That's not true anymore. The Hetz (Arrow) system, developed (mostly) in Israel claims consistent success in doing just that. Our American partners are happy with it, too. I really recommend that you read Cresson Kearney's "Nuclear Survival Skills". It was written by a doctor that participated in US nuke tests. To summer, Chernobyl (and Fukushima) scenarios are only reproducible by repeatedly nuking the same place. That laid aside, TWO WEEKS after nuking the radiation level allows half day work in the open, every day. Radiation level start high (not at time=0 though, it takes between 1 and 8 hours for the fallout to descend from the mushroom cloud) and decrease exponentially, halving every 7 hours.