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Nuclear fusion is a process in which two or more atomic nuclei unite to generate one or more distinct atomic nuclei as well as subatomic particles such as protons or neutrons. The mass differential between the reactants and products causes a huge quantity of energy to be released or absorbed. A nuclear fusion reactor is a thermonuclear reactor that generates electricity from the energy generated during a nuclear fusion process. Deuterium and tritium, the fuels utilised in nuclear fusion processes, are plentiful on Earth and across the cosmos.
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Key Terms: Nuclear Fusion, Nuclei, Energy, Atom, Reactor, Hydrogen
What is Nuclear Fusion?
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The process by which the nuclei of two light atoms join to generate a new nucleus is known as nuclear fusion. This is a method of creating nuclear energy similar to nuclear fission, except that in nuclear fission the nucleus of a heavier atom divides. Let us now look at how nuclear fusion generates energy.
When two light nuclei fuse in a fusion process, the combined mass is smaller than that of the individual nuclei. This implies that the reaction emits energy in accordance with Einstein's mass-energy equivalence.
A fusion process involves the combining of Deuterium and Tritium, which are Hydrogen isotopes, to produce Helium while releasing a neutron and emitting roughly 17 MeV of energy.
Nuclei Class 12 Important Notes PDF
Nuclei Class 12 Important Notes
Fuels of Nuclear Fusion Reactor
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Nuclear fusion reactors require fuels that can withstand the high temperatures and pressures required for fusion reactions. At the moment, the most promising nuclear fusion fuels are:
Deuterium: It is a stable hydrogen isotope that may be recovered from seawater. Deuterium is plentiful and easy to get, making it an appealing fuel for fusion processes.
Tritium: It is a radioactive hydrogen isotope that may be created from lithium. In fusion processes, tritium is combined with deuterium to form a more energetic reaction.
Helium-3: It is a rare isotope of helium that is not abundant on Earth. Helium-3, which can be collected from the moon's surface, has the ability to provide clean energy while generating no radioactive waste.
Hydrogen: It is the most plentiful element in the universe and might be used as a fuel in fusion processes. In comparison to deuterium and tritium, hydrogen requires greater temperatures and pressures to ignite fusion reactions.
Deuterium and tritium are the most often utilised fuels in modern nuclear fusion reactor designs.
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How to Start Nuclear Fusion Reactor
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First step: To initiate the fusion process, the nuclear fusion reactor needs an outside energy burst from a charged Laser Amplifier, as well as a tiny quantity of D-T Fuel.
Second step: The Hohlraum contains 10 units of D-T Fuel, which is necessary for the first reaction.
Third step: Ignition - The statistics tab section displays the temperature necessary for the reaction to begin. To attain the ignition temperature, an energy-charged Laser Amplifier is discharged into the Laser Focus Matrix. The laser is fired to start the fusion reaction with all of the energy stored in the Amplifier and Hohlraum in the Reactor Controller. The temperature must not dip below the ignition point for the reaction to proceed.
It is recommended to pump in Deuterium and Tritium individually at a rate larger than half of the prescribed injection rate in various fuel tabs for different types of fuel for a nuclear fusion reactor to function correctly at a steady pace.
Types of Fusion Reactors
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These reactors may be classified into two categories based on their containment.
Magnetic Confinement: Magnetic fields are used to keep the hot plasma from reaching the walls of the confining material. Because the temperatures reached are exceedingly high, they are not allowed to come into contact with any substance.
Inertial Confinement: The high energy density is placed in a tiny pellet of reactors, fusing them in such a brief period of time that they do not have time to touch the confining material.
Advantages of Nuclear Fusion
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- Nuclear fusion offers various potential advantages over conventional energy generating methods, including:
- Deuterium and lithium, the fuels utilised in nuclear fusion, are plentiful on Earth and in the cosmos. Fusion is a practically endless source of energy since deuterium can be taken from seawater and lithium can be recovered from the Earth's crust.
- Nuclear fusion generates no greenhouse gases or other hazardous pollutants. Helium, the only consequence of fusion processes, is non-toxic and does not contribute to climate change.
- Nuclear fusion reactors are intrinsically safe because they need exact temperature, pressure, and fuel composition conditions to sustain fusion reactions.
- Fusion reactors are far more efficient and compact than traditional power plants, and they can produce a large quantity of energy per unit of fuel.
- Fusion reactors can provide a steady and stable source of energy since they are not affected by weather or fuel supply, as are renewable energy sources such as wind or solar power.
- Nuclear fusion reactors create no nuclear waste, unlike nuclear fission reactors, which produce radioactive waste that must be stored for a long time.
Disadvantages of Nuclear Fusion
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Below are a few of the drawbacks of nuclear fusion.
- Nuclear fusion demands high temperatures and pressures to maintain reactions, posing considerable technical hurdles in terms of materials science and reactor design.
- Due to the high cost of materials and the complexity of the technology, developing and running nuclear fusion reactors is currently expensive.
- Because the energy required to launch and sustain nuclear fusion reactions is presently more than the energy generated, fusion reactors must be powered by an external source.
- Although nuclear fusion reactors are meant to be intrinsically safe, there is always the possibility of accidents or malfunctions that might discharge radioactive material or cause reactor damage.
- After decades of study and development, nuclear fusion is not yet a commercially viable source of energy, and practical, large-scale deployment may take many years.
Components of Magnetic Confinement Reactors
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Magnetic confinement reactors, such as tokamaks and stellarators, are generally made up of the following parts:
Vacuum Vessel: A vacuum vessel is a huge, toroidal container built of high-strength materials capable of withstanding extreme temperatures and pressures. The vacuum vessel holds deuterium and tritium plasma that will undergo fusion reactions.
Magnetic coils: This are enormous electromagnets that produce a magnetic field that is used to contain and regulate plasma. To achieve the necessary magnetic field geometry, the magnetic coils are stacked in a complicated pattern.
Plasma heating systems: In order to ignite fusion processes, plasma must be heated to extremely high temperatures. To deliver the necessary energy to the plasma, plasma heating technologies such as radio frequency (RF) heating and neutral beam injection are utilised.
Plasma diagnostics: A variety of devices are used to measure plasma parameters such as temperature, density, and confinement time. This data is utilised to enhance the reactor's performance and to detect any issues.
Tritium breeding blanket: Tritium is an important fuel for fusion processes, and it is created by a process known as "breeding," in which neutrons from fusion reactions interact with lithium. The tritium breeding blanket is a lithium-containing component that catches neutrons produced by fusion processes.
Control systems: Advanced control systems are utilised to monitor and regulate the reactor's many components, such as magnetic fields, plasma heating systems, and cooling systems. These mechanisms guarantee that the reactor runs smoothly and safely.
Cooling systems: To prevent damage from high temperatures, the plasma and other reactor components must be cooled. To remove heat and maintain stable operating conditions, water or other coolants are pumped through the reactor components.
Application of Nuclear Fusion
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There are various possible uses for nuclear fusion, including:
Energy generation: Fusion reactions may generate massive amounts of energy with minimal environmental effect, making them an appealing alternative for countries wanting to move to clean energy.
Space propulsion: Nuclear fusion might be utilised to power space propulsion systems like fusion rockets, allowing for speedier and more efficient space travel.
Isotope production: Fusion reactions can also be utilised to create isotopes for medicinal and industrial uses such as cancer therapy and materials science research.
Nuclear weapons: While this is not a good use, nuclear fusion processes may be utilised to create powerful thermonuclear weapons. Its application, however, is severely controlled and restricted by international law.
Basic science research: Nuclear fusion research can also reveal insights into the underlying workings of the cosmos and help develop our understanding of plasma physics, nuclear physics, and other scientific subjects.
Things to Remember
- With nuclear fusion reactors, safety is the main concern, and meticulous engineering and safety procedures are essential to prevent accidents or malfunctions that might harm people or the environment.
- To launch and maintain reactions, nuclear fusion processes require extremely high temperatures in the tens of millions of degrees Celsius range.
- Deuterium and tritium, the fuels utilised in nuclear fusion processes, are plentiful on Earth and across the cosmos.
- While tremendous progress has been achieved in nuclear fusion research, practical, large-scale fusion energy deployment is still years, if not decades, away.
- Nuclear fusion research and development is a complicated and multifaceted area that need collaboration across several organisations and nations.
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Sample Questions
Ques. What is the most significant difficulty confronting nuclear fusion technology today? (1 mark)
a) Identifying an appropriate fuel source
b) Creating innovative fusion reactor designs
c) Maintaining high temperatures and pressures necessary for fusion reactions
d) Radioactive waste management.
Ans. The Correct option is c) Maintaining high temperatures and pressures necessary for fusion reactions
Explanation: Maintaining the high temperature and pressure necessary for fusion reactions is one of the most difficult technological issues confronting nuclear fusion research. Creating and maintaining these conditions in a regulated and steady manner is a substantial problem that necessitates the use of modern materials, technologies, and engineering.
Ques. Which of the following nuclear fusion reactors uses magnetic fields to keep the plasma contained? (1 mark)
a) Magnetic confinement fusion reactors
b) Inertial confinement fusion reactors
c) Fusion reactors powered by lasers
d) All of the preceding.
Ans. The Correct option is b) Inertial confinement fusion reactors
Explanation: Tokamaks and other magnetic confinement fusion reactors employ high magnetic fields to contain and regulate the plasma in which nuclear fusion events take place. Inertial confinement fusion reactors, on the other hand, employ high-energy lasers to rapidly compress and heat a tiny target, resulting in fusion events.
Ques. Why are there never more protons than neutrons in stable nuclei? (1 mark)
Ans. Since protons are charged particles that resist one other, stable nuclei never contain more protons than neutrons. The repulsion is so strong that surplus neutrons only create attractive forces, which are sufficient to maintain stability.
Ques. What distinguishes nuclear fusion from nuclear fission? (1 mark)
Ans. Nuclear fusion is the process of fusing atomic nuclei, whereas nuclear fission is the process of separating atomic nuclei. Both processes provide energy, but fusion generates more energy and creates less radioactive waste than fission.
Ques. Is nuclear fusion a safe technology? (1 mark)
Ans. While nuclear fusion has the potential to be a safe and clean source of energy, it is not without concerns, such as the emission of radioactive elements in the case of an accident or malfunction. Fusion reactors, on the other hand, are built with numerous layers of safety safeguards to prevent and reduce such dangers.
Ques. How does a Nuclear Fusion Reactor generate energy? (2 marks)
Ans. A Nuclear Fusion Reactor generates energy by fusing two light nuclei, often hydrogen isotopes such as deuterium and tritium, to make a heavier nucleus such as helium. This fusion process generates a lot of energy in the form of heat and light.
Ques. The relationship R = R0A1/3, where R0 is a constant and A is the mass number of a nucleus, demonstrates that the density of nuclear matter is virtually constant (i.e., independent of A). (5 marks)
Ans. The relation R = R0A1/3 gives the radius (R) of a nucleus in terms of its mass number (A). Now, the volume of a nucleus can be given by the formula V = (4/3) πR3.
Substituting the value of R from the given relation, we get:
V = (4/3) πR03(A1) = (4/3) πR03A
The nuclear matter density (ρ) is defined as the ratio of the mass (m) of the nucleus to its volume (V), i.e., ρ = m/V.
The mass of a nucleus is proportional to its mass number, i.e., m ∝ A.
Substituting the expression for V and m, we get:
ρ = m/V = (constant x A)/ (constant x A) = constant
Therefore, we can see that the nuclear matter density is nearly constant and independent of the mass number A.
Ques. Which of the following cannot produce radiation, and why? The nucleus is excited, and the electron is energised. (3 marks)
Ans. An excited nucleus cannot release radiation since it is excited as a result of energy absorption, and to emit radiation, the nucleus must shift to a lower energy state. This transition can occur via electromagnetic radiation or particle emission such as alpha or beta particles. In the case of an excited nucleus, however, it will normally decay by producing radiation until it reaches a lower energy state, at which point it may emit radiation again if it is still unstable.
An excited electron, on the other hand, can release radiation. As an electron within an atom moves from a higher to a lower energy level, it can generate electromagnetic radiation in the form of a photon. Several key applications, such as lasers and LED lights, are based on this phenomenon.
Ques. T years is the half-life of a radioactive isotope. How long will it take to reduce the activity to (a) 3.125% and (b) 1% of its initial value? (7 marks)
Ans. The activity of a radioactive isotope is related to the amount of the isotope present by the equation:
A = λ × N
where A is the activity (number of decays per unit time), N is the number of radioactive atoms, and λ is the decay constant.
The decay constant is related to the half-life (T) by the equation:
λ = ln (2)/T
where ln (2) is the natural logarithm of 2 (approximately 0.693).
(a) To find how long it will take for the activity to reduce to 3.125% of its original value, we need to find the fraction of the original activity that remains after a time t. This can be expressed as:
A (t)/A (0) = (1/2) (t/T)
where A (0) is the initial activity, A (t) is the activity after a time t, and T is the half-life.
We can rearrange this equation to solve for t:
(1/2) (t/T) = 0.03125
Taking the natural logarithm of both sides, we get:
(t/T) ln (1/2) = ln (0.03125)
Solving for t, we get:
t = (-ln (0.03125))/ln (1/2) × T
t = 5T
Therefore, it will take 5 times the half-life of the radioactive isotope for the activity to reduce to 3.125% of its original value.
(b) To find how long it will take for the activity to reduce to 1% of its original value, we can use the same equation:
A (t)/A (0) = (1/2)(t/T)
But this time we set the fraction equal to 0.01:
(1/2)(t/T) = 0.01
Taking the natural logarithm of both sides, we get:
(t/T) ln (1/2) = ln (0.01)
Solving for t, we get:
t = (-ln (0.01))/ln (1/2) × T
t = 6.643 × T
Therefore, it will take 6.643 times the half-life of the radioactive isotope for the activity to reduce to 1% of its original value.
Ques. Every 5 years, a 1000-Megawatt fission reactor uses half of its fuel. How much 92235U was there at first? Suppose that the reactor is operational 80% of the time, that all of the energy produced is the result of 92235U fission, and that this nuclide is consumed only by the fission process. (7 marks)
Ans. The following calculation may be used to compute the quantity of 92235U burned in the reactor during 5 years:
m = (P * t) / (ε * E)
where m is the mass of 92235U consumed, P is the reactor's power output, t is the time span over which the fuel is spent, is the energy conversion efficiency, and E is the energy released per 92235U fission.
Assuming that the reactor produces 1000 MW of power and uses half of its fuel every 5.00 years, the total quantity of fuel burned may be computed as follows:
fuel consumed = (1000 MW) * (5.00 years) * (0.8) = 4000 million MWh
To convert this to joules, we can use the conversion factor:
1 MWh = 3.6 × 109 J
Therefore, the energy released by the reactor over the 5-year period is:
energy released = (4000 million MWh) * (3.6 × 109 J / MWh) = 1.44 × 1019 J
The energy released per fission of 92235U is approximately 200 MeV or 3.204 × 10-11 J.
Therefore, the number of fissions that occurred in the reactor is:
Nuclear fissions = energy released / (Energy per fission * ε) = 1.44 × 1019 J / (3.204 × 1011 J * 0.8) = 5.625 × 1028
Since each fission of 92235U produces two daughter nuclei, the total number of 92235U nuclei that were consumed in the reactor is:
N_U = Nuclear fissions / 2 = 2.812 × 1028
The molar mass of 92235U is approximately 235 g/mol. Therefore, the initial mass of 92235U in the reactor can be calculated as:
initial mass = N_U * (235 g/mol) / (6.022 × 1023 / mol) = 2.812 × 1028 * 235 / 6.022 × 1023 ≈ 1.1 × 106 kg
Therefore, the reactor initially contained approximately 1.1 × 106 kg of 92235U.
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