noun
nuclear weapons test
Refers to the testing of nuclear weapons, including underground, atmospheric, and underwater tests.
その国は地下で核兵器実験を行った。
That country conducted an underground nuclear weapons test.
核実験 is a broader term for any nuclear test, while 核兵器実験 specifically refers to tests of nuclear weapons.
Compound of 核兵器 (nuclear weapon) and 実験 (experiment, test).