Third Nuclear Device of Year Set Off Under Nevada Desert

PAHUTE MESA, Nev. —  A nuclear weapon nearly 12 times more powerful than the bomb that destroyed Hiroshima was detonated beneath the desert Tuesday in the third announced U.S. test of 1986. The test was condemned by the official Soviet news agency Tass, although the Soviet government had shunned an invitation to witness the blast.

Three anti-nuclear protesters were arrested for trespassing when they ignored government orders and crossed into the test site at the entrance about 40 miles from where the explosion took place.

The Greenpeace organization claimed four others were on the site at the time of the detonation, but their whereabouts were not immediately determined. Government officials said no one was observed near ground-zero at the time of the explosion.

Department of Energy spokesman Jim Boyer said the warhead, which had an explosive force of between 20 kilotons and 150 kilotons of TNT, was detonated without incident at 6:30 a.m. in a vertical shaft about 2,000 feet below the surface of Pahute Mesa.

The blast, code-named Jefferson, was felt slightly atop some high-rise buildings in Las Vegas, more than 100 miles away.

Tass said the continued U.S. testing ruins chances for a disarmament agreement.

“Washington . . . resorted to actions that complicate still more the tense situation in the world arena,” Tass said in a dispatch released in Moscow. “The nuclear explosions in Nevada dash the unique chance to set a real beginning in the disarmament process.”