Nuclear Fusion: A new alternative?
Recently, scientists of the Massachusetts Institute of Technology (MIT) added a new milestone to the nuclear fusion advance. For the first time since the Alcator C-Mod reactor was created 23 years ago , the conditions for a two atmospheres pressure and a temperature of 35 million Celsius degrees were met. The site, wich will be closed soon opened the door to many nuclear fusion achievements. Actually, the idea of a joint international fusion experiment was already born in 1885 within ITER Tokamak project, but it wasn’t until 2006 that an agreement was signed.
The European Union, India, the United States, Russia, China, Japan and Korea agreed to share the costs and benefits of the project in order to build together a new magnetic fusion device for 2035. Accordingly to it, a site in Marseille is already under construction (the last image) since 2010. France has managed to provide all necessary accommodations for ITER employees , including school for their children. In 2012, ITER organisation was licensed by the French administration as a nuclear operator, hence Hereof projects seems to be one the first projects to consolidate the nuclear fusion energy as a serious alternative to nowadays energy production.
First, the Tokamak 23 000 tonnes device is shaped by an internal doughnut-form vacuum chamber. The stainless steel vacuum vessels (in orange in the image) will host the fusion reactions and will be protected by blanket shields (in purple). Superconducting magnets (in blue) will be part of the internal machine, and the divertor (in red) wich is placed at the bottom of the chamber, will have the function of exhausting waste gases and impurities. Finally the cryostat (in white) is an external element that covers the vacuum chamber and ensures an ultra-cool adjacent environment. In order to initiate the reaction, atoms of deuterium (D), tritium (T), and two isotopes of hydrogen, are introduced into the vacuum chamber at a temperature that is above 150 million Celsius degrees and a pressure of at least 2 atmospheres. The vessels charged with a powerful electric current will make the atoms of hydrogen lose their electrons. Therefore they become ionised and under the influence of heat and pressure plasma is created. With a given density of plasma, particles and their magnets-controlled confinement will collide at a very high speed (fast and disordered movement caused by the high temperature) despite the natural electrical repulsion of the atoms charged positively. While a particle of deuterium fuses with one of tritium, a new atom is born: helium. Upon the reaction, a neutron is produced together with huge amounts of energy (due to the loss of initial mass: the mass of the neutron). This energy can be calculated according to the formula E=MC², M referring to the mass of the neutron and C to the speed of light. Once the neutron hits the blanket shields, its kinetic energy (energy of speed) is transformed into heat energy. A similar phenomenon occurs on the sun at a much bigger scale releasing much more energy.
Possible advantages in the case of succes
Nuclear fusion could be a reaction that will allow to produce nearly four million times more energy than a conventional chemical reaction such as coal , gas or fuel burning. Moreover, fusion is expected to provide four times more energy than the fission reaction which is actually in use. Another advantage of nuclear fusion is its environmentally friendly characteristic: No greenhouse gas emissions. The nuclear fusion only releases helium which is an inert, non-toxic gas. The third, non-negligible benefit from the fusion equation is that no radioactive waste is released; a matter that raised the concerns of decision-makers throughout Europe, especially after the Fukushima incident of 2011. Thereof, Germany decided to dismantle all of its nuclear reactors by 2022. Anyway, if an unfortunate accident happens to occur again near a future Tokamak, the difficult conditions needed to reach and maintain the fusion reaction would guarantee a very quick cool down and limited consequences. At last, the cost per unit of energy produced out of fusion is expected to be similar to fission’s one, while at the same time, the operator will be using a new, more reliable technology.
Main challenges of Iter Tokamak
Iter aims to reach an output of over 500 Megawatt (MW) for an input power of 50 MW (ten times the initial input), when just in 1997 , the experiments of the older European Tokamak Jet led to an output of 16 MW for an input of 24 MW. To reach such a goal, bigger reactors and big advances on technology will be needed to conclude such positive results. Research and experiments will be required to improve heating, control, diagnostics, remote maintenance. The implementation of future fusion power plants able to transform heat energy into electric energy (maybe via integrated turbines and generator?) will also become an absolut necessity.
Concerning the availability of deuterium and tritium atoms on earth. The first one is easily produced by the distillation of water whereas the second one is rarer and more difficult to produce. Tritium reserves are actually estimated at 20 kilogrammes knowing that after Iter Tokamak, 300 grams of tritium per day will be required to produce 800 MW capacities. Employees working for Iter Group are expected to develop a self-sufficient tritium breeding system within Iter Tokamak vacuum vessels: lithium, incorporated to the blanket, would interact with the detached neutrons. As a result, new tritium atoms would be formed and the fusion reaction could thereby hold for a longer time. For the same purpose of increasing the duration of the fusion reaction, scientists hope to find a way to keep the optimal temperature inside the vacuum chamber. According to them, this could occur via the concept of the burning plasma: a plasma sufficiently confined to benefit from the heat already released by the reaction. Consequently, a longer fusion reaction would procure more energy for the same input.
In conclusion, nuclear fusion is a mechanism that transforms the energy generated by electro-magnetic power into heat energy through the interaction of certain atoms and under certain conditions. The benefits of such a mechanism are certain, thanks to a less polluted, and dangerous production of energy for the same cost. Meanwhile, some challenges such as increasing the duration of the fusion reaction, finding and producing the necessary input materials, and the implementation of enough power plants, must be reached. Nevertheless, there is no choice: In 2035 fossil fuels will become rarer and rarer: countries will either have to fight against each other’s within a combat to death, or fight together within a combat of life…
Sources: -iter.org -weforum.com