ML20245H974
| ML20245H974 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 02/24/1989 |
| From: | Larson C NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-011, IEB-88-11, NUDOCS 8903060111 | |
| Download: ML20245H974 (5) | |
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Northern States Power Company
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414 Nicollet Mall Minneapohs, Minnesota 55401 Telephone (612) 330-5500 February 24, 1989 NRC Bttiletin 88-11 Director of Nuclear Reactor Regulation U S Nuclear Regulatory Commission Attn: Document Control Desk Wa shing ton',. DC 20555 j
l PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 l
Alternative Schedule for Evaluation of Pressurizer Surge Line Thermal Stratification On December 20, 1988, the NRC issued Bulletin No. 88-11 " Pressurizer Surge Line Thermal Stratification." It requests all addressees to establish and implement a program to contirm pressurizer surge line integrity in view of the occurrence of thermal stratification, and requires them to inform the
, staff of the actions taken to resolve this issue.
Pursuant to satisfying the requirements and schedules of Bulletin 88-11, Northern States Power is participating in a program for partial resolution
. of.this issue through the Westinghouse Owner's Group (WOG).
This program was approved at the October 1988 Westinghouse Owner's Group meeting and has the following objectives:
Develop a generic Justification for Continued Operation (JCO) to o
assure that plant safety is not compromised while the effects of thermal stratification are being determined, o
Collect and summarize relevant design, operational, analytical, and test data for as many WOG 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.
o Evaluate data and identify and prioritize significant parameters contributing to this issue.
Categorize (group) plants based on these parameters.
'O 8903060111 890224 PDR ADOCK 05000282
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/ Director of NRR February 24, 1989:
Northem States Power Company' 1
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' Recommend additional monitoring to supplement;the existing transient--
database required to bound all WOG plants.
o Estimate the effect of thermal stratification on fatigue life as a function of key parameters.
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.o-Recommend,short: term and long term actions; The WOG program'is designed to benefit from the experience: gained. in. the
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performance of several plant specific analyses on Westinghouse PWR surge.
lines. :These detailed analyses included definition of revised thermal transients.(including stratification) and evaluations'of pipe stress, fatigue usage factor thermal' striping, fatigue crack' growth, leak before -
- p break, and support. loads.
The overall analytical approach used in all of these analyses has been consistent and has been reviewed, in detail, by the 3
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 continues to be made available within the WOG, resulting in a steadily increasing database. A significant amount of progress has been accomplished toward meeting these objectives.
To date, the WOG has completed approximately 80% of the effort of assembling plant specific design information on all domestic Westinghouse PWRs (55 units total.); This effort will establish the range of key design parameters and 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 (>100*F) has been measured on all surge lines for which monitoring has been performed and which have been reviewed by the WOG to date (7 plants).
2.
The amount of stratification measured and its variation with time (cycling) varies.
This variation has been conservatively enveloped and applicability 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.
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Director of'NRR-1
- February 24,(1989-E Northem States Power Company >
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Significant factors which can influence'theistructural: effects ofL
- stratification are:
'a.
Location'and design..of rigid supports and restraints 4
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'b.
Pipe layout geometry and size j.
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Type and locatio'n of piping componen s 4.
Although the material and fabrication techniques for Westinghouse surge:11nes are reasonably consistent and of high quality,'PWRs.
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,, a design parameters;11sted in item 3 vary among Westinghouse This variationiin' 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.
s' These observations developed through the'on-going WOG program, indicate that the development'of thermal ~ stratification loadings and the evaluation of fatigue, considering'these loadings, is a complex process.
Therefore, in' order to precisely. evaluate stratification, additional time is needed.
While?more-time is needed to evaluate the stratification issue in detail,
'the NDE inspection history at Prairie Island, as well as all other. domestic,
- Westinghouse designed PWR.'s,thas not revealed any service'inducedi degradation in'the-surge line. piping that has been attributed to thermal stratification.
(In. addition,..all the plant specific analyses performed to date that have included the loadings due to stratification and striping have validated the s
" 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, JThe WOG expects to complete a grouping evaluation, for-the purpose of
. recommending a list of additional plants where thermal monitoring is.
needed, by March 1, 1989.
The time required for this additional monitoring will.be dependent on plant outage schedules.
To assure that.the plant safety is not compromised within the requested
. period of schedule extension, a JC0 will be submitted to the staff. -The JCO.which is currently being developed, will be submitted by Northern States' Power'to the staff within 4 months of receipt of bulletin. 'The JC0 will utilize the information, experience, and monitoring data obtained through the WOG. program, and will support the alternate schedule discussed j
C herein.
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.c 1 Director of.NRR February 24, 1989 Northern States Power Company Page 4 Northern States Power hereby requests an alternate schedule to that requested in Bulletin 88-11..A schedule of two years, from receipt of_the
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. Bulletin, is considered. sufficient time to obtain the necessary additional
' monitoring data,. define thermal transients, perform all. required analyses and update the' stress and fatigue analyses to ensure compliance with applicable code and regulatory requirements. This schedule, though different from that requested in action 1.b of Bulletin 88-11, is consistent with the requirement to update the stress and fatigue analyses within two, years as. stated in action 1.d of the Bulletin.. As previously stated, the JC0 which is currently being developed, will-be submitted to the staf f within 4 months of receipt of the bulletin.
At this time, our request for an alternate-schedule applies only to item 1.b of NRC Bulletin 88-11.
We intend to comply with all other requirements of the bulletin.
Please contact us if you have any questions related to this request for an alternate schedule.
1 M
C E Larson Vice President Nuclear' Generation c:
Regional Administrator - Region III, NRC NRR Project Manager, NRC Senior Resident Inspector, NRC G Charnoff 1
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UNITED STATES' NUCLEAR REGULATORY COMMISSION.
h.i NORTHERN STATES-POWER COMPANY
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PRAIRIE ISLAND-NUCLEAR GENERATING PLANT DOCKET NO. 50-282 50-306-Alternative Schedule for Evaluation of-Pressurizer Surge'Line Thermal Stratification Northern States Power Company, a Minnesota corporation, with this letter is submitting an' alternative schedule for the evaluation of Pressurizer. Surg'e Line Thermal. Stratification as-requested by NRC Bulletin 88-11.
ThisLletter contains no restricted or other defense information.
NORTHERN STATES POWE OMPANY By MM i
C E Lar on Vice Pre den Nuclear Generation Onthisj ay of
~St<Qe/ '/979 before me a notary public in and for said County, personally appeafel C E Larson, Vice President Nuclear Generation, and being first ably sworn acknowledged that he is authorized to execute this document on behalf of Northern States Power Company, that he knows the contents thereof, and that to the best of his knowledge, information, and belief the statements made in it are true and that it is not interposed'for delay.
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