Kurchatov was told to build a bomb by 1948, less than three years away. Stalin also put the ruthless Beria in charge of the project to insure its success.
A new urgency was felt by Stalin, Beria, Kurchatov, and the scientists. The West had the bomb and they showed the world that they weren't afraid to use it. Although they had defeated Germany as allies, relations between the Soviet Union and the west were already strained.
Soviets were afraid the United States would use the threat of nuclear
weapons to push their interests on the rest of the world. Although the
Soviet Union had greatly suffered during the War, Stalin had gained territories
and had lifted the Soviet Union to a super power. He did not want the
U.S. to take back what he had gained.
A Russian Scale