fast

slow

in bulk

static

used fuel should be reprocessed

moderator should be used

coolant should be employed

control rods should be used

chain reaction can be initiated

it becomes uncontrollable

it explodes

it produces no power

infinite

zero

exactly balanced by the loss of neutrons through leakage

initiated

at the lower rate than the consumption

at a higher rate than the consumption

at an equal rate of the consumption

depends on other considerations