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  • Nuclear Fusion Update

    Posted on October 17th, 2016 Helian No comments

    At the moment the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory is in a class by itself when it comes to inertial confinement fusion (ICF) facilities.  That may change before too long.  A paper by a group of Chinese authors describing a novel 3-axis cylindrical hohlraum design recently appeared in the prestigious journal Nature.  In ICF jargon, a “hohlraum” is a container, typically cylindrical in form.  Powerful laser beams are aimed through two or more entrance holes to illuminate the inner wall of the hohlraum, producing a burst of x-rays.  These strike a target mounted inside the hohlraum containing fusion fuel, typically consisting of heavy isotopes of hydrogen, causing it to implode.  At maximum compression, a series of shocks driven into the target are supposed to converge in the center, heating a small “hot spot” to fusion conditions.  Unfortunately, such “indirect drive” experiments haven’t worked so far on the NIF.  The 1.8 megajoules delivered by NIF’s 192 laser beams haven’t been enough to achieve fusion with current target designs, even though the beams are very clean and uniform, and the facility itself is working as designed.  Perhaps the most interesting thing about the Chinese paper is not their novel three axis hohlraum design, but the fact that they are still interested in ICF at all in spite of the failure of the NIF to achieve ignition to date.  To the best of my knowledge, they are still planning to build SG-IV, a 1.5 megajoule facility, with ignition experiments slated for the early 2020’s.

    Why would the Chinese want to continue building a 1.5 megajoule facility in spite of the fact that U.S. scientists have failed to achieve ignition with the 1.8 megajoule NIF?  For the answer, one need only look at who paid for the NIF, and why.  The project was paid for by the people at the Department of Energy (DOE) responsible for maintaining the nuclear stockpile.  Many of our weapons designers were ambivalent about the value of achieving ignition before the facility was built, and were more interested in the facility’s ability to access physical conditions relevant to those in exploding nuclear weapons for studying key aspects of nuclear weapon physics such as equation of state (EOS) and opacity of materials under extreme conditions.  I suspect that’s why the Chinese are pressing ahead as well.  Meanwhile, the Russians have also announced a super-laser project of their own that they claim will deliver energies of 2.8 megajoules.

    Meanwhile, in the wake of the failed indirect drive experiments on the NIF, scientists in favor of the direct drive approach have been pleading their case.  In direct drive experiments the laser beams are shot directly at the fusion target instead of at the inner walls of a hohlraum.  The default approach for the NIF has always been indirect drive, but the alternative approach may be possible using an approach called “polar direct drive.”  In recent experiments at the OMEGA laser facility at the University of Rochester’s Laboratory for Laser Energetics, the nation’s premier direct drive facility, scientists claim to have achieved results that, if scaled up to energies available on the NIF would produce five times more fusion energy output than has been achieved with indirect drive to date.

    Meanwhile, construction continues on ITER, a fusion facility designed purely for energy applications.  ITER will rely on magnetic plasma confinement, the other “mainstream” approach to harnessing fusion energy.  The project is a white elephant that continues to devour ever increasing amounts of scarce scientific funding in spite of the fact that the chances that magnetic fusion will ever be a viable source of electric power are virtually nil.  That fact should be obvious by now, and yet the project staggers forward, seemingly with a life of its own.  Watching its progress is something like watching the Titanic’s progress towards the iceberg.  Within the last decade the projected cost of ITER has metastasized from the original 6 billion euros to 15 billion euros in 2010, and finally to the latest estimate of 20 billion euros.  There are no plans to even fuel the facility for full power fusion until 2035!  It boggles the mind.

    Magnetic fusion of the type envisioned for ITER will never come close to being an economically competitive source of power.  It would already be a stretch if it were merely a question of controlling an unruly plasma and figuring out a viable way to extract the fusion energy.  Unfortunately, there’s another problem.  Remember all those yarns you’ve been told about how an unlimited supply of fuel is supposed to be on hand in the form of sea water?  In fact, reactors like ITER won’t work without a heavy isotope of hydrogen known as tritium.  A tritium nucleus contains a proton and two neutrons, and, for all practical purposes, the isotope doesn’t occur in nature, in sea water or anywhere else.  It is highly radioactive, with a very short half-life of a bit over 12 years, and the only way to get it is to breed it.  We are told that fast neutrons from the fusion reactions will breed sufficient tritium in lithium blankets surrounding the reaction chamber.  That may work on paper, but breeding enough of the isotope and then somehow extracting it will be an engineering nightmare.  There is virtually no chance that such reactors will ever be economically competitive with renewable power sources combined with baseline power supplied by proven fission breeder reactor technologies.  Such reactors can consume most of the long-lived transuranic waste they produce.

    In short, ITER should be stopped dead in its tracks and abandoned.  It won’t be, because too many reputations and too much money are on the line.  It’s too bad.  Scientific projects that are far worthier of funding will go begging as a result.  At best my descendants will be able to say, “See, my grandpa told you so!”

  • Another Fusion White Elephant Sighted in Germany

    Posted on October 27th, 2015 Helian 2 comments

    According to an article that just appeared in Science magazine, scientists in Germany have completed building a stellarator by the name of Wendelstein 7-X (W7-X), and are seeking regulatory permission to turn the facility on in November.  If you can’t get past the Science paywall, here’s an article in the popular media with some links.  Like the much bigger ITER facility now under construction at Cadarache in France, W7-X is a magnetic fusion device.  In other words, its goal is to confine a plasma of heavy hydrogen isotopes at temperatures much hotter than the center of the sun with powerful magnetic fields in order to get them to fuse, releasing energy in the process.  There are significant differences between stellarators and the tokamak design used for ITER, but in both approaches the idea is to hold the plasma in place long enough to get significantly more fusion energy out than was necessary to confine and heat the plasma.  Both approaches are probably scientifically feasible.  Both are also white elephants, and a waste of scarce research dollars.

    The problem is that both designs have an Achilles heel.  Its name is tritium.  Tritium is a heavy isotope of hydrogen with a nucleus containing a proton and two neutrons instead of the usual lone proton.  Fusion reactions between tritium and deuterium, another heavy isotope of hydrogen with a single neutron in addition to the usual proton, begin to occur fast enough to be attractive as an energy source at plasma temperatures and densities much less than would be necessary for any alternative reaction.  The deuterium-tritium, or DT, reaction will remain the only feasible one for both stellarator and tokamak fusion reactors for the foreseeable future.  Unfortunately, tritium occurs in nature in only tiny trace amounts.

    The question is, then, where do you get the tritium fuel to keep the fusion reactions going?  Well, in addition to a helium nucleus, the DT fusion reaction produces a fast neutron.  These can react with lithium to produce tritium.  If a lithium-containing blanket could be built surrounding the reaction chamber in such a way as to avoid interfering with the magnetic fields, and yet thick enough and close enough to capture enough of the neutrons, then it should be possible to generate enough tritium to replace that burned up in the fusion process.  It sounds complicated but, again, it appears to be at least scientifically feasible.  However, it is by no means as certain that it is economically feasible.

    Consider what we’re dealing with here.  Tritium is an extremely slippery material that can pass right through walls of some types of metal.  It is also highly radioactive, with a half-life of about 12.3 years.  It will be necessary to find some way to efficiently extract it from the lithium blanket, allowing none of it to leak into the surrounding environment.  If any of it gets away, it will be easily detectable.  The neighbors are sure to complain and, probably, lawyer up.  Again, all this might be doable.  The problem is that it will never be doable at a low enough cost to make fusion reactor designs based on these approaches even remotely economically competitive with the non-fossil alternative sources of energy that will be available for, at the very least, the next several centuries.

    What’s that?  Reactor design studies by large and prestigious universities and corporations have all come to the conclusion that these magnetic fusion beasts will be able to produce electricity at least as cheaply as the competition?  I don’t think so.  I’ve participated in just such a government-funded study, conducted by a major corporation as prime contractor, with several other prominent universities and corporations participating as subcontractors.  I’m familiar with the methodology used in several others.  In general, it’s possible to make the cost electricity come out at whatever figure you choose, within reason, using the most approved methods and the most sound project management and financial software.  If the government is funding the work, it can be safely assumed that they don’t want to hear something like, “Fuggedaboudit, this thing will be way too expensive to build and run.”  That would make the office that funded the work look silly, and the fusion researchers involved in the design look like welfare queens in white coats.  The “right” cost numbers will always come out of these studies in the end.

    I submit that a better way to come up with a cost estimate is to use a little common sense.  Do you really think that a commercial power company will be able to master the intricacies of tritium production and extraction from the vicinity of a highly radioactive reaction chamber at anywhere near the cost of, say, wind and solar combined with next generation nuclear reactors for baseload power?  If you do, you’re a great deal more optimistic than me.  W7-X cost a billion euros.  ITER is slated to cost 13 billion, and will likely come in at well over that.  With research money hard to come by in Europe for much worthier projects, throwing amounts like that down a rat hole doesn’t seem like a good plan.

    All this may come as a disappointment to fusion enthusiasts.  On the other hand, you may want to consider the fact that, if fusion had been easy, we would probably have managed to blow ourselves up with pure fusion weapons by now.  Beyond that, you never know when some obscure genius might succeed in pulling a rabbit out of their hat in the form of some novel confinement scheme.  Several companies claim they have sure-fire approaches that are so good they will be able to dispense with tritium entirely in favor of more plentiful, naturally occurring isotopes.  See, for example, here, here, and here, and the summary at the Next Big Future website.  I’m not optimistic about any of them, either, but you never know.

    Stellarator