ML20117P786
| ML20117P786 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 08/12/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20116D885 | List:
|
| References | |
| FOIA-96-237 NUDOCS 8708180393 | |
| Download: ML20117P786 (5) | |
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4 ENCLOSURE 1 4
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
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RELATING TO THE USE OF RETRAN COMPUTER CODE FOR BEST ESTIMATE TRANSIENT ANALYSES BALTIMORE GAS AND ELECTRIC COMPANY (BG8E)
CALVERT CLIFFS NUCLEAR POWER PLANT, UNITS 1 AND 2 DOCKET N05. 50-317 AND 50-318 1.0 INTR 07UCTION The BG&E Topical Report A-85-11. "RETRAN Computer Code Reactor System transient Analysis Model Qualification", was submitted to demonstrate BG&E's capability to perform best estimate thennal-hydraulic transient analysis using the RETRAN 02/ MOD 03 Computer Code. This submittal was made in response to NRC Generic Letter 83-11. This analysis capability is to be utilized by BG&E to the evaluate proposed changes to operating procedures for Calvert Clifts Nuclear Power Plant, Units 1 and 2.
The subject topical report was submitted by BG&E in a letter dated January 31, 1986. In response to the staft requests for additional information, additional supporting materials were submitted in BG&E letters dated February 24, 1987 and June 9, 198/. The staff has completed its review of the BG&E submittals with technical assistance from its contractors at the International Technical Services, Inc. (ITS). The staff evaluation is addressed below. A technical evaluation report prepared by ITS is attached to this report.
2.0 COMPUTER MODELING BG&E Topical Report A-85-11 briefly describes primary and secondary system configurations, major plant parameters and reactor protective system functions for Calvert Clifts plant as follows:
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RETRAN One Loop Model of Calvert Cliffs - This model was developed to analyze sy m etrical transients. The one loop model explicitly uses a single hot leg, cold leg and reactor coolant pump (RCP) to represent the combination of the two hot legs, four cold legs ano four RCPs actually in the Calvert Cliffs design.
2.
RETRAN Two Loop Model of Calvert Cliffs - This model was developed to analyze loop asymmetric transients. The two loop model explicitly models each steam generator, main steam line and hot leg at Calvert Cliffs. Two cold legs are modeled, one for each steam generator, each actually representing two cold legs and two RCPs,
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RETRAN Four Loop Model of Calvert Cliffs - This model was developed to analyze individual cold leg /RCP transients. The four loop model explicitly simulates the two hot legs and four cold legs geometry of the i
Calvert Cliffs design.
One of the above three models will be selected for analyzing each transient depending upon the expected plant thermal hydraulic behavior during the specific transient.
In response to the staff request, BG&E has provided sufficient information which demonstrated its understanding of the details and limitations of those models.
BG&E uses the RETRAN 02/ MOD 03 computer code which was modified from RETRAN 02/ MOD 02. There are more than two hundred changes made for this modification.
These changes are a result of 1) user reported errors, 2) changes requested by the Utility Group for Regulatory Application (UGRA) Design Review Team, and 31 changes requested by NRC after the staft review of the RETRAN 02/M00 02 for error corrections.
In a letter to NRC dated February 4, 1985, Mr. T. W.
Schnatz of UGRA stated that the total effect of all those changes made in RETRAN modification as measured by sample problems used to test each RETRAN version was insignificant in that the differences were well within the
3 uncertainties in the original calculations. This corrected version of the code has not been approved by the staff. Nevertheless, we believe that there is reasonable assurance that this version of the code was adequate for use in this topical report. Unless the NRC's review of that version establishes ground for concern in the future, we accept its use in the BG&E's best-estimate model.
- 3.0 VERIFICATION OF RETRAN MODELS FOR CALVERT CLIFFS PLANT BG&E has compared the results from analyses using the RETRAN models developed for the Calvert Cliffs Plant with the actual plant operation data, results from analyses using'the TRAC code, and the results from the LOFT tests.
t In the comparison on the results from analyses using the RETRAN models.with the actual plant operation data, BG&E compared the following cases:
1)
Multiple secondary side malfunction event 2) four pump coastdown from 20%
-l power, 3) reactor coolant operation pump combination flow tests at hot zero power, 4) one pump coastdown from 80% power, and 5) total loss of flow / natural circulation test from 40% power. Various RETRAN models were used in the comparisons and the results of the comparisons are reasonably close.
1 Sensitivity studies was conducted by the BG&E to detennine which parameters tould affect the transient results.
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In the comparisons on the results from analyses using the RETRAN models developed for Calvert Cliffs Plant with the results obtained from analyses perfonned by los Alamos National Laboratory (LANL) using TRAC-PF1 nodalization of the Calvert Cliffs plant. BG&E compared the following cases:
- 1) cooldown to residual heat removal (RHR) entry using atmospheric steam dump valves (ADVs) and auxiliary pressurized spray system (APS), and 2) runaway main feedwater to cne steam generator. Overall, the results of comparisons exhibited similar trends despite large differences in the computer code models and the degree of detail and capabilities in plant nodalization. BG&E has provided a sufficient amount of explanation which demonstrated its understanding of the results from
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RETRAN models and the reasons for differences from the TRAC-PFI results.
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4 BG&E also compared RETRAN calculations with the data from LOFT tests L6-1 and L6-3.
In the comparison made with LOFT Test L6-1, the BG&E RETRAN calculated primary and secondary pressure transient behavior did not precisely follow the test results. Overall, RETRAN calculated results with respect to both the general trends and the relative magnitudes of the data are within acceptable bounds.
In the comparison with LOFT Test L6-3, the primary side parameters agreed well between the test data and RETRAN results. Also the overall RETHAN calculated results with respect to both the general trends and the relative magnitudes of the data are within acceptable bounds.
4.0 CONCLUSION
S The staff has determined that BG&E has demonstrated in its submittals, the capability to properly develop RETRAN models of Calvert Cliffs and perform best-estimate simulation of reactor system non-LOCA transient using these models. Therefore, the staff concludes that BG&E is qualified to use the i
RETRAN models documented in the BG&E Topical Report A-85-11 for performing system transient calculations to support the evaluations of proposed changes and revisions to operating procedures.
It is noted that BG&E used RETRAN 02/ MOD 03 which was developed as a result of making corrections necessitated after the NRC staff review of the RETRAN 02/ MOD 02 computer code. This corrected version of the code has not been approved by the staff. Nevertheless, we believe that there is reasonable assurance that this version of the code was adequate for use in this topical report and we accept its use in the BG&E's best-estimate model.
For future licensing analyses, BG&E should submit sufficient information to demonstrate that the licensing calculations are performed using a plant model incorporated with appropriate conservatism to assure that uncertainties in both plant operating conditions (dealt with by modifying code input) and phenomenological models (usually dealt with by use of more conservative models in the code) are treated in each analysis in a conservative manner.
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ENCLOSURE 2 4
TECHNICAL EVALUATION REPORT PREPARED BY i
INTERNATIONAL TECHNICAL SERVICES, INC.
ON THE REVIEW OF BG&E TOPICAL REPORT A-85-11 l
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