But a few -- approximately 0.7 percent in a U-235 - fueled reactor operating at steady - state -- are produced through the relatively slow radioactive decay of certain fission products .
Most neutrons ( the prompt neutrons ) are produced nearly instantaneously via fission .
A few -- approximately 0.7 percent in a U-235 - fueled reactor operating at steady - state -- are produced through the relatively slow radioactive decay of certain fission products .
Most neutrons ( the prompt neutrons ) are produced nearly instantaneously via fission .