SAS,
Get down in your bunker mate and we'll let you know when it's all clear.
If you're struggling for rations, go to the local store and acquire a load of honey as it has an indefinite shelf life.
Three feet of earth cover should give a protective factor of at least x1000. Stay down there for a fortnight, then you can come out for brief periods for the next month or so. After that, wash fruit and veg thoroughly to decontaminate. Don't eat the 6 legged cows.
Good luck
Edit: Excessive sideslip by No.2 finger