Enrichment, or how I learned to stop worrying and love the SWU, part 4
Sorry it’s been so long since I last posted, but since I got on this topic I’ve had to “run the numbers” a fair number of times, and each time that I do that, I remember that we have computers that are a lot better at that sort of thing than I am, so after a little while I break down and start writing a code to “run the numbers” for me. And codes, as you probably know, are no smarter than the guy who writes them, so it ends up taking longer than I think it will.
Nevertheless, here’s a little code I wrote to go along with this series on enrichment. It runs in Java, and most people probably already have the stuff on their computers to make it work. It really shouldn’t matter if you’re running on a PC or a Mac or a Linux or Unix box. That’s the beauty of writing things in Java. And if for some reason you don’t have Java then you can pop over to java.sun.com to get it for free.
Anyways, the code incorporates the results of the equations that I presented in the last two parts of this series along with a few more that I may or may not get into tonight. The computational part of the code took me about five minutes to write. The pretty graphics and the user interface took much much longer. So I hope you like those. They’re there to make things easier for you at the expense of making them harder for me.
What the code shows is a little picture that looks like a Pac-Man eating some cheese. In the default case (isotopic separation of uranium), the Pac-Man represents the fraction of the feed that ends up in the tails. Which is most of it, which is why it looks like a Pac-Man. The thing that looks like a little cheese wedge is the fraction of the feed that ends up in the product. That part wasn’t all that hard to get to work, but what really took a while was the clever little graphics that show a pattern of dots in the midst of blue. Those dots are in proportion to how much of the enriched isotope is in the feed or the product. You can use the slider controls on the right-hand side of the program to change the enrichment values of the tails and product and you’ll see the density of those little dots go up and down in proportion.
I hope you like that. It took a while.
Anyway, you can see just by looking at Pac-Man and his little cheese that in a typical case of uranium enrichment (from natural levels to 3.5% or so) that most of the feed ends up in the tails, and a smaller fraction ends up in the product.
Let’s consider another case of enrichment—near and dear to my heart as an advocate for thorium and fluoride reactors: lithium. In the case of lithium, the isotope we want is lithium-7, which makes up more than 90% of natural lithium. But the problem with lithium is that we REALLY need to make sure that we get that pesky lithium-6 out of our mixture. Even a little bit of lithium-6 will make real trouble for a fluoride reactor. So when you switch the material over to lithium, the product slider in on a logarithmic scale, from 99% to 99.9999%. You’ll see that effect in the “dot density” on the picture and also in the amount of SWU’s required to reach that level of purity. As far as the tails enrichment of lithium, I’m not really sure what it should be, but I know what the product should be.
Another isotope of interest for future chloride reactors is chlorine. Chlorine-37 is the less common (~24% of natural chlorine) but more useful isotope for chloride reactors, and it is likely we’ll need to use high purity chlorine-37 in those reactors. Again, I’ve used a log-scale for the product from chlorine enrichment and a normal (linear) scale for the tails enrichment. For both lithium and chlorine I threw in some guesses as to what the feed and separative work might cost, but the reality is that I have no idea what those values should be. If anyone does know I’ll be more than happy to change the code to reflect those values.
Finally I looked at hydrogen enrichment in order to recover deuterium. This a really interesting case, because deuterium is such a tiny fraction of natural hydrogen that the feed-to-product ratio is CRAZY high. You have to go through a massive amount of hydrogen to recover a little tiny bit of deuterium. You won’t even see it on the graph—it’s so tiny. So it takes a lot of SWU’s and a lot of feed to recover deuterium, and deuterium is very valuable. A liter of heavy water (D2O) costs about $5000 the last time I checked.
Anyway, have a little fun with the program and I’ll tell you more about some of the other interesting aspects of enrichment that I have learned about in upcoming posts.