Nuclear explosions are not controlled. Nuclear reactors are controlled.

The first controlled nuclear reaction in the US was on December 2, 1942.

The first nuclear explosion in the US was on July 16, 1945.

When and what explosion? One of the nuclear test shots. If so which?

Remember Chernobyl was not a nuclear explosion, it was a steam explosion and graphite fire.

The only nuclear explosions in Japan were the two in WW2, on Hiroshima and Nagasaki.

However I believe you meant the Japanese nuclear reactorexplosion, which was not a nuclear explosion it was either a steam explosion and/or a hydrogen/oxygen chemical explosion. That occurred at Fukushima.