ML19329C221

Forwards Revised Response to Question 9 of NRC 750225 Request for Addl Info Re ECCS Analysis.Updates 760517 Info

ML19329C221
Person / Time
Site:	Davis Besse
Issue date:	06/04/1976
From:	Roe L TOLEDO EDISON CO.
To:	Rusche B Office of Nuclear Reactor Regulation
References
NUDOCS 8002120941
Download: ML19329C221 (6)

Text

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Rev'ised Response to Question # 9 of the Requests

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( 1 Signed Cy, Received)

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Mr. Benard C. Rusche, Director .] ) ,

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Dear Mr. Rusche:

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The enclosed revised response to Question #9 o Itd W$'

AYts for Ad-ditional Information concerning the ECCS analysis ror Davis-Besse Unit 1 transmitted in your letter dated February 25, 1975 supersedes the response to Question #9 which was included in our letter dated May 17, 1976.

Yours very truly, d

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l 5 bio l TH2 TOLEGO EO! SON COMPANY EDISON PLAZA 300 MAOISON AVENUE TOLECO, OHIO 43652

Question 9 It is noted that no additional flow resistance was added toEvaluate the cold the 1 cgs ,,

due to the HP' pumps injecting ECC water during reflood. n effect of an additional 0.25 psi cold leg AP upon the reflood rate and cladding temperature.

For the LOCA limit analysis, compare the existing time at which the reflood rate goes below 1 in/see to the new time calculated using the additional cold leg resistance. .

Response -

To evaluate the impact of an additional 0.25 psi cold Icg AP upon the DE break at pump reflood transient, the 10 foot LOCA limit case (8.55 f t discharge, CD = 1.0, 17 kw/ft at the 10 foot elevation) was examined assuming k

two HP1 pumps availtble with injection points in both the broken and unbro en loop.

One half of one HPI pumps injection, however, was assumed to exit the The assumptions regarding break and be unavailable for core cooling purposes.

d in BAW-10.* '5; that is

,the other ECCS systems remained the same as reporte d active during the [

. one LPI pump and two core flooding tanks were assume transient.

The conditions stated above maximize the effect of the additional steam Other conditons, such as the venting resistance on the reflood transient.

use of one HPI with additional resistance in only one loop, would be less severe. The additional flow from the HPI system (no credit was taken for HP1 in BAW-10105) has the potential to produce a beneficial eff ect only Once the during the time period during which the downcomer is filling.

downcomer. liquid level reaches the bottom of the cold leg nozzle the ECCS I

injection capability is in excess of that required to maintain the downconer liquid level. Direct spillage of excess ECC fluid out the break then results.

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Thus, the actual magnitude of HPI flow would be relatively unimportant sin The additional for the majority of the transient, it spills out of the break.

AP in both loops of the reactor coolant system, however maximizes the stean venting resistance during the entire reflood transient.

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.,. 3 -t Table 9-1 shows a comparison of time average flooding r'ates between the reflood transients utilizing the normal assumption as used in BAW .0105 and the case where both HP1 pumps are available with the additional AP in both loops. As shown in Table 9.1, little difference is observed during the first 5 seconds of the reflood transient. The add!.ticnal injection (HP1) is able to counteract the incrcased resistance to steam venting.

During subsequent time intervals, however, a reduction in the flooding rate

'was observed. Over the 241 second time period shown, the flooding rate was reduced by approximately 1.4". In terms of peak cladding temperature, the inclusion of the additional cold leg AP produces an increase of approximately 35F at the 10 foot elevation. Calculations at both the 8 and 10 foot elevations within the core have been performed (NRC Question List 28, question 5) with the additional cold leg AP; the results are acceptable under 10CFR50.46. At the remaining lower elevation, the effect of the 0.25 psi cold leg AP on cladding temperature is expected to be le'ss severe. At these lower elevations, peak cladding te=peratures occur much earlier in the reflood transient when flooding rates are relatively high. Small changes in the ,

flooding rates during these early time periods would not significantly effect the resulting heat transfer and/or cladding temperature.

Prior to hot spot quench for the 10 foot LOCA limit case the flooding rates drop below 1 in/sec due to the partial equilization of the downcomer and core liquid levels. For the same cases shown in Tables 9-1, this occurs at 264.8 see (BAW-10105 assumptions) and 261.6 see af ter the end of blowdown with the additional 0.25 psi cold leg AP. The subsequent steam cooling period was also extended from 12.8 see to 18.8 see when the 0.25 psi cold leg AP was used. This 6 second increase in the steam cooling period would n'

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only slightly impact the cladding temperature just prior to, the hot spot quench, and would have little or no impact on the overall transient because peak cladding temperatures occur earlier in the transient. Further discussion of the impact of the 0.25 cold Icg AP and also steam cooling is presented in B&W responses to NRC Questien list 28. .

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Time Average Flooding Rates Table 9-1 Flooding Rates Time Intervals -(in/s) Wich 0. 25 pt:1 __

Af ter the End _ Normal AP

Asstrrp tionr_

of Blowdown .,

l (s) l 1 -

0-9 2.880 2.884' 9-14 2.265 2.294 14-20 1.878 1.930 1.611 20-30 1.650 30-50 1.417 1.443 1.218 50-100 1.231 100-200 1.075 1.084 200-250 I

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