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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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13.3.2.3 RPV Models. When the RPV and cavity models are invoked, the user should remember<br />

that both an RPV and cavity cell must be designated, and that these two <strong>CONTAIN</strong> cells must be<br />

connected by a single flow path. Furthermore, a regular flow path must be used, not an engineered<br />

vent. The characteristics <strong>of</strong> this flow path must be specified as usual in the <strong>CONTAIN</strong> input, but<br />

the user should be aware that the presence <strong>of</strong> debris in the RPV cell will start the RPV and cavity<br />

models in <strong>CONTAIN</strong>. After this point, the RPV and cavity models take control <strong>of</strong> the flow path<br />

between the RPV and cavity cells according to the input that has been provided in the RPVCAV<br />

input section.<br />

The RPV models begin to function when debris is placed in the trapped debris bin in the RPV cell.<br />

The user may accomplish this in any manner allowed by <strong>CONTAIN</strong>; however, the user should be<br />

aware <strong>of</strong> the physical situation the RPV models were intended to model. The models are primarily<br />

designed <strong>for</strong> a situation in which a large initial mass <strong>of</strong> molten debris resides in the RPV cell, and<br />

is moved out <strong>of</strong> the RPV through single-phase and two-phase debris ejection. It is recommended<br />

that the user place all the desired debris inventory into the trapped debris bin over a period <strong>of</strong> time<br />

smaller than the current <strong>CONTAIN</strong> timestep. The user can also specify debris initially by putting<br />

mass in the ATMOS block. It is possible to add and subtract debris in the RPV cell as the<br />

calculation progresses, but the user should be aware <strong>of</strong> how the individual RPV models function.<br />

The single-phase debris dischaxge model and the hole ablation model are insensitive to chmges in<br />

the amount <strong>of</strong> debris in the RPV, so long as the conditions <strong>for</strong> gas blowthrough are not created in<br />

the process <strong>of</strong> adding or subtracting debris. However, the gas blowthrough model was developed<br />

with the assumption that after the height <strong>of</strong> the debris surface above the RPV hole reaches a certain<br />

critical value, the amount <strong>of</strong> debris in the RPV will continue to decrease. Adding debris to the RPV<br />

cell after gas blowthrough has occurred may produce unexpected results, because the surface <strong>of</strong> the<br />

debris pool in the RPV might be returned to a value larger than the critical pool height required <strong>for</strong><br />

gas blowthrough. If debris is added to the RPV cell after gas blowthrough has occurred, the user<br />

should carefidly scrutinize the results to ensure that the RPV models continued to function correctly.<br />

13.3.2.3.1 Hole Ablation. The rate <strong>of</strong> hole ablation can be controlled through the use <strong>of</strong> the<br />

ARMULT parameter, which is a direct multiplier to the ablation rate; however, parts <strong>of</strong> the entrained<br />

fraction option rely on having a non-zero value <strong>for</strong> the ablation rate <strong>of</strong> the RPV hole. The safest way<br />

to create a fixed RPV hole size <strong>for</strong> a calculation is to set HFWALL to some very large value, rather<br />

than setting ARMULT to be zero.<br />

13.3.2.3.2 Gas Blowthrough. The time at which gas blowthrough occurs is calculated internally by<br />

the code. However, it can be manipulated indirectly by changing the RPV hole size or the RPV<br />

diameter. The initial hole size can be specified through the AHOLE1 parameter. Smaller hole sizes<br />

will prolong the single-phase debris ejection period, and lengthen the time until gas blowthrough<br />

occurs. If the entrained fraction option is invoked, the hole size can then be reset through the<br />

AHENF parameter after gas blowthrough occurs. A smaller diameter, which can be specified<br />

through the DIARPV parameter, will also lengthen the time until gas blowthrough occurs. The user<br />

cannot directly select a specific gas blowthrough time.<br />

O 13 51 6/30/97

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