A thermonuclear weapon, fusion weapon or hydrogen bomb (H bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lower mass, or a combination of these benefits. Characteristics of nuclear fusion reactions make possible the use of non-fissile depleted uranium as the weapon's main fuel, thus allowing more efficient use of scarce fissile material such as uranium-235 (235U) or plutonium-239 (239Pu). The first full-scale thermonuclear test was carried out by the United States in 1952 and the concept has since been employed by most of the world's nuclear powers in the design of their weapons. Modern fusion weapons essentially consist of two main components: a nuclear fission primary stage (fueled by 235U
or 239Pu) and a separate nuclear fusion secondary stage containing thermonuclear fuel: heavy isotopes of hydrogen (deuterium and tritium) as the pure element or in modern weapons lithium deuteride. For this reason, thermonuclear weapons are often colloquially called hydrogen bombs or H-bombs.