Controlled or uncontrolled, this is a process in which neutrons released in fission produce additional fissions
If each neutron releases two more neutrons, then the 
number of fissions... [DOC] [TLE] Controlled Nuclear Fission | Nuclear Fission | Science ... [PAR] To maintain a sustained controlled nuclear reaction, for every 2 or 3 neutrons 
released, only one must be allowed to ... if it is greater than one it will grow 
uncontrolled (an atomic explosion).