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Code Manual for CONTAIN 2.0 - Federation of American Scientists

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DCH Heat Transfer. In the model <strong>for</strong> heat transfer between airborne debris and the gas, the only<br />

nondefault parameter setting recommended is the black-body multiplier (RADGAS) <strong>for</strong> debris-gas<br />

radiation. Given the particle size, this debris-gas heat transfer model is considered to be adequate.<br />

Effects <strong>of</strong> any uncertainties in this model will be qualitatively similar to, and smaller in magnitude<br />

than, the effect <strong>of</strong> the uncertainties in particle size upon the heat transfer rates. If sensitivity<br />

calculations <strong>for</strong> particle size are carried out, additional sensitivity studies involving debris-gas heat<br />

transfer parameters are not needed.<br />

The presence <strong>of</strong> dense clouds <strong>of</strong> hot aerosols during DCH events is expected to enhance atmospheric<br />

ernissivities above what is calculated by the <strong>CONTAIN</strong> default atmospheric emissivity model; hence<br />

the standard input includes specifying an atmosphere emissivity (GASSUR) equal to 0.8 during the<br />

DCH event. In code versions prior to <strong>CONTAIN</strong> <strong>2.0</strong>, this option is not available, but the user may<br />

specify KMX equal to -0.8 in the RAD-HEAT input block in order to obtain a similar result ins<strong>of</strong>ar<br />

as the DCH calculation itself is concerned. However, when this option is employed, the userspecified<br />

emissivity will be used <strong>for</strong> the entire calculation, not just during the DCH event. Hence<br />

the GASSUR option is preferred <strong>for</strong> <strong>CONTAIN</strong> <strong>2.0</strong>. However, a sensitivity calculation <strong>for</strong> the<br />

Sequoyah plant indicated that the inappropriate use <strong>of</strong> KMX = -0.8 prior to vessel breach had very<br />

little effect upon containment pressures (-0.001 MPa).<br />

Although dense clouds <strong>of</strong> hot aerosols have been assumed to enhance emissivities in defining the<br />

standard prescription, concerns do exist that the ernissivity could actually be reduced if the aerosol<br />

clouds are so dense that the optical mean free path is less than that <strong>of</strong> the thermal boundary layer,<br />

so that structures cannot “see” the hot gas/aerosol cloud beyond the boundary layer. In this event,<br />

the standard value could prove nonconservative. Little quantitative guidance as to the possible<br />

magnitude <strong>of</strong> this effect is currently available, however.<br />

Sensitivity studies given in Reference Wi195 <strong>for</strong> the SIWAET-3 and SNLOET-11 experiments<br />

indicated that use <strong>of</strong> the default radiation treatment or using KMX=- 0.4 had at most a moderate<br />

impact on AP (S 11% enhancement). Totally eliminating atmosphere-structure radiant heat transfer<br />

enhanced AP by 32% in the SNIJIET- 11 experiment, a relatively severe event in which high<br />

atmosphere temperatures resulted in radiation being especially important. Since totally eliminating<br />

radiant transfer is clearly unrealistic, even as a bound, we believe that more realistic uncertainty<br />

estimates are provided by running sensitivity calculations with the default radiation treatment ador<br />

with ISMX = –0.4.<br />

DCH Chemistry. The user <strong>of</strong> code versions prior to <strong>CONTAIN</strong> <strong>2.0</strong> should take care to specify the<br />

drop diffusivity (LIQSIDE) as in Table 13-1, which will eliminate drop-side reaction rate limits<br />

through an infinite drop diffusivity. The default diffusivity in the previous code versions, 10-8m2/s,<br />

can yield strongly nonconservative results; e.g., underpredicting hydrogen production by more than<br />

a factor <strong>of</strong> two in the SNLJIET-lR and SNIJIET-3 experiments, and underpredicting zIP by -35%<br />

<strong>for</strong> SNIAET-3, in which combustion <strong>of</strong> the DCH-produced hydrogen is a major contributor to the<br />

DCH load.<br />

The default value <strong>of</strong> the reaction threshold temperature (THRESH = 273.15) is obviously<br />

unrealistically low, but is specified <strong>for</strong> the standard prescription in order to avoid spurious quenching<br />

Rev. O 13-38 6/30/97<br />

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