Australia has the largest uranium reserves, but I've never heard radon mentioned here as a concern, so I assume it just comes down to the reserves being very specifically located.
>In 1990, ARPANSA conducted a nationwide survey of more than 3300 Australian homes to determine the radiation dose to the Australian population from exposure to natural background radiation, including radon. Based on this survey, the average concentration of radon in Australian homes is about 10 Bq m⁻³. This is less than in many other countries and compares to a global average indoor value of 40 Bq m⁻³. Average radon levels in Australian homes are only a little larger than the radon levels in outside air and are of minimal concern to health.
