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On a more serious note; the ITER project building the hot fusion reactor in Cadrache, France, expects to see the beginning of commercial fusion power in the year 2040, if everything goes according to plan. That's a date that sounds real without being depressing.

The walls of the reactor will heat up due to neutron collisions and radiative heat transfer. In ITER, this heat will be conducted to a water cooling system. Temperatures in the plasma will be millions of degrees. Temperatures at the first structural layer, the "blanket" will be somewhere around 1000 K, I believe. Definitely below the melting temperature of reasonable materials. The gigantic electromagnets keep the superhot plasma stable and away from the walls, as much to keep the plasma hot as to keep the walls "cold."

ITER, however, will not operate as a power plant. The cooling water will just dump heat through cooling towers. It's purely a research reactor to study the stability and sustainability of plasma's with Q > 1, and establish operational conditions for the next reactor, known as DEMO. Because it's not really intended to run for more than about 500 seconds at a shot, it's not economical to try to get useful amounts of electricity out of ITER, although adding a turbine in loop with the cooling system is not fundamentally out of the question.

DEMO will be designed for continuous or near-continuous operation. Depending how successful ITER is (and the International Fusion Materials Irradiation Facility, which will develop the appropriate materials for the high neutron flux in a fusion reactor), DEMO may be another intermediate research reactor to finalize a workable commercial design, or it may be the final prototype, with other commercial reactors starting construction about the same time. The plan is to use a similar cooling system, but connect a steam turbine to it.

Regarding the operational byproducts (primarily stable helium), there is a feature in the bottom of the reactor called a diverter. I'm not sure exactly how it works, but my understanding is the helium reaction product being heavier, it tends to the bottom of the plasma, where being on the periphery it cools more and falls out the vents or is magnetically guided out. Moving away from your question, the article says the first commercial reactors will be built in the 2035 time frame. Oddly the ITER team doesn't think so. My understanding is 2035 is potentially feasible if they are able to build DEMO as an operational prototype rather than an additional research plant, but if they need to do further research with DEMO, it will be at least 10, probably more like 15 more years before commercial plants will be available.

Of course, all of this assumes the member countries follow through on their financial and in-kind committments in a timely manner. The US butchered our budget for ITER contributions for 2008. Not a good move on our part, IMO.

As a final note, the article makes a big deal about MIT's PSFC. This strikes me as slightly odd. I'm sure the work being done at MIT is valuable for understanding plasma stability, but in my opinion the Japanese JT-60 reactor, which holds the endurance record for a sustaining a 28 second plasma burn and achieving conditions which with a different fuel mix would have exceeded unity, or the Joint European Torus, which is currently the largest Tokamak in operation (and fuels the reaction by shooting frozen pellets of deuterium into the core 50 times per second...how cool is that?) are both much more exciting.

Yes, I also remember how fission plants would give us electricity so cheap that it wouldn't be worthwhile to meter it.

However there are proposed roadmaps to commercial fusion that are a bit more detailed than "ask me again in 20 years". The plan in that link puts the first commercial fusion reactor at around 2050 though.

Related links: * LDX@MIT
* Physics of magnetically confined fusion [pdf]
* The main principles of magnetic fusion
* Magnetic fusion experiments at LANL
* High density magnetic fusion
* Has a good bit on magnetic confinement
* Can a magnetic field be used to contain plasma?
* International Thermonuclear Experimental Reactor
* What's happening in fusion?
* Design of magnetic fields for fusion experiments [pdf]
* Wikipedia article on the topic
* Magnetized target fusion bibliography
* Plasma physics bibliography
* Databases for plasma physics

* Plasma physics laboratories
* List of plasma physicists
* Plasma on the internet

No it isn't. Water vapor is the most significant. If you eliminate water vapor, than it is the most significant but not by far.

Ok, yes, but we don't usually consider water vapor when we're talking about greenhouse gasses from human activity.

There are a few other good energy sources. Nuclear for example. US has a problem with storing nuclear waste, but it is political, not practical problem. Can you point me to a working "clean coal plant" or is it another piece of vaporware? It does not reduce the CO2 emissions, at best you will be able to store temporarily some of them underground. And I have heard of even crazier ideas of pumping the CO2 deep in the ocean.

On clean coal, yes, it's a matter of not letting the carbon into the atmosphere. Here are the basic options for clean coal. And there are other ways to make much cleaner, more efficient conventional power plants. Here is an example from my city.

That said, I couldn't possibly be more in agreement with you on the subject of nuclear power. It's a political problem, and a classic "NIMBY" problem. The energy production per mass input and per output of managed waste is something that can't be touched. I wish the US was even more involved with ITER than it is. In fact, I've often wondered what would happen if the US could muster the kind of public and political will it would take to devote the kind of resources we're able to collectively justify for wars - no matter one's opinion of a particular war - but could never justify for, e.g., full-scale fusion research.

If they're smart, they'll just leave at the ITER door. That's a big IF...

nuclear power is the answer but we have a fairly limited amount of fuel so a complete switch to fission power isn't workable. Everyone has to keep their fingers crossed that the ITER project pans out or other fuel technology for alternative isotope decay to fissile material works out. The latter is getting very little funding, as far as I understand.

I'm doing my masters in fusion. Grandparent is indeed correct. The reason being, the products of the fusion reaction are regular helium, and neutrons. The neutrons will activate the building which is the source of the low level waste. So we just keep things that get really hot out of the reactor design.

Right now, after ITER's 10 year lifetime, the only components that will need to be considered nuclear waste is are the tungsten components of the first wall (the wall facing the plasma) The products of activated tungsten have a very short half life, so after a year or so, the copper heat sinks will be the hottest components, and they'll be cooler than the tonnes of medical nuclear waste that gets shipped in and out of hospitals every year. There will be no leakage as neither tungsten nor copper are water soluble. The bigger risk is a steam explosion, which has the potential to release some tritiated water and maybe some tungsten oxide (some of which would have been activated by the neutrons) into the local community. But ITER is designed, that in the worst case scenario, there would be no need for evacuation. http://www.iter.org/a/index_faq.htm Choose the safety bullet to read about this. The worst case scenario is assuming the worst possible weather conditions, and that 100% of anything radioactive that could possibly be in the reactor becomes airborne and ingestible.

which, were we smart, would involve putting them in the Marianas trench and folding them back into the earth's mantle to be reprocessed

The trench is an interesting idea. Mind you, the really hot nuclear waste (spent fission fuel rods) are packed full of useable uranium. They can be re-refined and used again. We just... don't yet.

Aha. Costs. I was just at a conference where they were discussing the finer points of ITER. Trust me. International funding sources + over 10 years of them bickering over costs. Decommissioning costs have been included right down to the cardboard boxes for the scientists to pack up their offices.

It's poor speculation. Reagan was very much in favor of ITER. In fact, it was founded due to dialog between him and Gorbachev. If you want to pick an American president to criticize, it was during Clinton's term in 1999 that the US withdrew from the ITER project (along with 10% of ITER's funding). Fortunately, we rejoined in 2003.

http://www.iter.org/a/index_nav_6.htm They've got some speeches here for anyone interested.

And from http://www.iter.org/I.htm

ITER - "The way" in Latin. Formerly interpreted to stand for International Thermonuclear Experimental Reactor, although this usage has been discontinued.

http://www.iter.org/a/index_nav_6.htm They've got some speeches here for anyone interested.

And from http://www.iter.org/I.htm

ITER - "The way" in Latin. Formerly interpreted to stand for International Thermonuclear Experimental Reactor, although this usage has been discontinued.

"With this achievement, the Delegations are pleased to declare that their work is finished, opening the way towards concluding the negotiations at political level." http://www.iter.org/N_12_Joint_Press_Release.htm

The news title should read: "Political Green Light..."
or else is old news...

And why is this submitted to Hardware? Is it because it was so HARD getting to this point?

Now when we finally get a sustainable fusion reaction that produces more energy that it uses, that would be something to write about!

On the day that an international agreement to spend $12 billion is signed, the news is about what some kid is doing in his backyard. Sigh.

Bizarrely enough, not only are they funding it (along with the rest of the developed world), they will sign the consortium agreement today.

If this fusion thing were to miraculously work and we did have a new source of energy, we'd be in the exact same place as the current oil crisis... We'd have to mine for boron-11. And since, like all matter on this planet, it is finite in quantity, we'll eventually have to depend on countries like Turkey for our boron. The same goes for the ITER http://www.iter.org/ technology... they need lithium to generate the fuels required by the device, and eventually, we'll run out of lithium. This is complete bullshit. We should be focusing on ways to store electrical energy more efficiently and working towards more efficient solar technologies.

Well there's always ITER. It's a step in the right direction.

The plan for ITER, as well as any future machine that will use D-T as a fusion fuel, is to utilize a lithium-contining 'blanket' on the interior of the vacuum vessel walls. Lithium can absorb the 14 MeV neutrons that will be flying around as a result of D-T fusion and convert into tritium, aiding the fueling of the reactor! The blanket, in addition to providing fuel for the reaction, will be the primary source of neutron shielding for the device.

More information regarding the technical details of the ITER blanket design can be found here (PDF), and general technical information about ITER here.

The plan for ITER, as well as any future machine that will use D-T as a fusion fuel, is to utilize a lithium-contining 'blanket' on the interior of the vacuum vessel walls. Lithium can absorb the 14 MeV neutrons that will be flying around as a result of D-T fusion and convert into tritium, aiding the fueling of the reactor! The blanket, in addition to providing fuel for the reaction, will be the primary source of neutron shielding for the device.

More information regarding the technical details of the ITER blanket design can be found here (PDF), and general technical information about ITER here.

This has nothing to do with the nuclear reaction itself, but rather than with the mean the nuclear reaction is triggered into a torus-shaped plasma. One of the great challenges is to produce a self-sustained plasma. Since, this Zeus-like experiment seems to prove there is a way to produce a self-sustained plasma for much more long times than it is possible right now in all other fusion experimental reactors, this single thing may lead to significant advances in the nuclear fusion industry if well understood and applicable to plasmas produced inside Tokamak-like devices.

Hope this helped you to better understand the link between these apparently unrelated two things.

Also, ITER is huge. (Picture -- see the little man on the left side?) Furthermore, the extensive use of superconducting materials impedes construction, as they are difficult to construct.

There's a lot of subtlety hiding in that 9 years. As a researcher in the field, I certainly hope that it goes well!

All of your questions are answered in the "Development Programme" section of the ITER FAQ:

http://www.iter.org/a/index_faq.htm

These devices are not fusion reactors, in the power-generation sense. They are research machines used to understand the fundamental physics of plasma confinement and stability. They do not use D-T fuel, as tritium is radioactive and therefore must be strictly controlled. (Besides, the device isn't built for the neutron load of active fusion.) The fuel used is deuterium; the fusion cross-sections are sufficiently low for D-D fusion that at the temperatures achievable in the device D-D fusion events are negligible.

The idea is to discern the physics behind the ELMs and then supress them if it turns out to be beneficial. (This is an open question.) The real prototype fusion reactor will be ITER (at least before the prototype commercial electric plant DEMO comes online following ITER), soon to be under construction in France.

As we're discussing long term solutions, should we bring fusion into the mix?

ITER (and the other tokamak projects) are talking about producing commercial power in the near term, and should at least solve the problem of waste...even if there are other issues.

http://www.iter.org/ (Check out the cheesy front page)

Iter project anyone?

http://www.iter.org/ Apparently it is good to encourage children to stare into the sun, but only if it's man-made.

Background on Iter: Multi-national project involving many forward thinking nations in the interests of capturing fusion power. I beleive the list was something like France, Germany, Japan, Canada... Zimbabwe. It's also fairly old news, I remember my father speaking about it late 2001, while driving past one of the prospective building sites, alas Canada was outbid.

Actually, the z-machine is a relatively cheap device. 100's of millions instead of billions. Much cheaper than other fusion test devices like NIF http://www.llnl.gov/nif/ or ITER http://www.iter.org/

These are multi-billion dollar devices.

The left thinks global warming is caused by humans.

The right thinks global warming is not caused by humans.

Who's right? It actually doesn't matter a whole lot. What we know is that over the last 100 years the temperature has risen about 1 degree celcius. If, in the next 100 years, the temperature rises another degree, we're probably going to be just fine. In 100 years we will have so many other options that don't cause global warming and besides we will run out of Oil well before 2100 if we keep using it at the current pace. Within 100 years, the ITER project will enable us to use Nuclear Fussion which will allow us to use sea water to power the entire world for millions of years. Within 100 years, we will likely have some breakthroughs in Nanotechnology that either allow us to use electric cars (and drive for hundreds of miles without refueling) or use fuel cells. Within the next 100 years, we will probably have break throughs in Solar that allow super cheap self supplied solar power to power houses and power our cars that are now electric. Maybe I'm an optomist, but I just see a cheap clean green future for energy by the time _our_ effects on the environment will matter. If it turns out that global warming is not caused by us, we still need to fix it. How do we do that? Well, there are proposals to pump SO2 into the atmosphere to reverse the global warming effect. When we have mature nanotechnology, this capability will be easily acheived.

Oh that's right, we don't have any or even any real idea how to build them... I forgot.

http://www.iter.org/

Slashdot has nixed all of the stories I've submitted about fusion efforts.

Break even (or the equivalent of break even) was achieved on the JT-60U tokamak in Japan in the late 90's (1998 I think). No fusion occured because tritium wasn't used in the reactor since I don't believe that JT-60U is equipped to handle tritium (for reasons of radiation). The performance of the plasma, being the energy confinement time, fuel density and ion temperature, was such that the equivalent energy gain had tritium been present would have been 1.25. Some of the problems with the current generation of machines are the use of copper coils rather than superconducting niobium-tin coils as copper coils require a tremendous amount of power to generate the magnetic fields necessary to confine the plasma (typically 3-5 Tesla at the machine major radius). The coils on the small tokamak I work on are copper and require a few tens of kilowatts of power to generate a 0.7 Tesla magnetic field we use and we have the benefit of having very small coils. The largest machines, where the copper coils are much larger (about 3m diameter, roughly compared to .4m on our machine) require hundreds of megawatts to generate their magnetic fields. Superconducting coils present the ability to greatly reduced the power required to operate the machine. The problems with plasma performance are generally centered around energy loss from the plasma, through particles, heat or EM radiation. Radiation isn't a big problem, but particle and heat loss are. The plasma is very turbulent and this turbulence leads to what is referred to as anomalous losses, anomalous in the sense that they are not well explained by theory and are orders of magnitude larger than what is predicted by theory. These losses can be reduced by elaborate modes of operation, generally referred to as H-modes (H meaning high confinement). There are some other drawbacks to these modes, but without getting into much detail, the scaling of confinement with various parameters of the machines shows that a machine the size of ITER (http://www.iter.org/ should have a plasma performance that is good enough to achieve a fusion power gain of 10, that is 50 MW of heating to the plasma and 500 MW of fusion power output. The ideal would be to be able to turn off the plasma heating, but if ITER works as predicted it will be very good. There is also some concern over what will happen to the alpha-particles produced after they give up there energy to other species in the plasma. They have to be removed as they will degrade the plasma performance. I believe that there is an idea of a way to remove them, but this is outside of my area of research. There are other problems with an actual power producing machine. Most of these are engineering problems and have to do with such things as building some sort of lithium blanket that can withstand being bombarded with 14 MeV neutrons, breeding and extracting the tritium fuel and handling the tritium fuel.

Except that ITER (in France) *may* be able to generate a net positive energy output. Due to budget restrictions that's no longer a primary goal, but the design parameters still make it a possibility even if that's now on the edge of it's capabilities due to the cutbacks (it'll still cost ~$3B to build).

http://www.iter.org/index.htm

To insinuate that France is some kind of tech backwater is straight out of the warped and slowly dying rednekkk bullshit freedom fry loving ass hats that now inhabit the White House, et al.

Even though I could mention AirBus, I won't...

A simple acronym will suffice to put this Franco-Bashing to bed:
ITER

the Tokamak was to fusion as the Shuttle was to cheap access to space.

I just attended a talk on Tokamaks and ITER by one of the major guys working at a Tokamak on the west coast somewhere. It really gave me a lot of interesting information -- namely, that they hold a lot of promise. The US recently rejoined ITER, an international collaberation between China, Russia, Japan, the EU, France, and (I hear) soon India.

The goal of ITER is to construct a large Tokamak, and after that, a demonstration of the use of the technology in a commercially attractive power plant. I questioned the guy during the talk and was surprised to learn that there don't appear to be any huge theoretical leaps required for this to work.

IIRC, in 2003 ITER was named by some major government list as the #1 priority of 28 for energy research for the future.

So, what I have learned: Tokamaks are getting really good, and they hold a lot of promise in the next number of years. Interesting note: the efficiency, roughly the ratio of power out to power in, scales with size. That's why they're building the ITER tokemak to be monstrously huge.

ITER will cost about $10 billion to build with a running cost of about $4 billion over 20 years (although that seems a little low to me). With what it will cost to play on the moon we could build 10 fusion reactors and probably crack that particular technology.

http://www.iter.org/site.htm/ They have finally chosen France over Japan, and hopefully this technology will prive to be useful comercially.

One should always question new technologies but in the case of nuclear fusion the way it will most likely produce energy [1] the propability the benefits [2] exceed the down-sides [3] ist very high.
To compare He with CO2 is nonsens as the amount of He produced in this process is factor 1M smaller than there would be CO2 produced for the same amount of electric power.
I do agree that we should save our resources. Thats because this real clean energy will most likely not be widely spread within our lifetime.

[1] see http://www.iter.org/, JET, ASDEX upgrade (http://www.ipp.mpg.de/eng/for/projekte/asdex/for_ proj_asdex.html), WENDELSTEIN 7X and similar fusion-experiments

[2] evenly distributed resources, small amounts of waste, practically no way to burn through, neutrallity to global warming

[3] radioactive waste such as the concrete of the hull, very expensive to build and no perspective to scale it down also leading to losses due to transport and last but not least: we still don't know, if it is manageable to build a plant that actually runs with profit within this century

Simple physics. You can't get more energy out of a reaction than it takes to reverse it. The same reason why hydrogen cars that run on electrolyzed water don't work.

I don't know who will make the next great human acheivment, but I do know this : it has nothing to do with space travel

ITER or NIF will lay the seeds that will one day free humanity from oil dependence.

Why a manhattan style project is not launched immediately to break the energy gridlock is beyond me. It's the most crucial issue facing humanity.

Space is great, but when this dude was a kid, oil was cheap and plentiful. Deal with the big problem first, I say.

From their site: http://www.iter.org/

It is an international project involving The People's Republic of China, the European Union (represented by Euratom), Japan, the Republic of Korea, the Russian Federation, and the United States of America, under the auspices of the IAEA.

I may not be the GP, but I'll throw in my $.02 as a fusion science researcher. (I work on a magnetic confinement device myself.)

1) The running joke of fusion is that it's always 30-50 years away. This is more due to meager funding levels than anything else. At a talk by a PPPL scientist a few years back, it was mentioned that if one plots the price of oil and the amount allocated for fusion research versus year, they track rather nicely. (The 70's were a great time to be in the field!)

Why the meager funding? Fusion researchers kind of shot themselves in the foot in the late 50's and 60's, before much of the underlying plasma physics was well understood. TFTR (the Tokamak Fusion Test Reactor, built in the late 70's, ran through the 90's) turned up physics phenomena that were unexpected and needed to be understood. (That can still be said for many devices today, which are built to specifically analyze these phenomena.) When Nature deals you a bum hand, you have to go back to the drawing board -- and push things off for another decade. Politicians don't like that -- especially when they've been coerced into thinking past their next election!

ITER will be a very large-scale test device. Some of the phenomena that we see disrupting our current experiments are related to physical device size. Additionally, fusion power production is volumetric, while losses from the plasma come from the surface area of the confined plasma. Therefore, scaling up the size will boost fusion output, making it easier to "breakeven" (power out == power in) and, in ITER's case, very likely "ignite" (after reaching a critical temperature, you can turn off external heating and the plasma burning supplies the rest).

Of course, such scaling takes Lots of Money. Superconducting magnet coils are pricey; so is requisite neutron shielding. Current designs incorporate a Lithium "blanket" which will both absorb the 14 MeV neutrons (shielding) and produce tritium (amazingly, more T than you seed the plasma with initially!). One of the biggest question marks is in the field of materials. Nothing has been built that is going to take the neutron punishment that ITER will dish out to plasma-facing surfaces. It is such an important task to design materials that can sustain bombardment that a separate facility will be constructed simultaneously with ITER in Japan to study neutron bombardment exclusively. This has implications in the divertor material (high-Z tungsten or something lighter?) as well as blanket design.

2) My personal opinion is that it is best to stick with our Gen-IV nuclear plants when it comes to fission. These are meltdown-proof, high-efficiency plants that are designed for rapid implementation, should there be a willing buyer. A tabletop-size fusion device would be a relatively inefficient method of starting a fission plant; there are plenty of natural neutron sources that can be made by mixing radioactive materials together. Essentially, it'd be cheaper to use our existing designs for a big fission plant than mixing a fusion reactor's blanket design with a subcritical fission design.

ITER is made up of several governments. Until lately, they could not agree on a place to build a fusion reactor.

While crying and moaning about dupes and rejected submissions isn't exactly constructive criticism, I have to voice my disappointment with the Slashdot editors, especially Timothy, on this one.

I feel particularly annoyed about this news bit. Why is that? Well, I happened to submit this story early tuesday morning (about 10 am GMT / 6 am EST) and it got rejected. It happens and as such is not a big deal. But the following is imho rather embarrassing.

Not only was this news piece accepted and posted on Slashdot later as someone elses submission, it was actually accepted & posted twice (becoming yet another infamous Slashdot dupe). And in this case the poster of the dupe was no other than Timothy, who rejected my submission.

It seems he initially didn't think this particular news was important and rejected my submission. I knew it was an important bit of news to anyone who follows physics and nuclear stuff, a category which many slashdotters fall into. Potentially and on the long run this could be important news to everyone on the planet who uses electricity.

Anyway, the next day Timothy seems to have decided that a less comprehensive and informative submission on the same subject is worth posting, and as icing on the cake, he does it without even bothering to check the site's own news from yesterday (the already posted story was actually still on the frontpage!) thus creating a dupe story.

Only on Slashdot do you find editors who don't even read their own site's frontpage when posting a news story (to avoid dupes), nor remember that they rejected the very same story yesterday. We're all human and mistakes happen. And I'm sure the editors get swamped by a huge number of submissions, which probably aren't exactly a joy to wade through trying to pick the worthy ones.

However, these sort of things seem to happen a bit more often than they could or should. Perhaps the editors could put a little more time and effort into the process, since many of the previous, similar mistakes seem rather easily avoided (at least to a /. reader like myself).

Ps. Here's my original Slashdot submission about this story just for reference (with a forgotten BBC link added):

After 18 months of wrangling over the construction site of the ITER (International Thermonuclear Experimental Reactor) the participants (China, EU, Japan, Russia, South Korea and USA) finally agreed upon Cadarache in France over Rokkasho-Mura in Japan. Japan withdrew its bid after getting a concessions package deal. The 10 billion ($12bn) project will be the 2nd most expensive joint scientific project after the ISS and hopefully a gateway to a commercial fusion reactor prototype. Construction should begin this year and be completed in 2015.

Disclaimer: I am a plasma physicist conducting active research on a magnetic confinement device.

TFA implies towards the end that crystal fusion has potential to become an energy source (i.e. exceeding "breakeaven," the condition where energy input is balanced by energy output). I sincerely doubt this will be the case. That said, the real benefit to this crystal fusion device is not producing energy, but as a cheap neutron generator.

To put things in perspective, consider the fusion rates between crystal fusion and TFTR (the most successful D-T "hot" fusion device built to date). From the FIRE place:

"Note: crystal fusion produced 800 deuterium-deuterium fusion reactions per second compared to 50,000,000,000,000,000 deuterium-deuterium fusion reactions per second in magnetic fusion (e.g., TFTR)."

Small, cheap neutron sources would be a great boon for many fields, such as petroleum reserve discovery and material science research. When it comes to a real energy source, though, a practical first step is to actually decide where to build the ITER.

http://www.iter.org/

All that is needed is money to build a test reactor based on *current* knowledge (no pun intended :), work out final nicks in application of the theory, and then we can build the first commercial fusion reactor.

The obstacle to fusion is not science (or lack thereof), but lack of funding. You see, what people heard in the 60s about fusion, they still think it applies today.

Have you heard about ITER?

My understanding is it could start being built any time now...

Michael

Looks like we'll have to do this the hard way...

I think you mean fusion, not fission. And we're already exploring it. There's project called ITER which has the goal of building an experimental fusion reactor, to help in the development of commercial fusion reactors. They are currently in the process of choosing a site.

Does this make the bazillions we paid for ITER (http://www.iter.org/) useless?

Now if we can just get that fusion reactor to work...

The first wall will contain lithium, which can transmute to T when bombarded by the fast neutrons generated by the fusion reactions. For more info, see Boeing's blurb on the shield/breeding blanket designs.

Of course, with improving technology, higher beta (a measure of fusion plasma confinement capability), and hotter plasmas, D-T can be forsaken for other reactions. :)

IANANP (I am not a nuclear physicist) but a lot of people don't seem to know much about fusion so here are some links which explain a bit more about it:

http://www.jet.efda.org/pages/content/fusion2.html
http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/ fusion.html
http://en.wikipedia.org/wiki/Timeline_of_nuclear_f usion
http://www.fusion.org.uk/
http://www.iter.org/