LAS VEGAS (AP) - Government scientists conducted an underground nuclear materials experiment Friday at the Nevada Test Site, the National Nuclear Security Administration said. The subcritical experiment, dubbed Piano, involved detonating high explosives to chart the behavior of plutonium in a non-nuclear explosion. It did not trigger a self-sustaining nuclear reaction, NNSA spokesman Kevin Rohrer said. Scientists from the Lawrence Livermore National Laboratory in California completed the test at 1:44 p.m. in a cavern 960 feet below ground, Rohrer said. No abnormalities and no surface damage were reported at the vast site, about 85 miles northwest of Las Vegas....