Nuclear weapon using the energy released during the fission of U-235 or Pu-239. The explosive force of a nuclear weapon is indicated in kilotonnes (kt) or megatonnes (Mt) of TNT equivalents (TNT (trinitrotoluol) is a chemical explosive). The bombs dropped on Hiroshima (U-235 bomb) and Nagasaki (Pu-239 bomb) had an explosive energy equal to 13 and 22 kt TNT. In each case about 1 kg fission material was fissioned in one millionth of a second. A minimum mass of fission material is required for a nuclear blasting charge, e.g. 52 kg of U-235. The highly developed weapon technology in the nuclear weapon countries partly enables lower values, e.g. 15 kg and less for metallic U-235. An ignition device is also required to shoot these fission materials together to a critical configuration within a very short period so as to initiate the chain reaction. Experts quote a velocity of some kilometres per second for weapon plutonium and a multiple of this impact velocity is necessary for reactor plutonium with its high share of other plutonium isotopes. See ‘hydrogen bomb’.


Type of fission

Quantity in kg

as a metal

as an oxide

Weapon plutonium 10 30
Reactor plutonium >13 40
93% enriched U-235 52 100
3% enriched U-235 (LWR-fuel) not possible not possible
U-233 16 40

Estimated minimum quantity of fission material for nuclear blasting charges.

According to UNSCEAR 504 atmospheric explosion (plus 39 safety tests) and 1879 underground explosions were carried out till mid of Februar 2013.