Plutonium and the Return to Nuclear Power

I’m on board when it comes to restarting the nuclear industry – with reservations. What’s not to like? No carbon footprint. Less release of dangerous radionuclides into the atmosphere than coal plants. No need to pave thousands of square miles of environmentally fragile desert with solar collectors, windmills, and similar “environmentally friendly” and “sustainable” energy sources.

There is one big potential problem, though. When you burn uranium in a conventional nuclear reactor, you breed plutonium. The spent fuel rods currently stored on site at every nuclear plant in the country are laced with the stuff. You don’t need fancy centrifuges or gas diffusion plants to separate the plutonium. Any reasonably skilled chemist could do it. Once you’ve separated the plutonium, you have the one key ingredient you need to make a nuclear weapon. Oh, I know, it won’t be weapons grade plutonium, but no matter. The United States conducted a successful nuclear test with reactor grade plutonium.

Why, you ask, haven’t terrorists already stolen a batch of fuel rods if it’s so simple. Well, at the moment, the problem is that they’re so highly radioactive that bad actors would probably fry themselves before they could do any damage. They won’t stay that way, though. The radionuclides that make fuel rods so “hot” when it comes to emitting radiation have a certain half life. They decay, and become less radioactive at an exponential rate. At some point, they will become safe enough to handle, even without specialized equipment. The exact time will depend on the material configuration of the fuel rods when they were produced, and the degree of risk the person handling them is willing to take. True, we’re probably talking hundreds or thousands of years in the future, but beyond what date can we ignore the welfare of future generations? When does it become OK to subject them to the risk of nuclear annihilation?

Fortunately, there are solutions to the problem. One is fuel recycling, in which the plutonium from spent rods would be extracted and recycled into new fuel rods. An even better one is building breeder reactors to go along with the recycling. The problem with conventional reactors is that they use up the U235 in natural uranium as fuel. Unfortunately, only seven tenths of one percent of natural uranium is isotope 235, and the rest is 238. Depleted uranium is mostly U238, being what’s left over when the U235 is separated.

With breeder reactors, the U238 can be gradually converted into plutonium 239, a reactor fuel. In that way, a much greater percentage of the natural uranium could be converted to energy, greatly extending the time available to us for figuring out what to do when that fuel supply runs out. Alternatively, thorium, which can be converted into U233, another fissile material, could be used in the breeders. U233 has the very significant advantage of not being chemically separable from other uranium isotopes, and would, therefore be much more difficult to weaponize than plutonium.

Plutonium-based energy production is not benign. It would require tight security standards at every step along the fuel chain. But, then again, no known method of producing energy is benign, including the “environmentally friendly” ones noted above. If the choice were mine to make, I think I would agree with the guys over at Atomic Insights.

Meanwhile, it strikes me as a little crazy that we are gratuitously pumping potentially energy rich depleted uranium slugs out of the barrels of gatling guns. If we really start running out of energy, others might notice there are better uses for the stuff as well.

Nuclear Terrorism and Nuclear Smuggling: Will Portal Radiation Detectors Save Us?

Well, no. Not if you’re talking about interdicting a nuclear weapon or its components. The syllogism works like this: 1) Anyone with enough Special Nuclear Material (SNM) to assemble a bomb would have to be brain dead to try to tote it through a radiation portal. 2) Anyone clever enough to acquire enough SNM to make a bomb is not brain dead. 3) Therefore, anyone with enough SNM to make a bomb will not attempt to carry it through a radiation portal. (Apropos SNM, the image to the left shows a guy holding a plutonium “button.” He probably wouldn’t do that if it were radioactive enough to kill him outright.)

The location of radiation portals and their approximate performance parameters are easily accessible to potential nuclear smugglers at any of a host of “intelligence” websites online. The question then becomes, can they avoid passing them? Of course! How many of the millions of illegal immigrants currently in the country do you suppose passed through radiation portals? There are a virtually infinite number of ways to smuggle SNM into the country that don’t involve passing through radiation detectors, ranging from slingshots to personal submarines. The unclassified amounts of SNM deemed sufficient for a nuclear explosive device are 25 kilograms of highly enriched uranium, or 4 kilograms of weapons grade plutonium. However, there’s no need whatsoever to smuggle such large quantities all at once. Terrorists could “smuggle by components.” In other words, they could simply smuggle the SNM into the country bit by bit until they had enough for a weapon.

By the way, dear reader, if you are one of those whose tastes run to calculating how much SNM it would “really” take to make a bomb, here’s some advice for you: Don’t do it! In general, don’t try to impress everyone with how clever you are by speculating on the design details of nuclear weapons. You will take yourself right out of the dialogue, because anyone who really knows anything about such matters is liable to have a “Q” security clearance, and, according to DOE guidelines, will be unable to comment on whatever brilliant conclusions you’ve come to on the subject.

In fact, it is absolutely unnecessary to wander into classified territory in discussions of nuclear terrorism, or at least into the classified territory relating to the design of nuclear weapons. Once upon a time, the National Weapons Laboratories and others used to (and maybe still do) come up with silly menageries of “threat objects” to “help” the radiation portal operators focus in on what to look for. Of course, the radiation signature of such “threat objects” can vary over a wide range depending on what kind of shielding and other objects surround it, and even in which direction the “threat object” is pointing when it passes through the portal. Other than that, there are an infinite variety of potentially lethal weapon configurations that are quite different from those in whatever menagerie you happen to consult.

Look, the “threat object” is SNM. That’s what terrorists have to have to assemble a nuclear device, and that’s what you have to look for, period. Do they have to smuggle it in 4 kg or 25 kg chunks? No! Depending on how patient they are, they can smuggle in bits as small as they please, and then assemble them at the target. Would it be hard for them to assemble a weapon at the target. Well, much has been said about the great technical virtuosity terrorists must have to assemble a nuclear weapon. Here’s the reality:

1. Take two chunks of SNM, well separated, that, when combined, form a critical mass.
2. Put one of the chunks on the ground.
3. Climb up a medium size step ladder with the other chunk.
4. Take careful aim.
5. Drop the chunk you’re carrying on top of the other chunk.

Not exactly rocket science, is it? Now, this admittedly rather crude nuclear weapon isn’t going to outperform Fat Man, but, before the critical mass you’ve just created disassembles because of its own energy release, it will create a radioactive mess, paralyze all economic activity for a while in the surrounding area, and have a huge psychological impact. That may be just the result that potential terrorists have in mind. Why sacrifice the good will of potential sympathizers and collaborators by vaporizing hundreds of thousands of people? Why risk getting caught with the SNM while you try to figure out how to put together a high yield weapon? Furthermore, to assemble such a weapon at the target, you don’t have to bring in all the SNM at once. You can transport it in arbitrarily small chunks.

In a word, anyone who gains possession of SNM to begin with will not be deterred or stopped by radiation portals. In the first place, there’s no need whatsoever for them to go through the portal to begin with. However, if they insist on taking risks, they can spoof the radiation detectors by surrounding the SNM with appropriate shielding, or putting it next to a medical radioisotope or other innocent radiating material, or the SNM can be carried through in small enough bits to avoid detection.

The ineffectiveness of radiation portals will become increasingly obvious as more and more nuclear smugglers are caught. I an not aware of a single incident to date in which SNM smugglers were stopped by radiation detectors. The ones that have been caught tend not to be top drawer professional smugglers, but unsophisticated crooks who happened to have access for one reason or another. They were stopped, not by radiation detectors, but by good intelligence and police work. I suspect this pattern will continue into the future.

Does all this mean that all our attempts to detect illicit radioactive materials are a waste of time and money? I think not. In the first place, SNM is not the only kind of radioactive material the portals can detect. They have successfully detected scrap metal contaminated with radioactive waste, commercial radioisotopes without proper documentation, etc. As we build more of them, and devote more funding to their development, radiation detectors will become better and cheaper, perhaps to the point that a more effective detection strategy becomes feasible. Then, of course, there is a political side of the question to consider. If a smuggled nuclear device really does go off in a US city, how would you assess the chances of reelection of an Administration that had made a deliberate decision to discontinue funding of radiation portals?