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Code Manual for CONTAIN 2.0 - Federation of American Scientists

Code Manual for CONTAIN 2.0 - Federation of American Scientists

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13.3.2.4 Cavity Models. When using the cavity models, the user should recognize that the basic<br />

physics governing debris dispersal fractions and entrainment rates is extremely complex. The new ~<br />

models incorporated in the <strong>CONTAIN</strong> code represent the best available models <strong>for</strong> these processes,<br />

but are still highly simplified approximations <strong>of</strong> a complex and not fully understood phenomena.<br />

The use <strong>of</strong> these models involves large uncertainties, and the models’ per<strong>for</strong>mance and ability to<br />

predict behavior as part <strong>of</strong> an integrated systems analysis code such as <strong>CONTAIN</strong> has not yet been<br />

carefully assessed against all <strong>of</strong> the available experimental database. As a result, the <strong>CONTAIN</strong><br />

Project is very interested in receiving feedback from users.<br />

The user should be extremely carefid when defining all <strong>of</strong> the many user-defined parameters that are<br />

required by the entrained fraction and entrainment rate models in <strong>CONTAIN</strong>. Some guidance on<br />

parameter selection is provided below, and the user is urged to review the original references <strong>for</strong><br />

these models when questions tise. Some <strong>of</strong> the entrainment rate and entrained fraction models are<br />

complex, and have been developed from an experimental database in specific geometries and under<br />

low temperature conditions. The models in CONTNN are meant to be applied to a variety <strong>of</strong><br />

different circumstances, but the governing parameters provided in input must be carefully selected<br />

to ensure that the model per<strong>for</strong>ms as intended in the geometry and under the conditions <strong>of</strong> the<br />

specific <strong>CONTAIN</strong> application.<br />

13.3.2.4.1 Entrainment Rate. An entrainment rate model must be specified through the lENRAT<br />

parameter. If no entrained fraction option is specified through the IENFRA parameter, the<br />

entrainment and ejection <strong>of</strong> debris from the cavity will be controlled completely by the selected<br />

entrainment rate model. The total fraction <strong>of</strong> debris that is dispersed from the cavity depends on the<br />

integrated entrainment rate over the course <strong>of</strong> the calculation, and can be controlled by selection <strong>of</strong> ~<br />

the cavity constant I& (CCENR) or the other input parameters <strong>for</strong> the selected rate model.<br />

13.3.2.4.2 Entrained Fraction. If an entrained fraction model is invoked through the IETFRA<br />

parameter, the entrainment rate in the cavity will be modified within the code to produce the<br />

calculated or specific total fraction dispersed. At the moment gas blowthrough occurs, the gas flow<br />

area that will be used between the RN and cavity cells <strong>for</strong> the duration <strong>of</strong> the entrainment depends<br />

on the user input. If no value <strong>of</strong> AHENF has been specified, the code will calculate the gas flow area<br />

internally. If AHENF has been specified in input, the code will use that value. If TSTOP has been<br />

specified in input without AHENF, the gas flow area will change linearly from its value at the time<br />

<strong>of</strong> gas blowthrough to the value calculated internally by the code over the time interval t~lOWto t~lOW<br />

+ “tstop,” where t~lOWis time <strong>of</strong> gas blowthrough. If TSTOP has been specified in conjunction with<br />

AHENF, the gas flow area will change linearly from its value at the time <strong>of</strong> gas blowthrough to the<br />

value specified in AHENF over the time interval t~lOWto t~lOW+ “tstop.”<br />

When an entrained fraction model is invoked through the IENFRA parameter, it is possible to<br />

speci& the entrainment interval through the input parameter TDISP. However, the user should be<br />

cautious when invoking this option. If TDISP is specified, the entrainment rate will produce the<br />

desired total fraction dispersed over the specified interval. However, the sudden end <strong>of</strong> entrainment<br />

in the cavity may produce a sharp drop in both temperature and pressure in the cavity if the<br />

entrainment rate was still high at the cut<strong>of</strong>f time, depending on the entrainment rate model and the<br />

Rev O 13 52 6/30/97

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