MacArthur couldn’t use nukes for two reasons:

1. There would have been immediate condemnation and retaliation from the USSR and China, the former of which had nukes of their own at the time.
2. Nukes were used against Japan because the US concluded that they would lose millions of troops in a conventional invasion because the Japanese would rather fight to the last man than surrender. The Korean War was also on a much smaller scale than WWII, and Congress had not declared war on Korea.

The radiation hazard symbol was created by members of a nuclear research group at Berkley in 1946. The symbol was adopted because it was simply, easy to discern at a distance, and symbolized radiation coming from an atomic nucleus. Kind of does look a film reel too though, never saw that before.

Fukushima is habitable a decade after the accident because

1. Much of the radioactive material spilled into the ocean and was carried away.
2. The contaminated topsoil was removed and replaced.
3. The Japanese learned from Chernobyl how not to cleanup after a meltdown and implemented better practices.

Total death toll from Three Mile Island: 0, though a slight uptick in cancer cases was detected in the surrounding area.