ML20195H518
| ML20195H518 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood, 05000000 |
| Issue date: | 11/09/1988 |
| From: | Chrzanowski R COMMONWEALTH EDISON CO. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| References | |
| 5314K, IEB-88-008, IEB-88-8, NUDOCS 8811300444 | |
| Download: ML20195H518 (2) | |
Text
Commonwealth Edison l
On? First National Pit,2a. Chicago, lihnois a
Address R: ply to: Post Othce Box 767 Chicago, lllinois 60690 x
November 9, 1988 Mr. Thomas E. Mur?.ey, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Byron Station Units 1 and 2 Braidwood Station Units 1 and 2 NRC Bulletin 88-08 Additional Information HRC_Duket_Itoru__ fig-4HL4jis and 50 _iM/_411
Dear Mr. Murley:
Telephonically, on November 1, 1988, a meeting was held between Commonwealth Edison and members of the NRC Staff. At that time, a request fo~ additional information regarding clarification of the Westinghouse report MT-SME-427(88) Rev 1. relating to stratification and thermal cycling issues.
A specific question about the assumptions and the valaes of U (net thermal resistance between fluid and snblent) and Keff (effective thermal conductivity) was asked. The enclosure to this letter contains the explaination of how these values were calculated and the intended purpose of the thermohydraulic calculations.
Please direct any further questions on this matter to this office.
Very truly you Gt480f R. g arzanowski Huglear Licensing Administrator
/ sci 5314K Encl.
ces Byron Resident Inspector Draidwood Resident Inspector S. P. Sands Region III Office 00444 00110s G
ADOCK 050
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Attachment For, estimating tom)erature on unisolable pipe sections Wostinghouse constructed a grap1 titled "Effect of Molecular Conduction and Froo Convection on Axial Temperature Distribution" (Figure 2-1 in the referenced report).
The methodology was developed by Westinghouse based on lieat and Mass Transfer by ERG Eckert, McGraw-lii11,1959 Edition.
Calculations woro performed for cylindrical fin models with water (at 2500 psig and 600'F).
Schedule 160 pipe and 2-inch calcium silicato insulation (K - 0.025 Btu /hr-ft2*F) were assumed.
Th resistance between insulation and air was 1 Btu /hr-ft 'FIthermal Based on 2
those assumptions, U was calculated to be 0.13 Btu /hr-ft 'F.
As for Keff, calculation is presented as follows:
Koff -
effective increase in normal molecular water thermal conductivity K to account for free convection currents based on experimental data.
Assume delta T = 300'F over 7 ft. of pipe Grashoff number: Gr is approximately - to 1.7 x 10I4 Prandt1 number:
Pr is approximate Gr x Pr - 3.4 x 10 g to 2.0 From figure 11-14 of Eckert (p. 331, 1959 od.),
K2ff is approximately - to 250.
K This is a typical number for the convection case, for the conduction caso, Kaff would be equal to 1.
K The curve labeled "Conduction" can be applied to unisolablo pipe sections where only conduction heat transfer is possible (e.g., vertical downward segments).
The curve labeled "Free Convection" is for pipe segments whero convection heat transfer is possible (e.g., vertical upward pipe segments).
The purpose of the graph is to allow for qualitative assessment of temperature on unisolable pipe sections.
Those estimates are needed for two purposes:
i)
Tu comparo which location on the unisolable section has the highest
~
pipe metal tnmporature.
Since thermal stress is arosortional to change in temperature over time, the location witi t1e highest (relatively speaking) temperature will be subjected to the highest thermal stress should valvo leakage occur.
These locations are recommended for ISI and temperature monitoring.
ii) To provide an expected temperaturo range for guidance in temperature monitoring.
Based on the temperature estimated at the monitoring locations, a i 25'F range was given to allow for environmental uncertaintios such as insulation misalignment, forced convection on the reactor coolant loop, etc.
Temperature estimations based on thermohydraulic calculations are inherently inaccurate. Westinghouse recognizes the limitations of such calculations and has only used them for estimation purposos.
,