Sunday, December 03, 2006



France got It.

Photo of CEA in Cadarache with simulation of ITER, backgroundIter, I mean. Which stands for International Thermonuclear Experimental Reactor. OK, the decision to build ITER in France - more exactly in Cadarache, some sixty kloms north of Marseilles - was taken back in June 2005 already, but implementation of that decision is only now speeding up, since halfway November 2006 ministers from the EU, US, China, India, Japan, South Korea and Russia signed an agreement to establish the international organisation that will oversee the Iter fusion energy project. ITER's goal is to generate at least 10 times the power needed to sustain the hot heavy hydrogen mixture during at least 400 seconds in order to demonstrate the scientific and technical feasibility of fusion. Now, usion, as opposed to fission, will cause a certain percentage of people following the energy debate to smirk, if not scold. After all, it has been called the energy project of the future for half a century now, and fusion research has consumed billions of dollars without yielding significant results, or so it seems. Indeed, it's almost 50 years since EURATOM was founded, back in 1957, with the aim of coordinating national fusion research and finding ways of using controlled fusion as a source of energy. This European cooperation resulted in the construction, starting in 1978, of the JET, or Joint European Torus, in Culham (UK), and to this day, JET is still the largest experimental fusion reactor yet built. Towards the end of the eighties, the European Community intended to build JET's successor, which was to be called NET, or Next European Torus. But soaring costs led to the EU reaching out to other countries to help fund NET. However, the then-Soviet Union, Japan and the US, all of which had their own fusion experiments, gave the EU the cold shoulder as long as NET would remain a European undertaking, and this is how the "international" ITER project was born.

Ironically, fifteen years later the ITER Project does strongly look European, and this despite the involvement (and funding) of India and South-Korea, despite strong competition from Japan to have the new fusion site erected on its territory (Japan lobbied hard for the Rokkasho site), and despite China having joined the club in early 2003. As French President Jacques Chirac said in June 2005, after the decision had finally been made to construct ITER in Cadarache, birthplace of France's atomic energy programme in 1959: "It is a big success for France, for Europe and for all the partners of Iter." The French cannot be trusted.

When the search for fusion energy is still going on after half a century and when all the world's powerbrokers are involved, it's hard to dismiss the whole idea of creating a sun on earth - because that's what fusion is - as a pipe dream, as so many have called it. True, even the most successful of the fusion reactors to date, JET, still absorbs more energy than it yields, and true, with an estimated cost of 10 billion EUR (some 13 billion US $) Iter will be the most expensive joint scientific project after the ISS. But in today's world, the decision to continue with it is spurred more and more by the converging realities of the ever increasing global hunger for Megawatts and the necessity of finding a non-polluting energy source. The world's Energy Consumption is scheduled to rise 54% over the timespan 2001-2025, and its Carbon dioxe emissions over the same period by an estimated 55%. I am very reluctant to go along with the Al Gore hysteria and think that the whole climate scare is horribly politicized, but you don't have to be a greenie to realize that 28,000 tonnes of CO2 pumped in the atmosphere every minute can't be a good thing to the earth, even if it would appear that it does not cause global warming. For the time being, a mix between fossil fuels, nuclear energy and renewable energy allows humanity to soldier on, but with the first being limited, the second causing radioactive pollution for tens of thousands of years and the third downright insufficient, the idea of fission seems like the only long-term answer to earth's energy needs. Especially knowing that one kilogram of fusion fuel can theoretically produce the same amount of energy as 10,000,000 kg of fossil fuel.


Excuse me, but I will now have to resort to some physical shorthand if I want to explain the quintessential difference between fission and fusion. In a fission reaction, a heavy Uranium 235 atom is shot at with a neutron – a small electrically neutral particle - with the aim of breaking it up. Indeed, really splitting it so to say, the way an apple is supposed to be sliced in two halves if you shoot at it with a broad arrowblade.

FissionWhy split it? Because energy is freed in the process. Think of a U235 atom as a core made up of 235 little balls. 92 of them are loaded electrically positive – they are called protons, the red balls to the left. The remainder, 143, are electrically neutral – we call them neutrons, they are the yellow ones. When you look at the drawing you see the denomination U235/92. It's not the most correct analogy, but try to think in terms of weights relevant to a truck. That would be its maximum authorized weight (the sum of its own mass plus its payload), and what really matters, the payload itself. In the same manner, the atomic weights relevant to this particular Uranium atom are 235 (its maximum weight), and what really matters, the 92 protons. So you really have to understand that the 92 "weight" is also included in the 235! Or put differently, the maximum atomic weight, 235, is the sum of the "protonic" weight, 92, and the "neutronic" weight, 143. Well, when a neutron similar to the ones in that Uranium core is shot inside that core, the core becomes a 236-ball constituency – but only for a splitsplitsplitsplit second, since unstable. It breaks up. It breaks up into two smaller cores, one with 144 balls and one with 89 balls. The former is called a Barium atom (Ba), the latter a Krypton atom (Kr). But hold it! Oops, 144 + 89 = 233??? That’s right, the breakup process produced two lighter cores and 215MeV of energy but… three little balls went missing. All three of them neutrons again, flying away at a mighty speed and as luck will have it smacking into three other U-235 atoms, which will again split and produce 3 x 215MeV = 645 MeV! Which is what is called a self-sustaining chain reaction. More details with excellent graphs here.

Now, if one can somehow control this proliferation of loose neutrons flying away at high speeds you have a controlled self-sustaining chain reaction. You get a reliable, stable source of energy. If you don’t give a hoot about controlling the chain reaction, you get an atomic bomb. That's it in a nutshell, except that if you belong to the latter category, like Ahmadanutjob, you need uranium containing at least 90% of U235, which is called weaponsgrade uranium. Don't worry, he's working on it.


Now fusion. Fusion is the process whereby energy is released not by splitting atom cores, but, on the contrary, by fusing them! The cores to be fused are Deuterium and Tritium, and please, don't run away now, it really isn't that complicated! Above we have already met the Uranium atom, one of the heavier atoms, consisting a.o. of 92 protons. Well, the very simplest atom has just one proton, and is called Hydrogen (H). Coupled with two Oxygen (O) atoms, Hydrogen forms a fluid we use tens of litres of each day - water: H2O. Now, while a Hydrogen atom thus consists of a core with just one positively laden proton (and one negatively laden electron circling around it), there are hydrogen atoms with heavier cores, because the sole proton is accompanied by either one electrically neutral neutron, and then we speak of Deuterium, or either two, and then we speak of Tritium. Deuterium and Tritium are the two isotopes of Hydrogen: the core's electrical charge is the same (in all three cases only one proton), but the weights differ. See the picture above, which is from the UC Berkeley, Nuclear Department's site. If you ever heard the phrase "Heavy Water", well, here it is: a heavy deuterium or tritium core can also combine with two Oxygen atoms, and then you have either D2O, or T2O - heavy water! One of the main dead ends the Germans entered in their development of a nuclear bomb is that they focused on heavy water to sustain - moderate - their controlled experimental fission reactions (which makes the diring Telemark Raid, albeit spectacular, to some extent an exercise in futility). The American effort used graphite for moderator, which is why the US was the first country with a working atomic bomb - but I digress.

When deuterium and tritium fuse, for a brief instant they form an unstable nucleus of two protons and three neutrons, or a Helium atom with a mass of 5. This bursts apart as seen in the figure to the left, in a stable 4He helium nucleus (core consisting of two protons and two neutrons) with 3.5 MeV (1 MeV = 1 million eV) of kinetic energy swerving off in one direction, and a neutron with four times as much energy, 14.1 MeV, going off in the other. With its positive charge the helium 4He nucleus, also called an alpha particle (the so-called alpha rays, with a very low penetration ability, are merely rays of helium atoms), interacts strongly with surrounding material and stops rapidly, depositing 3.5 MeV of heat close to the site of the fusion reaction. The electrically neutral neutron can only slow down by colliding with other nuclei, transferring small amounts of kinetic energy to each just as a cue ball when it hits a pool ball, until finally the neutron is absorbed by some atom's nucleus, potentially several meters from the original fusion reaction. Thus, fusion results in kinetic energy transforming in heat. So far so good. However, in order to make Deuterium and Tritium to collide like that, one needs to put much more energy first. E.g., while not exactly a reactor, the so-called RTNS (Rotating Target Neutron Source), developed by Lawrence Livermore Labs and commissioned in the mid-seventies needs and input of thousands of watts to produce just two (2) watts of fusion energy - and this for a process in which six trillion fusion reactions take place every second! (note: the RTNS was actually merely a source of so-called 14.1 MeV neutrons necessary for the actual fusion energy programs of the US and Japan - the fusion phenomenon was only used to generate neutrons). The drawing to the right, from a Dutch textbook, shows once again the fusion principle.


NOT!!! Only kidding, thank God. The graph above shows, in fact, what is in se quite obvious. Fission is something for heavy atoms and fusion something for light atoms. See the principles above. I scanned this graph from a course Electrical Engineering I took some 18 years ago, when I was a student Electromechanical Engineering in the town of Aalst. So yes, the handwriting is mine. Pops likes to say I have the ugliest handwriting on the whole planet, but I don't agree. I think the would be nuke scientist to the right's scribbles are far more puke-provoking. The good thing is, I don't think he will ever be a second Abdullah Qadeer Khan. The bad thing is, he may have enough gray mass to fabricate IEDS. But I digress again! That graph. The horizontal axis depicts rising atomic mass numbers. So the more to the right you go, the heavier the atom. To the extreme left on that axis you'll find thus Hydrogen and its isotopes, to the extreme right heavy atoms like Uranium. The vertical axis stands for the energy binding together protons and neutrons in a core. This is thus also the energy freed either through fusion or fission. On the fusion "side", the higher the graph goes, the higher the binding energy, and you can see that the "ideal" zone corresponds with a mass number between 40 and 100. On the fission side, towards the right, the graph goes downhill. This is all theory of course. Theoretically, if you'd fuse somewhat heavier atoms than the ultralight hydrogen isotopes, you'd get more power ouput. Similarly, if you'd split lighter atoms than Uranium, you'd also get more output. In practice however, for a variety of reasons, uranium is used for fission and deuterium/tritium for fusion. Keep in mind though that a mixture of Deuterium and the heavier Helium is also considered to be a possible fusion fuel.


Compared to fusion, economically extracting energy from fission seems like small beer. The first nuclear fission powerplant dates from 1957 already, and forty years later the latest technological development is the so-called PBMR or Pebble Bed Modular Reactor, a Generation IV-development. But fusion... that is another matter. After all, you need to attract non-opposites: fusing a deuterium and tritium core means essentially forcing two particles with the same electrical charge together. Try to imagine forcing trillions of tiny horsehoe magnets together with the repelling ends against each other. However, it does happen in nature: in our Sun's core and in all other stars. There, unimaginable gravitational pressure allows fusion to happen at temperatures of about 10 million degrees Celsius. Naturally, on Earth it is impossible to simulate a gravity of that magnitude, so the only means to make fusion happen anyway, is at temperatures even far exceeding the Sun's core temperature - above 100 million degrees Celsius. Fusion is thus actually creating something even much hotter than a mini-Sun on Earth. No materials on Earth or possibly in the entire Universe could withstand direct contact with such heat. Scientists have come up with two solutions: on the one hand the Inertial Confinement Fusion (ICF) devices, like the US's Shiva laser or Japan's GEKKO XII. While it was at first thought ICF could move beyond the experimental stage and provide the working principle for, it was hoped, Inertial Fusion Energy (IFE) plants, that hope has now been largely been abandoned, due to the ICF's laser's very low efficiency (1 - 1.5%). On the other hand there are the magnetic confinement devices, whereby a super-heated gas, or plasma, is held and squeezed inside an intense doughnut-shaped magnetic field.. In a plasma, the electrons have been separated from their atomic nuclei, so it's all charged particles (except the neutrons of course) whirling through each other. Examples are the EU's JET, the US's Alcator C-Mod, Japan's JT-60 or Russia's T-15. The last one is very important, because the T-15 was the first fusion reactor based on the Tokamak configuration. "TOKAMAK" is an acronym of the Russian words "TOroidalnay KAmera ee MAgnitaya Katushka", which means: "Toroidal Chamber with Magnetic Coil". The Tokamak principle was invented in the fifties by Igor Yevgenyevich Tamm and... Andrei Sakharov, father of the Russian H-Bomb. Both elaborated an earlier idea of a certain O.A. Lavrent'ev. In life, there are a great number of things you should never do and one of them is never, ever, underestimate the Ruskis.

In a Tokamak the hot plasma is held in its place, not touching any solid matter, by strong toroidal and poloidal magnetic fields, see figure to the right. Absolutely necessary for the toroidal field is the huge central solenoid magnet. The poloidal field however... is generated by a large current, up to several million amperes, which flows through the plasma. This current is first induced by transformers and, after that, must be maintained "by non-inductive current drive or by self-generation of currents inside the plasma". Actually it's crazy: imagine that with a couple of colleagues all wearing isolating gloves and standing in a circle all of you try to hold an incredibly hot donut shaped balloon in place, one which writhes frantically to expand/explode, and you are still far off.

So, what does a Tokamak reactor look like from the inside? The photo shows the interior of an American Tokamak, the TFTR, or Tokamak Fusion Test Reactor, an experimental built at Princeton Plasma Physics Laboratory in New Jersey in 1980. With TFTR, Princeton PPL hoped it would achieve fusion energy break-even (energy input = energy output). Unfortunately, like with all other Tokamaks, this did not happen. The record holder thus far is still the EU's JET, which began operation in 1983 and which in 1997 produced a peak output of 16MW (an absolutely sizeable amount of energy) with a Q-value of 0.7. Q is the ratio of fusion alpha heating power to input heating power, which means that during this test input power was 16MW/0.7 = 22.86 MW. Personally, I think this is an amazing result.


ITER - which in Latin means "the way" - is now the next step. Or, for optimists, the last but one step before starting commercial energy production through fusion. Fusion has already been achieved a thousand times. It is up to Iter to prove that fusion is also economically viable. After ITER will, it is hoped, come the prototype of the first commercial fusion reactor. Here would be an energy source acceptable to all, except Chavez and oil sheikhs. Using fuel derived from seawater (100 kilograms of deuterium and tritium would be sufficient to fuel a one-gigawatt (1GW) fusion plant to operate for a year), not polluting the atmosphere, and not emitting greenhouse gases. And while fusion does irradiate the reaction chamber, the only waste would come out in the open if that reactor chamber would be scrapped. And even then, the radioactivity would decay and become safe after about one hundred years. As for safety, I found this hard to believe, but it seems there can't be anything like a blowup, and certainly not a meltdown. It seems that if the magnetic fields holding the plasma in place would fail for some reason, contact of the plasma with the reactor's interior would immediately stop the process. Not without simultaneously melting that same interior, I figure, and I wouldn't want to be near when it happens. But a disaster like Chernobyl badly affecting half Europe seems to be out of the question. Well, let's hope for the best. ITER won't generate electricity yet, only heat, some 500MW. There's no turbines and generators attached to the complex. But it will determine for good whether we can count, by 2040/2050 or so, on an inexhaustible and clean energy source. If the answer is no, then the future looks bleak, so it better work. In the meantime, look at the ITER simulation below. Compare the reactor's size to that small figure below. Yes, that's a human size. See how big it will be? Say to yourself, if the brightest minds would not think this thing has a serious chance to fly, would they build a mammoth like that?



No comments: