Nuclear weapons interfere with carbon dating
Pre-initiation can substantially reduce the explosive yield, since the weapon may blow itself apart and thereby cut short the chain reaction that releases the energy.
Nevertheless, even if pre-initiation occurs at the worst possible moment (when the material first becomes compressed enough to sustain a chain reaction) the explosive yield of even a relatively simple first-generation nuclear device would be of the order of one or a few kilotons.
Because of the preference for relatively pure Pu-239 for weapons purposes, when a reactor is used specifically for creating weapons plutonium, the fuel rods are removed and the plutonium is separated from them after relatively brief irradiation (at low "burnup").
The resulting "weapons-grade" plutonium is typically about 93 percent Pu-239.
Such physical characteristics make reactor-grade plutonium difficult to manipulate and control and therefore explain its unsuitability as a bomb-making ingredient.
The isotope plutonium-238 would typically consitute only 0.036 percent of weapons-grade plutonium.
For the production of weapons-grade plutonium with lower Pu-240 concentrations, the fuel rods in a reactor have to be changed frequently, about every four months or less.
Some nuclear weapons are typically designed so that a pulse of neutrons will start the nuclear chain reaction at the optimum moment for maximum yield; background neutrons from plutonium-240 can set off the reaction prematurely, and with reactor-grade plutonium the probability of such "pre-initiation" is large.
Because these even numbered plutonium isotopes are more radioactive, their presence accelerates the formation of defects that occur within the metal during alpha decay of plutonium.
While this yield is referred to as the "fizzle yield," a one-kiloton bomb would still have a radius of destruction roughly one-third that of the Hiroshima weapon, making it a potentially fearsome explosive.
Regardless of how high the concentration of troublesome isotopes is, the yield would not be less.
Pu-239 in the order of 90-95 %, is known as weapon-grade plutonium.
Plutonium containing lower concentrations, in the range of 50-60 % is known as reactor-grade plutonium.