ML19351D625

Forwards Comparative Analysis of Natural Circulation Between Diablo Canyon & Farley to Justify 800922 Assumption That Results of Prototype Testing Would Be Similar for Both Plants

ML19351D625
Person / Time
Site:	Farley
Issue date:	10/06/1980
From:	Clayton F ALABAMA POWER CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
NUDOCS 8010140288
Download: ML19351D625 (4)

Text

s AED:ms Power Company 600 North 18tn Street Post office Box 2S41 Birmingham. Alabama 35291 Telephorie 205 250-1000 F. L. CLAYTO N, JR.

m Senior Vice President Alabama Power tre sout.nem evrtrc system October 6, 1980 Docket No. 50-364 Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention: Mr. A. Schwencer Gentlemen:

In our September 22, 1980 submittal to the commission in response to Mr. R. L. Tedesco's letters of August 25, 1980 and September 10, 1980, Alabama Power Company answered questions re-lated to Cold Shutdown (BTP 5-1). In the response to Question 5 related to prototype testing of cooldown under natural circula-tion flow and attendant boron mixing, Alabama Power Company stated that the results of such tests to be conducted at Diablo Canyon would be reprocentative of results which would be expected for the Farley Gait 2. As committed to in the September 22, 1980 sub-mittal, enclosed is a comparative analysis of the natural circula-tion between Diablo Canyon and Farley Nuclear Plant justifying this assumption.

If there are any questions, please contact us.

Very truly yours, C '

N O m s~ Y..

F. L. Clayton, Jr.

FLC/HRF :nac Enclosure cc: Mr. R. A. Thomas Mr. G. F. Trowbridge Mr. L. L. Kintner (w/ enclosure)

Mr. W. H. Bradford (w/ enclosure) )O b s

/ I 801014o

{

COMPARISON OF FARLEY 2 TO DIABLO CANYON Farley Unit 2 and Diablo Canyon Unit 1 have been compared in detail to ascertain any differences between the two plants that could poten-tially effect natural circulation flow and attendant boron mixing.

The general configuration of the piping and components in each reactor coolant loop is the same in both Farley 2 and Diablo Canyon. Both plants have Model 51 steam generators and Model 93A reactor coolant pumps, and the elevation head represented by these components and the system piping is the same in both plants.

To compare the natural circulation capabilities of Parley 2 and Diablo Canyon, the hydraulic resistance coefficients were compared. The co-efficients were generated on a per loop basis to permit such a compari-son between a three loop and a four loop plant. The hydraulic resis-tance coefficients applicable to normal flow conditions are as follows:

Diablo Canyon Unit 1 Farley Unit 2

-O Reactor Core & Internals 7.6 x 10- 10.7 x 10 f t/ (loop gpm) 2 Reactor Nozzles 36.8 33.4 RCS Piping 24.0 24.0

, Stgam Generator 114.4 114.6 182.8 182.7 Flow Ratio arley 2 _)

Diablo Canyon / =

182.8)l/2 =1 182.7/

The general arrangement of the reactor core and internals is the same in Farley 2 and Diablo Canyon. The coefficients indicated represent

_ the resistance seen by the flow in one loop. As exhibited, the differ-ence between the internals of a three loop and a four loop plant results l

in a higher coefficient for Farley 2.

l The reactor vessel outlet nozzle configuration for both plants is the i

same. The radius of curvature between the vessel inlet nozzle and downcomer section of the vessel on the two plants is different. Based on 1/7 scale model testing performed by Westinghouse and other litera-ture, the radius on the vessel nozzle / vessel downcomer juncture in-fluences the hydraulic resistance of the flow turning from the nozzle

~

to the downcomer. The Diablo Canyon vessel inlet nozzle radius is significantly smaller than that of Farley 2, as reflected by the higher coefficient for Diablo Canyon.

G The resistance (coefficient) for the RCS piping for both plants is the same.

l

[,- . _ . . . . . -

]

t .

a Details of the specific steam generator units were also compared to ascertain any variation (e.g., primary volume, tube height, tube dia-meter) that could affect natural circulation capability by changing the effective elevation of the heat sink or the hydraulic resistance seen by the primary coolant. It was concluded that there are no differences in the design of the steam generators in the two plants that would affect the natural circulation characteristics.

F As indicated, the difference between the total resistance coefficients

, for the two plants la insignificant. It is expected that the relative effect of the coeff:.csints would be the same under natural circulation conditions such tha : the natural circulation loop flowrate for Farley 2 would be essentially equivalent to that for Diablo Canyon.

The coefficients provided reflect the flowrate and associated heat re-

moval capability of an individual loop in the plant. The comparison, therefore, does not take into consideration the number of loops avail-able nor.the core heat to be removed. An evaluation of the Farley 2 Steam Relief and Auxiliary Feedwater Systems has been performed to dGmonstrate that cooling can be provided via two steam generators' 1 following the most limiting single active failure, i.e., the failure of an atmospheric relief valve. Loop natural circulation flow is dependent on reactor core decay heat which is a function of time based on core power operating history. Under natural circulation flow con-ditions, flow into the upper head area will constitute only a small percentage of the total core natural circulation flow and therefore

will not result in an unacceptable thermal / hydraulic impedance to the

-l y natural circulation flow required to cool the core.

e For typical 3-loop and 4-loop plants (including Farley 2 & Diablo Canyon) there are two potential flow paths by which flow crosses the upper head region boundary in a reactor. These paths are the head cooling spray nozzles, and the guide tubes. The head cooling spray nozzle is a flow path between the downcomer region and the upper head region. The temperature of the flow which enters the head 'via this path corresponds to the cold leg value (i.e. Tcold). Fluid may also

~

be exchanged between the upper plenum region (i . e. , the portion of the reactor between the upper core olate and the upper support plate) and the upper head region via the giide tubes. Guide tubes are dispersed in the upper plenum region from the center to the periphery. Because of the nonuniform pressure distribution at the upper core plate ele-vation and the flow distribution in the upper plenum region, the pressure in the guide tube varies from location to location. These guide tube pressure variations create the potential for flow to either enter or exit the upper head region via the guide tubes.

To ascertain any difference between the upper head cooling capabilities j between Diablo Canyon and Farley 2, a comparison of the hydraulic re-  !

sistance of the upper head regions was made. These flow paths were I considered in parallel to obtain the following results.

4 l A L

2

Diablo Canyon Unit 1 Farley Unit 2 Flow Area (ft 2) 0.77 0.67 Loss Coefficient 1.51 1.43 Overall Hydraulic Resistance 2.57 3.18 (ft'4)

Relative Head Region Flowrate (based on hydraulic resistance) 1.00 0.90 Head Region Flow Rate Relative to Loop Flow 1.00 1.20 As indicated above the effective hydraulic resistance to flow in Farley 2 is 1.24 times greater than DiaF'n Canyon. Assuming that the same pressure differential existed in - tn plants the Farley 2 head flow rate would be 90 percent of the ' ablo Canyon flow. Farley 2 is a 3-loop plant and Diablo Canyon is i-loop;.therefore, in terms of relative portions of loop flow commusicating with the head region, the Farley 2 head flow as a fraction of loop flow is 20 percent greater than the corresponding Diablo Canyon fraction. In addition the overall mass of metal associated with the Farley 2 upper head is significantly less than for Diablo Canyon due to the smaller physical size. Thus the upper head cooling capability at Farley 2 would be no worse and would likely be better than demonstrated by the Diablo Canyon natural circulation cooldown test.

It can, therefore, be concluded that the results of the natural circula-tion cooldown tests performed at Diablo Canyon will ba representative of the natural circulation and boron mixing capability of Farley 2. The results of these tests will be reviewed for applicability. A natural circulation cooldown test will be performed at Farley 2 if the Diablo Canyon prototype test does not provide satisfactory results during the first fuel cycle at Farley 2.

D E

3 1