Polyanna Pinker’s Power Profundities







According to the Huffpo article referenced above,




No, We Don’t Need to Resume Nuclear Testing






Fisking a Fusion Fata Morgana

Why is it that popular science articles about fusion energy are always so cringe-worthy? Is scientific illiteracy a prerequisite for writing them? Take the latest one to hit the streets, for example. Entitled Lockheed Martin Now Has a Patent For Its Potentially World Changing Fusion Reactor, it had all the familiar “unlimited energy is just around the corner” hubris we’ve come to expect in articles about fusion. When I finished reading it I wondered whether the author imagined all that nonsense on his own, or some devilish plasma physicist put him up to it as a practical joke. The fun starts in the first paragraph, where we are assured that,


Trust me, dear reader, barring divine intervention no such prototype system, capable of both generating electric energy and fitting within a volume anywhere near that of a shipping container, will debut in the next year, or the next five years, or the next ten years.  Reading on, we learn that,


Well, not really.  Fission is caused by free neutrons, not by “atoms hitting each other.”  It would actually be more accurate to say that fusion takes place when “atoms hit each other,” although it’s really the atomic nuclei that “hit” each other.  Fusion doesn’t involve “atomic structure getting disrupted from pressure.” Rather, it happens when atoms acquire enough energy to overcome the Coulomb repulsion between two positively charged atomic nuclei (remember, like charges repel), and come within a sufficiently short distance of each other for the much greater strong nuclear force of attraction to take over. According to the author,


This is like claiming that a solid can be in a liquid state. A plasma is not a gas. It is a fourth state of matter quite unlike the three (solid, liquid, gas) that most of us are familiar with. Shortly thereafter we are assured that,


25 pounds of fuel would include about 15 pounds of tritium, a radioactive isotope of hydrogen with a half-life of just over 12 years. In other words, its atoms decay about 2000 times faster than those of the plutonium 239 found in nuclear weapons.  It’s true that the beta particle (electron) emitted in tritium decay is quite low energy by nuclear standards but, as noted in Wiki, “Tritium is an isotope of hydrogen, which allows it to readily bind to hydroxyl radicals, forming tritiated water (HTO), and to carbon atoms. Since tritium is a low energy beta emitter, it is not dangerous externally (its beta particles are unable to penetrate the skin), but it can be a radiation hazard when inhaled, ingested via food or water, or absorbed through the skin.”  Obviously, water and many carbon compounds can be easily inhaled or ingested. Tritium is anything but benign if released into the environment. Here we will charitably assume that the author didn’t mean to say that 25 pounds of fuel would be available all at once, but would be bred gradually and then consumed as fuel in the reactor during operation.  The amount present at any given time would more appropriately be measured in grams than in pounds.  The article continues with rosy scenarios that might have been lifted from a “Back to the Future” movie:


Great shades of “Dr. Fusion!” Let’s just say that “vehicles on land” is a bit of a stretch. I can only hope that no Lockheed engineer was mean-spirited enough to feed the author such nonsense. Moving right along, we read,


I have no idea what “emission” of the fission process the author thinks is “dangerous to the ozone layer.” Again, as noted above, tritium is anything but “relatively harmless” if ingested. Next we find perhaps the worst piece of disinformation of all:


Good grief, the highly energetic neutrons produced in a fusion reactor are not only capable of breeding tritium, but plutonium 239 and uranium 233 from naturally occurring uranium and thorium as well.  Both are superb explosive fuels for nuclear weapons.  And tritium?  It is used in a process known as “boosting” to improve the performance of nuclear weapons.  Finally, we run into what might be called the Achilles heel of all tritium-based fusion reactor designs:


I think not. Breeding tritium will be anything but a piece of cake.  The process will involve capturing the neutrons produced by the fusion reactions in a lithium blanket surrounding the reactor, doing so efficiently enough to generate more tritium from the resulting reactions than the reactor consumes as fuel, and then extracting the tritium and recycling it into the reactor without releasing any of the slippery stuff into the environment.  Do you think the same caliber of engineers who brought us Chernobyl, Fukushima, and Three Mile Island will be able to pull that rabbit out of their hats without a hitch?  If so, you’re more optimistic than I am.

Hey, I like to be as optimistic about fusion as it’s reasonable to be. I think it’s certainly possible that some startup company with a bright idea will find the magic bullet that makes fusion reactors feasible, preferably involving fusion reactions that don’t involve tritium. It’s also quite possible that the guys at Lockheed will achieve breakeven, although getting a high enough gain of energy in versus energy out to enable efficient generation of electric power is another matter.  There’s a difference between optimism and scientifically illiterate hubris, though.  Is it too much to ask that people who write articles about fusion at least run them by somebody who actually knows something about the subject to see if they pass the “ho, ho” test before publishing?  What’s that you say?  What about me?  Please read the story about the Little Red Hen.

Whither Nuclear Power? A Few Comments on Thorium and the End of the “Nuclear Renaissance”

About a decade ago there was much talk of a “nuclear renaissance” amid concerns about greenhouse gas emissions and the increasing cost of fossil fuel alternatives.  The Nuclear Regulatory Commission received applications to build no less than 31 new nuclear plants as the price of crude oil spiked to over $140 per barrel.  Now, however, with last month’s decision by SCANA Corp. to abandon the V. C. Summer project, a pair of nukes that had been under construction in South Carolina, nuclear’s future prospects look dim, at least in the United States.  Two plants remain under construction in Georgia but, like the ones abandoned in South Carolina, they are to be AP1000s, designed by Westinghouse.  Westinghouse filed for bankruptcy in March.  Delays and massive cost overruns similar to those that led to the demise of V. C. Summer also afflict the Georgia project, and its future seems doubtful at best.

In short, the dream of a nuclear renaissance has evaporated.  For the time being, at least, nuclear in the U.S. is no match for more agile competitors like wind, solar, and natural gas.  However, there may be a silver lining to this cloud.  Plants like Westinghouse’s AP1000 waste most of the energy in their nuclear fuel, creating massive amounts of avoidable radioactive waste in the process.  To the extent that it makes sense to build nuclear plants at all, these are not the kind we should be building.  To understand why this is true it is first necessary to acquire some elementary knowledge about nuclear physics.

The source of the energy produced in the core of nuclear reactors is a nuclear fission chain reaction.  Only one material that exists in significant quantities in nature can sustain such a chain reaction – uranium 235, or U235.  U235 is an isotope of uranium.  Isotopes of a given element consist of atoms with the same number of positively charged protons in their central core, or nucleus.  Like all other isotopes of uranium, U235 has 92.  There are also 143 neutrally charged neutrons, making a total of 235 “nucleons.”  Natural uranium consists of only about 0.7 percent U235.  Almost all the rest is a different isotope, U238, with a nucleus containing 146 neutrons instead of 143.

When we say that U235 can sustain a nuclear chain reaction, we mean that if a free neutron happens to come within a very short distance of its nucleus, it may be captured, releasing enough energy in the process to cause the nucleus to split into two fragments.  When this happens, more free neutrons are released, that can then be captured by other uranium nuclei, which, in turn, fission, releasing yet more neutrons, and so on.  As noted above, U235 is the only naturally occurring isotope that can sustain such a nuclear chain reaction.  However, other isotopes can be created artificially that can do so as well.  The most important of these are U233 and plutonium 239, or Pu239.  They are important because it is possible to “breed” them in properly designed nuclear reactors, potentially producing more usable fuel than the reactor consumes.  U233 is produced by the reactions following absorption of a neutron by thorium 232, or Th232, and Pu239 by those following the absorption of a neutron by U238.  In other words, we know of three practical types of nuclear fuel; U235, U233 and Pu239.  The first occurs naturally, and the other two can be readily “bred” artificially in nuclear reactors.

Let’s consider what this means in the case of conventional nuclear reactors like the Westinghouse AP1000.  These are powered by fuel elements that typically are enriched in U235 from the naturally occurring 0.7 percent to from three to five percent.  The remaining 95 to 97 percent of the uranium in these fuel elements is U238.  When the fission process starts, some of the neutrons released are captured by the U238, eventually resulting in the production of Pu239.  Some of this plutonium fissions along with the U235, contributing to the total energy produced by the fuel elements.  However, only a small fraction of the U238 is converted to Pu239 in this way before the fuel is consumed and it becomes necessary to replace the old fuel elements with fresh ones.  In addition to a great deal of U238, these spent fuel elements contain a significant amount of plutonium, as well as other transuranic elements such as americium and curium, which can remain dangerously radioactive for thousands of years.  The “waste” plutonium might even be used to produce a nuclear weapon.

Obviously, if possible it would be better to extract all the energy locked up in natural uranium rather than just a small fraction of it.  In fact, it is possible, or very nearly so.  Breeder reactors are feasible that could burn nearly all the U238 in natural uranium as well as the U235 by converting it into Pu239.  In the process they could destroy much of the transuranic waste that is the main source of radioactive danger from spent fuel.  In as little as 500 years the residual radioactivity from running a nuclear plant for 30 years could potentially be less than that of the original naturally occurring uranium.  Unfortunately, while all this is scientifically feasible, it is not economically feasible.  It won’t happen without massive government subsidies.  Perhaps such subsidies are warranted in view of the threat of climate change and perhaps not, but, regardless, breeder reactors won’t be built without them.  Since they are really the only types of reactors it makes sense to build, we would probably be better off, at least for the time being, building no reactors at all.  That’s the “silver lining” I referred to above.  Perhaps a time will come when the world runs out of expendable sources of base load electrical power, such as oil, coal and natural gas, and no way has been found to take up the slack with renewables.  In that case, it may once again make economic sense to build breeder reactors.  Until that time, the United States would do well to build up a healthy stockpile of uranium, and put a stop to the stupid, wasteful, and counterproductive use of depleted uranium that could potentially become a source of vast amounts of energy to produce munitions and armor.

But wait, there’s more!  What about thorium?  Thorium by itself can’t sustain a nuclear chain reaction.  It can, however, be converted into U233 by neutron absorption, and that is an ideal reactor fuel.  Among other things, it generates more neutrons per fission at lower neutron “temperatures” than either Pu239 or U235.  That means that extra neutrons are available to “breed” fuel at those lower temperatures where nuclear reactors are easier to control.  By “temperature” here, we’re referring to the average speed of the neutrons.  The slower they are, the more likely they are to be absorbed by a nucleus and cause fission reactions.  Neutrons are slowed in “moderators,” which can be any number of light types of atoms.  The most common is plain water, consisting of the elements hydrogen and oxygen.  Think of a billiard ball hitting another billiard ball head on.  It comes to a complete stop, transferring its energy to the other ball.  The same thing can happen with neutrons and the proton nucleus of hydrogen atoms, which are of approximately equal mass.  To breed plutonium effectively, reactors must be run at significantly higher neutron temperatures.

There’s more good news about thorium.  It can be dissolved in various exotic mixtures and breed U233 in a reactor with a liquid instead of a solid core.  This would have a number of advantages.  In the first place, a “meltdown” would be impossible in a core that’s already “melted.”  If the core became too “hot” it could simply be drained into a holding pan to form a subcritical mass that would quickly cool.  It would also be possible to extract waste fission products and introduce fresh fuel, etc., into the core “on the fly.”  As a result the reactor would be able to stay in operation longer between shutdowns for maintenance and refueling.  The necessary technology has already been demonstrated at places like Oak Ridge, Tennessee and Shippingport, Pennsylvania.  Recently, a Dutch team finally began experiments with molten salt technology intended to take up where these earlier experiments left off after a hiatus of more than 40 years.

Perhaps thorium’s biggest problem is the tendency of its proponents to over-hype its promise.  It even has a founding myth based on bogus claims that thorium technology isn’t dominant in the energy industry today because “it’s much harder to weaponize.”  For example, according to the article about the Dutch experiments linked above, entitled, ‘Safer’ thorium reactor trials could salvage nuclear power,

But, if it’s so safe and reliable why hasn’t thorium been used all along? Because (unlike uranium) it’s much harder to weaponize. As a result, it’s historically been sidelined by nations in search of both energy and a potential source of weapons-grade plutonium.

This yarn about a benign source of energy that might have benefited all mankind being torpedoed by evil weaponeers might sound good, but it’s complete nonsense.  Thorium itself can’t be weaponized, because it can’t sustain a nuclear chain reaction on its own.  The sole reason there’s any interest in it at all as a source of nuclear power is the possibility of transmuting it to U233.  Of course, it can’t be used to produce weapons-grade plutonium.  However, there is no better material for making nuclear bombs than U233.  As is the case with Pu239, four kilograms is sufficient to make a nuclear weapon, compared to the 25 kilograms that is a sufficient quantity of U235.  It’s main drawback as a weapons material is the fact that small amounts of U232 are produced along with it in thorium-based reactors, and U232 decays into radioactive daughters that are deadly sources of powerful gamma rays.  However, the amount of U232 produced can be reduced dramatically by cooling the neutron spectrum to a low “temperature.”  In short, thorium could definitely be used to make weapons.  The reason it isn’t the dominant technology for that purpose is the same as the reason it isn’t the dominant technology for producing electric power; it would be significantly more complex and expensive than using natural or slightly enriched uranium as a fuel.  That reason is as valid now as it was in the days of Little Boy and Fat Man.  The “dominant technology” would be the same as it is today whether nuclear weapons had ever been produced or not.

When it comes to the technology itself, thorium proponents also tend to be coy about mentioning problems that don’t afflict other reactor types.  For example, the materials needed for practical molten salt reactors are extremely corrosive.  There has been progress towards finding a metal that can hold them, but no ideal alloy has yet been found.  This isn’t necessarily a show stopper, but it’s not an insignificant problem, either.  Such material issues have been largely solved for conventional reactors.  If, as would seem to be the case, these are no longer economically competitive with their rivals, then molten salt is pretty much out of the question, at least for the time being.  It’s important to point out that, if breeder reactors ever do become economically feasible again, it will always be necessary to insure that they are secure, and that the materials they produce can’t be diverted for making weapons.  That concern applies to both plutonium and thorium breeders.

Meanwhile, it might behoove our political leaders to consider the question of why it was once possible to build more than 50 experimental reactors at what is now Idaho National Laboratory alone in a relatively short period of time for a small fraction of what similar reactors would cost today.  Merely negotiating the regulatory hurdles for building a power reactor based on anything as novel as the thorium fuel cycle would take the better part of a decade.  All these hurdles have been put in place in the name of “safety.”  That begs the question of how “safe” we will be if we lack reliable sources of electric energy.  There is a point beyond which excessive regulation itself becomes unsafe.

The Bomb and the Nuclear Posture Review








3+2: More Tinkering with the Nuclear Arsenal








Nuclear Update: Molten Salt, Rugby Balls, and the Advanced Hydrodynamic Facility

I hear at 7th or 8th hand that the folks at DOE have been seriously scratching their heads about the possibility of building a demonstration molten salt reactor.  They come in various flavors, but the “default” version is a breeder, capable of extracting far more energy from a given quantity of fuel material than current reactors by converting thorium into fissile uranium 233.  As they would have a liquid core, the possibility of a meltdown would be eliminated.  The copious production of neutrons in such reactors would make it possible to destroy the transuranic actinides, such as americium and curium, and, potentially, also some of the most long-lived radioactive products produced in fission reactions.  As a result, the residual radioactivity from running such a reactor for, say, 30 years, would potentially be less than that of the ore from which the fuel was originally extracted in under 500 years, a far cry from the millions commonly cited by anti-nuke alarmists.  Such reactors would be particularly attractive for the United States, because we have the largest proven reserves of thorium on the planet.  Disadvantages include the fact that uranium 233 is a potential bomb material, and therefore a proliferation concern, and the highly corrosive nature of the fluoride and/or chloride “salts” in the reactor core.  More detailed discussions of the advantages and disadvantages may be found here and here.

The chances that the U.S. government will actually provide the funding necessary to build a molten salt or any other kind of advanced reactor are, unfortunately, slim and none.  We could do such things in the 50’s and 60’s with alacrity, but those days are long gone, and the country seems to have fallen victim to a form of technological palsy.  That’s too bad, because private industry won’t take up the slack.  To the extent they’re interested in nuclear at all, the profit motive rules.  At the moment, the most profitable way to generate nuclear energy is with reactors that simply burn naturally occurring uranium, wasting the lion’s share of the potential energy content, and generating copious amounts of long-lived radioactive waste for which no rational long term storage solution has yet been devised.  In theory, DOE’s national laboratories should be stepping in to take up the slack, doing the things that industry can’t or won’t do.  In reality what they do is generate massive stacks of paper studies and reports on advanced systems that have no chance of being built.  Enough must have accumulated since the last research reactor was actually built at any of the national labs to stretch back and forth to the moon several times.  Oh, well, we can take comfort in the knowledge that at least some people at DOE are thinking about the possibilities.

Moving right along, as most of my readers are aware, the National Ignition Facility, or NIF, did not live up to its name.  It failed to achieve inertial confinement fusion (ICF) ignition in the most recent round of experiments, missing that elusive goal by nearly two orders of magnitude.  The NIF is a giant, 192 beam laser system at Lawrence Livermore National Laboratory (LLNL) that focuses all of its 1.8 megajoules of laser energy on a tiny target containing deuterium and tritium, two heavy isotopes of hydrogen.  Instead of generating energy by splitting or “fissioning” heavy atoms, the goal is to get these light elements to “fuse,” releasing massive amounts of energy.

Actually, the beams don’t hit the target itself.  Instead they’re focused through two holes in the ends of a tiny cylinder, known as a hohlraum, that holds a “capsule” of fuel material mounted in its center.  It’s what’s known as the indirect drive approach to ICF, as opposed to direct drive, in which the beams are focused directly on a target containing the fuel material.  When the beams hit the inside walls of the cylinder they generate a burst of x-rays.  These are what actually illuminate the target, causing it to implode to extremely high densities.  At just the right moment a “hot spot” is created in the very center of this dense, imploded fuel material, where fusion ignition begins.  The fusion reactions create alpha particles, helium nuclei containing two neutrons and two protons, which then smash into the surrounding “cold” fuel material, causing it to ignite as well, resulting in a “burn wave,” which spreads outward, igniting the rest of the fuel.  For this to happen, everything has to be just right.  The most important thing is that the implosion be almost perfectly symmetric, so that the capsule isn’t squished into a “pancake,” or squashed into a “sausage,” but is very nearly spherical at the point of highest density.

Obviously, everything wasn’t just right in the recently concluded ignition experiments.  There are many potential reasons for this.  Material blowing off the hohlraum walls could expand into the interior in unforeseen ways, intercepting some of the laser light and/or x-rays, resulting in asymmetric illumination of the capsule.  So-called laser/plasma interactions with abstruse names like stimulated Raman scattering, stimulated Brillouin scattering, and two plasmon decay, could be more significant than expected, absorbing laser light so as to prevent symmetric illumination and at the same time generating hot electrons that could potentially preheat the fuel, making it much more difficult to implode and ignite.  There are several other potential failure mechanisms, all of which are extremely difficult to model on even the most powerful computers, especially in all three dimensions.

LLNL isn’t throwing in the towel, though.  In fact, there are several promising alternatives to indirect drive with cylindrical hohlraums.  One that recently showed promise in experiments on the much smaller OMEGA laser system at the University of Rochester’s Laboratory for Laser Energetics (LLE) is substitution of “rugby ball” shaped targets in place of the “traditional” cylinders.  According to the paper cited in the link, these “exhibit advantages over cylinders, in terms of temperature and of symmetry control of the capsule implosion.”  LLNL could also try hitting the targets with “green” laser light instead of the current “blue.”  The laser light is initially “red,” but is currently doubled and then tripled in frequency by passing it through slabs of a special crystal material, shortening its wavelength to the shorter “blue” wavelength, which is absorbed more efficiently.  However, each time the wavelength is shortened, energy is lost.  If “green” light were used, as much as 4 megajoules of energy could be focused on the target instead of the current maximum of around 1.8.  If “green” is absorbed well enough and doesn’t set off excessive laser/plasma interactions, the additional energy just might be enough to do the trick.  Other possible approaches include direct drive, hitting the fuel containing target directly with the laser beams, and “fast ignitor,” in which a separate laser beam is used to ignite a hot spot on the outside of the “cold,” imploded fuel material instead of relying on the complicated central hot spot approach.

Regardless of whether ignition is achieved on the NIF or not, it will remain an extremely valuable experimental facility.  The reason?  Even without ignition it can generate extreme material conditions that are relevant to those that exist in exploding nuclear weapons.  As a result, it gives us a significant leg up over other nuclear weapons states in an era of no nuclear testing by enabling us to field experiments relevant to the effects of aging on the weapons in our stockpile, and suggesting ways to insure they remain safe and reliable.  Which brings us to the final topic of this post, the Advanced Hydrodynamic Facility, or AHF.

The possibility of building such a beast was actively discussed and studied back in the 90’s, but Google it now and you’ll turn up very little.  It would behoove us to start thinking seriously about it again.  In modern nuclear weapons, conventional explosives are used to implode a “pit” of fissile material to supercritical conditions.  The implosion must be highly symmetric or the pit will “fizzle,” failing to produce enough energy to set off the thermonuclear “secondary” of the weapon that produces most of the yield.  The biggest uncertainty we face in maintaining the safety and reliability of our stockpile is the degree to which the possible deterioration of explosives, fusing systems, etc., will impair the implosion of the pit.  Basically, an AHF would be a system of massive particle accelerators capable of generating bursts of hard x-rays, or, alternatively, protons, powerful enough to image the implosion of the fission “pit” of a nuclear weapon at multiple points in time and in three dimensions.  Currently we have facilities such as the Dual-Axis Radiographic Hydrodynamic Test Facility (DARHT) at Los Alamos National Laboratory (LANL), but it only enables us study the implosion of small samples of surrogate pit material.  An AHF would be able to image the implosion of actual pits, with physically similar surrogate materials replacing the fissile material.

Obviously, such experiments could not be conducted in a conventional laboratory.  Ideally, the facility would be built at a place like the Nevada Test Site (NTS) north of Las Vegas.  Experiments would be fielded underground in the same way that actual nuclear tests were once conducted there.  That would have the advantage of keeping us prepared to conduct actual nuclear tests within a reasonably short time if we should ever be forced to do so, for example, by the resumption of testing by other nuclear powers.  With an AHF we could be virtually certain that the pits of the weapons in our arsenal will work for an indefinite time into the future.  If the pit works, we will also be virtually certain that the secondary will work as well, and the reliability of the weapons in our stockpile will be assured.

Isn’t the AHF just a weaponeer’s wet dream?  Why is it really necessary?  Mainly because it would remove once and for all any credible argument for the resumption of nuclear testing.  Resumption of testing would certainly increase the nuclear danger to mankind, and, IMHO, is to be avoided at all costs.  Not everyone in the military and weapons communities agrees.  Some are champing at the bit for a resumption of testing.  They argue that our stockpile cannot be a reliable deterrent if we are not even sure if our weapons will still work.  With an AHF, we can be sure.  It’s high time for us to dust off those old studies and give some serious thought to building it.


Do We Really Need New Nukes?













Comments on Some Comments on the National Ignition Facility







Another “anonymous” writes in a similar vein:




Another “anonymous” writes,





Anonymous number 4 chimes in,








The United States’ Nuclear Future






