New Reactors in the UK and the Future of Nuclear Power

A consortium led by France’s EDF Energy, including Chinese investors, has agreed with the government of the UK on terms for building a pair of new nuclear reactors at Hinkley Point in the southwest of the country, not far from Bristol.  If a final investment decision is made some time next year, and the plants are actually built, they will probably be big (about 1600 Megawatts) pressurized water reactors (PWR’s) based on the French company Areva’s EPR design.  These are supposed to be  (and probably are) safer, more efficient, and more environmentally friendly than earlier designs.  In general, I tend to be pro-nuclear.  I would certainly feel a lot safer living next to a nuclear plant than a coal plant.  However, I’m a bit ambivalent about these new starts.  I think we could be a lot smarter in the way we implement nuclear power programs.

Reactors of the type proposed will burn uranium.  Natural uranium consists mostly of two isotopes, U235 and U238, and only U235 can be burnt directly in a nuclear reactor.  Why?  The answer to that question depends on something called “the binding energy of the last neutron.”  Think of a neutron as a bowling ball, and the nucleus of a uranium atom as a deep well.  If the bowling ball happens to roll into the well, it will drop over the edge, eventually smacking into the bottom, and releasing the energy it acquired due to the acceleration of gravity in the process.  The analogous force in the nucleus of a uranium atom is the nuclear force, incomparably greater than the force of gravity, but it acts in much the same way.  The neutron doesn’t notice this very short range force until it gets very close to the nucleus, or “lip of the well,” but when it does, it “falls in” and releases the energy acquired in the process in much the same way.  This energy is what I’ve referred to above as “the binding energy of the last neutron.”

When this binding energy is released in the nucleus, it causes it to wiggle and vibrate, something like a big drop of water falling through the air.  In the case of U235, the energy is sufficient to cause this “liquid drop” to actually break in two, or “fission.”  Such isotopes are referred to as “fissile.”  In U238, the binding energy of the last neutron alone is not sufficient to cause fission, but the isotope can still actually fission if the neutron happens to be moving very fast when it hits the nucleus, bringing some of its own energy to the mix.  Such isotopes, while not “fissile,” are referred to as “fissionable.”  Unfortunately, the isotope U235 is only 0.7 percent of natural uranium.  Once it’s burnt, the remaining U238 is no longer useful for starting a nuclear chain reaction on its own.

That would be the end of the story as far as conventional reactors are concerned, except for the fact that something interesting happens to the U238 when it absorbs a neutron.  As mentioned above, it doesn’t fission unless the neutron is going very fast to begin with.  Instead, with the extra neutron, it becomes U239.  However, U239 is unstable, and decays into neptunium 239, which further decays into plutonium 239, or Pu239.  In Pu239 the binding energy of the last neutron IS enough to cause it to fission.  Thus, conventional reactors burn not only U235, but also some of the Pu239 that is produced in this way.  Unfortunately, they don’t produce enough extra plutonium to keep the reactor going, so only a few percent of the U238 is “burnt” in addition to the U235 before the fuel has to be replaced and the old fuel either reprocessed or stored as radioactive waste.  Even though a lot of energy is locked up in the remaining U238, it is usually just discarded or used in such applications as the production of heavy armor or armor piercing munitions.  In other words, the process is something like throwing a log on your fireplace, then fishing it out and throwing it away when only a small fraction of it has been burnt.

Can anything be done about it?  It turns out that it can.  The key is neutrons.  They not only cause the U235 and Pu239 to fission, but also produce Pu239 via absorption in U238.  What if there were more of them around?  If there were enough, then enough new Pu239 could be produced to replace the U235 and old Pu239 lost to fission, and a much greater fraction of the U238 could be converted into useful energy.  A much bigger piece of the “log” could be burnt.

As a matter of fact, what I’ve described has actually been done, in so-called breeder reactors.  To answer the question “How?” it’s necessary to understand where all those neutrons come from to begin with.  In fact, they come from the fission process itself.  When an atom of uranium or plutonium fissions, it releases an average of something between 2 and 3 neutrons in the process.  These, in turn, can cause other fissions, keeping the nuclear chain reaction going.  The chances that they actually will cause another fission depends, among other things, on how fast they are going.  In general, the slower the neutron, the greater the probability that it will cause another fission.  For that reason, the neutrons in nuclear reactors are usually “moderated” to slower speeds by allowing them to collide with lighter elements, such as hydrogen.  Think of billiard balls.  If one of them hits another straight on, it will stop, transferring its energy to the second ball.  Much the same thing happens in neutron “moderation.”

However, more neutrons will be produced in each fission if the neutrons aren’t heavily moderated, but remain “fast.”  In fact, enough can be produced, not only to keep the chain reaction going, but to convert more U238 into useful fuel via neutron absorption than is consumed.  That is the principle of the so-called fast breeder reactor.  Another way to do the same thing is to replace the U238 with the more plentiful naturally occurring element thorium 232.  When it absorbs a neutron, it eventually decays into U233, which, like U235, is fissile.  There are actually many potential advantages to this thorium breeding cycle, such as potentially greater resistance to nuclear weapons proliferation, the ability to run the process at slower average neutron speeds, allowing smaller reactor size and easier control, less production of dangerous, long-lived transuranic actinides, such as plutonium and americium, etc.  In fact, if enough neutrons are flying around, they will fission and eliminate these actinides.  It turns out that’s very important, because they’re the nastiest components of nuclear waste.  If they could be recycled and burned, the amount of residual radiation from the waste produced by operating a nuclear plant for 30 or 40 years could be reduced to a level below that of the original uranium or thorium ore in a matter of only a few hundred years, rather than the many thousands that would otherwise be necessary.

So breeders can use almost all the potential energy in uranium or thorium instead of just a small fraction, while at the same time minimizing problems with radioactive waste.  What’s not to like?  Why aren’t we doing this?  The answer is profit.  As things now stand, power from breeder reactors of the type I’ve just described would be significantly more expensive than that from conventional reactors like EPR.  EPR’s would use enriched natural uranium, which is still relatively cheap and plentiful.  They would require no expensive reprocessing step.  Ask an industry spokesman, and they will generally assure you (and quite possibly believe themselves, because self-interest has always had a strong delusional effect) that we will never run out of natural uranium, that the radioactive danger from conventional reactor waste has been grossly exaggerated, and there is no long-term proliferation danger from simply discarding plutonium-laced waste somewhere and letting it decay for several thousand years.  I’m not so sure.

Now, I have no problem with profit, and I find Hollywood’s obsession with the evils of large corporations tiresome, but I really do think this is one area in which government might actually do something useful.  It might involve some mix of increased investment in research and development of advanced reactor technology, including the building of small demonstration reactors, continued robust support for the nuclear Navy, and eliminating subsidies on new conventional reactors.  Somehow, we managed to build scores of research reactors back in the 50’s, 60’s and 70’s.  It would be nice if we could continue building a few more now and then, not only for research into breeder technology, but as test beds for new corrosion and radiation resistant materials and fuels, exploration of high temperature gas-cooled reactors that could not only produce electricity but facilitate the production of hydrogen from water and synthetic natural gas from carbon dioxide and coal, both processes that are potentially much more efficient at high temperatures, and even fusion-fission hybrids if we can ever get fusion to work.

We aren’t going to run out of energy any time soon, but there are now over 7 billion people on the planet.  Eventually we will run out of fossil fuels, and depending entirely on wind, solar and other renewables to take up the slack seems a little risky to me.  Wasting potential fuel for the reactors of the future doesn’t seem like such a good idea either.  Under the circumstances, keeping breeder technology on the table as a viable alternative doesn’t seem like a bad idea.

Accelerator-Driven Thorium Reactors, or An Easy Way to Eliminate Surplus Population

The Daily Telegraph has just taken thorium wowserism to a whole new level.  According to the title of an article penned by International Business Editor Ambrose Evans-Pritchard, Obama could kill fossil fuels overnight with a nuclear dash for thorium.  Continuing in the same vein, the byline assures us that,

If Barack Obama were to marshal America’s vast scientific and strategic resources behind a new Manhattan Project, he might reasonably hope to reinvent the global energy landscape and sketch an end to our dependence on fossil fuels within three to five years.

And how is this prodigious feat to be accomplished?  Via none other than Nobel laureate Dr. Carlo Rubbia’s  really bad idea for building accelerator-driven thorium reactors.  It would seem that Dr. Rubbia has assured the credulous Telegraph editor that, “a tonne of the silvery metal produces as much energy as 200 tonnes of uranium.”  This egregious whopper is based on nothing more complicated than a comparison of apples and oranges.  Thorium by itself cannot power a nuclear reactor.  It must first be converted into the isotope uranium 233 via absorption of a neutron.  Natural uranium, on the other hand, can be used directly in reactors, because 0.7 percent of it consists of the fissile isotope uranium 235.  In other words, Rubbia is comparing the energy potential of thorium after it has been converted to U233 with the energy potential of only the U235 in natural uranium.  The obvious objection to this absurd comparison is that the rest of natural uranium is made up mostly of the isotope U238, which can also absorb a neutron to produce plutonium 239, which, like U233, can power nuclear reactors.  In other words, if we compare apples to apples, that is, thorium after it has been converted to U233 with U238 after it has been converted to Pu239, the potential energy content of thorium and uranium is about equal.

As it happens, the really bad news in the Telegraph article is that,

The Norwegian group Aker Solutions has bought Dr. Rubbia’s patent for an accelerator-driven sub-critical reactor, and is working on his design for a thorium version at its UK operation.

In fact, Aker has already completed a conceptual design for a power plant.  According to Aker project manager Victoria Ashley, the group needs a paltry $3 million, give or take, to build the first one, and another $150 million for the test phase to follow.  Why is that disturbing news?  Because the U233 produced in these wonderful new reactors will be ideal for producing nuclear weapons.

In fact, it will be even better than the “traditional” bomb materials; highly enriched uranium (HEU) and weapons grade plutonium.  The explosion of a nuclear device is produced by assembling a highly supercritical mass of fissile material, and then introducing a source of neutrons at just the right moment, setting off a runaway chain reaction.  The problem with plutonium is that it has the bad habit of occasionally fissioning spontaneously.  This releases neutrons.  If such a stray neutron were to happen along just as the bomb material became critical, it would set off a premature chain reaction, causing the device to “fizzle.”  As a result, plutonium weapons must rely on a complicated implosion process to achieve supercriticality before the stray neutrons can do their dirty work.  Implosion weapons are much more technologically challenging to build than the gun-assembled types that can be used with HEU.  In these, one subcritical mass is simply shot into another.  However, the required mass of HEU is much larger than the amount of plutonium needed in an implosion-assembled weapon.  As it happens, the amount of U233 sufficient to build a nuclear device is about the same as the amount of plutonium, but spontaneous fission is not a problem in U233.  In other words, it combines the plutonium advantage of requiring a much smaller amount of material, and the HEU advantage of being usable in gun-assembled weapons.

Why, then, you might ask, are we even giving Rubbia’s idea a second thought?  Because of people like Professor Egil Lillestol, who, Evans-Pritchard helpfully informs us, is “a world authority on the thorium fuel cycle at CERN.”  According to Lillestol,

It is almost impossible to make nuclear weapons out of thorium because it is too difficult to handle.  It wouldn’t be worth trying.

Rubbia has made similar statements, based on the same “logic.”  The rationalization for the claim that U233 is “too difficult to handle” is the supposed presence of U232, an isotope of uranium with a half-life of about 69 years, one of whose daughters (elements in its decay chain) emits a highly energetic and penetrating, and hence deadly, gamma ray.  In fact, avoiding the production of U232 in accelerator-driven reactors would be a piece of cake.  Rubbia and Lillestol must know this, making it all the more incomprehensible that they dare to foist such whoppers on unsuspecting newspaper editors.

Only one neutron absorption is needed for the production of U233 from naturally occurring Th232.  Two are needed to produce U232.  Thus, one way to keep the level of U232 within manageable levels is to simply extract the U233 before much U232 has a chance to form.  However, there’s an even easier way.  Very energetic neutrons, with energies above a threshold of around 6 million electron volts, are necessary to produce U232.  Not many fission neutrons have that much energy, and slowing down the ones that do is simple.  Simply pass them through a “moderator” rich in hydrogen or some other light element.  Think of billiard balls.  If one of them going at a good clip hits another dead on, it stops, imparting its energy to the second ball.  Neutrons and the proton nuclei of hydrogen atoms have nearly the same mass, so the same thing can happen when they collide.  A fast neutron will typically lose a large fraction of its energy in such a collision.  In other words, the “secret” of avoiding the production of dangerous levels of U232 is as simple as passing the neutrons through a layer of hydrogen-rich material such as paraffin before allowing them to interact with the thorium.  All this should hardly come as a surprise to people like Rubbia and Lillestol.  It’s been old hat in the literature for a long time.  For a more detailed treatment, see, for example, U-232 and the Proliferation-Resistance of U-233 in Spent Fuel, a paper that appeared in the journal Science and Global Security back in 2001.

In other words, the idea that “it is almost impossible to make nuclear weapons out of thorium” is a pipe dream.  That does not necessarily mean that thorium technology should be rejected root and branch.  It will always be necessary to exercise extreme care to insure that U233 isn’t diverted for illicit purposes.  However, managing the risk will be considerably easier in “conventional” thorium breeders, which rely on assembling a critical mass to supply the necessary source of neutrons.  Such reactors have already been built and successfully operated for years.  The U233 they produce will always be mixed with highly radioactive fission products, and can also be “denatured” by mixing it with U238, from which it cannot be separated using simple chemistry.  Such reactors would produce few of the transuranic actinides that are the main culprits in nuclear waste, potentially requiring it to be stored securely for millennia.  They could also consume the actinides produced in the current generation of reactors, so that the remaining waste could potentially become less radioactive than the original uranium ore in a few hundred years, instead of many thousands.

If, on the other hand, the accelerators necessary to provide the neutron source for Dr. Rubbia’s subcritical facilities were to become readily available, they would be much easier to hide than conventional reactors, could be configured to produce U233 with almost no U232 contamination, and with much less radioactive fission product contamination.  In other words, they would constitute an unacceptable risk for the proliferation of nuclear weapons.  One must hope that the world will wake up in time to recognize the threat.

Fusion Update: The NIF Inches Closer to Ignition

In a recent press release, Lawrence Livermore National Laboratory (LLNL) announced that it had achieved a yield of 3 x 1015 neutrons in the latest round of experiments at its National Ignition Facility, a giant, 192-beam laser facility designed, as its name implies, to achieve fusion ignition.  That’s nowhere near “ignition,” but still encouraging as it’s three times better than results achieved in earlier experiments.

The easiest way to achieve fusion is with two heavy isotopes of hydrogen; deuterium, with a nucleus containing one proton and one neutron, and tritium, with a nucleus containing one proton and two neutrons.  Deuterium is not radioactive, and occurs naturally as about one atom to every 6400 atoms of “normal” hydrogen, with a nucleus containing only a single proton.  Tritium is radioactive, and occurs naturally only in tiny trace amounts.  It has a half-life (the time it takes for half of a given amount to undergo radioactive decay) of 12.3 years, and must be produced artificially.  When tritium and deuterium fuse, they release a neutron, a helium nucleus, or alpha particle, and lots of energy (17.6 million electron volts).

Fortunately (because otherwise it would be too easy to blow up the planet), or unfortunately (if you want to convert the energy into electricity), fusion is hard.  The two atoms don’t like to get too close, because their positively charged nuclei repel each other.  Somehow, a way must be found to make the heavy hydrogen fuel material very hot, causing the thermal motion of the atoms to become very large.  Once they start moving fast enough, they can smash into each other with enough momentum to overcome the repulsion of the positive nuclei, allowing them to fuse.  However, the amount of energy needed per atom is huge, and when atoms get that hot, the last thing they want to do is stay close to each other (think of what happens in the detonation of high explosive.)  There are two mainstream approaches to solving this problem; magnetic fusion, in which the atoms are held in place by powerful magnetic fields while they are heated (the approach being pursued at ITER, the International Thermonuclear Experimental Reactor, currently under construction in France), and inertial confinement fusion (ICF), where the idea is to dump energy into the fuel material so fast that its own inertia holds it in place long enough for fusion to occur.  The NIF is an ICF facility.

There are various definitions of ICF “ignition,” but, in order to avoid comparisons of apples and oranges between ICF and magnetic fusion experiments, LLNL has explicitly accepted the point at which the fusion energy out equals the laser energy in as the definition of ignition.  In the experiment referred to above, the total fusion energy release was about 10,000 joules, give or take.  Since the laser energy in was around 1.7 million joules, that’s only a little over one half of one percent of what’s needed for ignition.  Paltry, you say?  Not really.  To understand why, you have to know a little about how ICF experiments work.

Recall that the idea is to heat the fuel material up so fast that its own inertia holds it in place long enough for fusion to occur.  The “obvious” way to do that would be to simply dump in enough laser energy to heat all the fuel material to fusion temperatures at once.  Unfortunately, this “volumetric heating” approach wouldn’t work.  The energy required would be orders of magnitude more than what’s available on the NIF.  What to do?   Apply lots and lots of finesse.  It turns out that if a very small volume or “hot spot” in the fuel material can be brought to fusion conditions, the alpha particles released in the fusion reactions might carry enough energy to heat up the nearby fuel to fusion conditions as well.  Ideally, the result would be an alpha “burn wave,” moving out through the fuel, and consuming it all.  But wait, it ain’t that easy!  An efficient burn wave will occur only if the alphas are slammed to a stop and forced to dump their energy after traveling only a very short distance in the cold fuel material around the hot spot.  Their range is too large unless the fuel is first compressed to a tiny fraction of its original volume, causing its density to increase by orders of magnitude.

In other words, to get the fuel to fuse, we need to make it very hot, but we also need to compress it to very high density, which can be done much more easily and efficiently if the material is cold!  Somehow, we need to keep the fuel “cold” during the compression process, and then, just at the right moment, suddenly heat up a small volume to fusion conditions.  It turns out that shocks are the answer to the problem.  If a train of four shocks can be set off in the fuel material as it is being compressed, or “imploded,” by the lasers, precisely timed so that they will all converge at just the right moment, it should be possible, in theory at least, to generate a hot spot.  If the nice, spherical symmetry of the fuel target could be maintained during the implosion process, everything should work just fine.  The NIF would have more than enough energy to achieve ignition.  But there’s the rub. Maintaining the necessary symmetry has turned out to be inordinately hard.  Tiny imperfections in the target surface finish, small asymmetries in the laser beams, etc., lead to big deviations from perfect symmetry in the dense, imploded fuel.  These asymmetries have been the main reason the NIF has not been able to achieve its ignition goal to date.

And that’s why the results of the latest round of experiments haven’t been as “paltry” as they seem.  As noted in the LLNL press release,

Early calculations show that fusion reactions in the hot plasma started to self-heat the burning core and enhanced the yield by nearly 50 percent, pushing close to the margins of alpha burn, where the fusion reactions dominate the process.

“The yield was significantly greater than the energy deposited in the hot spot by the implosion,” said Ed Moses, principle associate director for NIF and Photon Science. “This represents an important advance in establishing a self-sustaining burning target, the next critical step on the path to fusion ignition on NIF.”

That’s not just hype.  If the self-heating can be increased in future experiments, it may be possible to reach a threshold at which the alpha heating sets off a burn wave through the rest of the cold fuel, as described above.  In other words, ignition is hardly a given, but the guys at LLNL still have a fighting chance.  Their main challenge may be to stem the gradual evaporation of political support for NIF while the experiments are underway.  Their own Senator, Diane Feinstein, is anything but an avid supporter.  She recently turned down appeals to halt NIF budget cuts, and says the project needs to be “reassessed” in light of the failure to achieve ignition.

Such a “reassessment” would be a big mistake.  The NIF was never funded as an energy project.  Its support comes from the National Nuclear Security Administration (NNSA), a semi-autonomous arm of the Department of Energy charged with maintaining the safety and reliability of the nation’s nuclear arsenal.  As a tool for achieving that end, the NIF is without peer in any other country.  It has delivered on all of its performance design goals, including laser energy, illumination symmetry, shot rate, the precision and accuracy of its diagnostic instrumentation, etc.  The facility is of exceptional value to the weapons program even if ignition is never achieved.  It can still generate experimental conditions approaching those present in an exploding nuclear device, and, along with the rest of our suite of “above-ground experimental facilities,” or AGEX, it gives us a major leg up over the competition in maintaining our arsenal and avoiding technological surprise in the post-testing era.

Why is that important?  Because the alternative is a return to nuclear testing.  Do you think no one at NNSA wants to return to testing, and that the weapon designers at the National Weapons Laboratories wouldn’t jump at the chance?  If so, you’re dreaming.  It seems to me we should be doing our best to keep the nuclear genie in the bottle, not let it out.  Mothballing the NIF would be an excellent start at pulling the cork!

I understand why the guys at LLNL are hyping the NIF’s potential as a source of energy.  It’s a lot easier to generate political support for lots of electricity with very little radioactive waste and no greenhouse gases than for maintaining our aging arsenal of nuclear weapons.  However, IMHO, ICF is hopeless as a source of electricity, at least for the next few hundred years.  I know many excellent scientists will disagree, but many excellent scientists are also prone to extreme wishful thinking when it comes to rationalizing a technology they’ve devoted their careers to.  Regardless, energy hype isn’t needed to justify the NIF.  It and facilities like it will insure our technological superiority over potential nuclear rivals for years to come, and at the same time provide a potent argument against the resumption of nuclear testing.

More Plutonium Horror Stories in Germany

Germany is plagued by an unusually large number per capita of pathologically pious zealots of the type who like to strike heroic poses as saviors of humanity.  The number may even approach the levels found in the USA.  They definitely take the cake when it comes to the subspecies of the tribe whose tastes run to nuclear alarmism.  They came out of the woodwork in droves the last time an attempt was made to move radioactive waste via rail to the storage facility in Gorleben, tearing up the tracks, peacefully smearing a police vehicle with tar and setting it on fire, and generally making a nuisance of themselves.  Now, in keeping with that tradition, an article just appeared in the German version of New Scientist, according to which those evil Americans are actually planning to restart the production of (shudder) plutonium.

Entitled The Return of Plutonium and written by one Helmut Broeg, the article assumes a remarkable level of stupidity on the part of its readers.  Mimicking Der Spiegel, Germany’s number one news magazine, its byline is more sensational than the article that follows, based on the (probably accurate) assumption that that’s as far as most consumers of online content will read. Here’s the translation:

The USA stopped producing plutonium 25 years ago.  In order to preserve the ability to launch deep space missions, they will resume the production of the highly poisonous and radioactive material.

Only in the body of the article do we learn that the particular isotope that will be produced is plutonium 238, which, unlike plutonium 239, is useless for making nuclear explosives.  As it happens, Pu-238 is the ideal material for powering thermoelectric generators such as that used on the Curiosity Mars rover because it decays primarily via emission of alpha particles (helium nuclei) and has a half life of 87.7 years.  That means that its decay products are mostly stopped in the material itself, generating a lot of heat in the process (because of the short half life, or time it take half of the material to decay), which can be converted to electricity using devices with no moving parts.  The world supply of the material is currently very short, and more is urgently needed to power future deep space missions.

All this is very sinister, according to Broeg.  He quotes Heinz Smital, who, we are informed, is an “atomic expert” at Greenpeace, that, “the crash of such a satellite could contaminate large areas with radioactivity.  Don’t look now, Mr. Smital, but if you’re really worried about radioactive contamination by alpha emitters like Pu-238, you might want to reconsider building all the coal plants that Germany is currently planning to replace the nuclear facilities it has decided to shut down.  Coal typically contains several parts per million of radioactive uranium and thorium.    A good-sized plant will release 5 tons of uranium and 10 tons of thorium into the environment each year.  Estimated releases in 1982  from worldwide combustion of 2800 million tons of coal totaled 3640 tons of uranium (containing 51,700 pounds of uranium-235) and 8960 tons of thorium.  That amount has gone up considerably in the intervening years.  The cumulative radiation now covering the earth from these sources dwarfs anything that might conceivably result from the crash of a rocket with a Pu-238 power source, no matter what implausible assumptions one chose to make about how its containment would fail, how it would somehow enter the atmosphere at hypersonic speed so as to (optimize) its dispersion, etc.  Of course, the radioactive isotopes released from burning coal will also be with us for billions of years, not just the few hundred it takes for Pu-238 to decay.

But wait!  Dispersal of Pu-238 isn’t the only problem.  There’s also (drum roll) the BOMB!  Broeg drags in another “expert,” Moritz Kütt, a physicist at the Technical University of Darmstadt, who assures us that, “In the production of Pu-238, some Pu-239 is produced as well.  As a matter of principle, that means the US is resuming the production of weapons-useful material.”  Kütt goes on to ask what the world community would have to say if Iran announced that it would produce Pu-238 for a space mission?

To appreciate the level of gullibility it takes to swallow such “warnings,” one must spend a few minutes to check on how Pu-238 is actually produced.  Generally, it is done by irradiating neptunium 237 from spent nuclear fuel with neutrons in a reactor.  Occasionally the Np-237 captures a neutron, becoming Np-238.  This, in turn emits a beta particle (electron), and is transmuted to Pu-238.  It’s quite true that some of the Pu-238 will also capture a neutron, and become Pu-239.  However, the amounts produced in this way would be vanishingly small compared to the amounts that could be produced in the same reactor by simply removing some of the fuel rods after a few months and chemically extracting the nearly pure Pu-239, which would not then have to be somehow separated from far greater quantities of highly radioactive Pu-238.  In other words, if the world community learned that Iran had a nefarious plan to produce bomb material in the way suggested by Kütt, the reasonable immediate reaction would be a horse laugh, perhaps followed by sympathy for a people who were sufficiently stupid to adopt such a plan.  As for the US deciding to replentish its stocks of bomb material in this way, the idea is more implausible than anything those good Germans, the brothers Grimm ever came up with.  It only takes 4 kilos of Pu-239 to make a bomb, and we have tons of it on hand.  In the unlikely event we wanted more, we would simply extract it from reactor fuel rods.  The idea that we would ever prefer to attempt the separation of Pu-239 from Pu-238 instead is one that could only be concocted in the fevered imagination of a German “atomic expert.”

 

Plutonium 238
Plutonium 238

 

 

But Wait! There are More “Worries” from The Edge!

I won’t parse all 150+ of them, but here are a few more that caught my eye.

Science writer and historian Michael Shermer, apparently channeling Sam Harris, is worried about the “Is-Ought Fallacy of Science and Morality.”  According to Shermer,

…most scientists have conceded the high ground of determining human values, morals, and ethics to philosophers, agreeing that science can only describe the way things are but never tell us how they ought to be. This is a mistake.

It’s only a mistake to the extent that there’s actually some “high ground” to be conceded.  There is not.  Assuming that Shermer is not referring to the trivial case of discovering mere opinions in the minds of individual humans, neither science nor philosophy is capable determining anything about objects that don’t exist.  Values, morals and ethics do not exist as objects.  They are not things-in-themselves.  They cannot leap out of the skulls of individuals and acquire a reality and legitimacy that transcends individual whim.  Certainly, large groups of individuals who discover that they have whims in common can band together and “scientifically” force their whims down the throats of less powerful groups and individuals, but, as they say, that don’t make it right.

Suppose we experience a holocaust of some kind, and only one human survived the mayhem.  No doubt he would still be able to imagine what it was like when there were large groups of other’s like himself.  He might recall how they behaved, “scientifically” categorizing their actions as “good” or “evil,” according to his own particular moral intuitions.  Supposed, now, that his life also flickered out.  What would be left of his whims?  Would the inanimate universe, spinning on towards its own destiny, care about them one way or the other.  Science can determine the properties and qualities of things.  Where, then, would the “good” and “evil” objects reside?  Would they still float about in the ether as disembodied spirits?  I’m afraid not.  Science can have nothing to say about objects that don’t exist.  Michael Shermer might feel “in his bones” that some version of “human flourishing” is “scientifically good,” but there is no reason at all why I or anyone else should agree with his opinion.  By all means, let us flourish together, if we all share that whim, but surely we can pursue that goal without tacking moral intuitions on to it.  “Scientific” morality is not only naive, but, as was just demonstrated by the Communists and the Nazis, extremely dangerous as well. According to Shermer,

We should be worried that scientists have given up the search for determining right and wrong…

In fact, if scientists cease looking for and seeking to study objects that plainly don’t exist, it would seem to me more reason for congratulations all around than worry.  Here’s a sample of the sort of “reasoning” Shermer uses to bolster his case:

We begin with the individual organism as the primary unit of biology and society because the organism is the principal target of natural selection and social evolution. Thus, the survival and flourishing of the individual organism—people in this context—is the basis of establishing values and morals, and so determining the conditions by which humans best flourish ought to be the goal of a science of morality. The constitutions of human societies ought to be built on the constitution of human nature, and science is the best tool we have for understanding our nature.

Forgive me for being blunt, but this is gibberish.  Natural selection can have no target, because it is an inanimate process, and can no more have a purpose or will than a stone.  “Thus, the survival and flourishing of the individual organism – people in this context – is the basis of establishing values and morals”??  Such “reasoning” reminds me of the old “Far Side” cartoon, in which one scientist turns to another and allows that he doesn’t quite understand the intermediate step in his proof:  “Miracle happens.”  If a volcano spits a molten mass into the air which falls to earth and becomes a rock, is not it, in the same sense, the “target” of the geologic processes that caused indigestion in the volcano?  Is not the survival and flourishing of that rock equally a universal “good?”

Of the remaining “worries,” this was the one that most worried me, but there were others.  Kevin Kelly, Editor at Large of Wired Magazine, was worried about the “Underpopulation Bomb.”  Noting the “Ur-worry” of overpopulation, Kelly writes,

While the global population of humans will continue to rise for at least another 40 years, demographic trends in full force today make it clear that a much bigger existential threat lies in global underpopulation.

Apparently the basis of Kelly’s worry is the assumption that, once the earths population peaks in 2050 or thereabouts, the decrease will inevitably continue until we hit zero and die out.  In his words, “That worry seems preposterous at first.”  I think it seem preposterous first and last.

Science writer Ed Regis is worried about, “Being Told That Our Destiny Is Among The Stars.”  After reciting the usual litany of technological reasons that human travel to the stars isn’t likely, he writes,

Apart from all of these difficulties, the more important point is that there is no good reason to make the trip in the first place. If we need a new “Earth 2.0,” then the Moon, Mars, Europa, or other intra-solar-system bodies are far more likely candidates for human colonization than are planets light years away.  So, however romantic and dreamy it might sound, and however much it might appeal to one’s youthful hankerings of “going into space,” interstellar flight remains a science-fictional concept—and with any luck it always will be.

In other words, he doesn’t want to go.  By all means, then, he should stay here.  I and many others, however, have a different whim.  We embrace the challenge of travel to the stars, and, when it comes to human survival, we feel existential Angst at the prospect of putting all of our eggs in one basket.  Whether “interstellar flight remains a science-fiction concept” at the moment depends on how broadly you define “we.”  I see no reason why “we” should be limited to one species.  After all, any species you could mention is related to all the rest.  Interstellar travel may not be a technologically feasible option for me at the moment, but it is certainly feasible for my relatives on the planet, and at a cost that is relatively trivial.  Many simpler life forms can potentially survive tens of thousands of years in interstellar space.  I am of the opinion that we should send them on their way, and the sooner the better.

I do share some of the other worries of the Edge contributors.  I agree, for example, with historian Noga Arikha’s worry about, “Presentism – the prospect of collective amnesia,” or, as she puts it, the “historical blankness” promoted by the Internet.  In all fairness, the Internet has provided unprecedented access to historical source material.  However, to find it you need to have the historical background to know what you’re looking for.  That background about the past can be hard to develop in the glare of all the fascinating information available about the here and now.  I also agree with physicist Anton Zeilinger’s worry about, “Losing Completeness – that we are increasingly losing the formal and informal bridges between different intellectual, mental, and humanistic approaches to seeing the world.”  It’s an enduring problem.  The name “university” was already a misnomer 200 years ago, and in the meantime the problem has only become worse.  Those who can see the “big picture” and have the talent to describe it to others are in greater demand than ever before.  Finally, I agree with astrophysicist Martin Rees’ worry that, “We Are In Denial About Catastrophic Risks.”  In particular, I agree with his comment to the effect that,

The ‘anthropocene’ era, when the main global threats come from humans and not from nature, began with the mass deployment of thermonuclear weapons. Throughout the Cold War, there were several occasions when the superpowers could have stumbled toward nuclear Armageddon through muddle or miscalculation. Those who lived anxiously through the Cuba crisis would have been not merely anxious but paralytically scared had they realized just how close the world then was to catastrophe.

This threat is still with us.  It is not “in abeyance” because of the end of the cold war, nor does that fact that nuclear weapons have not been used since World War II mean that they will never be used again.  They will.  It is not a question of “if,” but “when.”

Fusion Update: Signs of Life from the National Ignition Facility

The National Ignition Facility, or NIF, is a huge, 192 beam laser system, located at Lawrence Livermore National Laboratory in California.  It was designed, as the name implies, to achieve thermonuclear ignition in the laboratory.  “Ignition” is generally accepted to mean getting a greater energy output from fusion than the laser input energy.  Unlike magnetic confinement fusion, the approach currently being pursued at the International Thermonuclear Experimental Reactor, or ITER, now under construction in France, the goal of the NIF is to achieve ignition via inertial confinement fusion, or ICF, in which the fuel material is compressed and heated to the extreme conditions at which fusion occurs so quickly that it is held in place by its own inertia.

The NIF has been operational for over a year now, and a two year campaign is underway with the goal of achieving ignition by the end of this fiscal year.  Recently, there has been a somewhat ominous silence from the facility, manifesting itself as a lack of publications in the major journals favored by fusion scientists.  That doesn’t usually happen when there is anything interesting to report.  Finally, however, some papers have turned up in the journal Physics of Plasmas, containing reports of significant progress.

To grasp the importance of the papers, it is necessary to understand what is supposed to occur within the NIF  target chamber for fusion to occur.  Of course, just as in magnetic fusion, the goal is to bring a mixture of deuterium and tritium, two heavy isotopes of hydrogen, to the extreme conditions at which fusion takes place.  In the ICF approach, this hydrogen “fuel” is contained in a tiny, BB-sized target.  However, the lasers are not aimed directly at the fuel “capsule.”  Instead, the capsule is suspended in the middle of a tiny cylinder made of a heavy metal like gold or uranium.  The lasers are fired through holes on each end of the cylinder, striking the interior walls, where their energy is converted to x-rays.  It is these x-rays that must actually bring the target to fusion conditions.

It was recognized many years ago that one couldn’t achieve fusion ignition by simply heating up the target.  That would require a laser driver orders of magnitude bigger than the NIF.  Instead, it is first necessary to compress, or implode, the fuel material to extremely high density.  Obviously, it is harder to “squeeze” hot material than cold material to the necessary high densities, so the fuel must be kept as “cold” as possible during the implosion process.  However, cold fuel won’t ignite, begging the question of how to heat it up once the necessary high densities have been achieved.

It turns out that the answer is shocks.  When the laser generated x-rays hit the target surface, they do so with such force that it begins to implode faster than the speed of sound.  Everyone knows that when a plane breaks the sound barrier, it, too, generates a shock, which can be heard as a sonic boom.  The same thing happens in ICF fusion targets.  When such a shock converges at the center of the target, the result is a small “hot spot” in the center of the fuel.  If the temperature in the hot spot were high enough, fusion would occur.  Each fusion reaction would release a high energy helium nucleus, or alpha particle, and a neutron.  The alpha particles would be slammed to a stop in the surrounding cold fuel material, heating it, in turn, to fusion conditions.  This would result in a fusion “burn wave” that would propagate out through the rest of the fuel, completing the fusion process.

The problem is that one shock isn’t enough to create such a “hot spot.”  Four of them are required, all precisely timed by the carefully tailored NIF laser pulse to converge at the center of the target at exactly the same time.  This is where real finesse is needed in laser fusion.  The implosion must be extremely symmetric, or the shocks will not converge properly.  The timing must be exact, and the laser pulse must deliver just the right amount of energy.

One problem in the work to date has been an inability to achieve high enough implosion velocities for the above scenario to work as planned.  One of the Physics of Plasmas papers reports that, by increasing the laser energy and replacing some of the gold originally used in the wall of the cylinder, or “hohlraum,” in which the fuel capsule is mounted with depleted uranium, velocities of 99% of those required for ignition have been achieved.  In view of the recent announcement that a shot on the NIF had exceeded its design energy of 1.8 megajoules, it appears the required velocity is within reach.  Another of the Physics of Plasmas papers dealt with the degree to which implosion asymmetries were causing harmful mixing of the surrounding cold fuel material into the imploded core of the target.  It, too, provided grounds for optimism.

In the end, I suspect the success or failure of the NIF will depend on whether the complex sequence of four shocks can really be made to work as advertised.  That will depend on the accuracy of the physics algorithms in the computer codes that have been used to model the experiments.  Time and again, earlier and less sophisticated codes have been wrong because they didn’t accurately account for all the relevant physics.  There is no guarantee that critical phenomena have not been left out of the current versions as well.  We may soon find out, if the critical series of experiments planned to achieve ignition before the end of the fiscal year are carried out as planned.

One can but hope they will succeed, if only because some of our finest scientists have dedicated their careers to the quest to achieve the elusive goal of controlled fusion.  Even if they do, fusion based on the NIF approach is unlikely to become a viable source of energy, at least in the foreseeable future.  Laser fusion may prove scientifically feasible, but getting useful energy out of it will be an engineering nightmare, dangerous because of the need to rely on highly volatile and radioactive tritium, and much too expensive to compete with potential alternatives.  I know many of the faithful in the scientific community will beg to differ with me, but, trust me, laser fusion energy aint’ gonna happen.

On the other hand, if ignition is achieved, the NIF will be invaluable to the country, not as a source of energy, but for the reason it was funded in the first place – to insure that our nation has an unmatched suite of experimental facilities to study the physics of nuclear weapons in a era free of nuclear testing.  As long as we have unique access to facilities like the NIF, which can approach the extreme physical conditions within exploding nukes, we will have a significant leg up on the competition as long as the test ban remains in place.  For that, if for no other reason, we should keep our fingers crossed that the NIF team can finally clear the last technical hurdles and reach the goal they have been working towards for so long.

Fusion ignition process,courtesy of Lawrence Livermore National Laboratory

START and the Resurrection of the Reliable Replacement Warhead

The Reliable Replacement Warhead is a really bad idea that never seems to go away.  Congress has wisely condemned it, and it was explicitly rejected in the nation’s latest Nuclear Posture Review, but now the RRW has popped up again, artificially linked to the New Start arms control treaty, in a couple of opeds, one in the New York Times by former UN ambassador John Bolton, and another in the Wall Street Journal by R. James Woolsey, former arms control negotiator and Director of the CIA.  Bolton writes, “Congress should pass a new law financing the testing and development of new warhead designs before approving New Start,” and Woolsey chimes in,

…the administration needs to commit to replacing and modernizing our aging nuclear infrastructure as well as the bombers, submarines and ballistic missiles – and the warheads on them – that provide our ultimate guarantee of national security. The Senate’s resolution of ratification should, for example, require the president to commit to specific modernization plans so we can be sure these programs will have his full support. The administration has particularly resisted warhead modernization, beginning with its Nuclear Posture Review last year. This led 10 former directors of the nation’s nuclear weapons labs to write to the secretaries of Defense and Energy urging them to revisit that misguided policy. The secretaries should commit to doing so.

In fact, one hopes they have enough sense not to follow that advice.  What Bolton and Woolsey are referring to when they speak of “modernizing” weapons isn’t the continued refurbishment of old weapons, or the adding of new conventional packaging around them, as in the case of the B61-11, to make them more effective for earth penetration or some other specific mission.  They are speaking of a new design of the nuclear device itself.  At the moment, the RRW is the only player in that game.

Going ahead with the RRW would be self-destructive at a number of levels.  In the first place, it’s unnecessary.  There is no reason to doubt the safety and reliability of the existing weapons in our arsenal, nor our ability to maintain them into the indefinite future.  A reason given for building the RRW is that low yield versions could be designed that would be “more effective deterrents,” because enemies would consider it a lot more likely that we would actually use such a weapon against them, as opposed to our existing high yield weapons.  The problem with that logic is that they would be right.  Given the alacrity with which we went to war in Iraq, it is not hard to imagine that we would be sorely tempted to use a mini-nuke to take out, say, a buried and/or hardened enemy bunker suspected of containing WMD’s.  Any US first use of nuclear weapons, for whatever reason, and regardless of the chances of “collateral damage,” would be a disastrous mistake.  It would let the nuclear genie out of the bottle once again, serving as a perfect pretense for the use of nuclear weapons by others, and particularly by terrorists against us.  Those who think the Maginot line of nuclear detectors we are installing at our ports, or the imaginary difficulty of mastering the necessary technology, will protect us from such an eventuality, are gravely mistaken. 

The building of a new weapon design would also provide a fine excuse for others to modernize their own arsenals.  It is hard to imagine how this could work to the advantage of the United States.  Our nuclear technology is mature, and it would simply give the lesser nuclear powers a chance to catch up with us.  More importantly, it would almost inevitably imply a return to nuclear testing, thereby negating a tremendous advantage we now hold over every other nuclear power, namely, our above ground experimental (AGEX) capability.  In the National Ignition Facility at Lawrence Livermore National Laboratory, the Z pulsed power machine at Sandia, the DAHRT radiographic test facility at Los Alamos, and a host of other experimental facilities, we possess an ability to study the physics that occurs in conditions near those in nuclear detonations that no other country comes close to matching.  It would be utterly pointless to throw that advantage away in order to build a new nuclear weapon we don’t need.

It does not surprise me that 10 former directors of the nation’s nuclear weapons laboratories signed a letter calling on the Secretaries of Energy and Defense to revisit our RRW policy.  It would certainly serve the interests of the nuclear weapons laboratories.  It is much easier to attract talented physicists to an active testing program than to serve as custodians of an aging stockpile, and new designs would mean new money, and the removal of any perceived existential threats to one or more of the existing labs on the basis of their redundancy.  The problem is that it would not serve the interests of the country. 

Let the RRW stay buried.  The nuclear genie will return soon enough as it is.

More Thorium Silliness

Thorium is a promising candidate as a future source of energy.  I just wonder what it is about the stuff that inspires so many people to write nonsense about it.  It doesn’t take a Ph.D. in physics to spot the mistakes.  Most of them should be obvious to anyone who’s taken the trouble to read a high school science book.  Another piece of misinformation has just turned up at the website of Popular Mechanics, dubiously titled The Truth about Thorium and Nuclear Power.

The byline claims that, “Thorium has nearly 200 times the energy content of uranium,” a statement I will assume reflects the ignorance of the writer rather than any outright attempt to deceive. She cites physicist Carlo Rubbia as the source, but if he ever said anything of the sort, he was making some very “special” assumptions about the energy conversion process that she didn’t quite understand. I assume it must have had something to do with his insanely dangerous subcritical reactor scheme, in which case the necessary assumptions to get a factor of 200 would have necessarily been very “special” indeed. Thorium cannot sustain the nuclear chain reaction needed to produce energy on its own. It must first be transmuted to an isotope of uranium with the atomic weight of 233 (U233) by absorbing a neutron. Strictly speaking, then, the above statement is nonsense, because the “energy content” of thorium actually comes from a form of uranium, U233, which can sustain a chain reaction on its own. However, let’s be charitable and compare natural thorium and natural uranium as both come out of the ground when mined. 

As I’ve already pointed out, thorium cannot be directly used in a nuclear reactor on its own.  Natural uranium actually can.  It consists mostly of an isotope of uranium with an atomic weight of 238 (U238), but also a bit over 0.7% of a lighter isotope with an atomic weight of 235 (U235).  U238, like thorium, is unable to support a nuclear chain reaction on its own, but U235, like U233, can.  Technically speaking, what that means is that, when the nucleus of an atom of U233 or U235 absorbs a neutron, enough energy is released to cause the nucleus to split, or fission.  When U238 or natural thorium (Th232) absorbs a neutron, energy is also released, but not enough to cause fission.  Instead, they become U239 and Th233, which eventually decay to produce U233 and plutonium 239 (Pu239) respectively. 

Let’s try to compare apples and apples, and assume that enough neutrons are around to convert all the Th232 to U233, and all the U238 to Pu239.  In that case we are left with a lump of pure U233 derived from the natural thorium and a mixture of about 99.3% Pu239 and 0.7% U235 from the natural uranium.  In the first case, the fission of each atom of U233 will release, on average, 200.1 million electron volts (MeV) of energy that can potentially be converted to heat in a nuclear reactor.  In the second, each atom of U235 will release, on average, 202.5 Mev, and each atom of Pu239 211.5 Mev of energy.  In other words, the potential energy release from natural thorium is actually about equal to that of natural uranium. 

Unfortunately, the “factor of 200” isn’t the only glaring mistake in the paper.  The author repeats the familiar yarn about how uranium was chosen over thorium for power production because it produced plutonium needed for nuclear weapons as a byproduct.  In fact, uranium would have been the obvious choice even if weapons production had not been a factor.  As pointed out earlier, natural uranium can sustain a chain reaction in a reactor on its own, and thorium can’t.  Natural uranium can be enriched in U235 to make more efficient and smaller reactors.  Thorium can’t be “enriched” in that way at all.  Thorium breeders produce U232, a highly radioactive and dangerous isotope, which can’t be conveniently separated from U233, complicating the thorium fuel cycle.  Finally, the plutonium that comes out of nuclear reactors designed for power production, known as “reactor grade” plutonium, contains significant quantities of heavier isotopes of plutonium in addition to Pu239, making it unsuitable for weapons production.

Apparently the author gleaned some further disinformation for  Seth Grae, CEO of Lightbridge, a Virginia-based company promoting thorium power.  He supposedly told her that U233 produced in thorium breeders “fissions almost instantaneously.”  In fact, the probability that it will fission is entirely comparable to that of U235 or Pu239, and it will not fission any more “instantaneously” than other isotopes.  Why Grae felt compelled to feed her this fable is beyond me, as “instantaneous” fission isn’t necessary to prevent diversion of U233 as a weapons material.  Unlike plutonium, it can be “denatured” by mixing it with U238, from which it cannot be chemically separated.

It’s a mystery to me why so much nonsense is persistently associated with discussions of thorium, a potential source of energy that has a lot going for it.  It has several very significant advantages over the alternative uranium/plutonium breeder technology, such as not producing significant quantities of plutonium and other heavy actinides, less danger that materials produced in the fuel cycle will be diverted for weapons purposes if the technology is done right, and the ability to operate in a more easily controlled “thermal” neutron environment.  I can only suggest that people who write popular science articles about nuclear energy take the time to educate themselves about the subject.  Tried and true old textbooks like Introduction to Nuclear Engineering and Introduction to Nuclear Reactor Theory by John Lamarsh have been around for years, don’t require an advanced math background, and should be readable by any intelligent person with a high school education.

A Nuclear 9/11: Can we Defeat Nuclear Terrorism by Securing the Ports?

In a word, no.  Anyone who wants to smuggle the key ingredients (highly enriched uranium or weapons grade plutonium, otherwise known as special nuclear material, or SNM) needed to make a nuclear weapon into this country can easily do so, and the installation of any combination of the most sophisticated radiation dectection devices on the planet at our ports will do nothing to alter the fact.  The idea that lots of expensive detection equipment at our ports, or any other ports, will significantly reduce the terrorist nuclear danger is based on a fallacy:  that terrorists capable of securing enough SNM to build a bomb will be brain dead.  They would have to be brain dead to try to sneak SNM past sophisticated detectors when there are a virtually unlimited number of ways one could get it into the country without taking that risk.  It’s not necessary to smuggle a nuclear weapon in one piece.  It could be brought in broken down into small components and assembled at the target.  The SNM could be smuggled across our borders in pieces small enough to be virtually undetectable by backpackers, on commercially available mini-submarines, light aircraft, small pleasure boats, or what have you.  The SNM could then be assembled and easily fabricated into any desired weapons configuration in place.  The whole debate about defeating nuclear terrorism sounds like it’s being conducted in a lunatic asylum.

For example, The Daily Caller (hattip Instapundit) cites a GAO report to the effect that, ”

The nation’s ports and border crossings remain vulnerable to a nuclear 9/11 despite a $4 billion investment since 2005 by the Department of Homeland Security (DHS) on a number of programs aimed at preventing nuclear smuggling around the world.

Senators similarly admonished DHS in a recent Senate hearing for failing to uphold its end of the bargain with the American people.

“Terrorists have made clear their desire to secure a nuclear weapon,” Maine Republican Sen. Susan Collins said at the Sept. 15 hearing. “Given this stark reality, we must ask: what has the department done to defend against nuclear terrorism on American soil? The answer, unfortunately, is not enough… not nearly enough.”

The Domestic Nuclear Detection Office (DNDO), responsible for the domestic aspect of DHS’s nuclear terror deterrence, received approximately half of the $4 billion investment, which it spent deploying over 1,400 radiation monitors at the nation’s seaports and border crossings in conjunction with U.S. Customs and Border Protection.

But these radiation monitors have a serious flaw: they can only detect radiation from lightly shielded radiation sources.

The only problem is that spending billions more to fix this “flaw” won’t help, unless you happen to have invested your nest egg in detection equipment.  The article continues,

The GAO report uncovered a bureaucratic nightmare involving DNDO and U.S. Customs and Border Protection, which resulted in the failure to properly develop and deploy detection equipment that could detect radiation from heavily shielded sources.

DNDO began working shortly after its founding in April 2005 on what it called the Cargo Advanced Automated Radiography System (CAARS) and the Advanced Spectroscopic Portal (ASP) ̶ intended to automatically detect radiation from heavily shielded sources in a user-friendly fashion in order to screen cargo containers in the nation’s ports and border crossings.

In the first place, radiation detection equipment doesn’t come in just two flavors; “good for heavily shielded sources” and “not good for heavily shielded sources.”  There are a great number of different types, all with their own strengths and weaknesses in terms of sensitivity, energy resolution, etc.  In the second place, it doesn’t matter what kind are installed at the ports, because terrorists will simply bypass them.  The whole port security paradigm is based on the premise that our opponents, in spite of their ability to acquire SNM in the first place, will be bone stupid.  They won’t, and there are much more effective ways to spend all the money we are throwing down this particular rathole.

The article goes on to cite Cato Institute budget analyst Tad DeHaven, who plays a familiar broken record to demagogue the sheep:

They are not subject to market forces and other controls, so they can screw up federal money,” DeHaven said. “There are not going to be any angry shareholders, and in most cases you are not going to lose your job, so the incentives for the federal government to efficiently and effectively procure goods … are poor.”

One wonders if he reallly gets paid to churn out such hackneyed stuff.  Tell me, Tad, do you actually know anything about the people who work for DNDO?  Did it ever occur to you that many of them might be ex-military, that they might be highly motivated and dedicated to their country’s welfare, and that it’s not out of the question that they care a great deal about working to “efficiently and effectively procure goods”?  You might actually try meeting and talking to some of them.  They work just down the street from you.  Did it ever occur to you that the problem might not be their lack of patriotism and dedication, but the fact that they’ve been given an impossible task?  And BTW, no, I don’t work for DNDO or DHS.

The article concludes in a somewhat more sober vein,

Heritage Foundation homeland security analyst Jena Baker-McNeill instead blames Congress for setting what she sees as an unrealistic goal of inspecting every container that passes through the nation’s ports and border crossings. Congress imposed the goal for political reasons without considering its practical implications, she said. Baker-McNeill believes more emphasis should have been placed on increased intelligence aimed at intercepting nuclear smugglers abroad due to the volume of cargo that enters the country and limited resources.

It seems to me Ms. Baker-McNeill might be on to something.  If we’re going to spend money to defeat nuclear terrorism, I suspect it will be much better spent on finding ways to keep terrorists from getting their hands on SNM in the first place.  Once they do, we can install the most efficient radiation detectors with the most clever software ever devised at all our ports, and it won’t deter them in the slightest.  We will only have bought ourselves a dangerous sense of false security.

Subcritical Thorium Reactors: Dr. Rubbia’s Really Bad Idea

The Telegraph (hattip Insty) turned the hype level to max in a recent article about the potential of thorium reactors.  According to the headline, “Obama could kill fossil fuels overnight with a nuclear dash for thorium.”  Against all odds, this is to happen in three to five years with a “new Manhattan Project,” and a “silver bullet” in the form of a new generation of thorium reactors.  The author is so vague about the technologies he’s describing that it’s hard to avoid the conclusion that he simply doesn’t know what he’s talking about, and couldn’t be bothered to spend a few minutes with Google to find out.  I’ll try to translate.

It’s claimed that thorium “eats its own waste.”  In fact, thorium is very promising as a future source of energy, but this is nonsense.  Apparently it’s based on the fact that certain types of thorium reactors actually could burn their own fuel material, as well as plutonium scavenged from conventional reactor waste and other transuranics, much more completely than alternative designs.  This is certainly an advantage, but the fission products (lighter elements left over from the splitting of uranium and plutonium) would still be highly radioactive, and would certainly qualify as waste.  Such claims are so obviously spurious that they play into the hands of opponents of nuclear power.

It is also claimed that “all (thorium) is potentially usable as fuel, compared to just 0.7% for uranium.”  In fact, thorium is not a fissile material, meaning that, unlike uranium 235 (U235), which is the 0.7% of natural uranium the author is referring to, it cannot sustain a nuclear chain reaction on its own.  It must first be converted to a lighter isotope of uranium, U233, which is fissile.  In fact, the U238 that makes up most of the rest of the leftover 99.3% percent of natural uranium is “potentially usable as fuel” in that sense as well, by conversion to plutonium 239, also a fissile material.

The author is vague about exactly what kind of reactors he is referring to, lumping Dr. Carlo Rubbia’s subcritical design, which depends on a proton accelerator to provide enough neutrons to keep the fission process going, and molten fluoride salt reactors, which do not necessarily require such an accelerator.  He claims that, “Thorium-fluoride reactors can operate at atmospheric temperature,” which they certainly could not if the goal were to generate electric power.  I suspect that what he means here is that, unlike plutonium breeders, which require a high energy neutron spectrum to produce more fuel than they consume, thorium breeders could potentially use “thermal” neutrons that have been slowed to the point that their average energy, when converted to a “temperature,” would be much closer to that of the other material in the reactor core. 

In any case, the design he seems to be so excited about is Dr. Rubbia’s “energy amplifier,” which, as noted above, would be subcritical, requiring a powerful, high current proton accelerator to keep the fission process going.  It would do this via spallation, a process in which a copious source of the neutrons required to keep the reaction going would be provided via interaction of the protons with heavy nuclei such as lead, or thorium itself.  This is the process used to produce neutrons at the Oak Ridge Spallation Neutron Source.  Such reactors could easily be “turned off” by simply shutting down the source of neutrons.  However, the idea that they would be inherently “safer” is dangerously inaccurate.  In fact, they would be an ideal path to covert acquisition of nuclear weapons.  Thorium reactors work by transmuting thorium into U233, which is the isotope that fissions to produce the lion’s share of the energy.  It is also an isotope that, like U235 and Pu239, can be used to make nuclear bombs. 

The article downplays this risk as follows:

After the Manhattan Project, US physicists in the late 1940s were tempted by thorium for use in civil reactors. It has a higher neutron yield per neutron absorbed. It does not require isotope separation, a big cost saving. But by then America needed the plutonium residue from uranium to build bombs.

“They were really going after the weapons,” said Professor Egil Lillestol, a world authority on the thorium fuel-cycle at CERN. “It is almost impossible make nuclear weapons out of thorium because it is too difficult to handle. It wouldn’t be worth trying.” It emits too many high (energy) gamma rays.

What Lillestol is referring to is the fact that, in addition to U233, thorium reactors also produce a certain amount of U232, a highly radioactive isotope of uranium with a half life of 68.9 years whose decay does, indeed, release potentially deadly gamma rays.  It would be extremely difficult, if not impossible, to remove it from the U233, and, if enough of it were present, it would certainly complicate the task of building a bomb.  The key phrase here is “if enough of it were present.”  Thorium enthusiasts like Lillestol never seem to do the math.  In fact, as can be seen here, even conventional thorium breeders could be designed to produce U233 sufficiently free of U232 to allow workers to fabricate a weapon without serious danger of receiving a lethal dose of gamma rays.  However, large concentrations of highly radioactive fission products would make it very difficult to surreptitiously extract the uranium, and it would also be possible to mix the fuel material with natural or depleted uranium, reducing the isotopic concentration of U233 below that necessary to make a bomb.

With subcritical reactors of the type proposed by Rubbia, the problem of making a bomb gets a whole lot easier.  Rogue state actors, and even terrorists groups if we “succeed” in coming up with a sufficiently inexpensive design for high energy proton accelerators, could easily modify them to produce virtually pure U233, operating small facilities that it would be next to impossible for international monitors to detect.  There are two possible pathways for the production of U232 from thorium, both of which involve a reaction in which a neutron knocks two neutrons out of a heavy nucleus of Th232 or U233.  Those reactions can’t occur unless the initial neutron is carrying a lot of energy as can be seen in figure 8 of the article linked above, the threshold is around 6 million electron volts (MeV).  That means that, in order to produce virtually pure U233, all that’s necessary is to slow the incoming spallation neutrons below that energy.  That’s easily done.  Imagine two billiard balls on a table.  If you hit one as hard as you can at the other one, what happens when they collide?  If your aim was true, the first ball stops, transferring all its energy to the second one.  The same thing can be done with neutrons.  Pass the source neutrons through a layer of material full of light atoms such as paraffin or heavy water, and they will bounce off the light nuclei, losing energy in the process, until they eventually become “thermalized,” with virtually none of them having energies above 6 MeV.  If such low energy neutrons were then passed on to a subcritical core, they would produce U233 with almost no U232 contamination. 

It gets worse.  Unlike Pu239, U233 does not emit a lot of spontaneous neutrons.  That means it can be used to make a simple gun-type nuclear weapon with little fear that a stray neutron will cause it to fizzle before optimum criticality is reached.  And, by the way, a lot less of it would be needed than would be required for a similar weapon using U235, the fissile material in the bomb that destroyed Hiroshima. 

We’re quite capable of blowing ourselves up without Rubbia’s subcritical reactors.  Let’s not make it any easier than it already is.  Thorium reactors have many potential advantages over other potential sources of energy, including wind and solar.  However, if we’re going to do thorium, let’s do it right.

UPDATE:  Steven Den Beste gets it right at Hot Air.  His commenters throw out the usual red herrings about the US choosing U235 and Pu239 over U233 in the Manhattan Project (for good reasons that had nothing to do with U233’s suitability as a bomb material) and the grossly exaggerated and misunderstood problem with U232.  You don’t have to be a nuclear engineer to see through these fallacious arguments.  The relevant information is all out there on the web, it’s not classified, and it can be understood by any bright high school student who takes the time to get the facts.