Again it should be pointed out that even if your water filter CAN filter out radioactive particles, you very much do NOT want that then-contaminated filter anywhere near you. The water won't be radioactive, but that filter sure as hell will be! If you're seriously concerned about it, what you need is a pre-filter to get those radioactive particles out of the water BEFORE your water source ever gets into your house (or shelter, if that's what you're trying to do).