This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Nuclear Reactor Components”.
1. Which nuclear fuel is usually used in thermal nuclear reactor to create fission?
a) U234
b) U235
c) U236
d) U237
View Answer
Explanation: In a thermal nuclear reactor the fission induced by neutrons using a fuel isotope U235 is one of the several isotopes used in nuclear power generation. Fuel isotopes which are capable of being fissioned by thermal neutrons are called fissile’s.
2. 90Th232 is fertile isotope produced by fission.
a) True
b) False
View Answer
Explanation: 90Th232 is a fertile isotope produced by nuclear fission. 90Th has 6 naturally occurring isotopes, none of these isotopes are stable; however, one isotope, 232Th is relatively stable, with a half life of 1.405× 1010 years, considerably longer than the age of earth.
3. Which parts function is to reduce the energy of fast neutrons to thermal neutrons in nuclear power plant?
a) Moderator
b) Coolant circulator
c) Control rods
d) Shielding
View Answer
Explanation: Function of moderator is to reduce the energy of fast neutrons to thermal neutrons. Due to high energy of fission neutrons relative to that required to trigger another fission event their probability of interacting with U235 is small.
4. What makes the best moderators in nuclear power plant?
a) Material with low atomic number
b) Materials with low atomic mass
c) Materials with high atomic number
d) Materials with high mass number
View Answer
Explanation: The moderator slows down the neutrons to thermal energies by collision with inert atoms (scattering). Speed of the neutrons is reduced within a small number of collisions as the moderator possesses a high scattering cross section. Materials with low atomic mass number make best moderators.
5. Select the desirable property of a moderator?
a) Moderator should absorb neutrons but slow down the neutrons as early as possible
b) It should have low thermal conductivity for better heat transfer
c) It shouldn’t be chemically unstable
d) It should have low resistance to corrosion
View Answer
Explanation: It should be chemically stable and should not e decomposed due to nuclear radiation. It should not absorb neutrons but slow down the neutrons as early as possible. It should have high resistance to corrosion as it has to work under high pressure and temperature.
6. What is used in nuclear reactor as a cooling method/device?
a) Coolant
b) Water jackets
c) Air cooler
d) Air vents
View Answer
Explanation: The coolant is used and its function is to remove the heat released by fission. The coolant should have high specific heat, high conductivity, good chemical stability, good pumping characteristics and low neutron absorption cross section. Coolant can either be liquid or gas.
7. Control rods are made of __________
a) Cesium
b) Cadmium
c) Tin
d) Gallium
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Explanation: Control rods are made of cadmium or boron or Hafnium. They have huge neutron absorption cross sections. The control rods are lowered or raised in the reactor core. Control rods are used in control rod assemblies and inserted into the guide fuels within a fuel element.
8. Reactor power is directly proportional to neutron density.
a) True
b) False
View Answer
Explanation: Reactor power is directly proportional to neutron density, lowering the control rods will remove neutron from the reactor core and will decrease the power and reaction rate and raising the control rods will increase the power and rate.
9. What types of rays are trapped by shielding?
a) Gamma rays
b) Beta rays
c) X-rays
d) IR rays
View Answer
Explanation: Shielding prevents the passage of radiation to the outside of the reactor. The primary shield prevents the leakage of neutron and gamma radiation present in the cooling circuits due to activation of coolant as passes through the core.
10. Shield is made of _________
a) Iron Metal enclosure
b) Concrete and water
c) Ceramics walls
d) Copper metal
View Answer
Explanation: Shield is frequently constructed in layers or heavy and light material like concrete and water. Shields for external circuit where only gamma radiation may be present is made up of steel, lead, polyethylene, concrete.
11. Which of the following part in a nuclear reactor minimizes the neutron leakage?
a) Shield
b) Control rods
c) Reflector
d) Moderator
View Answer
Explanation: Function of the reflector is to minimize the neutron leakage by reflecting them back into the reactor. The material used for reflector is same as that used for moderator. It scatters the neutrons that leak from core and returns the neutrons back into core by reflecting them.
12. In which of the following reactor is fission caused by slow or thermal neutrons?
a) Thermal reactor
b) Burner reactor
c) Fast reactor
d) Breeder reactor
View Answer
Explanation: A thermal reactor is a nuclear reactor that uses slow or thermal neutrons. Most nuclear power plants are thermal reactors and use neutron moderator to slow neutrons until they approach the average kinetic energy of the surrounding particles. Fission is caused by slow or thermal neutrons.
13. Which reactor has no moderator and its core size is less?
a) Fast reactor
b) Burner reactor
c) Thermal reactor
d) Breeder reactor
View Answer
Explanation: A fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons, as opposed to thermal neutrons used in thermal neutron reactors. The fission process is caused by fast neutrons and the reactor has no moderator and the core size less.
14. In which reactor is fertile material converted into initial fissile material?
a) Breeder reactor
b) Fast reactor
c) Burner reactor
d) Thermal reactor
View Answer
Explanation: A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. In this reactor fertile material is converted into initial fissile material. For e.g. natural uranium is the fuel, thorium is converted into U233.
15. Which reactor produces only heat?
a) Burner reactor
b) Breeder reactor
c) Thermal reactor
d) Intermediate reactor
View Answer
Explanation: Burner reactor is a type of reactor using U235 as fuel. Enriched uranium is used to increase efficiency. To prolong the fission reaction, fast neutrons are slowed down with a moderator and the rate of reaction is adjusted by control rods which can absorb neutrons. Some neutrons react to form plutonium, but in smaller amounts than the original uranium, and produces only heat as a product.
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