ML20137C121

Forwards Comments & RAI Re Wcobra/Trac Oregon State Univ Long Term Cooling Final Validation Rept

ML20137C121
Person / Time
Site:	05200003
Issue date:	03/20/1997
From:	Huffman W NRC (Affiliation Not Assigned)
To:	Liparulo N WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
References
NUDOCS 9703240157
Download: ML20137C121 (5)

Text

. _ . _ - _ _

March 20, 1997

~ '

Mr. Nicholas J. Liparulo, M'anag2r .

Nuclear h fety and Regulatory Analysis Nuclear and Advanced Technology Division Westinghouse Electric Corporation l P.O. Box 355 .

l Pittsburgh, PA 15230 i l

SUBJECT:

COMENTS AND REQUESTS FOR ADDITIONAL INFORMATION (RAIs) ON THE MCOBRA/ TRAC OREGON STATE UNIVERSITY.(OSU) LONG TERM COOLING (LTC)

FINAL VAllDATION REPORT

Dear Mr. Liparulo:

In support of the AP600 design certification review, the Nuclear Regulatory Commission (NRC) staff is evaluating the use of the WCOBRA/ TRAC large break loss-of-coolant-accident analysis computer code for assessing the LTC perfor-mance of the AP600. Westinghouse letter NSD-NRC-96-4877, dated November 6, 1996, submitted the WCOBRA/ TRAC OSU LTC Final Validation Report, WCAP-14776.

The staff submitted RAI's on this report on March 4, 1997. On March 12, 1997, 1 the staff and Westinghouse had a meeting to discuss additional calculations Westinghouse has performed related to LTC analyses. Based on input from the staff's contractor and discussion from the March 12, 1997 meeting, the staff has additional RAls which are provided as an enclosure to this letter.

If you have any questions regarding this matter, you can contact me at (301) 415-1141.

Sincerely, original signed b -

William C. Huffman, y: Project Manager Standardization Project Directorate Division of Reactor Program Management Office of Nuclear Reactor Regulation Docket No.52-003 I

Enclosure:

As stated cc w/ enclosure:

See next page

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. Mr. Nicholas J. Liparulo Docket No.52-003 Westinghouse Electric Corporation AP600 cc: Mr. B. A. McIntyre Mr. Ronald Simard, Director Advaheed Plant Safety & Licensing Advanced Reactor Programs Westinghouse Electric Corporation Nuclear Energy Institute Energy Systems Business Unit 1776 Eye Street, N.W.

P.O. Box 355 Suite 300 Pittsburgh, PA 15230 Washington, DC 20006-3706 Ms. Cindy L. Haag Ms. Lynn Connor Advanced Plant Safety & Licensing Doc-Search Associates Westinghouse Electric Corporation Post Office Box 34 Energy Systems Business Unit Cabin John, MD 20818

. Box 355

Pittsburgh, PA 15230 Mr. James E. Quinn, Projects Manager LMR and SBWR Programs

,' Mr. M. D. Beaumont GE Nuclear Energy Nuclear and Advanced Technology Division 175 Curtner Avenue, M/C 165 4 Westinghouse Electric Corporation San Jose, CA 95125 One Montrose Metro 11921 Rockville Pike Mr. Robert H. Buchholz Suite 350 GE Nuclear Energy Rockville, MD 20852 175 Curtner Avenue, MC-781 San Jose, CA 95125 Mr. Sterling Franks i U.S. Department of Energy Barton Z. Cowan, Esq.

NE-50 Eckert Seamans Cherin & Mellott 19901 Germantown Road 600 Grant Street 42nd Floor Germantown, MD 20874 Pittsburgh, PA 15219 Mr. S. M. Modro Mr. Ed Rodwell, Manager Nuclear Systems Analysis Technologies PWR Design Certification Lockheed Idaho Technologies Company Electric Power Research Institute Post Office Box 1625 3412 Hillview Avenue Idaho Falls, ID 83415 Palo Alto, CA 94303 Mr. Frank A. Ross Mr. Charles Thompson, Nuclear Engineer U.S. Department of Energy, NE-42 AP600 Certification Office of LWR Safety and Technology NE-50 19901 Germantown Road 19901 Germantown Road Germantown, MD 20874 Germantown, MD 20874

.- i d

• 1 AP600 REQUEST FOR ADDITIONAL INFORMATION 440.594 How were the boundary conditions of pressure, temperature, and void fraction at the break applied? Page 5-1 WCAP-14776 states that the break

• separator level, temperature, and pressure were used to determine the boundary conditions. However, page 5-4 states that reverse flow from the j break separator into the cold leg could not be predicted while page 5-5 4

states that reverse flow was predicted. Similar statements appear on

page 5-93. When reverse flow is predicted, is the inflow into the reactor coolant system at the appropriate conditions based on the measurements in the break separator? If so, isn't the separator l impiteitly modeled through the applied boundary conditions?

440.595 In WCAP-14776, the predicted downcomer level was 15 in below the I measured value for Test SB23. The predicted level was below the elevation of the DVI line while the measured level was at the bottom of the cold leg. The discrepancy is much larger than the error for the

other tests (about 5 in.). Is this discrepancy for Test SB23 sig-l nificant? Why was predicted downcomer level worse for this test?

4 440.596 WCAP-14776 states (page 6-2) that the pressure drop acrcss the ADS-4  ;

i lines is relatively small compared to the resistance of the DVI lines.

What are the calculated frictional pressure drops across the ADS-4 lines 1 1

and DVI lines during sump injection for one of the tests? What is the predicted void fraction at the ADS-4 flow nozzles for the corresponding i period?  ;

1  :

440.597 WCAP-14776 states on page 6-2 that sensitivity calculations showed that

the calculated levels were not significantly affected by ADS-4 losses. l

, Where are these sensitivity calculations documented? How sensitive was '

the total flow through the primary system to the ADS-4 losses during sump injection?

440.598 The calculated upper plenum liquid levels shown in WCAP-14776 are not l

consistent with the presentation Westinghouse made to the staff on l March 12, 1997. For example, Figure 5.1-23 of the report shows that the i calculated level is about 14 in..for Test SB01 while page 45 of the

presentation material shows that the calculated level is about 9 in. Why i are the calculated results different between the report and the presenta-

] tion?

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Enclosure l

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o s O. l

. 1 General Comments Related to WCAP-14776 i

1. Westinghouse should consider including the measured and calculated loss j factors for the ADS-123 and ADS-4 flow paths in Table 3-7. i

2. The report correctly states that the mass flow through the ADS-123 valves was negligible during the long-term phase. The comparisons between the calculated and measured values are then characterized as excellent for Test SB10, fair for Test 5812, and good for Test SB23. The variation in characterizations is inappropriate considering the uncertainty in the data. According to Appendix D of WCAP-14252, the uncertainty in the ADS-123 liquid flow measurement (FM4-601) is 1.342 gpm or about 0.18 lbs/s, which is much greater than the measured values. Furthermore, since the level is near the bottom of the pressurizer during the long-term phase, no liquid flow would be expected through ADS-123. Steam flow through ADS-123 would be expected, but no reliable casurements of the steam flow are available because the instruments were not ranged properly for the long-term phase. In fact, the reported steam flow rate (FVM-601) was less than zero, which is clearly impossible, .during the window period for three of the four tests. Thus, the staff has conclude that the ADS-123 flow measurements are very uncertain and that the apparent differences in the " goodness" of the comparisons for the tests are not meaningful.

3. The calculated DVI-l flow rate reported in the text on page 5-65 for Test SB12 (0.87 lbs/s) is inconsistent with Figures 5.5-3, 5.3-4, and 6-1 (about 1.2 lbm/s). Similarly, page 5-66 states that the total calculated ADS-4 flow is 1.12 lbs/s while Figures 5.3-14, 5.3-16, and 6-6 indicate that it is about 1.35 lba/s. These apparent discrepancies between the text and figures affect the global mass balance discussion on page 5-67 as well as the summary of results presented in Section 6 (including Figure 6-3).

4. The mass ratio comparisons shown in Figura 6-8 appear to be contra-dictory. The figure shows that the ratio of flow out to flow in is greater than unity for the tests (indicating that vessel levels should be decreasing) and less than unity for the calculations (indicating that vessel = levels should be increasing). Thus, the trends of the calculation appear to be wrong. The text should justify why these results are adequate.  !

Minor Editorial Comments I

1. "Using on this noding approach" should read "Using this noding approach" (first line of page 2-2).

l 1

2. The last sentence of Section 3.9 (page 3-3) does not read well. J

3. The word " valves" in the second sentence of the third complete paragraph on page 3-4 should be " values".  !

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4. The first paragraph of page 5-92 states that Test SB23 was initiated by a 2-in. cold leg break. The test was actually initiated by a 1/2-in.

break.

5. The last paragraph on page 5-94 refers to the broken DVI line. However, neither DVI line was broken for Test SB23, which was initiated by a cold leg break.

6. Paragraph 2 on page G-3 states that the total ADS-4 comparison shown in

. Figure 6-6 indicates scatter above and below the line while the figure shows that the predicted values are all below the line.

.