Nuclear Composting

Yesterday my wife sent me off to the local cotton gin to get some really good rich dirt for her garden beds. Fortunately my neighbor had just the appropriate pickup truck and the right disposition on a Saturday morning for such a job. So we headed off, stopped for gas and some Diet Cokes, and found our way to the cotton gin a few miles from my house.

I had never been to a real cotton gin before, but I had been especially curious for several weeks because we took our daughters to a nearby farm that hosts “agrotourists” each fall and we saw cotton fields as far as the eye could see. I took my daughters up to the edge of the field and explained to them how to pick cotton. If we had lived a century ago, my two oldest daughters (ages 7 and 5) would probably each have already spent one or more years in the backbreaking job of picking cotton by hand. But thanks to modern machinery, such picking is now done by machines with a fraction of the labor.

Cotton is a wonderful substance–it feels like a bit of fluffy white perfection in your hand. But rub it a little and you can feel the cottonseeds in there, and if you attempt to “gin” the cotton by hand you quickly find out just how difficult it is to extract the seeds. Who knows how many man-hours have been spent over the centuries picking out cottonseeds by hand?

So getting to see a real gin in action was a treat. Huge bales of cotton arrive and are fed into the gin on a large, slow-moving conveyor belt. Then the cotton is separated from the seeds and the seeds were literally falling like rain out of this huge machine (about the size of my garage) into a feed system that conveyed them elsewhere. I’m not sure exactly what all they do with the seeds, but eventually the seed hulls ended up in a huge pile in the back of the gin, and that’s what I was there for.

The gin composted the cottonseed hulls, and given enough time they would decompose into a very dark, rich, porous dirt that is like black gold for gardens and flowerbeds. We followed a front-loader behind the gin and while we sat in the air-conditioned truck and in a period of about two minutes, the fellow who drove the front-loader dumped two scoops of cotton dirt into the back of the pickup. I went to the office and paid $10 for these two scoops, and then for the cost of about a gallon of gas, that remarkable machine called a truck did all the work of conveying us and our load of cotton dirt the 5 or 6 miles back to my house while we drank our Diet Cokes.

I love technology. I love that machines can gin cotton and scoop dirt and drive us from here to there. Despite the fact that I had a lot of manual labor ahead of me that day, the vast majority of the work had already been done by the gin, the front-loader, and the truck. Then it was just me and my neighbor and some shovels and my wheelbarrow to finish out the job.

I had a lot of time to think yesterday and one of the things I thought about was the cotton dirt.

You see, those cotton-seed hulls were “waste” from the ginning process. The gin had more of them than they knew what to do with. Sure, they charged me $10 for the dirt, but they had lots of it and I wouldn’t be surprised if they wouldn’t have given it to me for free. The cotton-seed hulls weren’t very useful when you first had them, but stack them in a big pile and give them some time, and nature can turn them into something quite useful.

In a similar vein, I began thinking of the misnamed mixture we call “nuclear waste”. Does nature “compost” nuclear waste for us?

Anti-nukes love to say “NO!” to that idea. They will tell you that nuclear waste is an evil poison that is nature’s revenge for our wickedness for splitting the atom, and that it is toxic and dangerous forever and nothing will break it down.

But the more I research the subject, the more I am coming to another conclusion–nature does “compost” the results of fission, through the very natural process of nuclear decay.

Ever wonder what becomes of uranium after it fissions? I’ve wondered, so I went and found out. Here’s what it turns into, roughly in order of mass:

Xenon, zirconium, neodymium, molybdenum, cerium, cesium, ruthenium, barium, lanthanum, praseodymium, and a dozen or so other elements.

Now here’s what I found to be pretty neat–even though these elements are typically “born” from fission in an unstable and highly-radioactive state, they are decaying quickly towards a stable state, and most of them get there more quickly than you might think.

Take the first one on the list: xenon. There’s a number of radioactive xenon isotopes, including that little booger xenon-135, but the longest-lived among the radioactive isotopes of xenon is xenon-133 with a 5-day half-life. Taking the rule-of-thumb that “ten half-lives and you’re gone” by about 50 days after you pull the fission products out of the reactor, all the xenon would be stable and you could sell it. Is xenon easily to get out? Out of a fluid-fueled reactor like LFTR it’s a piece of cake–it comes right out of solution. Is xenon valuable? Yes! In fact at NASA we say that xenon’s one of the few things that costs about as much to launch into space ($10K/lb) as it is worth. So stable xenon gas could be a valuable byproduct of fission.

What’s next? Neodymium is pretty common from fission (#3 on our list). Neodymium’s longest lived radioactive isotope (147) only has a half-life of 10.9 days, so after 110 days (to be conservative) our neodymium could be extracted and sold. What do we use neodymium for? Hey, do you have any of those little earbud headphones? Ever wonder why they’re so small compared to those clunky headphones we had when we were kids? The answer is small, high-strength neodymium magnets. The wind industry needs lightweight neodymium magnets for their huge generators they put up on those absurdly tall towers. There’s neodymium in my children’s magnet toys. Neodymium is valuable.

Let’s talk about some more–molybdenum, whose longest-lived isotope (99) could be extracted through fluorination to MoF6 and used in medical procedures that would save lives (Tc-99m). Mo-99 has a half-live of 2.8 days, so in a month the molybdenum would have “composted” to readiness.

Barium: Ba-140 is the longest at 12.7 days. Give it 4 months and the barium is “composted”.

Lanthanum: La-140 at 1.7 days. Three weeks to “compost” lanthanum.

Praseodymium: Pr-143 at 13.5 days needs 4 months to “compost”.

Cerium: Ce-144 at 9.5 months takes about 7-8 years to “compost”.

Ruthenium: Ru-106 at 1 yr takes a decade to “compost”.

Then some of the longer-lived stuff is still useful even in its radioactive state. Cesium-137 is quite radioactive and has a half-life of 30 years. But we could use Cs-137 to sterilize medical instruments, destroy pathogens in sewage, or preserve easily-spoiled fruits and vegetables. Cs-137 could be more useful radioactive than stable!

So think about the results of fission like the folks at the gin think about the cottonseed hulls. Give them time and space and after a little while, there will be a lot of things in there that people will really want.

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