Introduction to Nuclear Reactor Terminology. 
Types of Fissionable Materials: There are three known fissionable 
isotopes known which can be used to support a chain reaction in nuclear 
reactors. These are: yn? , y33 and pue??. Only y?? exists in nature. 
Tt occurs as an isotope of the element uranium in an abundance of 0.71%. 
The others, y33 and pur”, are produced by transmutations that follow 
neutron capture in the parent materials mh-3- and w38 respectively. 
These latter two are known as fertile materials. 
The Fission Event: The fission event occurs with a certain probability 
function after a neutron is adsorbed in the nucleus of a fissionable material. 
The fissionable material then splits into approximately two equal fragments 
known as the fission products. Energy is released as kinetic energy of 
fission fragments, high energy neutrons, beta particles and penetrating 
electro-magnetic radiation. Most importantly, more than two neutrons are 
released in this splitting process. 
Neutrons, which have no charge, can penetrate the nucleus of a fission- 
able atom to produce an unstable state which causes fission. One of the 
neutrons produced in each fission event goes to produce another fission, 
thus continuing the chain reaction. The other one=-plus neutrons are 
available for capture by inactive reactor components and by a fertile 
material such as m3 or y3 to produce the other fissionable materials 
Pun> and p33 in the following manner: 
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If more than one neutron can be captured by a fertile material for each 
fission event, more fissionable material can be produced than is consumed in 
fission. This desirable circumstance is known as breeding. 
DECLASSIFIED 
