ML20066L350
| ML20066L350 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 01/31/1991 |
| From: | Bailey J WOLF CREEK NUCLEAR OPERATING CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-011, IEB-88-11, NO-91-0039, NO-91-39, NUDOCS 9102070002 | |
| Download: ML20066L350 (4) | |
Text
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c W$LF CREEK NUCLEAR OPERATING CORPORATION John A. Bailey Vko Pment January 31,1991 NO 91-0039 U. S. Nuclear Regulatory Commission ATTH: Document Control Desk Mail Station P1-137 Washington, D. C.
20555
Reference:
Letter VM 89-0158 dated May 31, 1989, from B. D. Withers, VCNOC to NRC
Subject:
Docket No. 50-482:
Summary of Results of Stress and Fatigue Analysis Associated with NRC Bulletin 88-11,
" Pressurizer Surge Line Thermal Stratification' Gentlemen:
The purpose of this letter is to transmit a summary of Wolf Creek Nuclear Operating Corporation's (WCNOC) results from updating the pressurizer surge line stress and fatigue analysis as requested by HRC Bulletin 88-11,
' Pressurizer Surge Line Thermal Stratification *.
The Attachment provides a description of the analytical approaches used to update the stress and fatigue analysis to ensure compliance with applicable Code requirements and a summary of the results.
The Attachment is being submitted in accordance with the commitments made in the Reference and NRC.Bulletin 88-11.
WCNOC participated in a program for resolution of this issue through the Westinghouse Owners Group (WOG). The WOG program provided a methodology for a generic detailed analysis based on ASME stress and fatigue evaluations of groups of plants.-
Subsequently, WCNOC utilized plant specific data to verify the applicability of the generic detailed analysis for Wolf Creek Generating Station.
If you have any questions concerning this matter, please contact me or Mr.
H. K. Chernoff of my staff.
Very truly yours,
~Q Q M
John A. Bailey j
Vice President Nuclear Operations JAB /jra Attachment cc: A. T. Howell (NRC), w/a R. D. Martin (NRC), w/a D. V. Pickett (NRC), w/a M. E. Skov (NRC), w/a
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Attachmsnt to NO 91-0039
- Page' 1 of 13
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RESULTS OF STRESS AND FATIGUE ANALYSIS REGARDING PRESSURIZER SURGE LINE THERMAL STRATIFICATION i
Background' On December-20, 1988, the NRC issued NRC Bulletin 88-11,_
" Pressurizer Surge
'Line Thenna11 Stratification'1which : requested utilities-to establish and
-implement a: program;-to confirm pressurizer surge line integrity.
The bulletin required utilities.to perform -the. actions summarized below =and--
Jinform the staff.of the-actions taken to resolve thisLissue.
-j Action-1=.a. - Perform a-visual inspection _(ASME,Section XI, VT-3).
Action
- 1. b'.
Perform a plant. specific or_ generic-bounding analysis to demonstrate:that the surge line meets applicable design codes and other FSAR and-regulatory = commitments-for the -design life-of the plant.. If the analysis'does'not. demonstrate compliance with these requirements, submit; a
' justification for.-continued operation. (JCO).or bring the plant _to cold shutdown, Eas appropriate and: implement-actions 1.c.
and 1.d.
to develop a
- detailed analysis.
Action 1.c. -'Obtain data on thermal; stratification, _ thermal striping, Land.
.line' deflections either by plant specific monitoring.or througho collective efforts'among plants with a-similar surge:11ne design.
LAction 1.d._
- Update detailed stress and fatigue analyses lof the surge line torensure compliance with applicable: _ code.-requirements incorporating any observations-from'1.a? The. analysis should be based on the applicable plant 4
l specific or referenced. data.
Westinghouse' Owners Group Program l
Boundina Evaluation-and JC0 In Octoberfl988,.the Westinghouse _ Owners Group.(WOG) implemented a._ program-to address-the issue of Laurge.line. stratification.-
As'part of the WOG program,. surge line = physical design" and _ plant. operational data.were collected forL all; domestic Westinghouse _PWRs.-
~A bounding; evaluation 1was; performed which compared WOGL plants to those for which detailed -plant-
,t specific -analysis-had been performed.
Since1this evaluation provided:less
._than' full design life verification, a generic 1 justification for_ continued operation- (JCO)' was,; developed.for use by each of the WOG plants.
.The
. technical. basis of the: generic JC0 was submitted tocthe NRC in WCAP-12277,-
" Westinghouse Owners Group Bounding Evaluati;.. for Pressurizer Surge Line Thermal 1 Stratification".
Welf Creek. Nuclear,0perating Corporation (WCNOC) submitted-a plant specific JC0 in letter-WM 89-0158 dated May 31, 1989 which
> concluded that it was acceptable for WCGS to continue poser operation for
.at'least ten additional heatup-cooldown cycles.
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Attachm:nt to NO 9:.-0039 Pags 2 of 3 Generic Detailed Analysis Since the ' evaluation discussed above provided less than full design life verification, Action 1.b.
of-the bulletin required tha' Actions 1.c.
and 1.d.
be implemented to develop a detailed analysis of tue surge line.
In June 1989, the WOG implemented a program for generic detailed analysis.
This program was based _on individual detailed analyses of groups of plants.
The WOG provided recommendations to utilities regarding the need for additional monitoring data.
Monitoring data was received by the WOG and used to redefine the existing design transients to account for the stratification phenomenon.
Based on the predicted similarity of response to stratification, analysis groups were formed for which system structural models were created for computer analyses.
Surge line fatigue evaluations are typically performed using the methods of ASME Section III, NB-3600 for all piping components.
Based on the requirements -in the bulletin, ASME Section III, 1986 Edition was used to evaluate fatigue on surge lines with stratification loading.
The results of the generic detailed analysis demonstrated acceptable ASME Section III equation 12 stress and fatigue usage in the surge line and reactor coolant loop nozzle for 15 plants including WCGS.
The results of the generic detailed analysis are documented in WCAP-12639,
" Westinghouse Owners-Group Pressurizer Surge Line Thermal-Stratification Generic Detailed Analysis Program Sunnary Report".
This WCAP was transmitted to the NRC on August 3, 1990 and in a subsequent meeting in November 1990, the NRC indicated acceptance of the technical content of the WCAP and the WOG program.
WCNOC Specific Analysis WCNOC performed additional plant specific analyes of the surge line piping and-Reactor Coolant System (RCS) loop nozzle to further verify -the applicability of the generic detailed analysis.
The verification analysis was performed using the methodology described in WCAP-12639 and utilized-WCGS surge line monitoring data gathered during two plant heatups and one
-cooldown.
In addition to the monitoring data, plant operating procedures and_ previous heatup and cooldown data were utilized to-support this analysis.- The results of-this analysis identified that the maximum equation 12 stress is 51.5 kai for past operation with system AT = 345 F and 47.9 kai for future operation with system AT 5 320 F.
The Code allowable stress is 57.9 kei.
System AT is the difference between pressurizer temperature and RCS hot leg temperature.
/dditionally, the analysis -resulted in a calculated cumulative usage factor of 0.4.
The Code allowable usage factor is 1.0.
This analysis also evaluated pipe supports for the stratification loads and displacement and the results were acceptable in accordance with ASME Section III Subsection NF.
Pipewhip ' restraint gaps and pipe displacement were evaluated and were found to be acceptable, l
u Attachmsnt to-NO 91-0039
.c- -
-pag,- 3 og 3 1
JThe pressurizer' nozzle was.not within the_ scope-of evaluation required by-
~
.y this. bulletin. The pressurizer nozzles at WCGS are oriented vertically, and-
.therefore do: _ not-experience local stratification effects.
In -the -
performance--of-the required evaluation' it-was-identified that -thermal stratification' in the piping typically causes higher global. bending moments at.the; pressurizer nozzle thaniconsidered in_the original design.
The WOG.
generic detailed. analysis did:not address-the affects of stratification on the stress-and fatigue of the pressurizer nozzle.
A1 stress and fatigue
. analysis-for the-pressurizer nozzle at WCGS is in progress.
Preliminary-review of the loads indicates that the nozzle is~ qualified since the loads are-estimated-to be :in the acceptable-range. -
The results1of the complete analysis on the. pressurizer nozzle will be completed by March 20, 1991.-
N Based on tha'WOG generic detailed, analysis and. the WCGS plant specific
- analysis,; WON 00 has demonstrated that.the pressurizer surge line meets-the-applicable design' codes'and other USAR and regulatory commitments for-the j
l licensed _=11fa-of thelplant.
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