Fizzle (nuclear explosion)

A fizzle occurs when the detonation of a device for creating a nuclear explosion (such as a nuclear weapon) grossly fails to meet its expected yield. The bombs still detonate, but the detonation is much less than anticipated. The cause(s) for the failure can be linked to improper design, poor construction, or lack of expertise.^[1][2] All countries that have had a nuclear weapons testing program have experienced some fizzles.^[3] A fizzle can spread radioactive material throughout the surrounding area, involve a partial fission reaction of the fissile material, or both.^[4] For practical purposes, a fizzle can still have considerable explosive yield when compared to conventional weapons.

In multistage fission-fusion weapons, full yield of the fission primary that fails to initiate fusion ignition in the fusion secondary (or produces only a small degree of fusion) is also considered a "fizzle", as the weapon failed to reach its design yield despite the fission primary working correctly. Such fizzles can have very high yields, as in the case of Castle Koon, where the secondary stage of a device with a 1 megaton design fizzled, but its primary still generated a yield of 100 kilotons, and even the fizzled secondary still contributed another 10 kilotons, for a total yield of 110 kT.