Fusion

Kieran and Helen__**
 * __[[file:RP3 W Nuclear Fusion Dossier & Lab.pdf]]

(word-for-word) The most concentrated form of energy that is available to Man is stored in nuclei. This energy can be released in the processes of fission (the splitting apart of heavy nuclei) and fusion ((Energy in Perspective, chapter 4, Sources of Energy, pg 73). Nuclear fusion is a process in which the nuclei of two atoms fuse to form a third nucleus, sometimes with the emission of an elementary particle such as a neutron, page v. This process liberates a great deal of energy – exceeding by many orders of magnitude that which is released in the molecular events of chemistry. Matter and energy are equivalent in the sense that an amount of matter, //m//, may disappear and a quantity of energy equal to //mc//2 appear in its place . This happens in nuclear reactions when the combined mass of the product nuclei is smaller than that of the initial reactants. The break-up of heavy elements such as uranium, or the fusing together of light elements, both produce large quantities of energy, which opens up the possibility of using such reactions as a source of power. The most important fusion reactions are those between the nuclei of the isotopes of hydrogen – the proton (or //p//), the deuteron and the triton. The energy available in a given mass of nuclear fuel is several million times greater than in the same mass of a fossil fuel. A total of about 10 billion tons of coal would be required to produce enough energy to meet the annual worldwide needs, whereas only 3000 tons of uranium could produce the same amount of energy. (Energy in Perspective, chapter 4, Sources of Energy, pg 76) The primary fuel for fusion power will be deuterium or, in some of the proposed systems, deuterium plus lithium. The world’s oceans constitute a huge source of deuterium in the form of water – about one molecule of every 3000 water molecules contains an atom of deuterium. The deuterium in 1 m3 has an energy equivalent to that of 300 metric tons of coal. There are about 1.4 x 10 18 m3 of water in the oceans, with an energy equivalent of more than 1024 kWh. If we can succeed of a practical source of fusion power, then Mankind is assured of a plentiful supply of energy for millennia! (Energy in Perspective, chapter 4, Sources of Energy, pg 76)
 * __ Intro; Rationale/Purpose __**

Because like electrical charges repel each other with a force which is inversely proportional to the square of their distance apart, the repulsive force between two nuclei is very great at distances comparable with their dimensions. For fusion to take place, it requires that the two nuclei approach each other with speeds sufficiently great to overcome this repulsion. If the matter of which they are part is sufficiently hot, their thermal motion will ensure that some of them will do just this, but temperatures of the order of a hundred million degrees are necessary. This type of reactions is called ‘thermonuclear’, and the rate at which such reactions proceed depends on the nuclei concerned and the conditions of temperature and pressure. It takes many millions of years for a small fraction of the protons in the stars to become helium nuclei; in the hydrogen bomb this happens to deuterons in less than a millionth of a second. The **problem** which is being studied in many laboratories all over the world is to establish conditions under which fusion energy can be liberated at a controlled rate, so that it can be made to do useful work Because Coulomb repulsive forces between particles are proportional to Z1Z2, the product of the two atomic numbers, our best chance of achieving fusion in the laboratory will be by using the lightest elements, isotopes of hydrogen (Z = 1) page 20. The three most important reactions are shown below, together with the energies released: [for equations, refer to word document]
 * __Basic Principles: The Process__**

The first two reactions are of great importance because deuterium occurs, to the extent of one part in 6500 in natural hydrogen, and is thus relatively abundant. The third reaction involves the isotope tritium, which does not occur in nature to any appreciable extent and has to be made artificially, for example as in the second reaction. However, the third reaction has a much larger cross-section than the other two at the same energy and so we can hope to get it going at a lower temperature , page 20. There are two different reaction cycles that are proposed for fusion reactors. The first one, shown above, involves the use only of deuterium as fuel. Because of the enormous supply of deuterium in the oceans, the fuel for this system is essentially limitless. In the other scheme, lithium (actually, the isotope 6Li) is required in addition to deuterium. Lithium is widely distributed on Earth but does not naturally occur in elemental form due to its high reactivity. Although lithium must be mined from deposits in the Earth’s crust, where it is present in a range from 20 to 70 ppm by weight, the potential supply is very large and should last for 100,000 years or more, even at high consumption rates. In keeping with its name, lithium forms a minor part of igneous rocks, with the largest concentrations in granites. In both of the proposed fusion cycles, there is no limit to the fuel supply in the foreseeable future. (Energy in Perspective, Chapter 5, Nuclear Energy, pgs 95-137)

// Deuterium-lithium cycle: // 6Li + n → 4He + 3H + 4.8 MeV __ 2H + 3H → 4He + n + 17.6 MeV __ 6Li + 2H → 2 4He + 22.4 MeV

(Energy in Perspective, Chapter 5, Nuclear Energy, pgs 95-137)

(move up ) As previously mentioned, in a fusion reaction, the electrical repulsion between the two nuclei resists their combing into a single nucleus. Consequently, a fusion reaction between two deuterium nuclei will take place only if the nuclei are projected toward one another with high speeds. (We could use an accelerator of some sort, but such a method is not practical if we expect to produce useful amounts of fusion energy.) Another way is to take advantage of the fact that the atoms in a gas are continually in motion - if we need high speeds, we raise the temperature. However, in order to achieve the high speeds that are necessary to produce fusion reactions among deuterium atoms, a temperature of about 100 million degrees centigrade is needed! Nuclear reactions that require these extraordinarily high temperatures are called thermonuclear reactions. (Energy in Perspective, Chapter 5, Nuclear Energy, pgs 95-137) The interior of the Sun is at a sufficiently high temperature that fusion reactions take place. Indeed, the Sun’s source of energy is the fusing together of hydrogen in the core to produce helium. (On the earth, thermonuclear temperatures can be generated in the explosions of nuclear fission devices.) (Energy in Perspective, Chapter 5, Nuclear Energy, pgs 95-137) - at a temperature of 1 741 MK, a pressure of 60 atm is required for a substantial amount of energy to be formed, page 24. - needs containment (see google docs) - the temperature of the hottest furnace we can make on earth is about half that of the solar surface (around 3000 K), but even with the best vacuum we can produce, the degree of ionization of hydrogen is only about 10-13. Heat, therefore, is of no practical use in producing a plasma, and we must seek some other way. (LOOK UP ON INTERNET ) (Unfortunately, we do not know how to obtain useful amounts of energy from nuclear fusion reactions; the one new source of energy that we do know how to exploit is nuclear fission energy.) (Energy in Perspective, Chapter 5, Nuclear Energy, pgs 95-137)
 * __ Geographic, Geologic, & Environmental Requirements __**
 * __ Concerns __**

Deuterium-Tritium fusion results in the stable He with 4 nucleons. This isotope has a natural abundance of 99.999863% and may be considered harmless. However, to procure the amount of tritium needed for the fusion of deuterium and tritium, tritium must be synthetically manufactured through one of the following reactions: 10 n + 63 Li →  31 T + <span style="font-family: 'Verdana','sans-serif'; font-size: 8pt;">42 <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">He <span style="font-family: 'Verdana','sans-serif'; font-size: 8pt;">10 <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">n + <span style="font-family: 'Verdana','sans-serif'; font-size: 8pt;">73 <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Li <span style="font-family: 'Arial','sans-serif'; font-size: 10pt;">→ <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;"> <span style="font-family: 'Verdana','sans-serif'; font-size: 8pt;">31 <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">T + <span style="font-family: 'Verdana','sans-serif'; font-size: 8pt;">42 <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">He + <span style="font-family: 'Verdana','sans-serif'; font-size: 8pt;">10 <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">n These reactions show that either one of two isotopes of lithium are needed in order to synthesize tritium, therefore the mining of lithium must be considered. The obtainment of the reactants for this form of nuclear fusion suggest no environmental threat. <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: 150%;">Reactants necessary: D-T, Lithium, deuterium, tritium, neutron D-D, Deuterium D-He, Deuterium, Helium p-B, Boron, proton
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Environmental Impacts of Reactants/Products **<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">

<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Products: D-T, Helium, neutron, tritium D-D, Tritium & Hydrogen OR Helium & neutron D-He, Helium, high energy proton p-B, Helium

<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: 150%;">After looking at these products and reactants, it may be concluded that nuclear fusion reactants and products do not present any harm to the environment. (SPECIFICALLY, look up a good site about non-ionizing radiation, which is produced through nuclear fusion and does not have enough energy per photon to ionize atoms or molecules.)

However, neutron interactions are largely ionizing, for example when neutron absorption results in gamma emission and the gamma subsequently removes an electron from an atom, or a nucleus recoiling from a neutron interaction is ionized and causes more traditional subsequent ionization in other atoms.<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: 150%;"> <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;"> Source Wikipedia....


 * Environmental Impacts due to Thermal Pollution**

Nuclear power plants, because of their lower efficiencies, present thermal pollution problems that are about 30% greater than electric generating plants. Assuming that a fusion power plant is generating electricity through the use of a steam powered turbine, the main concern is how the heated water is being disposed. If the water is being discharged into neighbouring aquatic environments, the aquatic life will likely be placed in an uncomfortable condition. The uncomfortable conditions are primarily characterized by a reduction in oxygen content in the water, which could then potentially reduce the growth rate of aquatic plants and animals. To combat thermal pollution, newer plants are equipped with cooling towers, whose purpose is dissipating excess heat into the atmosphere as opposed to the water system.

Source Energy in Perspective: Jerry B. Marion, Marvin L. Roush Ch 7, pg. 183-184

<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: 150%;">---
 * Environmental Impacts of Nuclear Plants**

I'm (Kieran’s) going to look at the bio textbook for info on this


 * __ Relativised Output Predictions __**

- Here's everything ADAM got out of that fusion library book: __Fusion: The Energy of the Universe__

Pg. 15 · Iron and nickel are the most stable elements (lowest mass defect per nucleon) o Mass defect: protons and neutrons have slightly less mass when combined into a nucleus than when they exist as a free particle § Based on Einstein: E = mc^2 (higher mass defect, more potential energy) o Lighter elements can release energy through fusion (more energy) Pg. 33-36 · In the sun, two hydrogen atoms fuse to form deuterium · For future nuclear fusion power plants, the most optimal reaction is between deuterium and tritium (has fastest reaction rate, requires lowest temperature) o 1g of deuterium will produce 300 GJ of electricity o There is an indefinite supply of deuterium on Earth (found in water, 1 in 6700) § Can extract deuterium from water using electrolysis o Tritium must be manufactured § Is radioactive (half-life 12.3 years) § Can be manufactured by bombarding lithium with a neutron § Found in Earth’s crust (30 000 year supply) (pg. 138) · Overall reaction: o Deuterium + tritium à neutron + helium-4 o Lithium-6 + neutron (from first reaction) à helium-4 o Fuels: deuterium (from water) and tritium (from lithium) o Waste: helium Pg. 36-41 · For fusion to occur, nuclei must be brought very close together o Must overcome strong electrical force of repulsion § At a certain distance, attractive nuclear force overcomes repulsive electrical force o Nuclei must be accelerated by 100 000 volts to have sufficient energy for fusion to occur § Only 1 in 100 million collisions will result in fusion o Need to increase fraction of successful collisions, prevent nuclei from unsuccessful collisions from escaping · Thermonuclear fusion: heat mixture of deuterium and tritium gas to 200 million degrees Celsius o Plasma formed: atoms become ionized, lose electrons o Need to contain hot plasma § Magnetic confinement: magnetic field prevents charged particles in plasma from contacting wall of container · Superconducting magnetic coils must be cooled to extremely low temperatures (e.g. liquid helium) (pg. 132) § Internal confinement: compress and heat fuel so fusion takes place before plasma can expand and touch the walls of the container Pg. 41-42 · Plasma must be heated to temperature necessary to sustain fusion o At first, plasma must be heated with external energy source o Once reaction begins, alpha particles (helium atoms) produced (releases energy) § Alpha particles cannot escape magnetic field; their energy is used to sustain the temperature of the plasma § Ignition: alpha heating sustains plasma temperature; fusion reaction becomes self-sustaining Pg. 96-97 · Plasma that escapes the magnetic field cools rapidly when it touches a solid surface o No danger of explosions or damage to environment Chapter 11 · Contains diagrams and schematics for proposed nuclear fusion power plants Pg. 129-131 · Structural surfaces of a fusion power plant will be placed under extreme stress o Proposed design: “concentric layers” § Plasma core, first wall, blanket (absorbs neutrons to produce tritium, heat energy is captured here, converted into steam which turns generators), neutron shield, vacuum vessel, magnetic coils (for magnetic confinement), second radiation shield o Since inner layers are trapped within outer layers, maintenance and repair are difficult o Structures will have to be replaced over time § Structures surrounding plasma will become radioactive (damaged by heat and radiation) § Maintenance and repair must be done by robots Pg. 141 · Fusion produces no radioactive by-products o Only the structure itself will become radioactive o With careful choice of structural materials, radioactivity levels may fall to very low values after only 100 years Pg. 150-151 · Fusion power is intrinsically safe o Fission plants can melt down because they contain enough fuel for many years o Fusion plants contain only enough fuel for a few seconds § If the fuel is not replaced, the reaction stops · Fusion fuel cycle produced no radioactive waste, only helium o Lithium and water (“fuels”) are not radioactive Pg. 49-50 · Magnetic confinement o Charged particle experiences magnetic force when moving through uniform magnetic field § No force for motion parallel to field § Magnetic force causes particles to move in circular paths Pg. 95-96 · Tokamaks: magnetic fields stabilize and contain plasma as of 1982, scientists had struggled in their construction of effective nuclear fusion reactors. One method thought of is to confine the plasma in a magnetic field while the nuclei interact. An experimental facility of this type is the Soviet "Tokamak." Similar machines have been constructed in the US and in Europe. Any proposed machines must exceed the point where the amount of energy released in fusion reactions is equal to the energy required to heat and confine the plasma. o Toroidal field: produced by copper coil wound into shape of torus (“donut ring”) o Poloidal field: generated by electric current that flows in plasma

=Geological, Geographic, and Environmental Requirements=

When harnessing the power of nuclear fusion, geologic, geographic, and environmental requirements must be addressed in order to properly gauge the effectiveness of the technology. To begin, the scarcity of reactants is of great importance, and must be considered when examining nuclear fusion. Since only a limited number of possible fusion reactions are currently being conducted, reactants specific to these reactions are most interesting. The easiest (according to the Lawson criterion) and most promising nuclear reaction involves the fusion of deuterium and tritium, two naturally occurring isotopes of hydrogen. Deuterium, often called heavy hydrogen, accounts for 0.015% of all naturally occurring hydrogen in the oceans on Earth, and as a result is relatively easy to extract. Until 1997, Canada was hailed as the world's leading producer in the form of heavy water. Consequently, until 1997, Canada was the largest producer (enrichor/concentrator) of deuterium (--). On the other hand, tritium occurs naturally in only negligible amounts due to its [|radioactive] [|half-life] of 12.32 years and must therefore be synthetically manufactured, often through the following reaction involving lithium: Although the supply of lithium is more limited than that of deuterium, it is still large enough to supply the world's energy demand for thousands of years. In order for nuclear fusion to become a player in the Canadian power industry, the country would have to either produce, or import quantities of deuterium and tritium.
 * <span style="-moz-box-orient: vertical; display: inline-block; font-size: 80%; line-height: 1em; margin-bottom: -0.4em; min-height: 1em; text-align: right; vertical-align: bottom;">[|63] [|Li] || + || [|n] || → || <span style="-moz-box-orient: vertical; display: inline-block; font-size: 80%; line-height: 1em; margin-bottom: -0.4em; min-height: 1em; text-align: right; vertical-align: bottom;">[|42] [|He] || ( || 2.05 [|MeV] || ) || + || <span style="-moz-box-orient: vertical; display: inline-block; font-size: 80%; line-height: 1em; margin-bottom: -0.4em; min-height: 1em; text-align: right; vertical-align: bottom;"> 3 1 T || ( || 2.75 [|MeV] || ) ||

Similar to hydrogen, tritium is difficult to contain and may leak from reactors in some quantity. Some estimates suggest that this would represent a fairly large environmental release of radioactivity.