ML20214P232
| ML20214P232 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 05/26/1987 |
| From: | Ainger K COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 3120K, TAC-63350, NUDOCS 8706030259 | |
| Download: ML20214P232 (5) | |
Text
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- One First National Plaza, Chicago, IEnois
- k " ;2 Address Reply to: Poet Omco Box 767
'd Chica00. IEncis 60600 0767 May 26, 1987 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
Subject:
Byron Station Units 1 and 2 Essential Service Water Cooling Towers TAC No. 63350 NRC Docket Nos. 50-454 and 50-455 References-(a): ' January 14, 1987 letter from K.A. Ainger to H.R. Denton (b): November 3, 1986 letter from l
K.A. Ainger to H.R. Denton l
l
. Gentlemen:
l l.
References (a) and (b) imposed operating restrictions on Byron Station because preoperational test data on the essential service water (ESW) cooling towers indicated a heat removal capacity that.wan lower than the initial design value. Until further cooling tower testing could be completed, a commitment was made to place the units in a shutdown condition upon occurrence of a'high ambient wet-bulb temperature. We have re-evaluated the basis for this temperature restriction and concluded that the assumptions-for the restriction are overly conservative.
The analysis in reference (b) that formed the basis for the wet-bulb temperature restriction assumed a steady state heat load on the cooling towers resulting from a LOCA in one unit and normal shutdown in the other unit. In actuality, the LOCA heat load peaks at approximately 100 seconds into the transient and then tapers off to a lesser value.
Furthermore, that analysis did not take credit for the amount of heat that could be absorbed into the water in the ESW system. The attached evaluation shows'that when the time dependence of the LOCA heat load and the heat capacity of_the essential service water are considered, the wet-bulb temperature restriction is not necessary to prevent exceeding the Technical Specification limit of 98'F for ESW pump discharge temperature.
Based on this analysis, we propose to delete the wet-bulb temperature restriction presented in reference (b) and modified in reference (a). In place of that restriction, we are proposing a temporary operating limit of 90'F on the ESW pump discharge temperature.
8706030259 870526 PDR ADOCK 05000454 P
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.;~. This limit will assure the Technical Specification limit of 98'F for ESW pump discharge temperature will not be exceeded following a design basis accident with the design basis wet-bulb temperature. Upon completion of the ongoing cooling tower testing program, this temporary operating restriction on ESW pump discharge temperature will be re-evaluated.
~ prompt NRC review and approval of this proposed ESW temperature limit is necessary to avoid restrictions on plant operation during the ensuing weather conditions where high ambient wet-bulb temperature is likely.
Please direct any questions regarding this matter to this office.
Very truly yours, Is#'
l\\.
K. A. Ainger Nuc1 car Licensing Administrator Attachment cc:- Byron Resident Inspector NRC Region III Office 3120K
y. c:
Re-evaluation of Wet-Bulb Temperature Operating Restriction 4
Essential Service Water System Functional Requirement The essentia1' service water system (SX) cooling towers are required to limit the SX pump discharge water temperature to less than or-equal to 98'F.to ensure adequate cooling for critical safety related equipment. This temperature limit is to be maintained during the worst case heat load on the towers, which results from a LOCA in one unit and simultaneous normal shutdown in the other unit.
Existing Evaluation (Wet-Bulb Restriction)
Because of the apparent reduction in cooling capacity of the SX towers,-an operating restriction, based on high wet-bulb temperatures, was placed on the plant to ensure meeting the SX system. functional requirements. The basis for this restriction is set forth in reference (b).
Figure 1 (attached) of this reference shows SX cooling tower heat removal capacity as a function of ambient wet bulb temperature. The line at 580 x 106 Btu /hr represents the peak heat load imposed on the tower from the LOCA and the normal shutdown.
For conservatism, this analysis assumed
.that the peak-load was constant over time and therefore plant operation was-restricted to times when cooling capability of the towers exceeded this load. No credit was taken for the time dependence of the load nor the heat capacity of the SX cooling system water inventory..Hence, operating l
restrictions were placed on the plant where the " performance curves" in Figure 1-intersected.the imposed-load at wet-bulb temperatures of approximately 67.8'F for three cell operation and 77.5'F for four cell operation. These temperatures were later reduced to 65'F and 75'F for additional conservatism as requested by NRC and'as stated in reference (a).
T Time-Dependent Heat Load Evaluation The LOCA heat load, as shown in Figure 2, is a' time dependent function that peaks at.about 100 seconds at a value ot 556x106 Btu /hr.
Using this LOCA load. profile in a time-dependent model for the cold water temperature, a. limit on initial starting cold water temperature can be established. Using conservative' assumptions of a starting BSW pump discharge temperature of 90'F, an ambient Wet bulb temperature of 78'F, and three cooling tower cells operating, the resulting ESW pump discharge temperature peaks at a value less than 98'F.
This analysis makes use of the thermal capacity of the water in the cooling tower basins and associated piping as well as the time dependence of the LOCA heat load. The heat load on.the towers is assumed to result from a LOCA in one unit and normal shutdown in the other.
We therefore propose to limit the ESW pump discharge temperature to less than or equal to 90'F in-place of the limit on wet bulb temperature. This restriction will not apply during cooling tower h
performance testing unless a tornado warning is issued.
In the event of a-tornado warning in the vicinity of the station during cooling tower performance testing, testing will be stopped and action will be taken to reduce the ESW pump discharge temperature to 90*F.
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