ML19093B048
| ML19093B048 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 02/17/1978 |
| From: | Stallings C Virginia Electric & Power Co (VEPCO) |
| To: | Case E, Reid R Office of Nuclear Reactor Regulation |
| References | |
| Serial No. 092 | |
| Download: ML19093B048 (23) | |
Text
Mr. Edson G. Case, Acting Director Office of Nuclear React.or Regulation Attn:
Mr. Robert W'. Reid, thief.
Operating Reactors Branch No. 4 Divisio~ of Reactor Licensing U.S. Nuclear Regulatory Cornmissio*n Washington, D. C.
20555
Dear Mr. Case:
Serial No. 092 FR/MLB LQA/DWSj r: kbo Docket Nos.
50-280 50-281 License Nos. DPR-32*
DPR-37 In our letter of August 26~ 1977 (Serial No. 372) and October 14, 1977 (Serial No. 4038), we requested an amendment to Operating Licenses DPR-32 and DPR-3Tfor the Surry Power Station, Units No. l a*nd 2.. The amendment requested was a change to the Technical Specifications desig-nated as Change No. 57.
The changes to the Technical Specificationi were approve*d as Amendments No. *35 and 34. by your letter of December 2,.
1977 for Unit 1 and Unit 2, respectively.
However, in the NRC Safety Evaluation Report, a requirement was imposed to provide, within approxi-mately ninety days, sufficient analytical studies to justify.the continued use of the appropriately adjusted standard design (center~peaked) axial power shape as the limiting shape in the LOCA-ECCS ~nalysis.
The required analy-tical study has been completed and is documented in the Attachment.
The results of the study justify the continued use of the appropriately adjusted standard design (center-peaked) axial power shape in all LOCA-ECCS analysis performed for Surry Units No. 1 and 2.
Should you have any questions, we would be most happy to meet with you at your earliest convenience.
Very truly yours,
'ZJ;;. )1/'l. '>dt-at:t~~,4/
C. M. Stallings Vice President-Power Supply and Production Operations Attachments cc:
Mr. James P. 0 1 Reilly, Director Office of Inspection and Enforcement R.eg ion 11
e ATTACHMENT 1 ANALYTICAL STUDY TO JUSTIFY CONTINUED USE OF THE CENTER-PEAKED AXIAL POWER SHAPE AS THE LIMITING SHAPE IN THE LOCA-ECCS ANALYSIS
I.
e An analysis of the Cn=0.4 DECLG break LOCA has been performed for an axial core power shape other than the standard design chopped cosine shape (i.e., centered-peaked* shape).
The base analysis for comparison purposes is documented in Re-ference 1 and is, currently, the applicable limiting LOCA-ECCS analysis *for Surry Units 1 and 2.
The axial core power shape used in this analysis is provided in Figure 1.
The shape was developed from a typical end-of-cycle reload power shape for Surry Units 1 and 2.
However, the shape was then adjusted to yield a F~g equal to the Technical Specifications limit for F~H/~8iiA*
As indicated in Figure 1, the shape was further adjusted to maximize the linear power at higher elevations in the core and to just touch the K(Z) envelope at 10.5 feet.
This shape was selected over other skewed axial power shapes because it peaks near the axial location of the peak clad temperature cal-culated in Reference 1, and it maximizes the enthalpy rise from the quench front to the peak clad temperature location.
Previous sensitivity studies have showed that a skewed axial power shape with a 10.5 ft peak is limiting (from a LOCA-ECCS standpoint) relative to other skewed shapes because its use results in the case exhibiting the greatest amount of time in reflood with a ~loading rate less than one inch per second (See Reference 2).
It should also be noted that the skewed axial power shape provided in Figure 1 can not be obtained during Condition I operation.
A review of measured axial power shapes from the Surry Units No. 1 and 2 confirms the above statement.
The analysis performed was consistent with the method described in Section F of Reference 2.
With the skewed power shape of Figure 1, the steam cooling model without blockage case was adjusted for better agreement with FLECHT case results.
However, even with the adjustment, the steam cooling model without blockage case still shows a significantly higher result than the FLECHT case and thus complies with NRC requirements.
The results of thi~
e case comparison are provided in Table 1.
The steam cooling model with flow blockage was then used in the analysis.
A comparison of the results from this analysis (skewed axial power shape of Figure 1) and the base case (chopped cosine shape of Reference 1) shows that the calculated peak clad temperature for the base case (chopped cosine shape of Reference 1) is still limiting.
(See Tables 1 through 3)
The difference between the skewed power shape case results and the base case results would be even greater if better agreement had b~n initially obtained between the results from the FLECHT case and the results from the steam cooling model without flow blockage case.
Additional resuJ.ts from this analysis are provided in Figures 2
. through 14.
REFERENCES
- 1.
Letter from Vepco to NRC dated August 26, 1977, Serial No. 372.
- 2.
WCAP-8471/8472, "The Westinghouse ECCS Evaluation Model: Supplementing Information", April 1975, (Westinghouse Electric Corporation).
- TABLE 1 COMPARISON OF CALCULATED PEAK CLAD TEMPERATURES FOR SKEWED POWER DISTRIBUTION CASE Calculated Peak Clad Temperature (°F)
Case (Powe~ Distribution)
A B
Cosine Power Shape 2177.
2104.
10.5' Power Shape 2109.
2084.
A - Steam Cooling Model with Blockage Geometry B - Steam Cooling Model without Blockage Geometry C -
FLECHT C
2086.
1988.
START Reactor Trip Signal S.I. Signal Acc. Injection End of Bypass End of Blowdown Pump Injection TABLE 2 TIME SEQUENCE OF EVENTS COMPARISON FOR DECLG (Cn=0.4)
Skewed Shape (sec) 0.0 0.646 2.25 15.8 23.6 26.83 27.25 Bottom of Core Recovery 37.13 Acc. Empty 55.*30
- From Reference 1 Cosine Shape (sec)*
0.0 0.649 2.26 15.8 23.71 27.94 27.26 37.18 55.46
TABLE 3 CO:MPARISON OF DECLG Cn=0.4 RESULTS Results Skewed Power Shape Cosine Power Shape*
Peak Clad Temp. OF 2109 2177 Peak Clad Location,Ft.
11.0 10.5 Local Zr/H20 RXN (max)i %
5.94 7.4 Local Zr/H20 Location, Ft, 11.0 9.0 Total Zr/H20 RXN, %
<0.3
<0.3 Hot Rod Burst Time1 sec.
25.9 24.2 Hot Rod Burst Location,Ft.
2.75 6.0
- From Reference 1
2.0 1.8 I. 6 I. ll I. 2 c,, 1.0
- u.
0.8 0.6 0 Li
- r 0.2 0.0 f:--:---:-------------------------1~
POWER I HCREASED TO TOUCH 2ND LINE SEGMENT AT 10.5, 0
2
.ll 6
8 10.
12 I ll CORE HEIGHT (FT)
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Figure 2. Mass Velocity - DECLG (C0 = 0.4)
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Figure 4. Heat Transfer Coefficient - DECLG (C0 = 0.4)
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Figure 5. Core Pressure - DECLG (C0 = 0.4)
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Figure 6. Break Flow Rate - DECLG (C0 = 0.4)
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Figure 7 - Core Pressure Drop - DEC LG (Co= 0.4)
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Figure 8. Peak Clad Temperature - DECLG (C 0 = 0.4) 350 l!OO i
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Figu~e 10. Core Flow - Top and Bottom - DECLG (C0 = 0.4)
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Figure 11a. Reflood Transient - DECLG (Co== 0.4) Core Inlet Velocity 500
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Figure 11b. Reflood Transient - DECLG (C0 = 0.4) Downcomer' and Core Water Levels
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Figure 12. Accumulator Flow (Slowdown) - DECLG (C 0 = 0.4)
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Figure 13. Core Power Transient - DECLG (Co= 0.4) j I ]--.)
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Figure 14. Break Energy Released to Containment N
of:
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