Tag Archives: recycling

Recycle nuclear waste

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In a world obsessed with stopping global warming by reducing US carbon emissions, you’d think there would be a strong cry for nuclear power, one of the few reliable sources of large-scale power that does not discharge CO2. But nuclear power produces dangerous waste, and I have a suggestion: let’s recycle the waste so it’s less dangerous and so there is less of it. Used nuclear fuel rods, in particular. We burn perhaps 5% of the uranium, and produce a waste that is full of energy. Currently these, semi-used rods are stored in very expensive garbage dumps waiting for us to do something. Let’s recycle.

I’ve called nuclear power the elephant in the room for clean energy. Nuclear fuel produces about 25% of America’s electricity, providing reliable baseline generation along with polluting alternatives: coal and natural gas, and less-reliable renewables like solar and wind. Nuclear power does not emit CO2, and it’s available whether or not the sun shines or the wind blows. Nuclear power uses far less land area than solar or wind too, and it provides critical power for our navy aircraft carriers and submarines. Short of eliminating our navy, we will have to keep using nuclear.

Although there are very little nuclear waste per energy delivered, the waste that there is, is hard to manage. Used nuclear fuel rods in particular. For one thing, the used rods are hot, physically. They give off heat, and need to be cooled. At first they give off so much heat that the rods must be stored under water. But rod-heat decays fractally. After ten years or so, rods can be stored in naturally cooled concrete; it’s still a headache, but a smaller one The other problem with the waste rods is that they contain about 1.2% plutonium, a material that can be used for atomic bombs. A major reason that you can’d just dump the waste into the ocean or into a salt mine is the fear that someone will dig it up and extract the plutonium for an a- bomb. The extraction is easy compared to enriching uranium to bomb-grade, and the bombs work at least as well. Plutonium made this way was used for the bomb that destroyed Nagasaki.

The original plan for US nuclear power had been that we would extract the plutonium, and burn it up by recycling it to the nuclear reactor. We’d planned to burry the rest, as the rest is far less dangerous and far less, long-term radioactive. We actually did some plutonium recycling of this sort but in the 1970s a disgruntled worker named Silkwood stole plutonium and recycling was shut down in the US. After that, political paralysis set in and we’ve come to just let the waste sit in more-or-less guarded locations. There was a thought to burry everything in a guarded location (Yucca Mountain, Nevada) but the locals were opposed. So the waste sits waiting to leak out or be stolen. I’d like to return to recycling, but not necessarily of pure plutonium as we did before Silkwood: there is no guarantee that there won’t be other plutonium thieves.

Instead of removing the plutonium for recycling, I’d like to suggest that we remove about 40% of the uranium in the rod, and all of the “ash”, this is all of the lighter atom elements created from the split uranium atoms. This ash is about 5% of the total. The resultant rods would have about 2% plutonium, 97.5% enriched uranium (about 1% enriched at this stage) plus about 0.5% higher transuranics. This composition would be a far less dangerous than purified plutonium. It would be less hot and it would not be possible to use it directly for atom bombs. It would still be fissionable, though, at the same energy content as fresh rods.

There is an uncommonly large amount of power available in nuclear fuel

Several countries recycle by removing the ash. Because no uranium is removed, the material they get has about half the usable life of a fresh rod. After one recycle, there is not much more they could do. If we remove uranium material is a lot more easily used, and more easily recycled again. If we keep removing ash and uranium, we could get many, many recycles. The result is a lot less uranium mining, and more power per rod, and fewer rods to store under guard.

The plutonium of multiply recycled rods is also less-usable for fission bombs. With each recycle, the rods build up a non-fisionabl isotope of plutonium: Pu 240. This isotope is not readily separated from the fissionable isotope, Pu 239, making multiply used rods relatively useless for fission bombs.

Among the countries that do some nuclear waste recycling are Canada, France, Russia, China, and Germany. Not a bad assortment. I would be happy to see us join them.

Robert Buxbaum September 9, 2019

Alkaline batteries have second lives

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Most people assume that alkaline batteries are one-time only, throwaway items. Some have used rechargeable cells, but these are Ni-metal hydride, or Ni-Cads, expensive variants that have lower power densities than normal alkaline batteries, and almost impossible to find in stores. It would be nice to be able to recharge ordinary alkaline batteries, e.g. when a smoke alarm goes off in the middle of the night and you find you’re out, but people assume this is impossible. People assume incorrectly.

Modern alkaline batteries are highly efficient: more efficient than even a few years ago, and that always suggests reversibility. Unlike the acid batteries you learned about in highschool chemistry class (basic chemistry due to Volta) the chemistry of modern alkaline batteries is based on Edison’s alkaline car batteries. They have been tweaked to an extent that even the non-rechargeable versions can be recharged. I’ve found I can reliably recharge an ordinary alkaline cell, 9V, at least once using the crude means of a standard 12 V car battery charger by watching the amperage closely. It only took 10 minutes. I suspect I can get nine lives out of these batteries, but have not tried.

To do this experiment, I took a 9 V alkaline that had recently died, and finding I had no replacement, I attached it to a 6 Amp, 12 V, car battery charger that I had on hand. I would have preferred to use a 2 A charger and ideally a charger designed to output 9-10 V, but a 12 V charger is what I had available, and it worked. I only let it charge for 10 minutes because, at that amperage, I calculated that I’d recharged to the full 1 Amp-hr capacity. Since the new alkaline batteries only claimed 1 amp hr, I figured that more charge would likely do bad things, even perhaps cause the thing to blow up.  After 5 minutes, I found that the voltage had returned to normal and the battery worked fine with no bad effects, but went for the full 10 minutes. Perhaps stopping at 5 would have been safer.

I changed for 10 minutes (1/6 hour) because the battery claimed a capacity of 1 Amp-hour when new. My thought was 1 amp-hour = 1 Amp for 1 hour, = 6 Amps for 1/6 hour = ten minutes. That’s engineering math for you, the reason engineers earn so much. I figured that watching the recharge for ten minutes was less work and quicker than running to the store (20 minutes). I used this battery in my firm alarm, and have tested it twice since then to see that it works. After a few days in my fire alarm, I took it out and checked that the voltage was still 9 V, just like when the battery was new. Confirming experiments like this are a good idea. Another confirmation occurred when I overcooked some eggs and the alarm went off from the smoke.

If you want to experiment, you can try a 9V as I did, or try putting a 1.5 volt AA or AAA battery in a charger designed for rechargeables. Another thought is to see what happens when you overcharge. Keep safe: do this in a wood box outside at a distance, but I’d like to know how close I got to having an exploding energizer. Also, it would be worthwhile to try several charge/ discharge cycles to see how the energy content degrades. I expect you can get ~9 recharges with a “non-rechargeable” alkaline battery because the label says: “9 lives,” but even getting a second life from each battery is a significant savings. Try using a charger that’s made for rechargeables. One last experiment: If you’ve got a cell phone charger that works on a car battery, and you get the polarity right, you’ll find you can use a 9V alkaline to recharge your iPhone or Android. How do I know? I judged a science fair not long ago, and a 4th grader did this for her science fair project.

Robert Buxbaum, April 19, 2018. For more, semi-dangerous electrochemistry and biology experiments.

An Aesthetic of Mechanical Strength

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Back when I taught materials science to chemical engineers, I used the following poem to teach my aesthetic for the strength target for product design:

The secret to design, as the parson explained, is that the weakest part must withstand the strain. And if that part is to withstand the test, then it must be made as strong as all the rest. (by R.E. Buxbaum, based on “The Wonderful, One-hoss Shay, by Oliver Wendell Holmes, 1858).

My thought was, if my students had no idea what good mechanical design looked like, they’d never  be able to it well. I wanted them to realize that there is always a weakest part of any device or process for every type of failure. Good design accepts this and designs everything else around it. You make sure that the device will fail at a part of your choosing, when it fails, preferably one that you can repair easily and cheaply (a fuse, or a door hinge), and which doesn’t cause too much mayhem when it fails. Once this failure part is chosen and in place, I taught that the rest should be stronger, but there is no point in making any other part of that failure chain significantly stronger than the weakest link. Thus for example, once you’ve decided to use a fuse of a certain amperage, there is no point in making the rest of the wiring take more than 2-3 times the amperage of the fuse.

This is an aesthetic argument, of course, but it’s important for a person to know what good work looks like (to me, and perhaps to the student) — beyond just by compliments from the boss or grades from me. Some day, I’ll be gone, and the boss won’t be looking. There are other design issues too: If you don’t know what the failure point is, make a prototype and test it to failure, and if you don’t like what you see, remodel accordingly. If you like the point of failure but decide you really want to make the device stronger or more robust, be aware that this may involve strengthening that part only, or strengthening the entire chain of parts so they are as failure resistant as this part (the former is cheaper).

I also wanted to teach that there are many failure chains to look out for: many ways that things can wrong beyond breaking. Check for failure by fire, melting, explosion, smell, shock, rust, and even color change. Color change should not be ignored, BTW; there are many products that people won’t use as soon as they look bad (cars, for example). Make sure that each failure chain has it’s own known, chosen weak link. In a car, the paint on a car should fade, chip, or peel some (small) time before the metal underneath starts rusting or sagging (at least that’s my aesthetic). And in the DuPont gun-powder mill below, one wall should be weaker so that the walls should blow outward the right way (away from traffic).Be aware that human error is the most common failure mode: design to make things acceptably idiot-proof.

Dupont powder mills had a thinner wall and a stronger wall so that, if there were an explosion it would blow out towards the river. This mill has a second wall to protect workers. The thinner wall should be barely strong enough to stand up to wind and rain; the stronger walls should stand up to explosions that blow out the other wall.

Dupont powder mills had a thinner wall and a stronger wall so that, if there were an explosion, it would blow out ‘safely.’ This mill has a second wall to protect workers. The thinner wall must be strong enough to stand up to wind and rain; the stronger walls should stand up to all likely explosions.

Related to my aesthetic of mechanical strength, I tried to teach an aesthetic of cost, weight, appearance, and green: Choose materials that are cheaper, rather than more expensive; use less weight rather than more if both ways worked equally well. Use materials that look better if you’ve got the choice, and use recyclable materials. These all derive from the well-known axiom, omit needless stuff. Or, as William of Occam put it, “Entia non sunt multiplicanda sine necessitate.” As an aside, I’ve found that, when engineers use Latin, we look smart: “lingua bona lingua motua est.” (a good language is a dead language) — it’s the same with quoting 19th century poets, BTW: dead 19th century poets are far better than undead ones, but I digress.

Use of recyclable materials gets you out of lots of problems relative to materials that must be disposed of. E.g. if you use aluminum insulation (recyclable) instead of ceramic fiber, you will have an easier time getting rid of the scrap. As a result, you are not as likely to expose your workers (or you) to mesothelioma, or similar disease. You should not have to pay someone to haul away excess or damaged product; a scraper will oblige, and he may even pay you for it if you have enough. Recycling helps cash flow with decommissioning too, when money is tight. It’s better to find your $1 worth of scrap is now worth $2 instead of discovering that your $1 worth of garbage now costs $2 to haul away. By the way, most heat loss is from black body radiation, so aluminum foil may actually work better than ceramics of the same thermal conductivity.

Buildings can be recycled too. Buy them and sell them as needed. Shipping containers make for great lab buildings because they are cheap, strong, and movable. You can sell them off-site when you’re done. We have a shipping container lab building, and a shipping container storage building — both worth more now than when I bought them. They are also rather attractive with our advertising on them — attractive according to my design aesthetic. Here’s an insight into why chemical engineers earn more than chemists; and insight into the difference between mechanical engineering and civil engineering. Here’s an architecture aesthetic. Here’s one about the scientific method.

Robert E. Buxbaum, October 31, 2013