7. The neutrons can strike other uranium atoms and cause additional fission and the continuing process of fissioning is known as a chain reactor.>> 8. Since two or three neutrons are liberated in each of fission whereas only one is required to mainta in a fission cha in. it would seem that once the fission reaction were initiated in n mass of fissile material, it would readily sustain itself>> 9. However, such is not the case because not all the neutrons produced in fission are available to carry on the fission chain, that is, some neutrons are lost in nonfission reactions(mainly r adioactive capture), whereas other neutrons escape from the system undergoing fission.>> 10. The minimum quantity of such material that is capable of sustaining a fission chain is call ed the critical mass UNIT 5 GENERAL FEATURES OF NECLEAR REACTORS<OS 1.A device in which nuclear fission energy is released in a controlled manner is called n uclear reactor 2. In outline. a reactor consists of an active core in which the fission chain is sustained a nd in which most of the energy of fission is released as heat.>> 3. The core contains the nuclear fuel, consisting of a fissile nuclide and usually a fertile material in addition.>> 4. The function of the moderator is to slow down the high-energy neutrons liberated in th e fi 5. The purpose of reflector is to decrease the loss of neutrons from the core by scattering back many of those which have escaped.>> 6. The heat generated in the reactor is removed by circulation of a suitable coolant, such as ordinary(light) water, heavy water, liquid sodium(or sodium-potassium alloy ), air and hel Ium etc.>> 7. The higher the temperature of the steam, the greater the efficiency for conversion into 8. If the energy released in the reactor is to be converted into electric power, the heat m ust be transferred from the coolant to a working fluid to produce steam. > 9. Reactor control, including startup, power operation and shutdown is generally by movin g control rods. >>7. The neutrons can strike other uranium atoms and cause additional fission and the continuing process of fissioning is known as a chain reactor.>> 8. Since two or three neutrons are liberated in each of fission whereas only one is required to maintain a fission chain, it would seem that once the fission reaction were initiated in a give n mass of fissile material, it would readily sustain itself.>> 9. However, such is not the case because not all the neutrons produced in fission are available to carry on the fission chain, that is, some neutrons are lost in nonfission reactions (mainly r adioactive capture),whereas other neutrons escape from the system undergoing fission.>> 10. The minimum quantity of such material that is capable of sustaining a fission chain is call ed the critical mass. UNIT 5 GENERAL FEATURES OF NECLEAR REACTORS<O 1. A device in which nuclear fission energy is released in a controlled manner is called n uclear reactor.>> 2. In outline, a reactor consists of an active core in which the fission chain is sustained a nd in which most of the energy of fission is released as heat.>> 3. The core contains the nuclear fuel, consisting of a fissile nuclide and usually a fertile material in addition.>> 4. The function of the moderator is to slow down the high-energy neutrons liberated in th e fission reactor.>> 5. The purpose of reflector is to decrease the loss of neutrons from the core by scattering back many of those which have escaped.>> 6. The heat generated in the reactor is removed by circulation of a suitable coolant, such as ordinary(light) water, heavy water, liquid sodium(or sodium-potassium alloy), air and hel ium etc.>> 7. The higher the temperature of the steam, the greater the efficiency for conversion into useful power.>> 8. If the energy released in the reactor is to be converted into electric power, the heat m ust be transferred from the coolant to a working fluid to produce steam.>> 9. Reactor control, including startup, power operation and shutdown is generally by movin g control rods.>>