I was perusing United Nuclear’s website one day (created by the guy who put Area 51 one the map, Bob Lazar) and I noticed that two of the items they had for sale were samples of heavy water and samples natural uranium metal. What would happen if you put the uranium in the water? My guess is nothing, but I was wondering if it would be dangerous to do so.
Thanks,
Rob
Heavy water is not radioactive, if that’s what you’re getting at.
It is often a mixture of water molecules, some of which have a different isotope of hydrogen than regular water. You can get pure D20 commercially.
As a result, the spin of the “heavy” hydrogen can be tracked differently than regular water in NMR/MRI type machines, for example. But it is not unstable, so not radioactive.
Plutonium, and less so uranium, are pyrophoric. They spontaneously combust when exposed to oxygen or water. It would be more dangerous to have a powder submersed in the water, both due to a higher surface to volume ratio, and the higher potential for uptake. When working with Pu or U in gloveboxes, they are filled with argon to prevent forming Pu0[sub]2[/sub] or UO[sub]2[/sub] (I believe it’s UO[sub]2[/sub], but I do a lot more plutonium research than uranium) with either oxygen in the air or oxygen in water vapor. I don’t know how it would react with heavy water, but I suspect it would be similar. Glovebox fires are one of the biggest dangers our facility faces, and quite a bit of our safety basis is devoted to fire suppression systems.
ETA: When I say uranium is less pyrophoric, I mean that the reaction is less violent, but it’s still a serious hazard.
You would get wet uranium.
Your guess is spot on. It wouldn’t be dangerous.
Heavy water is a very good neutron moderator, i.e. it slows neutrons down. If you divide your natural uranium into smallish pieces and separate them in heavy water, then the occasional neutrons they kick out will be slowed down by the water. This makes these neutrons more likely to trigger atomic fissions if they hit one of their neighbouring bits of natural uranium. Which means the very small neutron emmision from the natural uranium will increase by some trivial percentage, as each fission kicks out a few more neutrons. But this still isn’t dangerous.
If you get a real large amount of natural uranium, devide it appropriately, immerse it all in heavy water at the optimum spacing, you get more neutrons generated by fission inside the arrangement than escaping. The number of neutrons then increases rapidly, and you have a nuclear reactor. This IS dangerous. It also the design used by Canada in their CANDU reactors.
matt, it wouldn’t combust like it would in regular water?
To be honest, I’d forgotten about the pyrophoric factor! But probably not, even in regular water, unless you divided it quite finely. These guys have a comment in their safety section: follow the “Detector description” link, then “Safety at ZEUS”.
From: Chemical Reactions of Uranium
“With water uranium behaves rather passively [20.5.3]. Burning materials in the presence of uranium can be quelled by water.”
“Passive” behaviour in this context probably refers to the tendency to form a protective oxide layer that slows or prevents further reaction, like aluminium and chromium do. I couldn’t check their reference though - the references list isn’t there any more.
Right. In our safety basis documents, we always assume worst case scenario. IMHO, we go overboard with our conservatism in many cases. It’s better than the alternative, but it puts me in the mindset of always having a fine powder that instantly reacts completely with oxygen. The worst possible theoretical case and the realistic scenario are very often quite different.