it has more B.E. per nucleon than Iron-56 then it can only be ssioned and if it has less than it can only be fused. The further from the B.E. per nucleon of Iron-56 it is, the easier it is to fuse or ssion
2.6.3 The nuclear ssion reactor
We look at the basic parts of most nuclear ssion reactors. The key components are the control rods, the moderator and the coolant.
Control rods The control rods absorb neutrons. They are used for two purposes, to control the reaction and in the event of emergency, to shut it down. They start lowered and are raised to obtain a sustainable chain reaction (that is not out of control, i.e. not a weapon). The material used must a very good neutron absorber with a high melting point, a good example is high boron steel.
Moderator The moderator is used to slow down neutrons in order to increase the probability of ssion. A moderator should be a poor absorber of neutrons because we don’t want to absorb the neutrons, we need them for the ssion! Hence we need the moderator to be made of a material with a light nucleus to increase kinetic energy transferred and minimise absorption. Examples of moderators include graphite and steel.
Coolant The coolant controls the temperature of the reactor and takes away the thermal energy to our steam turbine and generator in order to generate electricity. The coolant should be a uid (liquid/gas) with a high heat capacity that doesn’t absorb neutrons or become radioactive. Examples of coolants include water and super-heated steam.
Another important de nition is chain reaction, which is where more neutrons come out than are put in; a chain reaction can either be exponentially increasing (i.e. a weapon) or equilibrium (or thereabouts) as is the case in a reactor used to generate electricity. You should also note that the waste from a ssion reaction is extremely problematic since it is highly radioactive (and will be for a long period of time).