ML20245D689
| ML20245D689 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/18/1989 |
| From: | Fox C TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-011, IEB-88-11, NUDOCS 8905010105 | |
| Download: ML20245D689 (5) | |
Text
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TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 37401 SN 157B Lookout Place APR 181989 U.S. Nuclear Regulatory Commission
' ATTN: Document Control Desk Hashington, D.C.
20555 Gentlemen:
In the Matter of
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Docket Nos.
50-327 LTennessee Valley Authority
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50-328 SEQUOYAH NUCLEAR PLANT (SQN) - NRC BULLETIN 88-11
" PRESSURIZER SURGE LINE THERMAL STRATIFICATION": ALTERNATE EVALUATION SCHEDULE On December 20, 1988,'the NRC issued the subject bulletin. The bulletin requests all addressees (e.g.,. holders of operating licenses or construction permits for pressurized water reactors IPHR]) to establish and implement a program to confirm pressurizer surge line integrity.in view of the occurrence of thermal stratification and requires them to inform the NRC of the actions taken to resolve this issue.
Pursuant to satisfying the requirements and schedules of Bulletin 88-11,.TVA
-is participating in a program for partial resolution'of this issue through the Westinghouse Owners Group (WOG).
The HOG program was approved at the October 1988 meeting and has the following objectives:
- Develop a generic justification for continued operation (JCO) to ensure that plant safety is not compromised while the effects of thermal stratification are being determined.
- Collect and sun:marize relevant design, operational, analytical, and test data for as many H0G plants as possible.
In addition, a representative sampling of approximately ten plants will be selected to perform a review of plant records and conduct interviews with Operations personnel.
- Evaluate data and identify and prioritize significant parameters contributing to this issue. Categorize plants based on these parameters.
- Recommend additional monitoring to supplement the existing transient data base required to bound all H0G plants.
- Estimate the effect of-thermal-stratification of fatigue life as a function of key parameters.
The H0G program is designed to benefit from the experience gained in the performance of-several plant-specific analyses on PWR surge lines.
These detailed analyses included definition of revised thermal transients (including stratification) and evaluations of pipe stress, fatigue usage factor, thermal e905010105 89 g h PDR ADOCK O g
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An Equal Opportunity Employer
. U.S. Nuclear Regulatory Commission APR 181989 striping, fatigue crack growth, leak before break, and support loads.
The overall analytical approach used in these analyses has been consistent and has been reviewed by the NRC staff. A significant amount of surge line thermal monitoring data has been obtained in support of these plant-specific analyses. Additional surge line thermal monitoring and plant system data continue to be made available within the WOG, resulting in a steadily increasing data base. A significant amount of progress has been accomplished toward meeting these objectives.
To date, the WOG has completed approximately 80 percent of the effort of assembling plant-specific design information on domestic Westinghouse PWRs (55 units total).
This effort will establish the range of key design parameters and will permit grouping of plants based on these parameters.
Based on the information assembled to date and the experience gained in plant-specific analyses and monitoring programs, the WOG evaluation has resulted in the following observations regarding plant similarity and thermal stratification:
1.
Thermal stratification (greater than 100 degrees Fahrenheit [F]) has been measured on the surge lines for which monitoring has been performed and reviewed by the WOG to date (7 plants).
2.
The amount of stratification measured and its variation with time vary.
This variation has been conservatively enveloped, and its applicability 4
demonstrated for plant-specific analyses. Additional monitoring data representing a wider range of surge line configurations may be needed in order to demonstrate the applicability of these thermal stratification transients to other Westinghouse units.
3.
Significant factors that can influence the structural effects of stratification are:
a.
Location and design of rigid supports and restraints, b.
Pipe layout geometry and size.
c.
Type and location of piping components.
4.
Although the material and fabrication techniques for Westinghouse surge lines are reasonably consistent and of high quality, the design parameters listed in item 3 vary among Westinghouse PWRs.
This variation in design is primarily a result of plant-specific routing requirements.
This variability is currently being examined in order to assess the feasibility of a bounding analysis approach.
These observations developed through the ongoing WOG program indicate that the development of thermal stratification loadings and the evaluation of fatigue, considering these loadings, are complex processes.
Therefore, in order to precisely evaluate stratification, additional time is needed.
1
. U.S. Nuclear Regulatory Commission APR 181989 While more time is needed-to evaluate the stratification issue in detail, the nondestructive examination inspection history at SQN, as well as other domestic WestingMuse-designed PWRs, has not revealed any service-induced degradation in the surge line piping that has been attributed to thermal stratification.
In addition, the plant-specific analyses performed to date that have included the loadings because of stratification and striping have validated the
" leak-before-break" concept and have substantiated a 40-year plant life.
Thus, a prudent approach for providing a detailed evaluation of the effects of surge line stratification would be to follow the WOG program grouping evaluation recommendations and monitor as determined to be appropriate.
The WOG is to complete a grouping evaluation for the purpose of recommending a list of additional plants where thermal monitoring is needed.
The time required for this additional monitoring will be dependent on plant outage schedules.
To ensure that the plant safety is not compromised within the requested peri'od of schedule extension, a JC0 will be submitted by TVA to the NRC.
The JC0 will be submitted no later than June 1,1989, and will utilize the information, experience, and monitoring data obtained through the WOG program.
TVA hereby requests an extension to the schedule requested in Bulletin 88-11, item 1.b.
An alternate schedule will be submitted to NRC, along with the JCO, by June 1, 1989.
At this time, TVA's request for an alternate schedule applies only to item 1.b of NRC Bulletin 88-11.
TVA intends to comply with the other requirements of the bulletin.
A summary list of commitments is provided in the enclosure to this letter.
If you have any questions, please telephone K. S. Whitaker at (615) 843-7748.
Very truly yours, TEN ES E V UTHORITY r
.Fx,
,, Vice President and Nuclear Te hnical Director Enclosure cc:
See page 4
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4 U.S. Nuclear Regulatory Commission APR 181989 Enclosure cc (Enclosure):
Ms. S. C. Black, Assistant Director l
for Projects.
'TVA Projects Division
- U.S. Nuclear Regulatory Commission
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One White Flint, North L
11555 Rockville Pike.
Rockville, Maryland 20852 Ms. L. J. Watson, Acting Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 i
Sequoyah Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry-Road Soddy Daisy, Tennessee 37379
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ENCLOSURE SEQUOYAH NUCLEAR PLANT NRC BULLETIN 88-11
SUMMARY
LIST OF COMMITMENTS l.
To ensure that the plant safety is not compromised within the requested period of schedule extension, a JC0 will be submitted by TVA to the NRC.
The JC0 will be submitted no later than June 1, 1989, and will utilize the information, experience, and monitoring data obtained through the WOG program.
2.
An alternate schedule for item 1 will be submitted to NRC by June 1, 1989.
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