ML20058M985
| ML20058M985 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 09/30/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20058M085 | List: |
| References | |
| NUDOCS 9310070220 | |
| Download: ML20058M985 (3) | |
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WASHINGTON. D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO THE TOPICAL REPORT ,
" TRANSIENT ANALYSIS METHODOLOGY FOR THE WOLF CREEK GENERATING STATION" WOLF CREEK NUCLEAR OPERATING CORPORATION j WOLF CREEK NUCLEAR GENERATION STATION DOCKET NO. 50-482
1.0 INTRODUCTION
By letter dated February 1,1991, Wolf Creek Nuclear Operating Corporation (WCNOC), submitted topical report, " Transient Analysis Methodology for the .
Wolf Creek Generating Station." The purpose of the report was to describe the WCNOC safety analysis and evaluation methodology of selected Updated Safety Analysis Report (USAR) Chapter 15 analyses and to demonstrate competence in the use of the RETRAN-02 MOD 03 computer code. This report was supplemented by letters dated July 16, 1992, January 15, 1993, and February 25, 1993.
2.0 EVALUATION The staff review and evaluation of the topical report addresses the acceptability of WCNOC'S RETRAN model for transient analysis and WCNOC's competence in the use of_RETRAN. The review of the topical report was performed with technical assistance from International Technical Services, Incorporated (ITS) and its review findings are contained in the attached Technical Evaluation Report (TER). WCNOC developed three Wolf Creek Generating Station (WCGS) RETRAN models for qualification in support of reload analysis. -The three models were best-estimate, comparative and evaluation.
The best estimate model is a modification of the WCGS generic based model and was used to validate the WCGS RETRAN model for qualification of reload analysis by conducting analyses of transient start-up tests and comparing the results with the start-up test data. It consists of a two-loop asymmetric model and the key features described in the TER are plant nodalization, steam generator modeling, pressurizer modeling, reactor kinetics modeling and reactor trip logic and control system modeling.
The USAR comparative model was created by modifying the base model and input code to correspond with the current USAR analysis. This model was used to perform USAR-type analyses and to validate the RETRAN models by comparison with current USAR results obtained with the nuclear steam supply system (NSSS) ,
vendor's model. The key assumptions of the vendor's model that were ;
incorporated in the comparative model are: key initial conditions, reactivity i 9310070220 930930 PDR ADOCK 05000482 P PDR..' :
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-g characteristics, the Jens-Lottes heat transfer correlation, transient specific setpoints, time delays and trip parameters and control system modeling. The attached TER describes some of the instances where matched modeling between the RETRAN model and the vendor's model was not possible due to differences in thermal-hydraulic models built into the computer codes, component representation, and setpoint value differences.
The evaluation model was intended for licensing-type analysis and the model was developed by changing some of the transient assumptions and component modeling. The key features discussed in the TER include reactor coolant system (RCS) modeling, safety valve modeling, steam generator modeling, auxiliary feedwater modeling, reactivity feedback modeling, startup test models, and accident analyses modeling.
3.0 CONCLUSION
AND FINDINGS The staff has reviewed the TER provided by ITS for topical report " Transient Analysis Methodology for the Wolf Creek Generating Station." The TER addresses the acceptability of the RETRAN model and WCHOC's competence in using RETRAN computer code for reload and licensing-type analyses. The staff concurs with its findings in that the RETRAN methodology has been compared, with acceptable results, to the USAR and plant data; and WCNOC has demonstrated their competence in the use of RETRAN-02 MOD 03. We conclude that the evaluation model, as described in the topical report and supplementary submittals, is acceptable for performing safety analysis subject to the conditions stated in the TER as clarified below.
4.0 REVIEW CLARIFICATIONS TER, Section 4.0, indicates that at the time of reload analysis, the licensee should review selection criteria for the initial conditions, assumptions and trip actuation logic and related parameters used in the safety analysis to assure that they are acceptably conservative, and demonstrate that any changes are based on a sound analytical foundation and do not result in less conservative results in the analysis. The staff considers such a review to be routine when re-analyzing an accident described in the safety analysis report with a new method and notes that any resulting changes to limiting conditions for operation in the technical specifications must be described with adequate technical justification in a submittal for prior staff review and approval.
Changes in assumptions and related parameters used in the safety analysis which are not covered by technical specifications, but reflect changes in the design or operation of the facility or procedures, as described in the safety analysis report, should be addressed in accordance with 10 CFR 50.59. In all cases, individual changes which reduce conservatism in the results of the analysis are acceptable as long as they are appropriately justified and the overall model continues to contain conservatism to compensate for calculational uncertainties.
Current regulations in 10 CFR Part 50, as discussed above, should be followed when changes are made that affect a plant, its technical specifications or its safety analysis. Additional assessments and submittals implied in Section 4.0 of the TER are required only when needed to satisfy the regulations.
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5.0 REFERENCES
- 1. Topical Report, " Transients Analysis Methodology for the Wolf Creek l Generating Station," Wolf Creek Nuclear Operating Corporation, dated t January 1991. I
- 2. EPRI NP-1850-CCM, Revision 2, "RETRAN-02-A Program for Transient Thermal-Hydraulic Analysis of Complex Fluid Flow Systems," November 1984. ,
Additional Information on the Transient Analysis Methodology for the Wolf !
Creek Generating Station," July 16, 1992. i
Additional Information Regarding Transient Analysis Methodology for the i Wolf Creek Generating Station," January 15, 1993, t
Additional Information Regarding Transient Analysis Methodology for the ;
Wolf Creek Generating Station," February 25, 1993.
Attac.1 ment:
Technical Evaluation Report ;
i Principal Contributor: S. Brewer, SRXB/NRR Date: September 30, 1993 f
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