The Soviet Union conducted an underground nuclear blast, its eighth since the Kremlin ended a 19-month testing moratorium on Feb. 28, the Tass news agency reported. The explosion at the Soviets' Asian test site near Semipalatinsk, in the republic of Kazakhstan, had a capacity of less than 20 kilotons, Tass said. One kiloton is the equivalent of the explosive power of 1,000 tons of TNT. The blast was made "to check results of research in the sphere of physics of nuclear explosion," Tass said. The news agency did not say whether the test was for military or other purposes.