ITER reactorPosted by shaik on Thursday, November 5, 2009
Under: science & technology - the latest revolutionary experiments
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Cut-away of a model of the ITER Vacuum Vessel showing part of the 440 Blanket modules attached to the inner wall and the Divertor cassettes at the bottom ITER (originally the International Thermonuclear Experimental Reactor) is an international tokamak (magnetic confinement fusion) research/engineering project that could help to make the transition from today's studies of plasma physics to future electricity-producing fusion power plants. It builds on research done with devices such as DIII-D, EAST,ADITYA, KSTAR, TFTR, ASDEX Upgrade, Joint European Torus, JT-60, Tore Supra and T-15.
[edit] Background On November 21, 2006, the seven participants formally agreed to fund the creation of a nuclear fusion reactor.[1] The program is anticipated to last for 30 years – 10 for construction, and 20 of operation. ITER was originally expected to cost approximately €5bn, but the rising price of raw materials and changes to the initial design may see that amount double.[2] The reactor is expected to take nearly 10 years to build and is scheduled to be switched on in 2018.[2] If completed, ITER would be one of the most expensive modern technoscientific megaprojects. Site preparation has begun in Cadarache, France and procurement of large components has started.[3] ITER is designed to produce approximately 500 MW of fusion power sustained for up to 1,000 seconds[4] (compared to JET's peak of 16 MW for less than a second) by the fusion of about 0.5 g of deuterium/tritium mixture in its approximately 840 m3 reactor chamber. Although ITER is expected to produce (in the form of heat) 5-10 times more energy than the amount consumed to heat up the plasma to fusion temperatures, the generated heat will not be used to generate any electricity. In assessing the potential for global and sustainable energy production in the long term it is clear that the diminishing availability and rising cost of energy based on carbon combined with the increased emphasis on low environmental impact energy sources generally, emphasizes the notion that nuclear fusion is one of very few candidates for the large-scale carbon-free production of base-load power. Fusion has many potential attractions, as it is considered to be essentially unlimited, intrinsically safe, widely available, using cheap fuel with no production of CO2 or atmospheric pollutants and producing relatively short-lived waste. ITER was originally an acronym for International Thermonuclear Experimental Reactor, but that title was dropped due to the negative popular connotation of "thermonuclear," especially when in conjunction with "experimental". "Iter" also means "journey", "direction" or "way" in Latin,[5] reflecting ITER's potential role in harnessing nuclear fusion as a peaceful power source. [edit] Objectives ITER's mission is to demonstrate feasibility of fusion power, and prove that it can work without negative impact.[6] Specifically, this includes:
[edit] Reactor overview See also: Nuclear fusion When deuterium and tritium fuse, two nuclei come together to form a helium nucleus (an alpha particle), and a high-energy neutron.
While in fact nearly all stable isotopes lighter on the periodic table than iron will fuse with some other isotope and release energy, deuterium and tritium are by far the most attractive for energy generation as they require the lowest activation energy (thus lowest temperature) to do so. All proto- and mid-life stars radiate enormous amounts of energy generated by fusion processes. Mass for mass, the deuterium-tritium fusion process releases roughly three times as much energy as uranium 235 fission, and millions of times more energy than a chemical reaction such as the burning of coal. It is the goal of a fusion power plant to harness this energy to produce electricity. The activation energy for fusion is so high because the protons in each nucleus will tend to strongly repel one another, as they each have the same positive charge. A heuristic for estimating reaction rates is that nuclei must be able to get within 100 femtometer (1 × 10−13 meter) of each other, where the nuclei are increasingly likely to undergo quantum tunnelling past the electrostatic barrier and the turning point where the strong nuclear force and the electrostatic force are equally balanced, allowing them to fuse. In ITER, this distance of approach is made possible by high temperatures and magnetic confinement. High temperatures give the nuclei enough energy to overcome their electrostatic repulsion (see Maxwell-Boltzmann distribution). For deuterium and tritium, the optimal reaction rates occur at temperatures on the order of 100,000,000 K. The plasma is heated to a high temperature by ohmic heating (running a current through the plasma). Additional heating is applied using neutral beam injection (which cross magnetic field lines without a net deflection and will not cause a large electromagnetic disruption) and radio frequency (RF) or microwave heating. At such high temperatures, particles have a vast kinetic energy, and hence velocity. If unconfined, the particles will rapidly escape, taking the energy with them, cooling the plasma to the point where net energy is no longer produced. A successful reactor would need to contain the particles in a small enough volume for a long enough time for much of the plasma to fuse. In ITER and many other magnetic confinement reactors, the plasma, a gas of charged particles, is confined using magnetic fields. A charged particle moving through a magnetic field experiences a force perpendicular to the direction of travel, resulting in centripetal acceleration, thereby confining it to move in a circle. A solid confinement vessel is also needed, both to shield the magnets and other equipment from high temperatures and energetic photons and particles, and to maintain a near-vacuum for the plasma to populate. The containment vessel is subjected to a barrage of very energetic particles, where electrons, ions, photons, alpha particles, and neutrons constantly bombard it and degrade the structure. The material must be designed to endure this environment so that a powerplant would be economical. Tests of such materials will be carried out both at ITER and at IFMIF (International Fusion Materials Irradiation Facility). Once fusion has begun, high energy neutrons will radiate from the reactive regions of the plasma, crossing magnetic field lines easily due to charge neutrality (see neutron flux). Since it is the neutrons that receive the majority of the energy, they will be ITER's primary source of energy output. Ideally, alpha particles will expend their energy in the plasma, further heating it. Beyond the inner wall of the containment vessel one of several test blanket modules will be placed. These are designed to slow and absorb neutrons in a reliable and efficient manner, limiting damage to the rest of the structure, and breeding tritium from lithium and the incoming neutrons for fuel. Energy absorbed from the fast neutrons is extracted and passed into the primary coolant. This heat energy would then be used to power an electricity-generating turbine in a real power plant; however, in ITER this heat is not of scientific interest, and will be extracted and disposed. [edit] History ITER began in 1985 as a collaboration between the European Union (through EURATOM), the USA, the then Soviet Union, and Japan. Conceptual and engineering design phases led to an acceptable, detailed design in 2001, underpinned by US$650 million worth of research and development by the "ITER Parties" to establish its practical feasibility. These parties (with the Russian Federation replacing the Soviet Union and with the USA opting out of the project in 1999 and returning in 2003) were joined in negotiations on the future construction, operation and decommissioning of ITER by Canada (who then terminated their participation at the end of 2003), the People's Republic of China, and the Republic of Korea. India officially became part of ITER on 6 December 2005. On 28 June 2005, it was officially announced that ITER will be built in the European Union in Southern France. The negotiations that led to the decision ended in a compromise between the EU and Japan, in that Japan was promised 20% of the research staff on the French location of ITER, as well as the head of the administrative body of ITER. In addition, another research facility for the project will be built in Japan, and the European Union has agreed to contribute about 50% of the costs of this institution.[7] On 21 November 2006, an international consortium signed a formal agreement to build the reactor.[8] On 24 September 2007, the People's Republic of China became the seventh party who had deposited the ITER Agreement to the IAEA. On 24 October 2007, the ITER Agreement entered into force and the ITER Organization legally came into existence. ITER will run in parallel with a materials test facility, the International Fusion Materials Irradiation Facility (IFMIF), which will develop materials suitable for use in the extreme conditions that will be found in future fusion power plants. Both of these will be followed by a demonstration power plant, DEMO, which would generate electricity. DEMO would be the first to produce electric energy for commercial use. A "fast track" plan to a commercial fusion power plant has been sketched out.[9] This scenario, which assumes that ITER continues to demonstrate that the tokamak line of magnetic confinement is the most promising for power generation, anticipates a full-scale power plant coming on-line in 2050, potentially leading to a large-scale adoption of fusion power over the following thirty years. [edit] Technical design Selected facts: The central solenoid coil will use superconducting niobium-tin, to carry 46 kA and produce a field of 13.5 teslas. The 18 toroidal field coils will also use niobium-tin. At maximum field of 11.8 T they will store 41 GJ. They have been tested at a record 80 kA. Other lower field ITER magnets (PF and CC) will use niobium-titanium. [edit] Location
Location of Cadarache, France, EU The process of selecting a location for ITER was long and drawn out. The most likely sites were Cadarache in Provence-Alpes-Côte-d'Azur, France and Rokkasho, Aomori, Japan. Additionally, Canada announced a bid for the site in Clarington in May 2001, but withdrew from the race in 2003. Spain also offered a site at Vandellòs on 17 April 2002, but the EU decided to concentrate its support solely behind the French site in late November 2003. From this point on, the choice was between France and Japan. On 3 May 2005, the EU and Japan agreed to a process which would settle their dispute by July. At the final meeting in Moscow on 28 June 2005, the participating parties agreed on the site in Cadarache in Provence-Alpes-Côte-d'Azur, France. Construction of the ITER complex began in 2008, while assembly of the tokamak itself is scheduled to begin in the year 2011.[10] [edit] Participants Currently there are seven national and supranational parties participating in the ITER program: the European Union (EU; see Fusion for Energy), India, Japan, People's Republic of China, science & technology - the latest revolutionary experiments |
ITER reactorPosted by shaik on Thursday, November 5, 2009
Under: science & technology - the latest revolutionary experiments
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