DEMO
2618773
206406360
2008-04-18T02:35:48Z
Johnfos
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future tag
{{future power plant}}
{{speculation}}
{{context|date=July 2007}}
{{otheruses3|demo}}
'''DEMO''' (DEMOnstration Power Plant) is a proposed [[nuclear fusion]] [[power station|power plant]] that is intended to build upon the expected success of the [[ITER]] (originally an acronym for International Thermonuclear Experimental Reactor) nuclear fusion power plant. Whereas ITER's goal is to produce 500 million [[watt|watts]] of [[fusion power]] for at least 400 seconds, the goal of DEMO will be to produce at least four times that much fusion power on a continual basis. Moreover, while ITER's goal is to produce 10 times as much power as is required for breakeven, DEMO's goal is to produce 25 times as much power. DEMO's 2 gigawatts{{Fact|date=January 2008}} of thermal output will be on the scale of a modern [[electric power]] plant.
To achieve its goals, DEMO must have [[linear]] dimensions about
15% larger than ITER and a [[Plasma (physics)|plasma]] density about 30% greater than ITER. As a [[prototype]] [[Commerce|commercial]] fusion [[Nuclear reactor|reactor]] DEMO could make fusion energy (which does not have the problems associated with [[fossil fuel]]s or [[Nuclear fission|fission]] energy) available within 20 years. Subsequent commercial fusion reactors could be built for nearly a quarter of the cost of DEMO if things go according to plan.<ref name="ITERorg">{{cite web | |work= The ITER Project |title = Beyond ITER | publisher = Information Services, Princeton Plasma Physics Laboratory | url = http://www.iter.org/Future-beyond.htm | accessdate = 2006-11-11 }}</ref>
<ref name="EFDA_Activities">{{cite web | |work= EFDA |title = Overview of EFDA Activities | publisher = European Fusion Development Agreement | url = http://www.efda.org/about_efda/downloads/EFDAoverview.ppt | accessdate = 2006-11-11 }}</ref>
While fusion reactors like ITER and DEMO will not produce [[transuranic]] wastes, some of the components of the ITER and DEMO reactors will become radioactive due to [[neutron]]s impinging upon them. It is hoped that careful material choice will mean that the wastes produced in this way will have much shorter half lives than the waste from [[fission reactor]]s, with wastes remaining harmful for less than one century. The process of manufacturing tritium currently produces long-lived waste, but both ITER and DEMO, it is hoped, will produce their own tritium, dispensing with the fission reactor currently used for this purpose.
==Timeline==
The following timetable was presented at the IAEA Fusion Energy Conference in 2004 by Prof. Sir Chris Llewellyn Smith.<ref name="ITERorg"/> These dates are conceptual and as such are subject to change.
*Conceptual design is to be complete by 2017
*Engineering design is to be complete by 2024
*The first 'Construction Phase' is to last from 2024 to 2033
*The first phase of operation is to last from 2033 to 2038
*The plant is then to be expanded/updated
*The second phase of operation is to last from 2040 onwards
==How the reactor will work==
[[Image:Deuterium-tritium_fusion.svg|250px|right|thumb|The [[deuterium]]-[[tritium]] (D-T) fusion reaction is considered the most promising for producing [[fusion power]].]]
{{See also|nuclear fusion|fusion power}}
When [[deuterium]] and [[tritium]] fuse, the two [[atomic nucleus|nuclei]] come together to form a [[helium]] nucleus (an [[alpha particle]]) and a high energy [[neutron]].
:<math>{}^{2}_{1}\mbox{H} + {}^{3}_{1}\mbox{H} \rightarrow {}^{4}_{2}\mbox{He} + {}^{1}_{0}\mbox{n} + 17.6 \mbox{ MeV} </math>
There are three problems that DEMO must solve: getting the nuclei to fuse, containing the resulting plasma, and capturing the liberated energy.
*The activation energy for fusion is very large because the [[proton]]s in each nucleus strongly repel one another; they are both positively [[Elementary charge|charged]]. In order to fuse, the nuclei must be within 1 [[femtometre]] (1 × 10<sup>−15</sup> metres) of each other, which is achievable using very high temperatures.
*High [[temperatures]] give the nuclei enough energy to overcome their [[electrostatic repulsion]]. This requires temperatures in the region of 100,000,000 [[°C]], using energy from [[microwaves]] and [[ion]] beams.
*Containment vessels melt at these temperatures, so the [[Plasma (physics)|plasma]] is to be kept away from the walls using [[magnetic confinement]].
Once fusion has begun, high [[energy]] neutrons will pour out of the plasma, not affected by the strong magnetic fields (see [[neutron flux]]). Since the neutrons receive the majority of the energy from the fusion, they will be the fusion reactor's source of energy output.
*The [[tokamak]] containment vessel will have a lining composed of ceramic or composite tiles containing tubes in which liquid [[lithium]] will flow.
*Lithium readily absorbs high speed neutrons to form helium and tritium.
*The lithium is processed to remove the helium and tritium.
*The deuterium and tritium are added in carefully measured amounts to the plasma.
*This increase in temperature is passed onto (pressurized) liquid [[water]] in a sealed, pressurized pipe.
*The hot water from the pipe will be used to boil water under lower pressure in a [[heat exchanger]].
*The steam from the heat exchanger will be used to drive the turbine of a generator, to create an [[electrical current]].
==References==
{{reflist}}
{{fusion experiments}}
[[Category:Fusion power]]
[[Category:Fusion reactors]]
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