ML20246L651

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Sser Accepting Util Efforts Re Action Items 1.a & 1.b of NRC Bulletin 88-011,per NRC Findings of Westinghouse & Plant Audit
ML20246L651
Person / Time
Site: South Texas  STP Nuclear Operating Company icon.png
Issue date: 02/22/1989
From:
NRC
To:
Shared Package
ML20245H595 List:
References
IEB-88-011, IEB-88-11, NUDOCS 8905180371
Download: ML20246L651 (5)
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SUPPLEMENTAL SER ON' SOUTH TEXA5 FLANT, UNITS 1 AND 2 REGARDING-SURGE LINE STRATIFICATION INTRODUCTION The staff of the Mechanical Engineering Branch and its consultant from Engineering Analysis Services, Inc., visited the Westinghouse office in f Pittsburgh, PA and the plant site of the South Texas Unit 2 during the week of January 30, 1989. .The purpose of the visits was to conduct an audit on the licensee's response to NRC Bulletin 88-11 regarding pres-surizer surge line thermal stratification. During our visits, a number of meetings were held to' discuss the licensee's response (Reference 3) to the staff's concerns as delineated in References 1 and 2. A detailed review of the piping stress calculation packages which include Westinghouse and Bechtel calculations was conducted for Code compliance, and a walkdown of the pressurizer surge line was performed to observe any evidence of thermal interference and discernable distress.

-EVALUATION AND FINDINGS The following is a summary of our evaluation and findings:

1. Design thermal transients based on eiiveloping the best known data from several Westinghouse plants were discussed. The approach is conservative and acceptable for the purpose of providing input to the bounding analysis performed by the licensee. Currently, the ifcensee had instrumented the surge line in Unit 1. As indicated in Reference 4, the monitoring program will cortinue until the first refueling outage on Unit 1. Upon completion l of the program, the licensee will review South Texas and available industry I

data to confirm the acceptability of the transient data currently used, s905180371 890509 PDR ADOCK0500ge P

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2. The basis for defining amplitude, duration and oscillation frequency of thermal striping was discussed. Westinghouse had presented evidence of several flow tests conducted in their Waltz Mill Laboratory and the results of the Mitsubishi tests. A detailed description was also pre-sented in Reference 3 and 5. The amplitude used was conservative in comparison with amplitudes actually observed in flow tests. The durations'were adequately defined to account for the decaying of striping effects to stress and fatigue calculations. We found that the approaches are acceptable.
3. The stratification induced global bending of the surge line in the South Texas plant was calculated using both the WECAN and ANSYS computer codes.

The computation of the WECAN code used finite element piping structural model with step-change thermal profiles. The IETS computation used a conventional pipe element model with linear thermal profiles to calculate equivalent non-linear effects. We have reviewed details of sample cal-culations and discussed the analysis techniques. Our review verifies that the results of both computations are similar in calculated surge line displacements, which were also compared favorably with measured displacement data in the South Texas Unit 1. Westinghouse indicated that they will continue to compare linearly calculated results with measured data for the first few Westinghouse plants when the monitoring program is implemented in these plants. We conclude that the calculated and measured results are adequate and acceptable for the surge line in the South Texas plant.

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4. We found that the licensee's response regarding the effects of mean stress to fatigue calculations for thermal striping was inadequate in Reference 3. The issue was resolved due te additional information 1

presented in the meeting. The licensee indicated that the maximum effect of the mean stress was included in a curve in the ASME Code.

Although any value of a mean stress above the curve values was not considered in the striping analysis, it was judged not to be necessary due to the various conservatism involved in the process of the striping l analysis and the process of fatigue calculations. We have reviewed the additional information (Reference 6) and found that they are acceptable.

5. We have conducted an audit of the surge line piping analysis performed by We'stinghouse and Bechtel, the NSSS and AE respectively to the South Texas plant. Our audit included a detailed review of the calculation packages and the verification of proper interface handling between NSSS and AE in various phases of the analysis. We found that the l calculations had considered all of the required loadings. The stresses j i

were properly combined to meet the limits delineated in the ASME III J

Code, Subsection NB-3650. The design calculations and piping isometrics drawings were found updated to reflect design changes. In addition, j the interface between NSSS and AE was found appropriate.

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6. We have performed a detailed audit on the pipe support calculations.

There is only one support in the surge line. The support was designed by Bechtel with the required stiffness specified by Westinghouse. Our review revealed that the support stiffness is in conformance with the requirements and is acceptable.

7. A walkdown along the entire surge line in Unit 2 was performed and a detailed review of the as-built piping isometrics was conducted.

We found that the clearances at the wall penetrations are adequate to accomodate thermal expansion of the surge line. The as-built con-figuration appeared correctly reflected in the isometric drawing. The removal of one support was properly indicated. In addition, although the surge line had experienced heatup transients, we found no discernable distress in the piping and pipe supports.

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CONCLUSION Based on our findings of the Westinghouse and the plant site audit, and our review of additional information provided in References 3, 4, 5 and 6, we conclude that the South Texas plant had made acceptable efforts to meet the  !

requested action item 1.a and 1.b as delineated in NRC Bulletin 88-11. The efforts had demonstrated that based on the available stratification data the surge line meets the applicable design codes. The licensee will verify their stress and fatigue analyses to ensure Code compliance when the plant-specific data from Unit 1 monitoring program is completed at its first refueling outage.

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References 1

1. Hemorandum,1. B. Marsh to G. Dick, SER for South Texas on Surge Line Stratification, December 15, 1988.
2. NUREG-0781, Supplement 6, SER related to South Texas Unit 2, January 1989.
3. WCAP-12067, Supplement 1, Additional Information in support of the evaluations for thermal stratification of the pressurizer surge lines of the South Texas Project, January 1989. .
4. Letter, Houston Lighting and Power Company to NRC, ST-HL-AE-2973, February 1,1989.
5. WCAP-12067, Revision 1, Evaluation of thermal stratification for the South Texas Units 1 and 2 Pressurizer Surge Line, January 1989 (Enclosure to Reference 4).
6. Letter, Houston Lighting and Power Company to NRC, ST-HL-AE-2987, 1

February 9,1989.

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