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.

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.

Hiroshima and the Revisionists

Another August 6, another round of historial revisionism. The fabricators of adjusted realities always make their appearance about this time every year to spin their yarns about how the atomic bombing of Japan wasn’t really necessary, how Japan was just on the point of surrendering but the bombs were dropped anyway for an assortment of nefarious and evil reasons by the nefarious and evil rulers of a nefarious and evil country, how the “real” reason for the surrender was the obvious and long expected Russian entry into the war, how this or that scrap of information or this or that “official” report “proves” that the bombings didn’t in any way hasten or even encourage surrender, etc., etc. These periodic attempts to reinvent the past come from any number of different sources. Of course, the pathologically pious head the list; those whose penchant for imagining themselves to be the “saviors of mankind” goes beyond mere daydreaming to the invention of alternate worlds, drawn in colors of stark black and white, in which they appear in the role of virtuous heros, eternally saving the rest of us from evil. Of course, they never quite accomplish that worthy goal, and the “victims” they strive so mightily to save somehow always seem to remain “victims” in spite of their most heroic efforts, because victims are indispensible. After all, if the victims were ever really saved, virtuous heros would become superfluous.

But I digress. Of course, there is also Japanese officialdom. Ever since the end of the war, they have been busy rationalizing, relativizing, and generally seeking to consign to oblivion such horrific crimes as the rape of Nanking, the deliberate slaughter of the civilian population of Manila (in both of which cities more civilians died than in Hiroshima), the Bataan Death March, the deliberate starving and murder of prisoners, the wholesale rape of a generation of Korean women,

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germ warfare experiments with human guinea pigs, etc., etc. The bomb has always been their most effective foil for diverting attention from their country’s criminal past. Other than that, there are the legions of Ameria-haters worldwide for whom the United States is well-suited for the role of “out-group,” satisfying the universal need wired in the human brain for an evil enemy.

It is usually easy to identify historical revisionists.  They tip their hands by insisting on a version of reality that allows no room for doubt, and that neatly fits their ideological preconceptions.  In this case, for example, in spite of the undeniable coincidence of the atomic bombing and the surrender of Japan, they insist that there was absolutely no connection, and that the bombing had nothing at all to do with the Japanese decision to capitulate.  Obviously, especially in view of the careful destruction of relevant documents by Japanese officials, it is irrational to claim that it has absolutely been proved that the bombing and the surrender were purely coincidental, and the former’s contribution to the latter was trivial at best.  That, however, is precisely what the revisionists claim.  Look at their books and essays, and you will also find that they invariably leave out salient facts that don’t fit the altered reality they are trying to construct, and that other facts are “reinterpreted” to give them a significance they don’t deserve. 

Readers who have been around long enough may recall a previous round of Hiroshima revisionism on the occasion of the 50th anniversary of the bombing back in 1995.  Earlier in the year, officials at the Smithsonian Institution, a magnet for leftist academics whose tastes run to interpreting all American history as the story of an oppressor’s playground on which a series of invariably  pure, noble and morally immaculate classes of victims were brutalized by an invariably greedy, selfish, and evil ruling class, had attempted to introduce the now familiar adjustments to reality in conjuction with the Institution’s planned display of the Enola Gay.  Fortunately, enough people with firsthand knowledge of what really happened and who objected to the bowdlerization of history, were around at the time to mount an effective resistance to the fabricators.  Now most of the eyewitnesses have passed from the scene.  It is, therefore, all the more important that the critical source material relating to the atomic bombing be preserved and made easily accessible. 

Revisionists of one stripe or another will always be with us.  At different times and in different places, they have succeeded in constructing alternate realities in spite of the existence of a far greater volume and variety of source material than exists in the case of the atomic bombing of Japan.  Schools in much of the US South, for example, raised generations of students who firmly believed that the Civil War “really” occurred for any number of reasons besides slavery, in spite of overwhelming evidence documenting that the leaders of the South believed it was about slavery, the leaders of the North believed it was about slavery, the populations in both sections believed it was about slavery, and foreign observers were unanimous in confirming that it was about slavery.  Today Holocaust deniers control the public narrative in much of the Middle East.  In both of those cases, the source material available to document what really happened was orders of magnitude larger than what remains pertinent to the atomic bombing of Japan.  The Hiroshima revisionists would seem to have a much easier task.  The amount of documentation it will be necessary for them to drop down the “memory hole” is a great deal smaller, and their attempts to construct a mythical reality may consequently turn out to be a great deal more successful than those of the Iranian theocracy, or the “Southern heritage” crowd.

History can and will be falsified.  In the case of Hiroshima, those who are attempting to revise it are influential and determined.  The antidote to revisionism is the preservation of facts.  The truth is important.  One must hope that enough facts about the atomic bombing of Japan will be preserved to give future generations at least a fighting chance of finding it.

UPDATE: This article by Richard B. Frank (hattip ChicagoBoyz), entitled “Why Truman Dropped the Bomb, which appeared in the Weekly Standard in 2005, is a must read for those seeking the facts about the atomic bombing of Japan.  Money quote: 

There are a good many more points that now extend our understanding beyond the debates of 1995. But it is clear that all three of the critics’ central premises are wrong. The Japanese did not see their situation as catastrophically hopeless. They were not seeking to surrender, but pursuing a negotiated end to the war that preserved the old order in Japan, not just a figurehead emperor. Finally, thanks to radio intelligence, American leaders, far from knowing that peace was at hand, understood–as one analytical piece in the “Magic” Far East Summary stated in July 1945, after a review of both the military and diplomatic intercepts–that “until the Japanese leaders realize that an invasion can not be repelled, there is little likelihood that they will accept any peace terms satisfactory to the Allies.” This cannot be improved upon as a succinct and accurate summary of the military and diplomatic realities of the summer of 1945.

Upgrading our Nuclear Weapons Infrastructure

Y-12 Nuclear Facility

As for the article’s assertion that we are “falling behind” other nations in this regard, I rather doubt it, especially if the source of the information is a United States senator from a state that would benefit directly from the proposed work. In fact, we’ve already undertaken some significant upgrades, and I know of no factual basis at the moment for the claim that other nations have done more, or are ahead of us in this regard. The case for upgrading our weapons infrastructure can stand on its own merits, based on the need to maintain the safety and reliability of the existing stockpile. There’s no need to invoke an imaginery “modernization gap.”

“Stealth” Fusion Progress

It didn’t take us long to master the destructive force of fusion, but taming it for more constructive applications, such as electricity production, has been harder than anyone imagined back in the day when a popular slogan was “online by ‘79.” Right, maybe in 2079 with any luck. We know of two scientifically feasible ways to get more energy out of fusion than it’s necessary to put in to ignite the fuel materials; magnetic fusion, as in ITER, or inertial confinement fusion (ICF) as at the National Ignition Facility (NIF). The problem with both approaches is not the science, but the engineering challenge of building reactors capable of generating electricity anywhere near as cheaply as the alternatives. At the moment, the chances that we will be able to do so any time in the foreseeable future seem remote.

If anyone around today lives to see the dawn of the era of fusion energy, it will probably be because some exceptionally clever researcher has hoodwinked Mother Nature and discovered how to finesse his way past the Coulomb barrier that usually keeps atomic nuclei too far apart to come within the range of the fusion-enabling strong force. Several promising candidates are already in the field, and one of them, Tri-Alpha Energy, has apparently managed to attract $50 million in private research funding. The company hasn’t revealed the nature of its approach, but it is apparently inspired by the work of Prof. Norman Rostoker of UC Irvine. One can get a broad hint from this paper co-authored by Rostoker and Tri-Alpha entitled, “Colliding Beam Fusion Reactors.” Rostoker is an emeritus professor who has been publishing papers since the 50’s, some co-authored with fusion superstars such as Nicholas Krall and Marshall Rosenbluth. Octogenarian physicists don’t often pull off such miracles, but you never know.

If he or someone else ever does manage to pull the fusion rabbit out of the hat, it would potentially put an end to our worries about energy for a very long time. It could also enable pure fusion weapons. Let’s keep our fingers crossed that it doesn’t.

Fusion Reaction

The Hiroshima Fallacy Lives On

In a briefing at the start of President Obama’s nuclear security summit on Monday, his top counterterrorism advisor, John Brennan, claimed,

Developing a nuclear device involves a highly sophisticated technical process, and al Qaeda doesn’t seem to have mastered it based on what we know now.

It boggles the mind that someone in his position could believe such nonsense. Unfortunately, he’s not alone. Any number of people who should know better have fallen for the Hiroshima Fallacy; the dangerously mistaken belief that an effective nuclear device would need to be at least as sophisticated as the weapon that destroyed Hiroshima. Here’s a tutorial for the benefit of Mr. Brennan on the “highly sophisticated technical process” necessary to assemble an effective nuclear weapon:

1. Acquire a critical mass of weapons grade plutonium or highly enriched uranium, otherwise known as Special Nuclear Material (SNM), well separated into two chunks of approximately equal size.

2. Purchase a step ladder.

3. Place one of the two pieces of SNM on the ground at your chosen target location.

4. Climb the step ladder with the other piece of SNM.

5. Take careful aim, and drop the piece of SNM you are holding on top of the other piece.

How’s that for a “highly sophisticated technical process,” Mr. Brennan?

The result of such a nuclear attack would not be a 20 kiloton explosion. It might not even cause any fatalities, assuming the attacker could run really, really fast. However, the effect would be the same as detonating a big “dirty bomb.” The immediate area would be poisoned with radioactivity, and the economic impact would be great. The political impact would be incalculable. Assuming the attacker cared to bother with an even more “highly sophisticated technical process,” the critical masses could be accelerated together with a strong spring, or a small explosive charge. One might add a crude gun barrel to enhance the effect. At each stage, more radioactivity would be released, and distributed more widely. Eventually, the device would explode. The size of the explosion would be unpredictable. It would all depend on when a stray neutron happened along.

I have a suggestion for Mr. Brennan. He should contact the weapon designers at Los Alamos and Livermore and ask them to fire up their codes and prepare a study on the likely effects of the weapons described above. He should then gather together as many members of Congress and high government officials as possible and sit down and listen to what they have to say. I can assure Mr. Brennan that, if he really believes the Hiroshima Fallacy, it will be an epiphany for him. If time allowed, it might also be useful for the weapons guys to describe how one might assemble a simple gun type nuclear weapon with an explosive yield in the kiloton range. I rather suspect Mr. Brennan will be surprised to learn the real level of sophistication necessary to build such a weapon.

It is not a good thing for the officials responsible for protecting us from nuclear attack to be ignorant about nuclear weapons. It would not be difficult, nor would it take a great deal of their time, to learn some of the elementary facts alluded to above from people at the weapons labs who know what they’re talking about. I appeal to them to do so.

Worker with plutonium disk

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.

Crunch Time for the National Ignition Facility

The news from California is encouraging.  In an article recently published in Science and summarized on the website of Lawrence Livermore National Laboratory (LLNL), scientists working at the National Ignition Facility (NIF) report efficient coupling of energy from all 192 beams of the giant facility into a hohlraum target similar to the one that will be used later this year in the first attempts to achieve fusion ignition and “breakeven,” usually defined as more energy production from fusion than was carried in the laser beams used to hit the target.  The design energy of the NIF is 1.8 megajoules, and, according to the latest reports from Livermore, the threshold of one megajoule has already been achieved. 

In inertial confinement fusion, or ICF, the target, a thin, spherical shell containing a mixture of deuterium and tritium, two heavy isotopes of hydrogen, is first compressed and imploded to very high densities.  A series of converging shocks then create a “hot spot” in the center of the compressed material, setting off fusion reactions which release enough energy to set off a ”burn wave.”  This wave propagates out through the remaining fuel material, heating it to fusion energies as well.  The process is known as inertial confinement fusion because it takes place so fast (on the order of a nanosecond) that the material’s own inertia holds it in place long enough for the fusion reactions to occur.  There are two basic approaches; direct drive, in which the laser beams hit the fusion target directly, and indirect drive, the process that will be used in the upcoming Livermore ignition experiments, in which the beams are shot into a hollow can or “hohlraum,” producing x-rays when they hit the inner walls.  These x-rays then implode and ignite the target.  

A potential problem that must be overcome in ICF is known as laser plasma interactions (LPI).  These are parasitic interactions which can soak up laser energy and quench the fusion process.  According to the Livermore paper, special grids at the hohlraum entrance holes were used in the latest experiments, allowing the use of LPI to “tweak” the incoming beams, steering them to just the right spots.  This recent (and elegant) innovation allows the exploitation of a process that has always been considered a major headache in the past to actually improve the chances of achieving igntion.

The BBC and Spiegel both have articles about the latest experiments today, conflating the energy and military applications of the NIF as usual.  According to the Spiegel article, for example, it will be necessary for the lasers in a fusion reactor to hit the target ten times a second, whereas hours are necessary between shots at the NIF.  The reason, of course, is that the NIF was never designed as an energy project, but is being funded by the National Nuclear Security Administration (NNSA) to conduct nuclear weapons experiments.  If ignition is achieved, the prospects for fusion energy will certainly be improved, but the prospects aren’t nearly as bright as the press releases from LLNL would imply.  It will still be necessary to overcome a great number of scientific and engineering hurdles before the process can ever become useful and economical as a source of energy.

I am not optimistic about the success of the upcoming experiments.  I suspect it will be too difficult to achieve the fine beam energy balance and symmetry that will be necessary to ignite the central “hot spot.”  It will take more than one converging shock to do the job.  Several will be necessary, moving inward through the target material at just the right speed to converge at a small spot at the center.  If they really pull it off, I will be surprised, but will be more than happy to eat crow.  A lot of very talented scientists have dedicated their careers to the quest for fusion, and I’m keeping my fingers crossed for them. 

Even if these ignition experiments fail, it won’t mean the end for fusion by a long shot.  We know we can achieve the high fuel densities needed for inertial fusion, and there are other ways of creating the “hot spot” needed to achieve ignition, such as “fast ignitor.”  Other approaches to fusion keep showing up in the scientific literature, and I can’t help but think that, eventually, one of them will succeed.

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.