ML20235Z486
| ML20235Z486 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood, Zion, 05000000 |
| Issue date: | 03/07/1989 |
| From: | Richter M COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-011, IEB-88-11, NUDOCS 8903150478 | |
| Download: ML20235Z486 (4) | |
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Commonwsslth Edison Q,
One First National Plaza, Chicago, llhnois C
Address Reply to: Post Office Box 767 Chicago, Illinois 60690 March 7, 1989 U.S. Nuclear Regulatory Commission l
Attn Document Control Desk l
Washington, D.C.
20555 l
Subject:
Byron Station Units 1 and 2 Braidwood Statlon Units 1 and 2 Zion Station Units 1 and 2 Alternative Schedule for NRC Dullstin 88-11 Pressurizer Surge Line Thermal Stratification NRC Docket tios. 50-35A2115. 50-456/457. and 50-295/303
Reference:
NRC Bulletin 88-11, dated December 20, 1988.
Dear Sir NRC Bulletin 88-11 requests all addressees to establish and implement a program to conflrm 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, Commonwealth Edison (Edison) is participating in a program for partial resolution of this issue through the Westinghouse Owner's Group (WOG).
The WOG program was approved at the October 1988 meeting and has the following objectives:
- Develop a generic Justification for Continued Operation (JCO) to assure that plant safety is not compromised while the effects of thermal stratification are being determined.
- 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 j
with operations personnel.
- Evaluate data and identify and prioritize significant parameters contributing to this issue. Categorize (group) plants based on these parameters.
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- Recommend additional monitoring to supplement the existing transient database required to bound all WOG plants.
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- Estimate the effect of thermal stratification on fatigue life as a function of key parameters.
- Recommend short term and long term actions.
l The WOG program is designed to benefit f rom the experience gained in the 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-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 NRC staff.
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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 enount of l
progress has been accomplished toward meeting these objectives.
Based on plant specific design 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 (>1000F ) 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 I
(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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Significant factors which can influence the structural effects of stratification ares a.
location and design of rigid supports and restraints, b.
pipe layout geometry and size, and 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 denign 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.
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~ d 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, Edison has performed the visual inspection requested in Action 1.a of the Bulletin for Zion Station Units 1 and 2, Draidwood Station Units 1 and 2, and Dyron Station Unit 2, and no discernable distress or structural damage in the pressurizer surge line was evident.
In addition, the Non-Destructive Examination (TIDE) inspection history at Dyron, Draidwood and Zion Stations has not revealed any service induced degradation in the surge line piping that has been attributed to thermal stratification.
Furthermore, all plant specific analyses performed by Westinghouse to date that have included the loadings due to 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 has recently completed a plant grouping evaluation based on plant specific design information, 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 assure that the plant safety is not compromised within the requested period of schedule extension, a JCO will be submitted to the staff.
The JCO which is currently being developed, will be subm1Lled by Edison to the staff within the time frame for Action 1.b of the Bulletin (i.e.,
4 months of receipt of the bulletin for Zion Station and within 1 year of receipt of the bulletin for Dyron and Draidwood Stations). The JCO will utilize the information, experience, and monitoring data obtained through the WOG program, and will support the alternate schedule discussed herein.
Edison requests an alternate schedule to that requested in Dulletin 88-11 for Dyron, Draidwood, and Zion Stations.
A schedule of two years, from receipt of the Bulletin, is considered sufficient time to obtain the necessary additional monitoring data, define thermal transients, perform plant specific analyses and updat.e 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 JCO which is currently being developed, will be submitted by Edison to the staff.
At this time, Edison's request for an alternate schedule applinn only t o Action 1.b of t1RC Dulletin 88-11.
Edison intends to comply with all ot hm requirements of the Bulletin.
To t.he best of my knowledge and belief, the statements contained I
above are true and correct.
In some respect these statements are not based on my personal knowledge, but obtained information furnished by other Commonwealth Edison employees, contractor employees, and consultants.
Such information has been reviewed in accordance with company practice, and I believe it to be reliable.
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'Please address any questions that.you or your staff may have concerning'this response'to this office.
Respectfully, w
M. H.JRichter-Nuclear Licensing Administrator rf/5540K10 cc:
A.B. Davis Resident Inspecter BY/BW/Z
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i Subscribed and Sworn to bero e th e D ' day of-OJt/
, 1989 CT$ Aid. h4om, Notary Pub 11'c l
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