Nuclear fusion reactions.The major issue faced with these attempts
Nuclear Fusion existed before climate change became everyone’s reality. It was discovered in the 1930’s as the “energy source for the sun”. During the 1940’s researchers developed a process to initiate and control fusion reactions.The major issue faced with these attempts was that fusion reaction requires a temperature greater than millions of degrees. During this era the containment of the reaction temperature within solid chambers became a challenge. After several experiments, scientist came up with the magnetic confinement as the most advanced solution that uses magnetic fields to contain hot plasma.Nuclear fusion’s initial purpose was to develop military weapons however it was deemed unsuccessful. Hence during additional years, researchers developed “Inertial confinement”. This process require the fuels to heated with a laser which resulted in the plasma remaining in its initial state before being burned in the fusion reaction, hence trapping its inertia. From this process, a plasma focus device was developed which eventually led to the tokamak. The tokamak in the 1960’s became a short-term solution to the oil crisis. Today in the 21st-century research and technology development is still being done on the tokamak.Due to the growing threat of climate change, countries are seeking alternative energy sources to replace the massive use of fossil fuel that could potentially become limited. The lists of alternatives that currently exist are renewables, nuclear fission and fusion. Of these three, nuclear fusion presents no threat to the environment and safety, with virtually inexhaustible resources. This technology once developed could serve as a backup for renewables solving their intermittency issues. As a result fusion research has become a worldwide effort.Nuclear power involves the production of energy from atomic nuclei by the use of a well-ordered nuclear reaction. Currently Nuclear power is being used worldwide and accounts for approximately 11% of the worlds continuous energy operated within 31 countries. The total capacity is globally is 390,000MWe. Worldwide the total number of reactors in the world is 400 power reactors (approximately 100 are in the USA). They base-load electricity throughout the year excluding pollutants (example CO2) into the atmosphere. They however, create radioactive nuclear waste which must be stored carefully. All the current power production from nuclear involves fission reaction, which is the splitting of heavy atomic nucleus into light smaller nuclei. Nuclear fusion that is being studied in this paper is consist of the combination of two nuclei of isotopes which is the fundamental difference between fission and fusion.2.0 The concept of Nuclear fusion The sun produces fusion by converting 4 protons into a helium-4 nucleus containing 2 neutrons. To replicate this on earth requires converting protons into neutrons by inverse beta decay with a very low probability. Economically this approach is not suitable for the earth. The solution to this has been found to be the reaction between two isotopes of hydrogen (deuterium and tritium) which combines to form a heavier nucleus, with a 1024 times higher reaction rate than the proton-proton process in the sun. D+T ? 4He (3.5 MeV)+n (14.1 MeV)6 The bonding of hydrogen isotopes.The emission of particles occurs after the binding of the hydrogen and isotopes. Nuclear fusion reaction releases energy in the form of gamma rays and kinetic energy of the emitted particles. The energy generated transforms matter to a plasma state.2.1 Fusion Fuel Resources The three main resources used in nuclear fusion are deuterium, tritium and lithium. Deuterium can be obtained from water. Majority of the earth’s surface is covered with water which makes its availability virtually inexhaustible and harmless.Tritium can be found within nature in fast-decaying radioelement of hydrogen. It is generated during the fusion reaction when the released neutron come into contact with lithium. Lithium can be easily extracted from land-based resources. Lithium can also be extracted from ocean water.The abundance of nuclear fusion reaction resources contributes to the feasibility of Nuclear fusion acting as a primary and alternative source of generating sustainable energy that meets the growing energy demand for future generation.2.2 Nuclear Fusion Principle and Energy Conversion ProcessFusion reaction or process happens throughout our universe and is a process by which the sun and the stars use hydrogen to release energy and also produce new elements. The energy released from the reaction is used to power the stars. The fundamental principle involved in fusion reaction is the combination of two light atoms to form a heavier atom and release energy (exothermic reaction). The energy released when these light elements combine is as a result of two opposing forces, namely; nuclear force and Coulomb force. The nuclear force brings protons and neutrons together whiles the coulomb force causes protons to repel each other because they are positively charged. The two light atoms can be fused together because there is another short-range force known as a nuclear attraction. Light nuclei (nuclei smaller than iron and nickel) are small and proton-poor, this condition permits the nuclear force to overcome the repulsive force (Coulomb force) enhancing the fusing of the two atoms. When the two atoms fuse together they lose mass compared to before the fusion reaction. This mass loss comes out as a form of energy as shown by Albert Einstein’s relativity equation (E=MC2) where this energy can be calculated by multiplying the mass(M) by the speed of light (C). The energy released is as result of extra energy from the net attraction of the two nuclei. Other products from the fusion reaction include the release of a neutron formation of a new element.In the case of the sun (solar fusion), two atoms of hydrogen fuse together to form helium and release energy in a series of proton-proton chain reactions. “In the sun’s core, 620 million metric tons of hydrogen are fused to make 606 million metric tons of helium each second” (en.wikipedia.org). The resulting mass loss is converted to energy. To produce this kind of reaction on earth is very difficult to achieve and requires a lot of years of research. There has been considerable research into creating this form of solar fusion on earth for the past 50 years. The painful and long research has come up with a simple fusion reaction that will produce sustainable energy for the world in the near future. This simple reaction involves the combination of two isotopes of hydrogen namely Deuterium and Tritium. The reaction is usually called D-T reaction.These two isotopes are rare. Tritium is not readily available naturally and has to be produced in-situ in the plant. This is done by using the products of fusion reaction namely neutron to interact with light metal lithium in a layer surrounding the reaction chamber in a breeding cycle.To produce sufficient fusion reactions, the core temperature of a D-T plasma has to be about 150–200 million o C. This is about 10– 15 times larger than the temperature in the centre of our sun, estimated to be about 15 million o C (en.wikipedia.org). Figure 1, is a schematic diagram showing nuclear fusion power production process. From the figure, tritium and deuterium combine at high temperature in the reaction chamber. High pressures and extreme temperatures are vital in forcing atoms together to release huge amounts of energy. the energy released as charged particles, neutrons-rays, and ultraviolet radiation and is absorbed in a lithium blanket surrounding the reaction chamber. The neutron converts the lithium into tritium fuel which is then used in the reactor. A conventional steam-generating plant is then used to convert the nuclear energy released to generate steam which drives a turbine to produce electricity. The end product of the reaction is helium (4He). 2.3 Calculation of Energy Released in the D-T reaction (Mass/Energy Balance)The method is to sum the mass of the products and subtract this from the mass of the reactants. This mass defect is then converted to energy units(MeV). u = unified atomic mass unit (1/12 mass of a C-12 nucleus) 1u = 1.660539×10-27 kg = 931.494 MeV Reactants: mass of D = 2.014102 u mass of T = 3.016049 u Products: mass of He-4 = 4.002602 u mass of neutron = 1.008665 u mass defect = mass of reactants – mass of products = (2.014102) u + (3.016049) u – (4.002602) u – (1.008665) u = 0.018884 u since 1 u = 931.494 MeV, mass defect = (0.018884) x (931.494) = 17.5903 MeVThe reaction products are a 3.5 MeV helium nucleus (alpha particle) and a 14.1 MeV neutron, i.e. in total about 17.6 MeV is released per fusion reaction3.0 Drawbacks / Challenges of Nuclear Fusion for Power Production Although fusion provides an environmentally clean and limitless energy source, the release of energy involves the heating of the fuel to a very high temperature of about hundreds of millions of degrees Celsius which is hotter than the temperature of the sun’s core temperature (i.e15 million oC). The challenge therefore is to provide a material that would be able to withstand such high temperature.Through research, two alternate ways have been found to solve this challenge. The first method is magnetic confinement which involves the use of the magnetic field to form an insulating layer around the hot fuel. Research into this method has taken about 50 years and is now at the stage where a prototype can be built. The second method is inertial confinement where the fuel is compressed and heated very quickly so that it burns and fusion energy is released before the fuel has time to expand.4.0 Advancements Made in Nuclear FusionInitially, fusion research in the USA and USSR was linked to atomic weapons development, and it remained classified until the 1958 Atoms for Peace conference in Geneva. Following a breakthrough at the Soviet tokamak, fusion research became ‘big science’ in the 1970s. But the cost and complexity of the devices involved increased to the point where international co-operation was the only way forward. There are currently about 100 fusion research labs scattered in nearly all continents. The EU, Japan, the Russian Federation and the USA undertake a large research effort, with fast growing contributions from China, India and South Korea. Brazil and Australia are participating as well with substantial investments (Ogena and Ogawa,2016). Research on nuclear fusion has moved from concept to reality. A new twist on fusion power could help bring limitless clean energy. Across the world, scientist have come out with a conclusion that a full scale demonstration power plant can be operating in some 20 – 25 years. This decision is as a result of accumulation of knowledge, fusion is now on the turning point with some clarity of seeing the way to the endpoint of commercializing it. However, the physics and engineering challenge still pertains but these challenges have been well envisioned that road maps of fusion to grid have been developed by most countries active in fusion research. So far International Thermonuclear Reactor ( ITER) tokamak design is the most advanced research with realistic result where the magnetic field developed is able to hold the plasma for 500 seconds for power output of 500MW. It is also able to produce by itself- sustaining burning plasma in which the plasma is self-heated by the power from the fusion reaction. A prototype of ITER is being built in France and it is expected to be ready by the year 2010 (McCracken and Stott, 2013). funding for the project is being provided by United States, along with the EU, China, India, South Korea, Russia and Japan .Recently, a new chapter of fusion energy research commenced with the formal opening of Wendelstein 7-X. This is an experimental fusion reactor built in Greifswald, Germany, to test a reactor design called a stellarator. What makes the W-7X particularly interesting is its stellarator design. It comprises a vacuum chamber embedded in a magnetic bottle created by a system of 70 superconducting magnet coils. These produce a powerful magnetic field for confining the hot plasma.The Wendelstein 7-X reactor recently came online with a successful test run reaching almost 180 million degrees 12. It is planned that by 2021 it will be able to operate for up to 30 minutes duration, which would be a record for a fusion reactor. This is an important step en-route to demonstrating an essential feature of a future fusion power plant.Although the W-7X and ITER employ different designs, the two projects complement each other, and innovations in one are likely to translate to an eventual working nuclear fusion power plant.Stellarators and tokamaks are both types of toroidal (doughnut-shaped) magnetic confinement devices that are being investigated for fusion power. In these experiments a strong toroidal (or ring) magnetic field creates a magnetic bottle to confine the plasma. At this stage, it’s too early to tell whether the tokamak design used by ITER or the stellarator used by W-7X will be better suited for a commercial fusion power plant. But the commencement of research operation of W-7X will not only help decide which technology might be best to pursue, but will contribute valuable knowledge to any future fusion experiments.Soviet physicist, Lev Artsimovich, the “Father of the Tokamak” may have summed it up best:”Fusion will be ready when society needs it.”( Source?)5.0 The Need for Nuclear Fusion as a Future Sustainable Energy SourceThe demand for energy in the world keeps increasing as a result of many factors. Among these factors includes industrialization by emerging and developing economies, population increase, and urbanization. In developed countries, energy has eliminated almost all of the labour intensive tasks in industry, agriculture and basic household chores. The daily life is of the people depended on energy and as such if there are any disruptions in electricity supply, work and lifestyle completely come to the quick halt. Sustaining the supply of energy therefore becomes a necessity for survival. There is , however existing global energy access gap that needs to be met in addition to the current growing demand. ………………………..According to the 2017 world energy outlook by international Energy Agency although the global energy needs will rise more slowly than in the past it will still expand by 30% by 2040, the equivalent of adding another China and India to today’s global demand ( https://www.iea.org/Textbase/npsum/weo2017SUM.pdf ).The energy resources we use today mainly comes from fossil fuels which are non-renewable and will get exhausted with time. These energy sources are used to mainly generate electricity which is the most preferred form of energy used globally. In addition, the use of these fossil fuels has environmental impacts such as emission of greenhouse gases which contributes to global warming and climate change. The alternative to fossil fuel would be renewable sources like solar and wind. However, these have problems with intermittency. The wind, for instance, is very variable and the sunlight energy is not available all the time. Although these and other renewable sources can be developed to provide a much greater proportion of the global energy demand, it is doubtful if they would be able to satisfy the total demand. The question, therefore is how then do we sustain our growing demand and ensure energy security in the future?. The answer will have to be a long-term solution to global warming and pollution and also be able to generate electricity from an environmentally friendly source; The answer is energy from nuclear fusion.Nuclear fusion has been shown to be scientifically possible on earth after many years of difficult research. The power from nuclear fusion offers the prospect of an almost inexhaustible source of energy for a future generation. “Each D-T fusion event releases 17.6 MeV (2.8 x 10 -12 joule, compared with 200 MeV for a U-235 fission and 3-4 MeV for D-D fusion). On a mass basis, the D-T fusion reaction releases over four times as much energy as uranium fission. Deuterium occurs naturally in seawater (30 grams per cubic metre), which makes it very abundant relative to other energy resources. Tritium occurs naturally only in trace quantities (produced by cosmic rays) and is radioactive, with a half-life of around 12 years” (www.world-nuclear.org, ..)Although there is a lot of public concern regarding ‘nuclear’ fusion has a significant advantage over as compared to fission. Fusion power plant is intrinsically safe, and cannot explode because the plant will only contain a very small amount of deuterium and tritium fuel which is just enough to keep the reaction going for just a few seconds and if is not continually replaced the reaction stops. Secondly the primary fuel for the fusion reaction, lithium and water are completely non-radioactive. Nuclear fusion power has an added advantage over fission and fossil fuel types because there is enough lithium to last for at least tens of thousands of years and also deuterium is abundant in the oceans. Predicting the cost of fusion energy involve different uncertainties. Nuclear fusion reactions do no emit greenhouse gases that cause climate change. it is therefore clean energy.Nuclear power is sustainable energy source that can be used to help meet the current energy needs of our society without compromising the ability of future generations to meet their needs. If we could ever get fusion power to work we would never have to worry about our energy problems again. But the scientific and technical hurdles ahead are still enormous. We still don’t have a full grasp on what all the hurdles might be. Still, the potential pay-off is so massive that countries have sunk billions and billions of dollars into fusion research. No one knows when a successful continuous controlled fusion reaction can be achieved or even if it is ultimately possible. Billions of dollars have been and continue to be invested in research since the potential benefit is considered so great. The advantages and disadvantages show that there is a lot of potential value in nuclear fusion technology as the future energy source. it also indicates that there is the need to take on several risks to turn this technology into a reality.6.0 ConclusionIn examining the issue of different fuel resources and damage to the environment in perspective, it is clear we do not have many options for sustainable energy sources for future energy requirements. If fusion is to be ready when needed, it would provide the world with its future energy demands.