ML19093B048

Submit Requested Analytical Study to Justify Continued Use of Appropriately Adjusted Standard Design (Center-Peaked) Axial Power Shape as Limiting Shape in LOCA-ECCS Analysis

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 Serial No. 092 Office of Nuclear React.or Regulation FR/MLB Attn: Mr. Robert W'. Reid, thief. LQA/DWSj r: kbo Operating Reactors Branch No. 4 Docket Nos. 50-280 Divisio~ of Reactor Licensing 50-281 U.S. Nuclear Regulatory Cornmissio*n License Nos. DPR-32*

Washington, D. C. 20555 DPR-37

Dear Mr. Case:

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

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 I . (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 C Cosine 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 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 Time 1 sec. 25.9 24.2 Hot Rod Burst Location,Ft. 2.75 6.0

• From Reference 1

2.0 1.8 f:--:---:-------------------------1~ TO TOUCH POWER 2ND I HCREASED LINE SEGMENT AT 10.5, I. 6 I. ll I. 2 c,,

u. 1.0 0.8 0.6 0

• Lir 0.2 0.0 0 2 .ll 6 8 10 . 12 I ll CORE HEIGHT (FT)

N

,I=

co I

Figure 1 en I [_I _ I_ .. !

I f  ! i

}

--1 100 50 u

UJ Cl) 1 N 0

-I-LL co

-50 1-u 0

w -100 Cl)

Cl)

<t

-150

-200 e 0.1 2 ii 6 I .0 2 ii 6 10 2 ii 6 100 2 . . ij 6 1000 TIME {SECONDS)

NI CD.

I Figure 2. Mass Velocity - DECLG (C 0 = 0.4) -.- - ~::. ---~ r* -

I ! LI

-* --1,.: ***--------

! :~:

I .2

........ I .0 I-z:

w

(..)

0::

w 0..

0.8 0

_J LL 0.6 LL 0

I-

_J 0 ,ll

<(

O' 0.2 0.0 ~~..___,__..._.._._...L.L..l...l.-~--L-~L........J'--'-...L.J......I....LJ~~...L--l...--L-...L-L...L..L..1-1-~--L~.L-.L...L-L.L..LLI

.~**.

0.1 0.2 0.4 0.6 1.. 0 2 4 6 10 2 4 6 10 2 2 4 6 10 3 TIME (SECONDS)

-N

-i=

CD I

0 Figure 3. Fluid Quality - DECLG (Co= 0.4)

! . / I i

. I

.. *~**...-*,

!.  :*.t!

IOOO 6

N lj.

-I-LL r- I ~2.75'

, 2 I-al I-z:

100 I I LU 0

-LL LL LU

.6

4. '"

0 0 2 µ* u 1111 I L_ 11.00'

(/)

z:

10 a:::

I- 6 I-

< 4, UJ

c 2

I I0 Il 50*, I I I I I I I I 00 150 200 250 300 350 lj.QQ e TIME (SECONDS}

N of:

' U)

I U)

Figure 4. Heat Transfer Coefficient - DECLG (C 0 = 0.4) *-**-- --*-

I .1 * .. [ ,

2500 2000 I .........

<(

Cl) 0.. 1500 LU ec::

Cl)

Cl)

LU 0:::

1000 0..

500 0 e 0 5 10 f5 20 25 30 35 lJO Tl ME ( ~ECONDS)

- I N

+=

co I

00 Figure 5. Core Pressure - DECLG (C 0 = 0.4) ------ **~***--*--*-*-**

l  ! ! .. ! . !

1.IOE+05 9 .OOE+OlJ.

-( ..)

-1.1.J

(/)

co

_J 7 .OOE+ OlJ.

3: 5 .OOEtOI~

0

_J u..

~

<(

1.1.J 0:::

co 3 .OOE+OLJ.

I ;OOE+OlJ.

-1 .OOEtOlJ.

0 5 10 I5 20 25 30 35 lJ.0 TIME (SECONDS)

N

~

co l.

Figure 6. Break Flow Rate - DECLG (C 0 = 0.4) __----- --_*- --.J-.

I I I I. I I .I*

IT 50 U) 25 0...

0...

0 a::

Cl 0

a::

0...

LJ.J a::

0 u -25

-50

-70 0 5 10 15 20 25 30 35 ijQ e TIME {SECONDS) tO I

U1 Figure 7 - Core Pressure Drop - DEC LG (Co= 0.4) . _- _*****. -* J

. I LL._l __ J

i I \

I 2500 u..

0.__.

2000 0

0 a::

f-0

x:

1500 0..

E w

f-(!)

. 1000 2. 75:

~

Cl

....J c.,

500 0

0 50 100 150 200 250 300 350 l!OO TIME {SECONDS)

N

~

(0 I

w Figure 8. Peak Clad Temperature - DECLG (C 0 = 0.4)

l~~**--**,~---"""7-*----.....

• • !l r -- r*11=~1

-_ -fi

. I

....._ .... -.-~----- ~.,

2000 1750

........ 1500 LL 0

w 1250 0::

J I-

<(

0::

w 1000 0..

rfi 2.75' I- 750 _

0

J

...I LL 500 250 0

0 50 100 150 200 250 300 350 IJOO _

TIME (SECONDS)

• N

.f:

<O I

.f:

Figure 9. Fluid Temperature - DECLG (Co= 0.4)

---

****-J r- ....1 I

I I t L :

D

• • 1 .. <  :*;i 7000

. I i

5000 *

-0 2500 LJJ Cl) al

...J LJJ I- 0 a:::

3:

0

...J LL N*

I

-2500

-5000

-7000 0 5 10 I5 20 25 30 35 ijO . e TIME ( SECOtWS)

N 4=

co U1 Figu~e 10. Core Flow - Top and Bottom - DECLG (C 0 = 0.4)

I

\ -ii .

• --***** 1 2.00 I. 75 c:..:,

UJ Cl) z:

I. 50 I. 25 I

II UJ 1.00 I:-

<t a:::

0 0.75 0

0

....J LL 0.50 0.25 0.00 I e

0.0 100 200 300 ijQQ 500 I TIME (SECONDS) i I

I I

Figure 11a. Reflood Transient - DECLG (Co== 0.4) Core Inlet Velocity

. *-* ....J -

I I !. I  !

f.;

I i **

1I I

( .,

1~1:1- i'

\

~- --i r

---

I.

z:

20.0 rn 0

• n L

11.5 DOWNCOMER I --i n,

-S,

...J UJ 15.0 I-12.5 I I

~I rn C,

. J:,.

0

z 0

(/)

UJ

...J 10.0 I ~**

0

(/)

0::::

UJ C f-

<( 7.5 tD

(/)

3: *... rn,.---

CORE *..a C:

n, 5.0 I- I I I :z:

-I

2. 5 I--.. I __..,........-- I ":x>

~I I I

o.o 0 100 200 TIME (SECONDS) 300 llOO 500

1(/)

rn

("")

-i I

z N

.f=

U) l>

Figure 11b. Reflood Transient - DECLG (C 0 = 0.4) Downcomer' and Core Water Levels L I. LI

tI:

6000 '1 5000

( .)

!+000 UJ en al

_J 3: 3000 0

_J LL

E:

(.) 2000

(.)

<(

1000 0 ...__ _____._ _ ___.__ _ ___._....___ ___,___ _ __.__ _ __.__ _ _.....___ ____,

0 5 10 15 20 25 30 35 TIME (SECONDS)

N of:

CD I

of:

Figure 12. Accumulator Flow (Slowdown) - DECLG (C 0 = 0.4) ***- ... _*. _J-I ! I I l .J I .1

: j ..I ]-- .) .!

1.0 -r:

11 i

0.8 - I.

.e

- 0.6 -

-0 a..

a..

0:::

UJ

~

0 0. ti -

a..

0.2 ,-

L o.o 0

I 5

I 10 I

15 I

20 I

25 I

30 35 I

!JO e

TIME (SECONDS)

<O I

0)

Figure 13. Core Power Transient - DECLG (Co= 0.4) -T I I I !

. I I I I.. I

5. 50E+07 . - - - - - - - - - - - - - - - - - - - - - - " ' - - - - - - - - - - ,

LJ.. 50E+07

(.)

e UJ Cl)

, 3. 50E+07 I-cc C!J 0::

2. 50E+07 UJ z:

UJ UJ I. 50E+07 0::

co

5. OOE+06

-5. OOE+ 06,____ ___._______...___ __._ _ _........__ _ _...___ ____._ _ __..__ ___,

0 5 10 15 20 25 30 35 4-0 TIME {SECONDS)

N of:

CD I

Figure 14. Break Energy Released to Containment ""'

I ! \ I l*