Well, well. A few months have passed since I wrote this and today (09-03-2017) it appears that North Korea has detonated a thermonuclear device. The estimated yield is around 100 kilotons.
My thoughts are that either …
- it’s not as difficult to build thermonuclear weapons as we (including me!) previously thought, or
- perhaps Pyongyang is more high-tech than everyone (also including me!) previously thought, or
- the test was actually a very powerful fusion-boosted fission type (discussed below), or maybe even more than one nuke detonated simultaneously to give a bigger-looking bang.
I Can Haz Nuke?
Every tin-pot dictator dreams of being part of the Nuclear Club(tm). They want to be respected on the world stage. Considered a Force To Be Reckoned With.
Pulling out your peasant’s eyeballs with pliers stops being fun after a while, and human rights groups whine and call you names, yadda, yadda. Aggravating. Boring.
But hey! If you have nukes, everyone else must take you seriously, amirite?
Naturally, most sane people would prefer that Mr. Tin Pot didn’t get nukes. But how can we prevent it? Can we prevent it? Are we just wasting our time?
Before I give you my opinion, I want to clear up some misconceptions that most people have about this. There’s a reason why I’m writing it.
About 11-1/2 pounds of weapons-grade plutonium,
enough for one bomb. It’s ring-shaped for a reason.
If You’re In A Hurry …
Here’s the most troubling thing that my admittedly-non-expert, layman-level research turned up. Getting the right isotopes (more in a moment) takes a lot of work, but basic nuclear technology nowadays is straightforward engineering.
I’m old enough to remember the Cold War era, complete with nuclear drills where we’d crawl under our school desks.[footnote 1] At the time, the USSR (Russians) were the big threat. We were told that nuclear weapons were extremely advanced and very hard to build. That’s why only we, the Russians and a few others had them. (That knowledge was certainly a relief as we huddled under our school desks, trying to keep old chewing gum from sticking to our hair.)
But in fact, simple fission devices like the ones we dropped on Hiroshima and Nagasaki in 1945 are based on well-known physics. You’re not going to build one in your basement, but the same math applies to nuclear reactors, so it’s taught in schools around the world. Gobs of information is available on the Web as well. That’s where this came from; I’m not revealing hidden secrets here, folks.
(Hey, you wanna play a funny joke on Superman? Hand him about 12 lbs of a certain isotope of plutonium, formed into a hollow sphere. Tell him to squeeze it into a solid ball, really hard, as fast as he can. You’ll be vaporized, but hah, hah! Can you imagine the shocked look on his face?)
Now, making a small and efficient nuclear weapon — or a not-so-small multi-megaton super weapon — takes advanced engineering. But consider this: North Korea has historically had more trouble building missiles than nukes. What does that tell you about which is more difficult?
It looks like a nightmare from IKEA, but actually,
it’s a picture of a disassembled Type B-61 nuclear
bomb … from our own US Department of Energy.
Now for some science.
Isotopes are the same chemical element with different numbers of neutrons. For example, “normal” carbon is C12 (or 12C in some literature): carbon 12. It has 6 protons and 6 neutrons. But if it captures a couple of extra neutrons, it becomes carbon 14 (C14), which is radioactive.
Because the number of protons hasn’t changed, C12 and C14 will act the same chemically. Plants can’t tell the difference. If there’s a lot of C14 in the atmosphere (for whatever reason), you could end up eating radioactive vegetables and never even know it.
Separating isotopes isn’t easy because they’re essentially the same chemically. The usual chem-lab methods don’t work, especially not with the radioactive isotopes that are used in nukes.
The initial effort to stop Tin Pot And Company from getting a nuke will require things like tracking the equipment used for isotope separation, monitoring the sale or transfer of fissile materials, and so on.
Certain radioactive isotopes are capable of fission — each atom can split into two or more smaller atoms. A very small percentage will split on their own, at random, which is usually the initial source of free neutrons flying around.
In a bomb, a device called an modulated neutron initiator[footnote 2] is used to throw out lots of neutrons to dramatically speed up the reaction. The goal is to make as much of the isotope split (fiss? fuss? flambe?) as possible before it blows itself apart.
The image below shows a free neutron (“n,” on the left) splitting an atom of U235 (uranium 235) into barium and krypton atoms. Extra neutrons are knocked loose (the dots to the right of the picture). A lot of energy is released: about 2.5 million times as much as burning the same weight of coal.
If you concentrate the U235 and/or reflect those extra neutrons back into it, they strike other U235 atoms, splitting them, releasing even more neutrons and energy, which split more atoms, and so on. You get a chain reaction. Physicists refer to this as reaching “critical mass,” or achieving “criticality.”
The goal in a weapon is to keep the fissile stuff from becoming critical until you want your Big Boom. That’s why the plutonium in the picture above was made into a thin, widely-spaced ring. Most of the free neutrons fly away into air.
However you reach criticality, this chain reaction is what makes nuclear reactors and weapons work. In a reactor, the fission is limited and carefully controlled. In a weapon, you want as many atoms to split as possible, very quickly, to make a big “boom.”
Tin Pot Man calls a press conference. In a dramatic display, tears fill his eyes. He tosses his pliers over his left shoulder [footnote 3] and says that he wants to be a better man.
“My people are suffering,” he sobs. “We need schools and hospitals and Burger Kings and Wal-Marts! We need … electricity.”
The world just loves this kind of thing, so they’ll actually build the maniac a reactor.
Tin Pot will argue that his little third-world country shouldn’t have to pour its treasure into other big, evil, rich nations to buy nuclear fuel, too. He wants to make his own.
Uranium in nature is about 99% U238, which is not fissile. Less than 1% is fissile U235. Tin Pot Man wants to enrich this to a higher percentage of U235. He wants some fluorine and some gas centrifuges.
He’s allowed to buy these … if he agrees to regular inspections. (Aha! Hold that thought.)
Wikipedia has a nice diagram for breeder reactors.
I added the cute bunny because it badly needed one.
Tin Man creates uranium hexafluoride gas, which is hot, radioactive, ridiculously corrosive and insanely toxic. It’s hilariously dangerous, but useful for one purpose: to enrich uranium. By running this gas repeatedly through a long string of centrifuges, the slightly lighter U235 will slowly separate from the slightly heavier U238.
To make a bomb, the U235 needs to be highly enriched (80-90% U235). Reactor-grade is refined to less than 10% U235. The inspections are supposed to ensure that he never goes past that.
Once he gets enough U235, Tin Pot can take some leftover (“depleted“) U238, put it in his reactor, and bombard it with neutrons. The length of time is critical, but this is how you “breed” fissile plutonium 239 (Pu239) in job lots.
Pu239 can be used as fuel for the reactor, but Tin Man wants it because it takes much less Pu239 than U235 to make a bomb. He wants his weapons to be sleek and sexy.
Now he’s ready to rock. He kicks out the inspectors. (Of course. See: North Korea. See: Iran. See … you get the idea.) Tin Potty starts enriching and breeding like mad to make lots of Pu239, all while insisting that he’s a peaceful man who just wants his people to have better lives.
Fat Man, the bomb that we dropped on
Nagasaki, was anything but sleek and sexy.
First Step: Fission
We were told for decades that this is very difficult, but it really isn’t, not for any reasonably technical society. The plutonium is usually formed into a hollow sphere, then surrounded by a bunch of carefully-arranged high explosives. A neutron initiator is put in the middle to provide a rich source of neutrons.
Normally, a critical mass will just get very hot and expand, or even blow itself apart, rather than do the Big Boom thing. If a nuclear reactor melts down, for example, the fuel typically gets extremely hot and might eat its way through the floor. The goal in a weapon is to crush that sphere into a critical mass very quickly, causing a runaway chain reaction.
If you accidentally assemble a critical mass on your lab bench, it’s called a “criticality accident.” Many people have been killed by them over the years.[footnote 4]
Once you compress that sphere, unless you completely blow it (heh — see what I did there?), you get a boom. Even with near-perfect compression, you’ll only induce fission in a small fraction of the U235 or Pu239 before the core blows itself apart, but it’s still very destructive.[footnote 5]
Relative Difficulty: not nearly as hard as we were once told.
Next Step: Fusion Boosting
Once Tin Pot has his fission weapon, he’s ready for the next step. If he can get his murderous hands on some deuterium and tritium (isotopes of hydrogen), he can fill that hollow sphere with it.
Now when the chain reaction starts, some of the deuterium and tritium will fuse. This doesn’t add much to the explosion, but it releases a bunch of additional free neutrons. This ensures that much more of the U235 or Pu239 will get involved in fission before the core blows itself apart. Instead of a bomb in the 10-30 kiloton range, Tin Man can at least double that (I’ve seen different figures online).
The details are classified, but it’s believed that virtually all modern nuclear weapons actually contain fusion-boost cores. When combined with other tricks (such as the beryllium “reflector” in the image below), a bomb can be made much smaller for the same “boom.”
(Small enough to fit in a suitcase? It would be an extremely heavy piece of luggage. That might arouse the curiosity of onlookers …)
Relative Difficulty: not hard if you have deuterium and/or tritium.
Next Step: Thermonuclear
This is what Tin Pot would undoubtedly love to get his grimy hands on, because it’s the thing of legends. The very thought of a gigantic explosion that breaks windows hundreds of miles away makes him dizzy with joy.
Fortunately, so-called “hydrogen bombs”[footnote 6] are indeed hard to make. The United States did it with top-notch scientists, a huge budget and years of trial-and-error research, as did the Soviets.
The idea is that, since you’ve already made a high-pressure fission explosion that reaches millions of degrees, why not use it to cause full-blown fusion? But everything must happen in precisely the correct order within a few millionths of a second: fission, then fusion, then (in some cases) even more fission and/or fusion. It’s not likely that Tin Pot can do this without help.
That’s great news … but go back and re-read the previous section. Even if Tin Guy, North Korea, Iran, Pakistan and all of the other “second string” nuclear powers never build a Megaton Monster, trust me, a 50-100 kiloton fusion-boosted bomb is quite destructive, thank you.
(The United States has been scaling down the size of its bombs for decades. Really, if you’re trying to destroy a city, 100-300 kilotons will probably do the job. Anything larger is just overkill.)
Relative Difficulty: very hard.
Never to be outdone, the Soviets just had to explode the
biggest one ever built: the 50 megaton Tsar Bomba. This
photo was taken from a hundred freekin’ miles away.
How do these inspections work? How can they be effective? You have to understand how these nuclear watchdogs work. They don’t think like we do.
A nuclear technician hands me a can of condensed soup.[footnote 7] “Heat this for lunch, please … oh, don’t add any salt. It’s already loaded with the stuff.” I plop the lump into the pan, add a can of water … and without thinking, start shaking table salt into the pot.
I catch myself after a few sprinkles, but I did add salt. I shouldn’t have. So … I add some extra water to the soup to thin it back out. It tastes OK, so I’ve gotten away with it! Besides, how can you prove that I added the salt? Nyah, nyah!
But the technician runs it through a zillion-dollar machine and says, “there’s excess iodine in this soup. Processed foods are usually made with non-iodized salt, but we use iodized salt at home. Therefore, you must have added salt to it.”
In fact, the scientists and experts who monitor nuclear programs are very, very good and have some really slick, really fancy equipment. They’ve got decades of data on hand, and they know exactly what properly-enhanced uranium or plutonium should look like down to the micro-teensy-gram.
People have tried to fool nuclear inspectors for years. For example, they’ll add some U238 back to the samples to make them look less enriched. But these inspectors have seen it all and they know what to look for.
At the risk of making your eyeballs explode, go back up and look at the diagram of products from a breeder reactor. (The one with the bunny.) Just note that you can take a long, tortuous route to get from U238 to Pu239. The breeder creates other short-lived isotopes that then decay into something else.
Here’s the key: even if Tin Pot “waters down” his samples with U238 to make it look like he’s only enriching to reactor-grade, if the inspectors find certain ratios of isotopes to decay products, they’ll know that Tin Pot-head has been naughty.
So … what about the possibility that Tin Pot can hide some of this from the inspectors? It’s not as easy as you’d think. (Critics of the Iran-nuclear deal miss this part). See the image below: modern centrifuges are smaller than the ones shown here (about 6-12′ tall), but you still need a ton of them, each feeding the next one in the chain.
Small nations that want to join The Club(tm) think that the US, the UK, and other nuclear powers are just being selfish bullies. Tin Pot insists that he just wants to generate electricity to bring his people out of poverty.
That kind of thing naturally appeals to our compassion and weakens our resolve.
If we agree to any nuclear deal that doesn’t include comprehensive inspections, with monitoring (ex., tamper-resistant cameras) between visits, it’s not going to work. I don’t think that it’s as easy to hide a nuclear program as some seem to think, but I’d rather err on the side of caution.
Even having said that, here’s what really bothers me: I showed you above how Tin Pot might join the nuclear club, but somewhere out there, for all we know, is a mad genius who is trying to get a “big boom” in some completely new way. We need to do the inspections, of course, but I’m afraid of inside-the-box thinking.
For that reason, I’m kind of pessimistic, especially since the world at large seems to have lost its commitment to stopping people like Tin Man. I’m afraid that eventually, terrorists are going to get their hands on nuclear weapons.
I’ll leave you with the story of the Revolt Of The Admirals, an excellent example of arrogant, inside-the-box thinking.
After WWII, our intelligence folks were convinced that it would be many, many years before anyone else would develop nuclear weapons. We were supreme! As a result (among many other cutbacks), we figured that big armies and aircraft carriers were a waste of time and money.
A year later, the Korean war began and we were badly hampered by (drum roll, please!) … a shortage of boots to put on the ground, and of aircraft carriers.
Food for thought, folks. If we can’t even work up the will and energy to insist on thorough inspections, what else might we be missing?
Ye Olde Footnotes:
1 – Because nothing will protect you from a one megaton nuclear blast like a gum-encrusted school desk! (back)
2 – If you’re starting to think that many of the terms used in nuclear science came from Marvin The Martian, you’re not alone. (back)
3 – Ironically, the pliers strike and kill a hapless peasant who’s cowering in the background, but the media is too focused on Tin Pot Man to notice. (back)
4 – Given that Tin Pot Man has a nearly endless supply of expendable labor — “Achmed, push these two pieces of shiny metal together while we watch from a mile away!” — he can afford to lose some people while he gets the hang of things. (back)
5 – Fat Man, the bomb that leveled Nagasaki, was only about 13% “efficient.” (back)
7 – Geniuses are inordinately fond of canned soup. (back)
8 – See above re: expendable labor. The Soviets were willing to kill people by the boatload to get their bomb. For example, Zeks (prisoners) were used to mine the uranium. (back)