ML20234D171
| ML20234D171 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood, 05000000 |
| Issue date: | 12/28/1987 |
| From: | Hunsader S COMMONWEALTH EDISON CO. |
| To: | Murley T NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM), Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8801060481 | |
| Download: ML20234D171 (3) | |
Text
_-_-
/^N Commonwealth Edison
) One First N:tional Plaza Chicago, lilinois
/
k U ] Address Rep!y to: Post Office Box 767
(,,/
Chicago, Illinois 60690 - 0767 December 28, 1987 Mr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 Attn: Document Control Desk
Subject:
Byron Station Units 1 and 2 Braidwood Station Units 1 and 2 Containment Recirculation Sump Screens NRC Docket Nos. 50-454, 455, 456 and 457
Dear Mr. Murley:
On December 15, 1987, a teleconference was held between Commonwealth Edison personnel and members of the NRC Staff. The purpose of the call was to discuss questions raised concerning the coolant flow velocity that occurs at the containment recirculation sump screens. At the conclusion of the call, the NRC staff requested that we provide additional information concerning this matter. This letter provides that additional information, which is presented in Attachment A, for NRC use. This information provides additional justification to support our compliance with Regulatory Guide 1.82, dated June, 1974, as committed to in the Byron /Braidwood FSAR.
please address any questions you may have concerning this matter to this office.
Very truly yours, A c. rLs S. C. Ilunsader Nuclear Licensing Administrator cc:
L. Olshan S. Sands NRC RIII Byron Resident Inspector Braidwood Resident Inspector I
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8801060481 871228 4040K PDR ADOCK 05000454 P
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ATTACHMENT A QU,ESTIONS REGARDING THE DESIGN OF THE CONTAINMENT RECIRCULATION SUMP SCREENS 1.
.Is the sump screen cover.ed.by water?.
The sump screen is totally submerged by l'2" of water during the recirculation phase following a LOCA. The top of the screen is at elevation 381'0".
The maximum flood level inside the containment following a large break LOCA is 5'2",
corresponding to a plant elevation of 382'2".
This is documented in calculation RAS-FL-1, Revision 1 dated 07/21/82, and in FSAR Appeadix A, page A1.82-1.
2.
Is the sump screen solid on the top?
Yes, the top deck of the sump screen is 1/4" stainless steel checkered plate.
(Reference drawing S-1065 and FSAR Appendix A, page A1.82-2.)
3.
Are all the sump screens for all four units identical?
The basic design of the sump screens is essentially identical for all four units. Minor as-built differences result in a small difference in the free surface area of the screens.
This is described further in the response to Question 4, below.
4.
What is the area of the recirculation sump screens fo.r..each of the. Byron
& Braidwood Units?
As stated in the response to Question 3, minor as-built differences result in a slight difference in the screen area for the Byron /Braidwood units. The table below lists the surface area of the recirculation sump screen enclosures for each unit. The surface area shown is the surface area of the screens which is unobstructed by the support steel. The area of the wire mesh making up the screen was not deducted from the free surface area listed below.
Surface Area Byron Unit 1 253 sq. ft.
Byron Unit 2 255 sq. ft.
Braidwood Unit 1 260 sq. ft.
Braidwood Unit 2 260 sq. ft.
4040K
l O
d j l
The screen areas were calculated from drawing S-1065 for all four units. The Braidwood Unit 2 screen size was verified by a field walkdown conducted by the S&L Braidwood site team. The free area of the screen openings is approximately 35% less than the above values, taking into account the wire mesh.
5.
How far in front of_the screen will the approach velocity be 0.2ft/sec?
At a distance less than 1" frorc the screen the approach velocity will be less than the recommended velocity of 0.2 ft/sec (Regulatory Guide 1.82).
The screen approach velocity is approximately 0.12 ft/sec based I
on the screen inlet area framed by structural steel.
The velocity through the screen is approximately 0.37 ft/sec with half of the free screen area blocked by debris deposited on the screen.
The flow through an opening in the screen is analogous to the flow through an orifice.
When utilizing an orifice for flow measurement, the upstream pressure tap is normally located 1 to 2 pipe diameters in front of the orifice, in an area of " undisturbed" flow.
Considering the 3/8" screen grid size, the " undisturbed" flow area would be approximately 3/4" in front of the screen (twice the screen opening of 3/8").
Therefore, over the distance approximately 1" in front of the screen, the approach velocity j
will increase from 0.12 ft/sec to the velocity through a screen opening of 0.37 ft/sec.
1 The table below indicates the various velocities calculated for the recirculation sump screens. All velocities are based on a flowrate of 13,600 gpm.
BASIS AREA VELOC.ITY original screen sizing calculation SI-03 with 50% blockage 198 sq. ft.
0.153 ft/sec Approach velocity approx. 1" in front of the screen based on the exposed screen surface area 253 sq. ft.
0.12 ft/sec Flow through 100% free screen area (openings of screen) 164 sq. ft.
0.185 ft/sec Flow through free screen area with 50% blockage 82 sq. ft.
0.37 ft/sec Away from screen with 5'2" water depth and full perimeter of screen 515 sq. ft.
0.06 ft/sec 4040K