Unit 2: Nuclear Energy- Energy Science and Engineering AKTU (B.tech)

Here We cover Unit 2: Nuclear Energy- Energy Science and Engineering AKTU (B.tech)
Topic Like : Fundamental forces in the universe, Quantum mechanics relevant for nuclear physics, Nuclear forces, energy scales and structure, Nuclear binding energy systematics, reactions and decays, Nuclear fusion,

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Important Questions For Energy science and engineering : 
*Unit-01     *Unit-02    
*Unit-03    *Unit-04 
*Unit-05    *Short-Q/Ans
*Question-Paper with solution 21-22 

Q1.What are the various fundamental forces present in nature?

Ans. Various fundamental forces present in nature are as follows:

i. Gravitational Force: It is the force of mutual attraction that exists between any two things due to their masses. It is a universal force because every object in the universe experiences it as a result of every other object in the universe.

ii. Electromagnetic Force: It is the force that exists between charged particles. At rest, charges exhibit both electric attraction (between unlike charges) and repulsion (between like charges). Magnetic force is produced by moving charges. They are referred to collectively as the electromagnetic forces.

iii. Strong Nuclear Force: In a nucleus, it is the attractive force between protons and neutrons. It has no charge and can act between a proton and a proton, a neutron and a neutron, and a proton and a neutron.

iv. Weak Nuclear Force: This force appears only in particular nuclear processes, such as nucleus decay. The nucleus emits an electron and an uncharged particle known as a neutrino during -decay.

Q2. What do you understand by a thermal neutron? Also, explain the properties of neutrons.

Ans. A. Thermal Neutron: A thermal neutron is a free neutron with an average energy of motion equal to the average energy of the particles in the surrounding materials.

B. Properties of Neutrons :

1. Neutrons are the basic building blocks of a nucleus. Neutrons remain forever inside a nucleus, but only for a short time as a projected particle outside of it.

2. The number of neutrons in heavier element nuclei exceeds the number of protons. This abundance of neutrons is what keeps the elements stable.

3. Because neutrons are uncharged particles, they are not affected by external magnetic or electric fields, nor are they impacted by the presence of protons when they enter or penetrate the nucleus.

4. Depending upon their speed, neutrons are put in two categories:

• i. Fast neutrons, and
• ii. Slow neutrons.

5. Both have the ability to penetrate a nucleus and cause artificial disintegration.

Q3. What do you mean by nuclear reactor? Explain its different parts.

Ans. A. Nuclear Reactor :

• 1. The nuclear reactor can be viewed as a replacement for a steam power plant’s boiler fire box or a gas turbine plant’s combustion chamber.
• 2. Nuclear reactors generate heat through the fission process, whereas steam and gas power plants generate heat through fuel combustion.
• 3. The other cycle of operation and components required are the same whether the unit is a steam or a gas turbine.
• 4. The operating fluid in a nuclear power plant could be steam or gas.

B. Different Parts of Nuclear Reactor:

i. Fuel Element:

• 1. The nuclear fuels which are generally used in reactors are ₉₂U²³⁵, ₉₄Pu²³⁹ and ₉₂U²³³
• 2. Out of the three, the ₉₂U²³⁵ is only naturally available upto 0.7% in the uranium are 239 and the remaining is ₉₂U²³⁸
• 3. The other two fuels ₉₄Pu²³⁹ and ₉₂U²³³ are the byproduct and formed in the nuclear reactor during fissioning process from ₉₂U²³⁸ and ₉₀Th²³² due to the absorption of neutrons without fission.
• 4. The shape of the fuels and their placement in the reactor are chosen with uniform heat production within the reactor in mind.
• 5. The fuel elements are developed with heat transfer, corrosion, and structural strength in mind.

ii. Moderator:

• 1. It is a substance that allows neutrons to be slowed from high kinetic energy (1 MeV or 13200 km/s) to low kinetic energy (0.25 eV or 2200 m/s) in a fraction of a second.
• 2. A moderator is also used to boost the likelihood of a reaction and to keep the chain reaction going due to slow neutrons.
• 3. The slowing down of the neutrons is effectively done by the light elements such as H₂, D₂, N₂, O₂, C and Be.

iii. Reflector:

• 1. It is crucial to conserve neutrons in order to keep the critical size of the reactor and thus the amount of fissionable material as little as possible.
• 2. This is accomplished by encasing the reactor core in a material that reflects escaping neutrons back into the core. This substance is known as a reflector.
• 3. A good reflector must have low neutron absorption and high neutron reflection, as well as high oxidation and irradiation resistance and radiation stability.
• 4. Many times the materials used as moderator is also used as reflector.
• 5. The H₂O, D₂O and carbon are also used as reflector.

iv. Coolant :

• 1. The primary function of the reactor coolant is to transmit the heat generated in the reactor and to keep the fuel assembly at a safe temperature to avoid melting and destruction.
• 2. The same heat carried by the coolant is utilised in the heat exchanger to generate power by either creating steam or using hot gas.
• 3. The water, heavy water, gas (He, CO₂), a metal in liquid form (Na) and organic liquids are used as coolant.

v. Control Rods:

• 1. The control system regulates the rate at which energy is generated. It initiates, increases, decreases, and terminates the reaction.
• 2. These rods, which can be fashioned like fuel rods, are distributed throughout the core.
• 3. Instead of containing fuel, they contain neutron absorber such as boron, cadmium or indium.

vi. Biological Shield:

• 1. The level of radiation and radioactive debris emitted by the reactor core is too great for the human body to handle.
• 2. As a result, shielding material must be used to surround the reactor to prevent radiation damage to the human body.

vii. Reactor Vessel:

• 1. The reactor vessel protects the reactor core, reflector, and shield from the elements. It also has tubes for coolant inlet and exit.
• 2. The reactor vessel has to withstand the pressure at 200 bar or above.
• 3. The reactor core (fuel and moderator assembly) is typically located at the vessel’s bottom.

Q4. Describe a pressurised heavy water reactor (PHWR).

Ans.

• 1. A pressurised heavy water reactor (PHWR) is a nuclear power reactor that uses heavy water (deuterium oxide D₂O) as its coolant and moderator and generally uses unenriched natural uranium as its fuel.
• 2. Because the heavy water coolant is kept under pressure, it may be heated to greater temperatures without boiling as much as it would in a traditional pressurised water reactor.
• 3. While heavy water is substantially more expensive than conventional light water, it produces significantly improved neutron economy, allowing the reactor to run without fuel enrichment facilities and overall improving the reactor’s ability to employ alternate fuel cycles more efficiently.
• 4. The CANDU reactor was the first and is now the most commonly utilized heavy water reactor.

Q5. Explain the nuclear fuel cycle with a block diagram.

Ans. 1. The nuclear fuel cycle is a set of industrial activities that involves generating electricity from uranium in nuclear power reactors.

2. After a reactor’s fuel has reached the end of its useful life, it can be reprocessed so that the majority of it can be recycled for fresh fuel.

3. The nuclear fuel cycle refers to the different operations related with the generation of power from nuclear reactors.

4. The nuclear fuel cycle begins with uranium mining and finishes with nuclear waste disposal. The stages form a true cycle when used fuel reprocessing is an option for nuclear energy.

5. Mining and milling, conversion, enrichment, and fuel manufacturing are all phases in preparing uranium for use in a nuclear reactor. These are the first phases of the nuclear fuel cycle.

6. After uranium has spent around three years in a reactor to produce energy, the used fuel may undergo a further sequence of operations including interim storage, reprocessing, and recycling before wastes are dumped. These processes are referred to together as the fuel cycle’s back end.

Q6. Discuss some safety measures for nuclear power plants.

Ans. Safety measures for nuclear power plants are as follows:

1. A nuclear power facility should be built far from human settlement. There should be a 106-kilometer exclusion zone around the facility where no public occupancy is authorised.

2. The materials used in the construction of a nuclear power plant must meet certain specifications.

3. Nuclear power plant waste water should be cleaned.

4. The nuclear power plant must be equipped with a safety mechanism that can safely shut down the unit when necessary.

5. Periodic inspections must be performed to verify that radioactivity does not exceed the allowable limit in the environment.

6. When disposing of nuclear waste, care should be taken to ensure that no water, river, or marine pollution occurs.

Energy science and engineering Important Links:

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