ML20129D819

Rev 1 to Suppression Pool Scrubbing Efficency (Including Pool Bypass)

ML20129D819
Person / Time
Site:	Browns Ferry
Issue date:	06/13/1996
From:	Leaver D, Metcalf J POLESTAR APPLIED TECHNOLOGY, INC.
To:
Shared Package
ML19353D888	List: ML20129D562 ML20129D639 ML20129D737 ML20129D760 ML20129D786 ML20129D810 ML20129D819 ML20129D844 ML20129D874 ML20129D883 ML20129D891 ML20129D898
References
PSAT-04011H.04, PSAT-04011H.04-R01, PSAT-4011H.4, PSAT-4011H.4-R1, NUDOCS 9610250154
Download: ML20129D819 (6)

Text

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PSAT 04000U.04 i

PSAT Calculation 04011H.04

" Suppression Pool Scrubbing Efficiency (Including Pool Bypass)"

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PSAT 04011H.04 Page: 1 of 5 Rev: 0@2 3 4 CALCULATION TITLE PAGE CALCULATION NUMBER: PSAT 04011H.04 i

CALCULATION TITLE:

" Suppression Pool Scrubbing Efficiency (Including Poc! Bypass)"

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4 REASON FOR REVISION:

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0 -InitialIssue N/A I - Change ofReference 2 N/A i

Addition ofReferences 5 and 6 Addition of pool DF calculation in accordance with References 2 and 5 2

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PSAT 04011H.04 Page:

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Rev: 01 34 Table of Contents i

Section EAgt Purpose 2

Methodology 2

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Assumptions 3

References 3

Calculation '

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Resulta 5

Conclusions 5

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Purpose The purpose of this calculation is to determine the maximum removal efBeiency that can be credited for the passage of particulates and of elemental iodine (including Te-132 which is being treated as elemental I-132 except for half-life) through (and around) the Browns Feny suppression pool for the purpose of applying the revised DB A source term ofReference 1.

Methodology The overall methodology is that ofReference 2 except for timing (which is specified in Reference

1) and the suppression pool DF which is explicitly calculated below (see Calculation section) in lieu ofusing the minimum value of 10 given as a " default" in Reference 2. (Per Reference 2, "in j

the absence of detailed analysis, a [ suppression pod decontamination) factor of 10 [may be] used, j

dthough this is likely to be significantly lower than what would be calculated"). To account for pool bypass, a steam mass flow corresponding to 10 times the drywel storus vacuum breaker surveillnace test acceptance value is used. It is compared to the mass flow out of the drywell during and immediately after the source tenn release (referred to as the slow drywell sweep and the fast drf wel' sweep, respectively) to determine the bypass fraction. No removal credit is taken -

for the frada of the drywell sweep-out flow which bypasses the suppression pool. The overall pool DF (expressed as a " filter efBeiency") is calculated accordingly.

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PSAT 04011H.04 Page: 3 of 5 Rev: Oh 3 4 Assumptions Assumption 1:

There is no dynamic pressure drop through the vent system during either the slow sweep or fast sweep of the drywell.

Justification: The fast sweep-out of the drywell occurs with a vent flow of about 32 lbm/sec (Reference 3). As was discussed in Reference 3, during the blowdown of the reactor vessel for a DBA recirc suction LOCA all coolant is released except for a portion in the lower reactor vessel. Ifit is estimated that: (1) the total coolant released is of the order of 400000 lbm, (2) about 40% of that flashes to steam (Reference 3 calculates 38%), and (3) the blowdown requires not more than 30 seconds (the start of the gap release in Reference 1). Thus, the average steam flow through the vent system is about 5300 lbm/sec. Considering that the vent system differential pressure would not be expected to exceed 30 psid for such an event, and further that pressure drop would be, at worst, linear with flow (and at best, proportional to flow velocity squared), the differential pressure for a flow ofonly 32 lbm/sec would be expected to be in the range of 0.001 to 0.2 psid. For a vent submergence of 3.5 ft (Reference 4, Item 8.14) the static differential pressure (to clear the vents) would be about 1.5 psid. Therefore, at worst, the dynamic pressure drop, even for the fast sweep-out flow of 32 lbm/sec, would be of the order of 10 percent of the static pressure difference and can therefore be neglected.

References Reference 1: Soffer, L., et al., " Accident Source Terms for Light-Water Nuclear Power Plants",

NUREG-1465, February 1995 Reference 2: Leaver,.9. E., et al., " Licensing Design Basis Source Term Update for the Evolutionary Advanced Light Water Reactor", DOE /ID-10298, September,1990 Reference 3: PSAT 0401IH.01, " Volumetric Flowrate as a Function of Time from Drywell to Torus (and Return)", Revision 0 Reference 4: PSAT 04000U.03, " Design Data Base for Application of the Revised DBA Source Term to the TVA Browns Feny Nuclear Power Plant", Revision 0 Reference 5: Powers, D. A., and Sprung, J. L., "A Simplined Model of Aerosol Scrubbing by a Water Pool Overlying Core Debris Interacting With Concrete", NUREG/CR-5901, November,1993 Reference 6: PSAT 04002H.09, " Elemental lodine Filter EfBeiency in Main Steam Lines",

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Revision 0 Calculation i

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Results

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The overall efHelency of the suppression pool as a filter for removing particulate and elemental iodine is 0.72 during the slow sweep-out (prior to 7230 second:) and 0.95 during the fast sweep-out (from 7230 seconds to 7890 seconds).

Conclusions Because of the relatively low flowrate conesponding to the slow sweep of the drywell, the pool bypass (which is not sensitive to flowrate since it depends only on the hydrostatic pressure difference needed to clear the vents) is relatively large during that pasiod leading to a relatively low overall efficiency. During the high flow of the fast sweep the pool bypass is correspondingly smaller and the efficiency correspondingly greater.

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