ML18139B888
| ML18139B888 | |
| Person / Time | |
|---|---|
| Site: | Surry, North Anna, 05000000 |
| Issue date: | 05/27/1982 |
| From: | Leasburg R VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Harold Denton, Eisenhut D Office of Nuclear Reactor Regulation |
| References | |
| 284, NUDOCS 8206040330 | |
| Download: ML18139B888 (9) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND~ VIRGINIA 23261 R. H. LEASBURG VICE PRESIDENT NucLEAR 0PEBATIONS May 27, 1982 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation Attn:
Mr. D. G. Eisenhut, Director Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C.
20555 Gentlemen:
TOPICAL REPORT VEP-FRD-33 Serial No. : 284 FR/KLB: bjc Docket Nos.: 50-280 50-281 50-338 50-339 License Nos. :DPR-32 DPR-37 NPF-4 NPF-7 "VEPCO REACTOR CORE THERMAL-HYDRAULIC ANALYSIS USING "THE *coBRA *urc/MIT COMPUTER CODE". provides our response to Nuclear Regulatory Commission (NRC) Staff questions on* the Vepco topical report VEP-FRD-33, "Vepco Reactor Core Thermal-Hydraulic,Analysis using the COBRA-Ille/MIT Computer Code,"
transmitted by th.e W. N. Thoinas (Vepco) to H. R. Denton (NRC) letter, Serial No. 795, dated September 28, 1979.
These questions were provided orally by the NRC Staff during a January 22, 1982 meeting with Vepco.
We request that the NRC review and provide any comments on these responses to us by June 25, 1982.
If you require additional information, please contact us.
Attachment cc:
Mr. R. L. Tedesco Assistant Director for Licensing Mr. C. H. Berlinger Branch Chief~ Core Performance Branch Mr. J. S. Berggren Standard:i.zati.on and Special Projects Branch
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e MP.C QUESTION The Vepco CO~RA code single-pass method should be benchmarked against a multi-pass code £or a range of operating conditions.
If the COBRA calculations are not conservative, an inlet flow multiplier should be developed to ensure that the COBRA results are conservative.
RESPONSE
One £or one comparisons between the COBRA 19 channel single-pass and the THINC-I multi-pass one-eighth core models were made for the six cases shown in Table 1.
These cases were chosen to span the general licensed operating range of the Vepco plants.
A consistent set of input was used for both computer codes.
Case 1 is a recalculation of the VEP-FRD-33 Section 6.3.2 statepoint.
It represents a ioint on the 2200 psi core thermal limit line at 112% powe~ and*conditions based on PAGE 1
the densification/positive moderator temperature coefficient reanalysis.
Case 2 computes a point which would exist on a COBRA generated 2400 psia core thermal limit line at 118% power.
Thermal design £low and the currently applicable heat flux spike were used.
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PAGE 2
Case 3 is a recomputation 0£ case 2, using a large positive axial offset power distribution instead 0£ the normal cosine shaped axial power distribution.
The power was adjusted to yield a COBRA minimum DHBR approximately equal to 1.30. (the actual value is 1.32).
This set of operating conditions was then applied to the THIHC-I calculation.
Case 4 ~hows the effect of reduced power and a large negative axial offset power distribution.
As in case 4, the power was adjusted to yield a COBRA minimum DHBR approximately equal to 1.30.
Case 5 shows the effect of reduced pressure and flow.
This statepoint corre~ponds to conditions on the existing Surry 1855 psia core thermal limit line at 112% power.
Current fuel stack height reduction and heat flux spike factors were used in this calculation, as opposed to the densifi-cation reanalysis values used in the limit line generation.
Case 6 shows the effect of reduced flow.
The loss-of-flow transient reported in VEP-FRD-33 section 6.4.3 was rerun with COBRA using corrected values for reduced fuel height and heat flux spike to yield minimum DHBR results identical to those from THIHC-III.
Case 6 on Table 1 is a statepoint calculation at the point of minimum DNBR for this transient.
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As can be seen £rom Table 1, in all cases the COBRA 19 channel single-pass model yielded either identical or conservative minimum DNBR's when compared with the THINC-I multipass model results.
No inlet £~ow multiplier was necessary to achieve these compazisons over this wide range 0£ operating conditions.
There£ore, no inlet
£low multiplier is required £or use with COBRA.
PAGE 3
e PAGE 4
TABLE 1:
Summary of Comparisons with THINC-I Case Pressure Power Flow Tin I FQE Axial.
I Minimum DNBR No.
Cpsia)
(%)
(%)
(OF) I Offset I
COBRA ITHINC-I
-------- ------- -------1----- --------- -- -----1--------
I I
1 2200.
112.
1 0 0.
554.
- 1. 24 ze:co
- 1. 27 I
- 1. 30 I
2 2400.
118.
100.
563.
- 1. 03 ze:co
- 1. 30
- 1. 33 3
2400.
101.
10 0.
563.
- 1. 03 la:cge
- 1. 32
- 1. 39 positive 2400.
- 81. 7 100.
618.4
- 1. 03 la:cge
- 1. 30
- 1. 33 negative 5
1855.
11 2 *
- 90.
515.
- 1. 03 zero
- 1. 47
- 1. 47 6
2220.
100.5 76.5 547.
- 1. 03 zero
- 1. 32
- 1. 32
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PAGE 5
-NRC QUESTION Dete%mine the COBRA sensitivity to the inlet £low dist%ibution.
RESPONSE
Vepco has confi%med the COBRA inlet £low sensitivities %epo%ted in Re£e%ence 1.
Fo% 0% to 10% hot assembly flow sta%vation, the minimum DNBR and the £low%ate at the point of MDNBR each change by less than 1% for the wide %ange of operating conditions shown in Table 1.
Vepco will continue to use 5% flow sta%vation to the hot assembly, consistent with the Westinghouse design basis assumptionsCZ-lt)
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PAGE 6
~RC QUESTION How will Vepco compensate for the effect of non-cosine core axial power distributions in their analysis of the core thermal limits li~es?
RESPONSE
The effect of non-cosine axial power distributions is accounted for by modifying the overtemperature AT setpoints with the £CAI) function.
Vepco will follow the approved Westinghouse methods detailed in Reference 5 for determining the £CAI) function.
t r,,
e PAGE 7
-REFERENCES
- 1.
R. N. Gupta, "Maine Yankee Core Thermal-Hydraulic using COBRA-IIIc," YAEC-1102, June 1976.
2.- J. Shefcheck, "Application of the THINC Program to PWR Design,"
WCAP-7359-L, August 1969
- 3.
"Westinghouse Reference Core Report -
17x17," WCAP-8185, December 1973
- 4.
L. F. Hochreiter, H. Chelemer, "Application of the THINC-IV Program to PWR Design," WCAP-8054, September 1973.
- 5.
S. L. Ellenberger, et al, "Design Bases for the Thermal Overpower AT and Thermal Overtemperature AT Trip Functions,"
WCAP-8746 (non-proprietary) WCAP-8745 (proprietary), March 1977