Mechanical decoupling zones

In the event that the fan is not operating or the ventilation ducting is decoupled from the fan, there is no mechanism to draw contamination out of the SCBs. Release of hazardous material under these circumstances would occur at a rate determined by diffusion. Evaluations of transport of radionuclides under these conditions indicate that buildup of fission products in Zone 2 of the HCF several hours after the event is less than one microcurie. Transport of these fission products outside the confines of the HCF would be negligible, and dose consequences at 3000 meters would be negligible. 

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