A chain-like process of knock-on and suprathermal fusion events due to the introduction of a primary 14-MeV neutron is examined, on the basis of transport equations for neutrons and recoil ions of all possible generations. In reactor-grade DT pellets, the ratio of suprathermal-fusion to primary 14-MeV neutrons becomes 0.1 or more. The maximum energy of neutrons leaking out of the pellet surface reaches to 45 MeV, though the population above 30 MeV is negligibly small.