The SGTS in unit 1 has two units capable of filtering 1800 m3/h each, capturing > 97% of iodine. In unit 2 and 3 there are also two units, capable of filtering 2700 m3/h each, capturing > 99.9% of iodine (source: http://fukushima.grs.de/sites/defaul...2011-06-08.pdf
-- page IV-15).
It's a good system except you can't use it when you really need it, because it needs power for its electric blowers and dehumidifiers and can't cope with high temperatures or pressures or very rapid releases.
The weight of 1800 m3 of steam at 100 deg C and 1 bar is just about a single ton of water. You can see how this was not designed to clean up vent gases from a boiling suppression chamber holding thousands of tons of water.