[Toaster]

I`m not sure how deep such a shelter would have to be on average to lessen the radioactivity within the shelter.
True, a rather hearty supply of clean potable water and other conumables is a must let alone a place to store "waste" in a fashion that wouldn`t be self defeating.
My first thoughts are "wheel" weights ground up and mixed with a latex or other "heavy body paint" to offer add`l protection. For the sake of argument, would you think radiation levels would decline to low enough levels any time soon or would you be doomed to life in a shelter?
Lets say a total of a 1 Giga-ton exchange where Australia were not directly attacked but impending radiation from the exchange was to arrive in say 2 months. Furthering this analogy would be that the moving radiation cloud (fallout) was at average 250 rads and only slightly diminishing.
At the point where this fallout reaches Australia, the estimated "potency" of this cloud would be 200 rads.
Lets also assume, that the background radiation is 20 rads and will climb at a rate of 5 rads per day begining on the 60th day.