, the acceptable analysis results that have been obtained from detailed stratification evaluations on other plants are indicative of a favorable fatigue situation at Farley Unit 2.
Probability of turce Line Failure J
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Inservice non-destructive examinations (NDE) have been performed on th 9
Farley Unit 2 surge line, meeting the 1983 Edition through Summer 1983 Page 7 of 12
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- Addenda of section XI of the ASME Code, and the enhanced methodology discussed in NRC Bulletin 88-08. S e NDE results have identified no cracks or recordable indications in the surge line.
c Westinghouse has performed several plant-specific, detailed surge line analyses that have included the loadings due to surge line p!
stratification. In each case, the leak-before-break (LBB) concept has
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been validated specifically for the surge line for a 40-year plant life.
l Although specific calculations have not been performed fo6.s,arley Unit 2, F
Westinghouse fracture mechanics experience indicates that the overall criteria which forms the basis for Las methodology, i.e. the substantial margin between a detectable leakage crack and an unstable crack, would also be valid for Farley tkiit 2. *. /.
Based on the similarity of the Farley Unit 2 surge line loadings and materials to other plants for which Westinghouse has performed analyses, and the fact that no recordable indications have been found during the' inspections of the Farley Unit 2 surge line, it would be unlikely that a through wall crack would be generated. Furthermore, even if such a crack were to develop, experience indicates that the crack would remain stable and would not cause catastrophic failure of the surge line.
Plant I4CA Design Basis he Farley Unit 2 plant design is based, in part, on the postulation of breaks in high energy piping,' including breaks in the pressurizer surge line. As a result of this design basis', pipe whip restraints have been iristalled, and the effects of pipe break on containment design, instrumentation qualification, and ECCS performance have been addressed.
Even in the extremely remote event that a full double ended break should occur in the surge line, the resultant effects of such a break have been
,,. 7 accounted for in the design of the plant.
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NRC Activities 1
Westinghouse has had a number of meetings with the NRC concerning surge line stratification involving a number of Westinghouse plants. The j
stratification phenomenon and its potential effect on piping integrity have been discussed. As a result of these meetings, as well as NRC meetings with the three PWR Owners Groups, the NRC issued Information Notice 88-80, " Unexpected Piping Movement Attributed To Thermal Stratification," dated October 7, 1988.
Increased fatigue ilsage is the primary thrust of this Notice.
More recently, the NRC has issued Bulletin 88-11, " Pressurizer Surge !.ine l
Thermal Stratification," December 20, 1988, identifying actions to be taken by licensees:
o Conduct visual inspection -- walkdown.
o Update stress and fatigue analysis to account for stratification.
o Install monitoring, as necessary.
It is mentioned in the bulletin that licensees may obtain monitoring data through collective efforts with other plants of similar design.
WOG Pressurizer Surae Line Stratification Program In October 1988, the Westinghouse Owners Group (WOG) authorized a program to perform a generic evaluation of surge line stratification in Westinghouse PWR's. This program will evaluate the design and operation of Westinghouse units with respect to the surge line, and determine the factors which could significantly contribute to thermal stratification.
The key objectives of this program are :
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Collect and summarize plant physical and operational data for all WOG plants.
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o Develop a generic Justification for Continued Operation.
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o Categorize and prioritize plants and parameters o
Estimate the extent of fatigue damage.
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o Provide short term and long term recommendations.
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The program has been presented to the NRC, and they are in agreement with the approach.
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4.
SUMMARY
AND CONCLUSIONS Significant efforts have been expended on the Farley Unit 2 surge line to assess the current condition of the surge line and to estimate the effects of thermal stratification. Aiabama Powr.r has conducted the visual inspection of the surge line as required by Bulletin 88-11.
In addition, extensive surface and volumetric NDE has been performed on all of the welds, as well as markings believed to be the result of unexpected pipe displacement due to stratification. No reportable indications or structural dam' age to the surge line piping were found.
A study has been performed to assess the effect of thermal stratification loading on tho' Farley Unit 2 pressurizer surge line. Both the condition with the damaged spring support and the current configuration with the support redesigned have been evaluated under maximum assumed stratification. conditions. Maximum thermal expansion stresses have been calculated, enabling an estimate of fatigue usage. Based on this effort, the continued integrity of the surge line piping system can be demonstrated in its current support configuration with redesigned spring support 2RC R3 under stratified conditions.
i Temperature and displacement monitoring instrumentation is being installed on the Unit 2 surge line. The data obtained from this program throughout the next fuel cycle will provide valuable data to support the detailed analysis required by Bulletin 88-11.
Westinghouse's extensive fracture mechanics experience in fatigue crack growth and LBB technology suggests a very small likelihood of a through wall crack in the surge line. The likelihood of a full couble ended break would be even more remote.
a In conclusion,' Westinghouse believes it is acceptable for Farley Unit 2 to
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continue power operation until a detailed analysis has been completed for
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Farley Unit 2, addres' sing the stratification phenomenon. Consistent with the requirements of NRC Bulletin 88-11, this analysis will be available in January 19g1, d
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