Post-Accident Activated Charcoal Fire

[UncaBuffalo]

Quick question about what could cause a fire in your charcoal filtration after a dropped fuel bundle accident.  I've got a text that says it's the decay heat from the fission gases...I'd always heard before it was some exothermic reaction with the activated charcoal...?

[tr]

Decay heat from halogens is the cause of the concern (most FSARs have information on charcoal filter loading).  The real concern is that too much decay heat can increase the charcoal tempberature such that the trapped radioactive materia is released.

Per the Nuclear Air Cleaning Handbook
https://hss.doe.gov/NuclearSafety/ns/techstds/standard/hdbk1169/

Protection of Carbon-Filled Adsorption Systems
To prevent loss of confinement for radioactive iodine and iodine compounds, carbon-bed temperatures must be maintained at a level where impregnants and trapped radioiodine cannot desorb. This requires the bed(s) to be large enough that specific loadings of iodine cannot exceed 2.5 mg/g of carbon, and that airflow through the bed can be maintained at some level in excess of 6 (preferably 10) linear fpm. If bed temperatures can be maintained below the level where desorption of impregnants and trapped radioiodine takes place, carbon ignition is unlikely. If a fire should start, however, total flooding or dumping of the carbon into a container of water is the only effective means of extinguishing a carbon bed fire that is known at this time. Carbon dioxide and gaseous nitrogen are ineffective against activated carbon fires because the fire feeds on the oxygen adsorbed in the pores of the carbon, and the quantity of liquid nitrogen required to provide effective cooling would be unavailable in most cases.

[UncaBuffalo]

Decay heat from halogens is the cause of the concern (most FSARs have information on charcoal filter loading).  The real concern is that too much decay heat can increase the charcoal tempberature such that the trapped radioactive materia is released.

Per the Nuclear Air Cleaning Handbook
https://hss.doe.gov/NuclearSafety/ns/techstds/standard/hdbk1169/

Protection of Carbon-Filled Adsorption Systems
To prevent loss of confinement for radioactive iodine and iodine compounds, carbon-bed temperatures must be maintained at a level where impregnants and trapped radioiodine cannot desorb. This requires the bed(s) to be large enough that specific loadings of iodine cannot exceed 2.5 mg/g of carbon, and that airflow through the bed can be maintained at some level in excess of 6 (preferably 10) linear fpm. If bed temperatures can be maintained below the level where desorption of impregnants and trapped radioiodine takes place, carbon ignition is unlikely. If a fire should start, however, total flooding or dumping of the carbon into a container of water is the only effective means of extinguishing a carbon bed fire that is known at this time. Carbon dioxide and gaseous nitrogen are ineffective against activated carbon fires because the fire feeds on the oxygen adsorbed in the pores of the carbon, and the quantity of liquid nitrogen required to provide effective cooling would be unavailable in most cases.

Okay, that makes sense...THANKS!

[alphadude]

isnt the heat generation from the mechanical process of sorption with some contribution from decay. (the iodine would be in the form of an iodate possible CsI.)  charcoal will heat upon sorption of many chemicals other than iodine. regeneration of charcoal is performed by heating the material and driving out the organics or absorbed material, thus the release potential.

[Already Gone]

I can relate from experience that any smoke from any fire in containment that gets sucked into your charcoal will releasemost if not all of the radioactive material that is trapped in the medium.  It seems that the charcoal has a higher affinity for smoke particles than it does for Iodine, or anything else.

[alphadude]

likes like like  organic to organic