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Nuclear Fusion Reactor  (Source: The Institute of Telecommunications Professionals)
Could lead to an endless supply of clean energy

Researchers from Purdue University have found mechanisms that are vital to interactions between surfaces inside a thermonuclear fusion reactor and hot plasma, which could lead to the development of coatings capable of tolerating radiation damage and ultimately, fusion power plants. 

The inner lining of a fusion reactor often faces horrific conditions leading to radiation damage due to the hot plasma. With the use of nanotechnology, nuclear engineers are looking to "define" small features in the coating as a way to understand and develop a new material that can come in contact with plasma and not be harmed. Finding a material durable enough to withstand such harsh conditions has been difficult, until now. 

Along with researchers at Princeton University in the Princeton Plasma Physics Laboratory, Purdue researchers are using the National Spherical Torus Experiment to test materials, which is the country's only spherical tokamak reactor. They will also study materials in a special "plasma-materials interface probe," then transfer these materials to an "in situ surface analysis facility laboratory."

"We will bring the samples in and study them right there, and will be able to do the characterization in real time to see what happens to the surfaces," said Jean Paul Allain, an assistant professor of nuclear engineering at Purdue University. "We're also going to use computational modeling to connect the fundamental physics learned in our experiments and what we observe inside the tokamak."

One of the tested linings is lithiated graphite, which consists of lithium being added to the inner graphite wall, and when it diffuses into the reactor wall. Then deuterium atoms and the lithiated graphite bind together in the fuel inside these tokamaks, which are what the fusion reactors are called. A magnetic field inside the tokamaks encloses a circular-shaped plasma of deuterium, which is an isotope of hydrogen. 

When a fusion reaction occurs, deuterium atoms hit the inner lining of the fusion reactor and can be sent back to the core and recycled back to the plasma, or they're "pumped," which causes them to bind with the lithiated graphite. 

"We now have an understanding of how the lithiated graphite controls the recycling of hydrogen," said Allain. "This is the first time anyone has looked systematically at the chemistry and physics of pumping by the lithiated graphite. We are learning, at the atomic level, exactly how it is pumped and what dictates the binding of deuterium in this lithiated graphite. So we now have improved insight on how to recondition the surfaces of the tokamak."

The use of a fusion power plant could cut exhaust completely because the deuterium fuel is in seawater. Also, it could produce 10 times more energy than a nuclear fission reactor. Plants like these would be an endless supply of clean energy.

This study was led by Chase Taylor, a doctoral student, Bryan Heim, a graduate student, and Allain. Two papers have been written on the topic, and one will be presented at the Fusion Nuclear Science and Technology/Plasma Facing Components meeting in August.



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Fusion Power - Is it really that clean?
By 3DoubleD on 7/28/2010 3:23:08 PM , Rating: 2
Fusion power is often held as the holy grail of energy production. Clearly it is as misunderstood as power from nuclear fission reactors. The waste from a fusion reactor would, in practice, differ only slightly from a traditional nuclear fission reactor. By this I mean that the entire reactor itself becomes radioactive, necessitating the same storage facilities that are required for current fission power plants. Fusion reactions create neutrons, which are not confined by the magnetic field. These neutrons cause nuclear reactions in the surround reactor components, as they do in fission reactors. Furthermore, the fusion reactor, by design and necessity, operates in much more extreme conditions than a fission reactor. Thermal fatigue and radiation damage in a fusion reactor will be more extensive than a fission reactor and will likely result in more frequent refurbishments and repairs (a topic that this article hints to). The removal of radioactive reactor parts is no trivial task.

So separate from the fuel that is required and their byproducts. The two technologies share similar problems: a) radioactive waste, b) long and difficult repairs, and c) high capital costs (~$2-5 Billion for a plant). In regards to the fuel supply, we can run on fission power for thousands of years and there is no immediate need change fuel sources. By then, hopefully we have figured out an alternative fuel source or how to reprocess fission fuel efficiently.

So I guess my point is, why does everyone drool over the "holy grail" of power generation when we already have a tried and tested solution: nuclear fission. It really isn't much different. And to answer the inevitable nuclear weapons proliferation argument before it is brought up - you don't need weapons grade uranium or plutonium to run a fission reactor.




RE: Fusion Power - Is it really that clean?
By bupkus on 7/28/2010 3:42:39 PM , Rating: 3
quote:
And to answer the inevitable nuclear weapons proliferation argument before it is brought up - you don't need weapons grade uranium or plutonium to run a fission reactor.
Just playing devil's advocate here.
However, the materials used can be incorporated into a simple dirty bomb.


By Wiggy Mcshades on 7/28/2010 4:30:29 PM , Rating: 3
should we honestly shy away from a clean source of energy (both fission and fusion) just because the by products could possibly be used in a negative way? They wouldn't be selling this stuff at yard sales nor do they leave it unguarded.


RE: Fusion Power - Is it really that clean?
By wiz220 on 7/28/2010 5:21:44 PM , Rating: 5
This quote from the Fusion Programme Evaluation Board report prepared for the European Commission seems to disagree with your comment about fusion waste being only "slightly" different from fission waste:

"Over their lifetimes, fusion reactors would generate, by component replacement and decommissioning, activated material similar in volume to that of fission reactors, but qualitatively different in that the long-term radiotoxicity is considerably lower [no radioactive spent fuel]. The use of advanced low activation materials and recycling could further ease the management of radioactive waste. Overall, the study indicates that fusion waste would not constitute a burden for future generations. ..."

More excerpts from the report can be read here:

http://fusion.org.uk/susdev/environ.htm


By menace on 7/28/2010 5:40:30 PM , Rating: 3
Yes that is what I recall from years ago (probably read in in Popular Science), the differences are in the half-lifes. Makes sense, I believe lighter unstable isotopes tend to decay faster and with fewer transitions to reach a stable isotope.


By 3DoubleD on 7/28/2010 6:30:38 PM , Rating: 2
The "slightly" different classification is certainly valid with intelligent fuel handling. The use of nuclear transmutation and designs such as a traveling wave reactor drastically reduce the amount of nuclear waste. With such technology, nuclear proliferation becomes a concern. However, the traveling wave reactor would rather safely stow such isotopes within the reactor for the duration of the fuel cycle. The length of this fuel cycle would be extremely long (~50-100 years). At the very least until nuclear fusion is a viable option, it would be ridiculous if this type of plant doesn't produce most of the base load power.

To read more: Wald, M. (2009-March/April). 10 Emerging Technologies of 2009: Traveling-Wave Reactor. MIT Technology Review.

In regards to your quote, the same techniques to reduce the radioactivity in fission reactor components are used. The big difference is that material requirements in a fusion reactor are far more extreme. Nuclear fission reactors almost exclusively use zirconium alloys as zirconium has a very small neutron capture cross-section in addition to good resistance to structural degradation by radiation. A small neutron capture cross-section only reduces the rate by which the zirconium atoms become radioactive. Furthermore, these zirconium alloys have serious creep problems under typical fission reactor temperatures, leading to their failure after ~20-30 years. In the case of a fusion reactor, zirconium may not even be a choice. Given the fact that no net power output has been achieved, I'd wager that their choice of reactor materials is mostly determined by "does it benefit the reaction?", not "how hot does this get after 10 years?". To summarize, I think they are really saying "we don't know yet, but we hope it's as good as what current day nuclear reactors achieve - minus the fission products". You already know my opinion on what should be done with fission products. Cheers.


By inighthawki on 7/28/2010 5:25:53 PM , Rating: 2
But even while the reactors themselves suffer from radiation damage, the fusion reactor does not incur the same "byproducts" of the nuclear reaction like fission does. While the fission process can produce large quantities of radioactive materials, the fusion reaction produces stable helium, but lots of radiation.


RE: Fusion Power - Is it really that clean?
By sleepeeg3 on 7/29/2010 2:45:23 AM , Rating: 1
We only have enough estimated fissile material for 80-200 years. That is why fusion is imperative to our future.

From this article, I am not sure what the advantage is of the lithiated graphite. Does it extend the life of the coating? From what I recall, graphite has the advantage of being cheap, but also requires the highest rate of replacement, creating the most low level radioactive waste.


By Fritzr on 7/31/2010 1:53:31 AM , Rating: 2
That limit assumes that only high grade naturally occurring fuel is used.

Breeder reactors convert nuclear "waste" into new fuel that can be used to fuel other reactors. The benefit of breeders is that the waste product of the reaction is a greater amount of usable fuel than is needed to charge the reactor. The "Great Evil" is that the common designs are meant to produce weapons grade plutonium. The designs that produce "poisoned" plutonium unsuitable for weapons were shelved as they could not be used for weapons production, but they do exist and have been tested.

The Traveling Wave reactor mentioned & linked in an earlier post is fueled with "spent" nuclear fuel.

There is also research into recycling nuclear waste to extract the remaining fuel usable for current generation reactors.

Fast Flux Breeder Reactors burn the nuclear waste from other reactor designs and convert long lived isotopes into short lived isotopes. The waste product is then processed to remove the residual usable fuel and the remaining mid grade nuclear waste only needs to be stored for a century or two. This reactor class could be used to burn the high level waste created by the effects of the fusion reaction on the reactor vessel and it's containment.

The difference between fusion and these alternate fission designs is that the alternative fission reactors exist and operate today whereas the fusion reactors for at least the last 40yrs will be producing power "within the next 10yrs".

That is 40 years ago researchers promised fusion power as early as 30yrs ago. 40 years later they are making the same promise..."We're almost there, only 10yrs more!"


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