radiation air flow Norway predicts

I was referred by other posts. Please check it out at the link. You may click the arrow on the right hand side to each area's radiation level.

http://transport.nilu.no/browser/fpv_fuku?fpp=conccol_I-131_region=DMANC1

This simulation shows a big

This simulation shows a big xenon plume again or shall I see, still going on.
Does anyone know why there is still so much xenon in the atmosphere?