ReactorSystem used to initiate, maintain and control a fission chai... in which the fuelSee 'nuclear fuel'. is a mixture with the moderatorMaterial used to "decelerate" fast neutrons to low energies,... or coolantAny substance used to remove the heat in a nuclear reactor. .... Liquid homogenous reactorSystem used to initiate, maintain and control a fission chai...: e.g. uraniumNatural radioactive element with the atomic number 92. The n... sulphate in water; solid homogeneous reactorSystem used to initiate, maintain and control a fission chai...: e.g. mixture of uraniumNatural radioactive element with the atomic number 92. The n... (UO2) in polyethylene.