People laughing at Australia might be missing the point. It's not only about scientific danger, but also about border security tradition. Australia is an island, and their border mindset is very different from land-border countries. That's why you can get huge penalties for bringing something as deadly as... a wooden chess, to enter Australia without declaration. Not to mention a piece of uranium. Respect the different culture please.
No need to respect a culture of paranoia and overcriminalization. The same culture is in the US with regard to lawful minority immigrants, do you respect it?
If the point is that bringing items into Australia could have a negative impact as they are not present (such as cane toads, rabbits, etc) then sure.
However, Australia already has much uranium. The mine at Rum Jungle has quite a lot left. Multiple nuclear explosions have taken place there.
This is not equivalent to keeping rabies out, nor a cultural issue.