ML20081D683

Forwards Justification for Raising Lower Containment Temp from 120 F to 125 F,Per 830922 Application for Amend to Licenses NPF-9 & NPF-17 Changing Tech Specs

ML20081D683
Person / Time
Site:	McGuire, Mcguire
Issue date:	10/26/1983
From:	Tucker H DUKE POWER CO.
To:	Adensam E, Harold Denton Office of Nuclear Reactor Regulation
References
TAC-52390, TAC-52391, NUDOCS 8311010299
Download: ML20081D683 (3)

Text

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Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attention: Ms. E. G. Adensam, Chief Licensing Branch No. 4 Re: McGuire Nuclear Station Docket Nos. 50-369, 50-370

Dear Mr. Denton:

Our letter of September 22, 1983 requested amendments to the Technical Specifications for McGuire Units 1 and 2 (License Nos. NPF-9 and NPF-17). The proposed amendments would involve allowing che containment lower compartment temperature to be between 120 and 125'F for up to 90 cumulative days per calendar year provided the lower compartment temperature averaged over the previous 365 days is less than 120*F.

Temperature information obtained since our original request now indicates that the existing temperature limit of 120*F will be exceeded any day now. When this occurs, both units will be required to shutdown. Therefore, we request that the proposed amendments be issued on October 26, 1983 and made immediately effective as an emergency license amendment, pursuant to 10 CFR 50.91. (a) . (5) .

The containment cooling system uses the cool, hypolimnion region near the bottom of Lake Norman for cooling water. Whenever the warmer lake surface cools suffi-ciently to mix with the hypolimnion region, the containment cooling water tempera-ture increases about 4-5'F. Based upon past experience, lower containment ambient temperature will increase about l'F for each 1*F increase in cooling water tempera-ture. Temperature profiles of the lake indicate that the mixing will occur any day now, depending upon weather conditions.

At the time of our original submittal, it could not be conclusively determined from containment temperature data that the 120*F limit would be exceeded when the lake " turnover" occurred; however, since that time, containment temperature has gradually increased. On October 26, 1983, Unit 1 lower containment tempera-ture was greater than 118'F while all four cooling units operated at full speed and the spray mist cooling system was operating. The same day, Unit 2 exceeded 120*F and entered the Action Statement of the Technical Specification. Later that day, Unit 2 experienced an inadvertent reactor trip and a decision was made to remain shutdown for several days to resolve an unrelated problem.

Based upon the preceding discussion, it is clear that the McGuire units will be derated by the failure to issue the proposed amendments in a timely manner and that Duke Power has not delayed application to take advantage of the emergency provisions of 10 CFR 50.91.

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liarold R. Denton I October 26, 1983 I Page 2 Attached is additional information in support of our original submittal which more specifically addresses the effects of the proposed amendments on plant response during a design-basis accident.

Very truly yours,

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ltal B. Tucker C.

REll:j fw cc: Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street NW, Suite 2900 Atlanta, Georgia 30303 Mr. W. T. Orders NRC Resident Inspector McGuire Nuclear Station i

JUSTIFICATION FOR RAISING THE LOWER CONTAINMENT TEMPERATURE FROM 120*F to 125'F The impact on the FSAR safety analysis of increasing the allowable lower containment temperature from 120*F to 125'F has been evaluated. This evaluation has identified two potential concerns regarding the containment response to a LOCA.

The first concern is the impact on the containment design basis analysis. The containment analysis assumes a low initial temperature of 100*F (Tech. Spec.

allowable is 100-120*F) in order to maximize the containment air mass. (FSAR pp 6.2-18, item 10). A higher initial air mass results in a higher peak pressure.

Since the proposed change is an increase in temperature, the impact on the con-tainment response would not be an increase, but rather a decrease in peak pressure.

Therefore, the increase in temperature does not affect the containment design basis analysis.

The second concern is the impact on the containment backpressure used in the LOCA analysis. This backpressure is important in that it affects to some degree, the reflooding rate and potentially the peak clad temperature. The minimum contain-ment pressure response for LOCA backpressure is given in FSAR Figure 15.4.1-62.

However, for simplicity, the reflooding analysis assumed only a constant back-pressure of 1.7 psig, which bounds the pressure response and is only applicable for the time period of 75 to 85 seconds. The minimum pressure is greater than 2.0 psig subsequent to 200 seconds. Since the impact of increasing the contain-ment temperature does result in a reduction in the containment pressure response, there is a potential for an adverse impact on the PCT. The following arguments demonstrate that this impact is negligible.

The only significant impact of increasing the containment temperature on the initial conditions fer a LOCA analysis, is a decrease in the initial containment air mass. The pressure response of the containment to a lower initial air mass can be determined by evaluating the partial pressure of air for each of the two initial air masses. Assuming the maximum containment free volume of 1,217,900 ft 3 (FSAR Table 15.4.1-2), the containment air masses are 83,339 lb (120*F) and 82,627 lb (125*F) . At the time of core reflood, the containment temperature can conservatively be assumed to be 200*F per FSAR Figure 15.4.1-65. The partial pressure of the 120*F initial air mass heated to 200*F is 16.73 psis. The partial pressure of the 125*F initial air mass heated to 200*F is 16.58 psia.

The effect of the lower initial air mass is only -0.15 psi.

Since the containment backprescure for LOCA analysis assumed a constant 1.7 psig, the existing FSAR analysis is valid except for the very brief duration where the containment pressure is less than 1.85 psig. This time period is limited to 70-90 seconds and 105-120 seconds following LOCA. The effect on the beginning of the reflood phase and on peak clad temperature of this very minimal reduction in containment backpressure for a very short duration is not significant. Many conservatisms are included in the minimum containment back-pressure for LOCA analysis (FSAR Table 15.4.1-2).

Based on the above justification, an increase in the allowable lower containment air temperature from 120-125'F does not adversely affect the results of the containment design basis analysis or the peak clad temperatures resulting from the LOCA analysis as stated in the FSAR.

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