Depends how much is released
Anybody within 20 miles of the cloud is given the full dose
By the time it hits the US it going to be alot less
Higher then normal background radiation but not going to cause death. Reason it going to spread out.
When it focused in one area you have problems it why they are moving people away from the plant.
12 miles right now standard measures
I think anybody within 25 miles is going to have damage done if it goes.
This image is based on wind patterns and how much could be released
Saying that
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For details i doubt this is going to happen soo far it only going to effect the local area. Unless they can't get the cooling systems under control it yet to reach melt down (which is going to cause that cloud)
Don't worry