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.

The Case of the Contraband Uranium

It appears that authorities in Moldova seized about four pounds of contraband uranium and arrested several suspects. The material in question turned out to be the isotope uranium 238 (U238), meaning that, unlike the fissile isotope U235, it couldn’t be used to make a bomb. Maybe it’s just me, but it seems that whenever I have personal knowledge of what happened in an incident that makes the news, or expertise regarding its subject, the mainstream media, with their layers of editors and fact checkers, manage to botch the story. For example, CNN uncritically quotes Kirill Motspan, a spokesman for Moldova’s Interior Ministry as saying that, “…it was his understanding that 1 kilo of uranium costs $6.3 million on the black market and that is what the smugglers were expecting to get.” I seriously doubt that Motspan meant just any uranium, and especially not U238. If that were the case, the guys who fly A10 Warthog ground support planes armed with Gatling guns that pump out rounds that contain just under a pound each of the stuff at 4,200 rounds per minute must be using caddies to recover them. He was probably referring to uranium highly enriched in isotope 235, which can be used to make a bomb. In other words, the smugglers were intending to snooker their customers. Anyone can Google the fact that natural uranium, which contains at least a little (about 0.71%) U235, is currently selling for just under $50 per pound.

Not to be outdone, the Telegraph reports that the material seized was “enriched uranium.”  Since the caption of the figure that appears in the article notes that the material was U238, commonly referred to as depleted uranium, none of their “fact checkers” apparently has a clue what they’re talking about.

BTW, have you noticed that whenever contraband radioactive and special nuclear material is seized, its usually due to good old fashioned police work, and not to those snazzy new radiation detectors that are being installed hand over fist at ports and border crossings?  That’s not a coincidence.

The Nuclear Posture Review and the Future of the Arsenal

The right and the left in this country have achieved a state of MAD (Mutually Assured Demonization). The recent attempts by the legacy media to whip up hysteria over threats of violence to those who voted for the health bill is a case in point. There was a time, not that long ago, when these “objective journalists” would have gotten away with it. There was no comparably audible public voice on the right to oppose them. Now there is, in the form of talk radio, powerful blogs, and Foxnews. Result: They only succeeded in, once again, making themselves look silly. The Right was in their face immediately, pointing out, among other things, the gross hypocrisy in the double standard they applied to violence and threats of violence depending on whether they come from the right or the left.

Overall, this form of MAD is a good thing. The sanctimonious, condescending attitude of the journalists of yesteryear was getting very old by the time Rush Limbaugh finally appeared on the scene. However, it does have its drawbacks, in the form of increasing levels of political polarization and the associated pious posing on both the right and the left. Indeed, when it comes to the ostentatious striking of sanctimonious public poses, the right has, at long last, achieved parity with the left. Reasoned debate becomes difficult when both sides are only interested in occupying the moral high ground.

Consider, for example, the right’s overwrought response to the latest Nuclear Posture Review (NPR). The NPR is a document submitted to Congress each year by the Department of Defense setting forth what the role of nuclear weapons in U.S. security strategy should be. The latest version contains a watered down “no first use” provision according to which we won’t respond with nuclear weapons even if attacked with chemical and biological weapons, with the caveat that for nations that don’t play according to the Nuclear Nonproliferation Treaty, everything is still on the table. Some of the other more significant provisions include:

• The United States will not conduct nuclear testing, and will seek ratification and entry into force of the Comprehensive Nuclear Test Ban Treaty.

• The United States will not develop new nuclear warheads. Life Extension Programs (LEPs) will use only nuclear components based on previously tested designs, and will not support new military missions or provide for new military capabilities.

• The Administration will study options for ensuring the safety, security, and reliability of nuclear warheads on a case-by-case basis, consistent with the congressionally mandated Stockpile Management Plan. The full range of LEP approaches will be considered: refurbishment of existing warheads, reuse of nuclear components from different warheads, and replacement of nuclear components.

The response Tunku Daravarajan at The Daily Beast:

I despair of this latest episode of gestural theater designed to make the U.S. look exquisitely reasonable (should we call it “Jimmy-Cartesian”?), but which in truth results in the U.S. looking flaccid, or worse, complacent. After all, who gains from a presidential posture that has, in effect, stigmatized our most potent deterrent? In terms of foreign policy—or, better put, foreign clout—the U.S. is going through a startling period of auto-emasculation.

and from Roger Simon at PajamasMedia:

Like some looney member of Code Pink, our president is abandoning the nuclear deterrent adhered to by every American president since Truman. And he is doing it in a manner that makes absolutely no sense… What are we to make of this and the man who is adopting this policy? Does he hate us? Does he hate this country? What would he do if there was, for example, a massive small pox attack on the U.S.? Send in the infantry? Call in the Marines? Try to reason with whoever did it and recommend they negotiate as the fatal disease spreads to millions of people?… Now I detest nuclear weapons as much as the next person, but this approach seems — I hate to repeat myself, but I will — deranged.

Now let’s think about this for a moment. Suppose, just for the sake of argument, that the ultimate reason for having a nuclear arsenal in the first place is to protect our security. What if Tunku and Roger, being human, and therefore not infallible, are wrong? What if, just hypothetically, the policy set forth in the NPR really will make us more safe, and the policy they prefer less safe. They have not limited themselves to a reasoned response to the NPR, setting forth, in their opinions, why they think it will not enhance our safety. Rather, they have villified the people who support it, accusing them, not only of being wrong, but of being crazy. When you demonize people, you make it very difficult for them to respond to your objections in a reasoned manner. Being human, they are more likely to strike back, trading tit for tat. I would even go so far as to say that, in some cases, that is the only rational way to respond. It seems rather obvious that convergence to correct policy decisions is not a likely outcome of this process of mutual demonization.

That is the reason that, as I have maintained elsewhere, when it comes to policy decisions as weighty as those relating to nuclear policy, moralistic posing, with all the associated pushing of emotional hot buttons, should be set aside in favor of some semblance of rational discussion. The goal here, I assume, is to survive. Let us, then, dispassionately consider what we should best do in order to survive.

According to Steve Schippert ant Liberty Pundits, the NPR not only does not serve that goal but is, in fact, pointless.  In his words:

There is none, really. Not beyond rhetoric and “historic” moments and – dare the Los Angeles Times say it – a “manifesto.”

No point at all – but for one critical aspect lost in all of the arguing back and forth. Clarity is dead. Nuance and the foolish self-assurance of perceived superior intellectual and/or moral capacity have rightly replaced clear understanding.

Admitting in advance my own fallibility, I beg to differ. In the first place, we have kept the nuclear genie in the bottle now for going on 65 years. I am far from believing that an all out nuclear exchange would result in the extinction of humanity, or anything close to it. It is, nevertheless, an understatement to say that it would be extremely destructive. That being the case, it would be well if, to the extent possible, we maintained a taboo on the first use of nuclear weapons.

Any first user of nuclear weapons likely would become and, it seems to me, should become, an international pariah. Roger paints a nightmare scenario in which millions of people are dying in a biological attack while our hands are tied. Given the known effects of the releases of biological and chemical agents to date, the chances of something like that happening are vanishingly small. If it did, the NPR would become a moot point, just as all our loud protestations against unrestricted submarine warfare prior to our entry into WWI became a moot point for our own submarine forces in the Pacific after Pearl Harbor. A far more likely first use scenario would be an attempt at eliminating enemy stocks of biological or chemical weapons with a nuclear bunker buster, either preemptively or after an ineffective and very ill-considered attack on the United States with such weapons. This kind of first use would be very attractive to many in the nuclear weapons community. It would, however, do anything but promote our national security. Rather, it would end the taboo on the use of nuclear weapons, greatly increasing the chances that we, in turn, would become the victims of a really devastating attack, not with ineffective chemical or biological agents, but with nuclear weapons.

I also agree with the other sections of the NPR that are major departures from past policy, or, at least, have been represented as such. One of these is the provision that the United States will not conduct nuclear testing. Again, there are many in the weapons community who would love to resume testing, basing their arguments on insuring the reliability of the stockpile. It would also help the national weapons laboratories solve the demographic problem they face with the retirement or impending retirement of most of the physicists and other technical experts who have actually taken part in nuclear tests, and the difficulty of attracting talented scientists to careers as custodians of an aging pile of nuclear weapons. It would also play directly into the hands of our enemies.

The United States has a huge advantage over potential nuclear rivals in its possession of above ground experimental facilities (known in the business as AGEX) second to none in the world. From the massive National Ignition Facility, with its ability to focus 192 powerful laser beams on a tiny point, to the Z pulsed power machine capable of producing bursts of X-rays at levels far beyond those of any comparable facility on the planet, to a host of other smaller but still highly impressive and technologically advanced experimental facilities, we can approach the physical conditions that exist within exploding nuclear devices more closely and for longer periods of time than any other nation can even dream of. To resume nuclear testing would be to stupidly throw away this huge advantage. At the same time, it would give our enemies all the moral authority they needed to resume testing or develop nuclear weapons themselves.

The decision to set in concrete in the NPR the decision not to develop new nuclear weapons is also a good one. The idea that the United States would do such a thing is anything but implausible. On the contrary, the National Nuclear Security Administration has been agitating for years to get the go-ahead to build the Reliable Replacement Warhead. When Congress wisely told them, not only no, but hell no, they kept up the pressure regardless. Congress has taken a lot of bad raps lately. They deserve a lot of credit for derailing NNSA’s determination to go ahead with the RRW. In the first place, the weapons in our stockpile are not fragile and unreliable. Any enemy that assumed so would be making a very grave mistake. In the second, if we developed the RRW, the pressure to test it would likely become irresistible. The idea of developing a nuclear weapon without testing it would never have passed the “ho-ho” test at the weapons labs back in the 70′s and 80′s. The claim that we wouldn’t need to test the RRW is likely wishful thinking. Again, all the objections to a resumption of nuclear testing I have cited above would apply. Finally, by building a new type of nuclear weapon we would once again sacrifice the moral high ground, handing our enemies all the justification they needed for building new weapons themselves. Again, we would sacrifice major advantages, simply to acquire a weapon that would be somewhat cheaper to maintain than those in the existing stockpile. For obvious reasons, the weapons designers at the labs would love it. For the rest of us, it would make no sense at all.

I am hardly in favor of unilateral nuclear disarmament. On the contrary, I am in favor of maintaining a powerful arsenal and assuring that the resources we need to keep it safe and reliable will always be available. However, the latest NPR is a reasoned response to the nuclear myopia that would have us sacrifice real advantages in return for extremely dubious returns. As such, it deserves our support.

Thorium: Wired Magazine Muddies the Water

Glenn Reynolds at Instapundit recently linked to an article by Richard Martin in Wired Magazine entitled, ‘Uranium is so Last Century:  Enter Thorium, the New Green Nuke.”  I cringed when I read it.  I suspect serious advocates of thorium did as well.  It was a piece of scientific wowserism of a sort that has been the bane of nuclear power in the past, and that its advocates would do well to steer clear of in the future.  It evoked a romantic world of thorium “revolutionaries” doing battle with the dinosaurs of conventional nuclear power.  Things aren’t quite that black and white in the real world.  Thorium breeders deserve fair consideration, not hype, as does nuclear power in general.  There are many good reasons to prefer it to its alternatives as a source of energy.  It doesn’t take a genius to understand those reasons, assuming one approaches the subject with a mind that isn’t made up in advance, and is willing to devote a reasonable amount of time to acquire a basic understanding of the technology.  Martin would be well advised to do so before writing his next article on the subject. 

In the first place, thorium is not a replacement for uranium, as implied by the title of the Wired article.  Rather, the point of putting it in nuclear reactors is to breed uranium, which remains the actual fuel material, albeit in the form of isotope U233 rather than U235.  Thus, when Martin writes things like,

Those technologies are still based on uranium, however, and will be beset by the same problems that have dogged the nuclear industry since the 1960s. It is only thorium… that can move the country toward a new era of safe, clean, affordable energy.

in comparing thorium reactors to their more conventional alternatives, it is evident he doesn’t know what he is talking about.  Referring to the physicist Alvin Weinberg, he tells us,

Weinberg and his men proved the efficacy of thorium reactors in hundreds of tests at Oak Ridge from the ’50s through the early ’70s. But thorium hit a dead end. Locked in a struggle with a nuclear- armed Soviet Union, the US government in the ’60s chose to build uranium-fueled reactors — in part because they produce plutonium that can be refined into weapons-grade material. The course of the nuclear industry was set for the next four decades, and thorium power became one of the great what-if technologies of the 20th century.

With all due respect to Weinberg, a brilliant scientist whose work remains as relevant to conventional reactors as to their thorium cousins, this picture of thorium knights in shining armor doing battle with the dark forces of the nuclear weapons establishment is certainly romantic, but it leaves out some rather salient facts.  In the first place, conventional power reactors do not even produce weapons grade plutonium, which contains a high concentration of plutonium 239.  Special reactors that run for a much shorter period of time are used for that purpose.    Furthermore, thorium is not a nuclear fuel.  A reactor using thorium alone would never work because thorium is not a fissile material.  In other words, unlike, for example, uranium 235 or plutonium 239, it cannot sustain a nuclear chain reaction.  The point of putting it in nuclear reactors is to breed uranium 233, another isotope that is fissile.  We began producing nuclear power with conventional nuclear reactors based on uranium 235 rather than thorium breeders because of their simplicity, not because of their usefulness as sources of bomb material.  The fuel needed to run them is available in nature as one of the isotopes in mined uranium, and doesn’t depend on a complex breeding cycle for its production.  There are other drawbacks to thorium breeders that Martin doesn’t mention in his article.  For example, in addition to uranium 233, they produce significant quantities of uranium 232, a short lived isotope with some nasty, highly radioactive daughters.  Separating it from U233 was out of the question, and its presence makes the production and handling of nuclear fuel elements a great deal more difficult. 

I’m certainly no opponent of thorium breeders.  In fact, I think we should be aggressively developing the technology.  However, before writing articles about the subject, it can’t hurt to have some idea what you’re talking about.  There are no lack of good articles about the subject on the Web within easy reach of anyone who can use Google.

The Iranian Bomb: Guessing the Date

According to the latest estimate by Israeli intelligence, Iran is capable of building a bomb by 2011. These estimates always beg the question of what kind of bomb one is talking about. In fact, Iran will have a perfectly adequate bomb or, more accurately, nuclear device, the moment it has enough bomb grade plutonium or uranium to assemble a critical mass. In the first place, it does not take a great deal of technical finesse to build a gun assembled atomic bomb. In the second, Iran needn’t bother, because, if she were really determined to carry out a nuclear attack, something much more crude would be more attractive from her point of view. By “crude” I mean, for example, a suicide bomber equipped with two subcritical masses that, when combined, would form a critical mass. This could be done by dropping one subcritical mass on top of another, or simply slapping them together. Unlike something as sophisticated as the device dropped on Hiroshima, such a “bomb” would preserve plausible denial for Iran. Even if the material could be traced to one of her reactors, she could claim that it had been stolen or diverted by terrorists. If assembled in the middle of a large city, it may not produce the familiar mushroom cloud, but it would certainly produce a radioactive mess that would inspire terror, likely cost billions to clean up, be much less likely to provoke nuclear retaliation than a high yield bomb, and spare Iran immediate relegation to the status of an international pariah for having once again unleashed the nuclear genie, committing mass murder in the process.

In a word, once Iran has sufficient special nuclear material to make a bomb, it will no longer be necessary to speculate about how long it will take her to build one. She will have the “bomb” the moment she has enough material to assemble a critical mass.

Jon Kyl and the Resumption of Nuclear Testing

In a recent article in the Wall Street Journal, Arizona Senator Jon Kyl called for a resumption of nuclear testing. Such a step would be both unnecessary and a potentially disastrous threat to our national security.

I am no pacifist, and I favor maintaining a strong and credible nuclear deterrent. It is for that very reason that I oppose a resumption of nuclear testing. It would in no way strengthen us. Rather, it would promote nuclear proliferation and result in a weakening of the nuclear posture of the United States vis-à-vis its potential nuclear armed opponents.

Obviously, Senator Kyl has heard some of these arguments, but they somehow don’t seem to sink in. He notes in his article that, “There’s a related theory, which is that the U.S. has to ratify the CTBT if it wants to have any credibility or leadership on nonproliferation,” but then dismisses these arguments with the claim that, “Aside from the fact that countries will act in their best interest whether or not the U.S. ‘leads’ them, no one can legitimately question U.S. commitment on proliferation issues.” I, for one, would question the U.S. commitment on proliferation issues if we resumed testing, whether Kyl considered it legitimate or not, and I would hardly be alone in that conclusion. Beyond that, his assertion that other countries will act in their own best interests ignores the reality that the actions of the United States can have a substantial bearing on what those best interests happen to be, particularly in matters relating to nuclear proliferation. Take, for example, Iran. If she tests a nuclear device after her oft-repeated denial of any desire to do so, she will become an international pariah, and likely subject herself to severe economic sanctions. She will also provide moral backing to those in Israel and the United States who advocate an attack on her nuclear facilities, greatly increasing the chances that one will occur. However, if she tested a nuclear device after the United States had resumed testing its own weapons, she could and would portray it as a legitimate act that had been forced on her by the actions of her enemies. The idea that the path chosen by the United States would have “no bearing” on her national interests is absurd.

Kyl cites the danger that clandestine nuclear tests cannot be verified and other nations will be able to test on the sly. To “prove” this dubious assertion, he notes that monitoring systems “failed to collect necessary radioactive gases and particulates to prove that a test had occurred” following the latest test by North Korea. In fact, seismic devices did detect it, in spite of the fact that its estimated yield was only a few kilotons. I have heard no credible argument to the effect that major nuclear powers could substantially enhance the power of their arsenals vis-à-vis the United States with clandestine tests that had a significant chance of going undetected. If anyone who actually knows what they’re talking about cares to make such an argument, let them put their cards on the table.

The part of Kyl’s argument that is likely to carry the most weight is the contention that there are serious concerns about the aging and reliability of our arsenal. To bolster his argument, he cites the testimony of C. Paul Robinson, former Director of Sandia National Laboratories, before the House Armed Services Committee last year. In fact, this testimony is very interesting in its own right, and, among other things has a direct bearing on the issue of the Reliable Replacement Warhead (RRW), which was promoted by the Bush Administration, but wisely rejected by Congress. It’s exactly what one might have expected to hear from a weaponeer at Los Alamos if one were transported back in time to the 1970’s or 80’s. In fact, that’s exactly what Robinson was at the time. In those days, the suggestion that a substantially new weapon could become part of the arsenal without previous testing would never have passed the “ho-ho” test.

Referring to his position on nuclear testing at the time that the Stockpile Stewardship program was first formulated in the early 90’s, Robinson said,

I will repeat only a few of the words that most of us with responsibilities for U.S. warheads said at the time—e.g. that “there is no precedent for such complex technological devices to be depended on unless they were periodically tested” and that “fielding of first-of-a-kind new devices without testing would be the most stressful challenge.”

Note the direct reference to a “first-of-a-kind” device here. The only such device anyone has seriously discussed building since the end of testing in 1992 is the RRW. Robinson goes on,

But in other areas we are just as uncertain today. My belief is that most weapons designers have less confidence about making changes to their designs than they had in the past. I particularly found the recent colloquy between the JASON group and the lab designers most curious —as they each speculated over the difficulties of fielding designs under the contemplated Reliable Replacement Weapon (RRW) effort. Although you will doubtless find a spectrum of views at the labs, my take is that uncertainties will necessarily (and quite naturally) grow over time for several of our systems.

Here again, although he speaks of other systems in general, Robinson specifically refers to the RRW as a system that it will be particularly problematic to introduce to the arsenal without testing. It is the only one he could be referring to when he cites the concerns of weapons designers about “making changes to their designs.” In spite of this, after an interesting bit on the genesis of the RRW concept, Robinson makes a remarkable intellectual double back flip a few sentences later:

After some discussion, the key idea of the RRW then emerged —that if we incorporated designs of “different genetic diversity” in each leg of the TRIAD, there would be a much lowered likelihood that all would fail at the same time from a common problem. Yet from what I’ve read, the Congressional support for the idea has been less than lukewarm —as evidenced by your canceling of the RRW funding, with some suggesting that the labs might be trying to “create new designs that would necessitate underground testing” in order to field the RRW. I assure you that this suggestion is just not true. RRW was conceived to lessen the likelihood that testing would be needed. At the very least I must conclude that “there has been a significant failure to communicate”, and I believe we must not let such misunderstandings perpetuate, when there is so much at stake.

This remarkable juxtaposition of the contradictory assertions that 1) new designs must be tested, but 2) the RRW will reduce the need for testing, is difficult to explain as other than a variant of Orwellian “doublethink” inspired by the need to stay “on message” on both the need to build the RRW and the necessity of resuming testing. In other words, Robinson and some of his fellow weaponeers at the National Labs want to have their cake and eat it too.

As is abundantly clear from Kyl’s article, there is no lack of people, both inside and outside the weapons labs, who want to resume nuclear testing. Trust me, if the RRW is built, it will result in a ratcheting up of the pressure to do so many fold. This is one of those rare instances when Congress actually got it right. Let’s forget about the RRW.

What, then, of the general assertion that testing is required because “concerns about aging and reliability have only grown?” In fact, if we stop hankering after the RRW and devote our attention to maintaining the weapons we already have, there is no credible reason to believe that they will not work as advertised. Let those who would maintain otherwise drop their vague assertions, put their cards on the table, and explain exactly what failure modes they are referring to. The weapons in our arsenal are robust, and any opponent who assumed otherwise would be making a very disastrous mistake.

Assuming, then, that we can really dismiss the negative political effects of resuming nuclear testing as Senator Kyl does with a cavalier wave of the hand, what would be the advantages of doing so? Surely, if we took the lead, the other nuclear powers would resume testing as well. The science of nuclear weapons has reached a high level of maturity in both the United States and Russia. It is much more likely that a resumption of testing will enable countries that have joined the nuclear club more recently to substantially improve their weapons designs than it will countries that have already developed highly sophisticated weapons. At the same time, it will negate the vast advantage we currently hold in possessing by far the most capable experimental facilities for validating nuclear weapons physics of any nation on earth. The experimental assets represented by Z facility at Sandia, the National Ignition Facility at Livermore, and a host of others give us a major leg up over the rest of the world in approaching the conditions that exist in nuclear weapons and investigating the relevant physics. When combined with our superiority in supercomputing power, they insure us a decisive advantage that it would be positively foolhardy for us to cast away with a resumption of testing.

Why then, the persistent pressure to resume testing? Once can only speculate. In Senator Kyl’s case, perhaps the increasing unsuitability of the Nevada Test Site as Las Vegas continues to sprawl in its direction may play a role. There are attractive alternative sites in his own state of Arizona that could potentially create many new jobs. As for the weapons designers, their lives were a lot more interesting during the era of nuclear testing. I suspect many of them would prefer a return to those “golden days of yesteryear” to their current role as custodians of an aging stockpile. These, however, are considerations that should not and cannot be allowed to play any role in our decision to resume testing or not.

Our weapons are reliable, and can be maintained with confidence. Let us preserve our advantage, and refrain from foolishly throwing it away with a resumption of nuclear testing.