ML20214J917

Forwards Request for Addl Info Re A-85-11, Retran Computer Code,Reactor Sys Transient Analysis Model Qualification, Per .Response Requested within 45 Days

ML20214J917
Person / Time
Site:	Calvert Cliffs
Issue date:	11/20/1986
From:	Mcneil S Office of Nuclear Reactor Regulation
To:	Tiernan J BALTIMORE GAS & ELECTRIC CO.
References
NUDOCS 8612020042
Download: ML20214J917 (6)

Text

November 20, 1986  !

M/v\3 Oh Docket Nos. 50-317 and 50-318 Mr. J. A. Tiernan Vice President-Nuclear Energy Baltimore Gas & Electric Company P. O. Box 1475 Baltimore, MD 21203

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION - RETRAN REVIEW Your letter dated January 31, 1986, submitted the Topical Report A-85-11, "RETRAN Computer Code, Reactor System Transient Analysis Model Qualification,"

for Commission review and approval. We have determined with the assistance of our contractor, International Technical Service, Inc. , that additional information is required to complete our review. The request for additional information is enclosed.

Please provide the information as requested within 45 days following the receipt of this letter to permit the expeditious completion of our review. If additional time is needed to provide the requested information, please inform us within 30 days of your proposed schedule for providing this information.

This request for information affects fewer than 10 respondents; therefore, OMB clearance is not required under P.L.96-511.

Sincerely, Origh! Q;uul by Scott Alexander McNeil, Project Manager PWR Project Directorate #8 Division of PWR Licensing-B

Enclosure:

Request for Additional Information cc w/ enclosure:

See next page TRIBUTION ACRS-10 ocket Filg ) BGrimes NRC PDR JPartlow L PDR SMcNeil PBD-8 Rdg PKreutzer FMiraglia Gray File OGC-Bethesda NThompson

.EJordan PBD#8, PBD#8 P8D#8 PKredtzer ft AThadani 11/c;/86 SMg/h>/86 II 11/p86 i

861202o042ggbob17 ADOCK PDR PDR P

y Mr. J. A. Tiernan Baltimore Gas & Electric Company Calvert Cliffs Nuclear Power Plant cc:

Mr. William T. Bowen, President Regional Administrator, Region I Calvert County Board of U.S. Nuclear Regulatory Commission

) Commissioners Office of Executive Director Prince Frederick, Maryland 20768 for Operations 631 Park Avenue D. A. Brune, Esq. King of Prussia, Pennys1vania 19406 General Counsel Baltimore Gas and Electric Company P. O. Box 1475 Baltimore, Maryland 21203 Jay E. Silberg Shaw, Pittman, Potts and Trowbridge 2300 N Street, N.W.

Washington, DC 20037 Mr. M. E. Bowman, General Supervisor Technical Services Engineering Calvert Cliffs Nuclear Power Plant MD Rts 2 & 4, P. O. Box 1535 Lusby, Maryland 20657-0073 Resident Inspector c/o U.S. Nuclear Regulatory Commission P. O. Box 437 Lusby, Maryland 20657-0073 Bechtel Power Corporation ATTN: Mr. D. E. Stewart Calvert Cliffs Project Engineer 15740 Shady Grove Road Gaithersburg, Maryland 20760 Combustion Engineering, Inc.

ATTN: Mr. W. R. Horlacher, III Project Manager P. O. Box 500 1000 Prospect Hill Road Windsor, Connecticut 06095-0500 Department of Natural Resources Energy Administration, Power Plant Siting Program ATTN: Mr. T. Magette Tawes State Office Building Annapolis, Maryland 21204

I REQUEST FOR ADDITIONAL INFORMATION BALTIMORE GAS AND ELECTRIC COMPANY RETRAN CODE REVIEW

1. BG&E used the RETRAN02/ modo 3 computer code which has not been generically approved by the NRC. Discuss the differences between this code and the RETRAN02/ modo 2 code (which is the NRC approved version) and the impact of these differences on transient and accident analyses.

2. Provide the data and comparison which support BG&E's conclusion that the use of a single node for the secondary side of the steam generator will produce acceptable results. In addition, provide and justify the types of transients for which such a single node secondary volume is valid.

3. Justify the use of a single node non equilibrium pressurizer regarding rapid insurge and outsurge transients.

4. For the Multiple Secondary Side Malfunction (MSSM) event, BG&E assumes three heat transfer slabs transfering thermal energy to a single hydraulic node in the pressurizer. Discuss the effect of not subdividing the hydraulic node in the pressurizer in light of the temperature stratification of the fluid in the pressurizer.

5. Based on our review of Section 4.1 of the topical report, we have identified several anomalies. Provide explanations for the following anomalies:

(1) BG&E had postulated that "possibly higher run-out auxiliary feedwater (AFW) pump flow rates and lower post trip main feedwater (MFW) temperatures caused more rapid cooldown after 160 sec in plant data." However, we note

. that the plant data show the SG21 level pegged at about 200 sec and that differences in level in SG21 existed from about 70 sec, not 160. The RETRAN calculation of level in SG21 lagged the actual refill data by roughly 20 see throughout the transient; (2) The slope difference in the steam generator level between the RETRAN calculation and the plant data for SG22 resulted in a difference in dry out time of about 40 sec.

(3) The effect on the transient of the broader spike in RETRAN analysis.

(4) What happened in the plant data at approximately 140 sec following the event? Why was this transient curve not followed by the RETRAN calculations?

Is it related to dryout of the steam generator? Would a more detailed steam generator secondary side nodalization give better results?

6. The statement that the " difference in SG pressure response accounts for differences in primary coolant systems cooldown after 160 sec" is not exactly accurate. The differences in secondary side pressure began at roughly 70 sec and the large change in slope in secondary pressure data at roughly 110 sec was not matched by the RETRAN calculation of the steam generator pressure although the general characteristics of the steam generator pressure was followed. Explain the sources of all the signifi-cant deviations and justify the differences between the RETRAN calculation and the plant data.

i l

.n_ __. _ , - - _ _ _ _ _ _ - - - _ _ - - -

I

7. Expand your discussions on the RETRAN model sensitivity study to support your conclusion stated on page 27 of the report. In particular, did BG&E perform sensitivity studies to determine what happened on the secondary side and its impact on the primary side? If not, then discuss the secondary side flow data and the RETRAN modeling thereof, and justify any differences by discussion of their impact upon the overall transient results.

8. What input loss coefficients were adjusted to establish initial conditions in the transient of four pump coastdown from 20% power? Were any reverse flow loss coefficients used for the reactor coolant pumps? If the reverse flow coefficients were used, describe what caused the steep changes in flow data at roughly 45 sec? Were the same coefficients used in Section 4.3?

Was there a change in flow regime which caused the flow meter to give a different correlation? If the plant data is correct as plotted, why was the slope change not followed by RETRAN? Finally, provide estimates of the natural circulation that is predicted by RETRAN and compare RETRAN's estimates with the expected values.

9. BG&E states that sensitivity studies were performed to adjust the downcomer cross flow and RCP reverse flow coefficients. Although the cross flow takes place across a large area, perhaps the flow modeling is inaccurate and/or incomplete due to failure to model cross flows in the above core region.

Explain how the flows in the above core region were modeled; and justify BG&E's modeling of the cross flow. Provide detailed results from sensi-tivity studies of variation of cross flows and reverse flow coefficients.

Provide plots to accompany the analysis and discussions on comparison of RETRAN results with the measured plant data for each of five combinations of RCP operation (4, 3, 2 in the in the same loop, 2 in opposite loops, and 1 RCP running). Explain how flowrates of various cross flows were determined for the calculations, including the bypass flows which " flows circumferencially around the downcomer and out the cold leg nozzle (s) in the reverse direction through the shut down RCP(s) to the steam generator outlet plenum."

Compare the predicted flows in these various combinations with vendor computations and explain any significant differences. Provide the data that are available to verify the " actual flow path" for reduced RCP operation configurations. Describe how the RCP locked rotor reverse flow coefficient was determined.

10. With regard to the transient of one pump coastdown from 80% power, discuss the basis for adjustment of reactor coolant pump (RCP) moment of inertia and torque including the uncertainty of such pump information.

Were any cross flow sensitivity studies performed for the one RCP coast-down transient? The transient computation seems to substantially over-predict the flow reduction in the shutdown loop. Identify and describe the likely sources of over prediction. What results are obtained without cross flow and with nominal reverse flow coefficients? Why does plant data show nearly instantaneous pressurizer response while RETRAN seems to show no response for approximately 5 sec? Describe why, even though both

~

t the hot leg temperature and the steam generator pressure increase for about 5 see immediately following the RCP trip, and the cold leg temperature remains constant, neither the primary nor the secondary side pressures ,

immediately increase in the RETRAN calculations. Describe and quantify to the extent feasible the differences in the results between the case in which BG&E adjusted the RCS total flow to match hot and cold leg temperatures, and the case usfng the initial conditions described in Sections 4.3 and 4.4.

11. It appears that the RETRAN calculation for a total loss of flow transient from 40% power was initiated with a slightly different hot leg temperature from the plant data. Was there any difficulty in initializing the calcu-lation at 40% power? Were any loss coefficients adjusted in setting up initial conditions? If so, how did they compare to adjustments in Sections 4.3 and 4.47 What happened in the steam generator at 10 sec (see Figures 4.5-2, 3, and 5) and why wasn't it modeled in RETPAN? (We note 3' that there was relatively poor transient computation of temperatures between 10 and 60 sec because of these differences.) Since the time between 60 to 130 min is considered to be the more important period, provide transient curves for that period. The transient curves of primary flow and pressure are in agreement but do not agree for the hot and cold leg temperatures and SG secondary side pressure. What is the reason to cause this effect and why did the secondary side not have a stronger coupling to the primary side?

12. One of the objectives of this topical report is to present BG&E's capability in modeling control systems. Since it is apparent that the major reason for disagreement between TRAC and RETRAN results is the differences in the ADV modeling, BG&E should match the ADV control system used in TRAC and 4

+

rerun the calculation.

BG&E states that in spite of the fact that " primary pressure compares very well, RETRAN predicts the pressurizer to empty while TRAC does not" and that "this is consistent with previous comparison." If this difference is present in the revised calculation, then explain why one code predicts the pressurizer to empty and the other does not.

13. Provide detailed transient curves of RETRAN and TRAC secondary flows, pressures, and temperatures. Correlate to the transient curves for the secondary side with parameters on the primary side. Explain why the PORY reaches its set point about 500 sec earlier than the TRAC predictions.

Explain why RETRAN predicts that the pressurizer water level will rise to the top of the pressurizer 1250 sec before the TRAC predicted time.

In addressing the differences between the results, explain the impact that the noding may have in computing downcommer temperature. It seems unlikely to us that these differences are caused by the coarse RETRAN noding in the downcomer (2 vs 54). Discuss the crossflow betweea nodes in the TRAC nodalization, and provide the theoretical foundation for the

statements that imply crossflow would increase with increasing nodalization.

In addition, explain why increasing the number of nodes in the secondary side of the SG 5 not considered as an option to reduce the void formation in the upper tu e volumes.

14. Describe any differences between the BG&E RETRAN model and the RETRAN model used in initial analysis of L6-1 and L6-3 by EPRI as presented to the ACRS on January 14, 1981.

15. Verify the slip impact on secondary swell level by plotting results with an infinite bubble rise model in the steam generator secondary side. Compare the results from an infinite bubble rise model with results from a single node secondary side model. Explain significantiv greater depressurization andwhythemainsteamflowcontrolvalve(MSFCV)wasopen40%longerthan the test, and provide the transient curve of experimental and predicted flowrates. Describe the control system which governs the MSFCV operation in the experiment and how this was simulated by RETRAN. The depressurization computed by RETRAN was 50-60% larger than the test result, therefore, it appears to be not merely due to 40% longer opening of the MSFCV.

16. (LOFT-6-3) Modeling of the secondary side appears to be inadequate (see Figure 6.4-1, 2, and 5), causing primary side behaviors to differ from the test data. Explain and justify the secondary side modeling including a thorough explanation of why RETRAN calculates "somewhat higher terminal steam flow and feedwater flow."

17. With respect to BG8E's general analysis of the LOFT tests, BG&E selected two transients that were initiated on the secondary side. Since BG&E did not accurately model the secondary events, the primary response may be

, incorrectly computed. Develop secondary controls and input which accurately represent the transients conducted in the LOFT test. Rerun these compu-tations to obtain a valid comparison of RETRAN results with LOFT test data.

9

- - - -- _ -h..- -. - . - . _ _ . . _ _ . _ - - - _ _ . - - - . - , - . _ _ . .