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Essay on Nuclear Fusion and Energy
Essay Contents:
- Essay on the Introduction to Nuclear Fusion Energy
- Essay on the Principle of Fusion Process
- Essay on the Tokamak Fusion Reactor
- Essay on the Inertial Confinement Reactor
- Essay on the Future Nuclear Fusion Power Plant
- Essay on the Advantages of Fusion Energy
Essay # 1. Introduction to Nuclear Fusion and Energy:
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Of all the currently known available sources, only nuclear and solar energy have the potential of supplying large amounts of power within the available time frame. These two sources can complement each other to meet the demand economically and safely. However, considerable technical and economic problems must be solved before large-scale utilization of these sources can become possible.
Energy is produced in the-sun and stars by continuous fusion reactions. Fusion of light nuclei to form a heavy nucleus releases large amount of energy. If the controlled fusion of light elements is carried out on our planet, enough energy can be generated to meet all the energy requirements of future generations.
The primary fuel for fusion is deuterium, sometimes called heavy hydrogen (H2). There is one atom of deuterium for every 6500 atoms of ordinary hydrogen in sea water. The total energy content of deuterium as fossil fuel is about 100,000 kWh of energy per gram of deuterium. This is about 10 million times more than released per gram in the combustion of fossil fuels.
The entire amount of world energy consumption of 6 × 1013 kWh per year could be supplied by the fusion of only 600 metric tons of deuterium. The amount of deuterium in the world oceans would be enough to sustain the present total world energy requirement for 100 billion years. Nuclear fusion would indeed present an ultimate solution of mankind’s energy needs for all the years to come.
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A nuclear fusion reaction can occur when two atomic nuclei approach very close to each other at velocities at least large enough to overcome their mutual electrostatic repulsion called “Coulomb barrier”. Fusion reaction occurs at very high temperature. Therefore, there is a problem of confinement of fusion. There are other essential difficulties lying to be overcome before this future energy source can be put to man’s use.
Fusion research is indeed being taken seriously by the major industrial nations. There are serious efforts by individual countries as well as combined effort by consortium of countries. It is almost certain that large practical fusion power plants will be built in the twenty-first century. Once this technology is developed, an almost unlimited supply of energy will be available for the world’s needs ushering in a better living standard for the human kind all over the world.
Essay # 2. Principle of Fusion Process:
Energy is produced in the sun and stars by the following continuous fusion reactions:
Four nuclei of hydrogen fuse in a series of reactions to yield one nucleus of helium and protons. There is a decrease in mass of about 0.0276 amu. The energy corresponding to the change to the in mass is calculated from Einstein’s law.
The energy released per nuclear reaction will be 25.7 MeV. The heat produced in these reactions maintains temperatures of the order of several million degrees in the cores of the sun and stars which serves to trigger and sustain succeeding reactions.
Artificial Fusion Reaction:
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The 4-hydrogen reaction shown above requires, on an average, billions of years for completion. On earth artificial fusion reaction may be accomplished when two light atoms fuse into a larger one as there is much greater probability of two particles colliding than of four.
In order to cause artificial fusion reaction, the following problems must be solved:
i. The positively charged nuclei must be accelerated to high kinetic energies in order to overcome the electrical repulsive forces.
ii. The temperature must be raised to hundreds of millions of degrees resulting in plasma.
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iii. The plasma must be prevented from contacting the walls of the container.
iv. The plasma must be confined for a certain period of time (of the order of a second) at a minimum density.
v. The fusion heat must be converted to electricity.
vi. All operational problems of a fusion power plant must be solved. There are several possible reactions between the nuclei of light elements that can be the basis for controlled thermonuclear fusion. These reactions along with energy released per reaction are given in Table 16.1.
The following symbols have been used:
Reaction 3 is the most favourable reaction which is self-sustaining at a temperature of 50 × 106 K releasing 17.6 MeV per reaction. The first two D-D reactions occur at 500 × 106 K and release less energy (3.2 MeV and 4.0 MeV). The fourth reaction releases very high energy (18.3 MeV), but requires very high temperature of 1000 × 106 K for fusion reaction.
The basic raw materials for the D – T reaction are water for deuterium and tritium. Deuterium in the form of heavy water (D2 O) is extracted from water on a large scale at a moderate cost. Tritium does not occur abundantly in nature. It can, however, be produced in a lithium “breeding blanket” that surrounds the plasma core of the fusion reactor. Lithium can be extracted from sea water at low cost.
Essay # 3. Tokamak Fusion Reactor:
There are two processes used for plasma confinement:
1. Magnetic confinement.
2. Inertial confinement.
The fusion reactor with magnetic confinement is called Tokamak reactor which in Russian means toroidal magnetic chamber. A schematic diagram of a Tokamak fusion reactor is shown in Fig. 16.1.
The plasma is contained inside an evacuated tube of about 4m. The surrounding vacuum wall through which 14 MeV neutrons from the plasma pass, is maintained at about 750°C. Outside this wall are two concentric regions, i.e., the lithium breeder modulator and the magnetic shield. Tritium is manufactured in the lithium blanket. Large cryogenic superconducting magnets of 7 to 8 m diameter maintain the magnetic field.
The breeding of tritium takes place as follows:
6Li + n → He + T + 4.78 MeV.
The heavy lithium isotope 6Li acts as breeding material and moderator.
The design parameters of a projected fusion reactor are given below:
The triple product is the index for positive energy balance on net release of energy. A sufficient number of fusion reactions per unit time must occur in the reactor.
Here T is the plasma temperature of the order of 108 K, t is the confinement time of 0.1s and n is the plasma density of the order of 1020 l/m3.
Essay # 4. Inertial Confinement Reactor:
A small pellet or sphere of a deuterium tritium mixture (solid or liquid) is heated by a very short burst of energy from either laser beams or beams of high energy charged particles. The pellet material is compressed to a high density and temperature also increases. The fusion reaction has to be completed in one trillionth (10-12) second so that inertia would prevent the pellet from flying apart while fusion is in progress. No magnetic confinement is needed. The development of this type of reactor is stopped due to unavailability of high power laser.
Essay # 5. Future Nuclear Fusion Power Plant:
The fusion reactor can be coupled to a triple Rankine cycle using potassium, biphenyl and steam as working fluid. A binary vapour power cycle consisting of potassium topping cycle and a conventional steam cycle is shown in Fig. 16.2. The tritium recovery system is also shown.
Essay # 6. Advantages of Fusion Energy:
i. The supply of deuterium is inexhaustible.
ii. No radioactive waste is produced.
iii. It is very safe to operate.
iv. High conversion efficiency (60%) can be achieved.
v. Low heat rejection per kW of electricity generated to atmosphere.