ML19105A835

02/17/1978 Letter Attached Analytical Study to Justify Continued Use of the Center-Peaked Axial Power Shape as the Limiting Shape in the LOCA-ECCS Analysis

ML19105A835
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
Download: ML19105A835 (24)

Text

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Fi:EC: c,;:::;E E G 1~iRG: STALLINGS C M OOCDATE: 02/17/78 VA ELEC &i- Pl.JR DATE RCVD: 02/21/78 NF:C DOCTY-F'E: 'LETTER NOTARI ZED: *NO COP IE:=; RECEIVED SUB,JECT: LTR 1 ENCL 40 ANALYTICAL STUDY TO JUSTIFY CONTINUED USE OF THE CENTER-PEAKED AXIAL POWER SHAPE AS THE LIMITING SHAPE IN THE LOCA-ECCS ANALYSIS.

PLANT NAME:SURRY - UNIT 1 REVIEJ...JER INITIAL: XRL

UF.'.F.'.Y - UN IT 2 DISTRIBUTER INITIAL

• • • • • • • • • • • • • • • • • DISTRIBUTION OF THIS MATERIAL IS AS FOLLOWS******************

GENERAL DI:::;TRIBUTION FOR AFTER I:=SUANCE OF OPERATING LICENSE.

CDISTRIBUTION CODE A001)

FOR ~1CT I ON: BR CHIEF SCHWENCER**W/7 ENCL INTEF:NAL: C: ~G FIL:E**W/ENEL r8~ E-W!iliZA~Eli;ft_.

> NRC PDR*"*l.J:/ENCL OELD**LTR ONLY HAN~1UER**l.J/ENCL CHECl<**W/ENCL.

EISENHUT**W/ENCL SHAO**W./ENCL BAER**l.J./ENCL BUTLER**W/ENCL GRIMES**W/ENCL J COLLINS**W/ENCL J. MCGOUGH**W/ENCL I. LPDR***s EXTERNAL:

WILLIAMSBURG, VA**W/ENCL TI C**l.J/ENCL N:3 I C**W./ENCL ACRS CAT B**W/16 ENCL I

I DI :::;TR I [::UT I ON: I_ TR 40 ENCL :3'? CONTROL NBR:

IZE: 1P+'22F'

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • THE END **************************~

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February 17, 1978 Mr. Edso~ G. Case, Acting Director Serial No. 092 Office of Nuclear Reactor Regulation FR/MLB Attn: Mr. Robert W. Reid, "chief LQA/DWSjr:kbo Operating R~actors Branch No~ 4. Docket Nos. 50--280 Divi*sio"n of Reactor Licensing . .50-281 U. S. Nuclear Regulatory Commission License Nos. DPR-3~.

Washi_ngton, D. "c. 20555

• DPR-37*

Dear Mr. Case:

In our letter of August 26~ 1977 (Serial No. 372) and October 14,. ~

1977 (Serial No. 403B), we requested an amendment to Operating- Licenses DPR-32 and DPR-37 for the Surry Power Station, Units No. 1 a*nd 2 *. The amendment requested was a change to the Technical Specifications desig-nated as Change No. 57. The :changes to the Technical Specifications*

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 analy.tical studies to. justify the continued use of the appropriately adjusted standard design* (center-peaked) axial power shape as the 1 im it i ng shape in the LOCA-ECCS analysis. The required anal y_-

t i ca 1 study has bee*n completed and is doctunented in the Attachment. The results of the study justify t~e continued use of the appropriately adjusted standard design (center-peaked) axial power shape in all LOCA-ECCS analysis performed for Surry Units No. l and*2.

Should you have any quest ions, we would be most happy to meet with you at your earliest convenience.

Very truly yours,

u. m..;.dt-at~~

C. M. Stallings Vice President-Power Supply and Production Operations Attachments cc: Mr. James P. O'Reilly, Director

• Office of Inspection and Enforcement R_egion 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

e Ari 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 Reference 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 i;;hape was then adjusted to yield a F~g equal to the Technical Specifications limit for F~H,~g~A. 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.cl~d 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 axi.al 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 flooding 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 Plockage case still shows a significantly higher result than the FLECHT case and thus complies with NRC requirements. The results of this I

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 been' initially obtained between the results from the FLECHT case and the results from the steam cooling model without flow blockage case.

Additional results 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 Evaluati*on Model: Supplementing Information", April 1975, (Westinghouse Electric Corporation).

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, TABLE 1 COMPARISON OF CALCULATED PF.AK CLAD TEMPERATURES FOR SKEWED POWER DISTRIBUTION CASE Calculated Peak Clad Temperature (°F)

Case (Power Distribution) A B C Cos:ine Power Shape 2177. 2104. 2086.

10.5' Power Shape 2109. 2084. 1988.

A - Steam Cooling Model with Blockage Geometry B - Steam Cooling Model without Blockage Geometry C - FLECHT

TABLE 2 TIME SEQUENCE OF EVENTS COMPARISON FOR DECLG (Cn=0.4)

Skewed Shape (sec) Cosine Shape (sec)*

START 0.0 0.0 Reactor Trip Signal 0.646 0.649 S. I. Signal 2.25 2.26 Acc. Injection 15.8 15.8 End of Bypass 23.6 23.71 End of Blowdown 26.83 27.94 Pump Injection 27.25 27.26 Bottom of Core Recovery 37.13 37.18 Acc. Empty 55.:30 55.46

• From Reference 1

• TABLE 3 e COMPARISON 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\% 5.94 7.4 Local Zr/H20 Location, Ft. 11.0 9.0 Total Zr/H20 RXN, % <0.3 <0.3 Hot Rod Burst Time,sec. 25.9 24.2 Hot Rod Burst Location,Ft. 2.75 6.0

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