Spent Uranium?

[heinzir]

The coverage of the nuclear disaster in Japan brought up a question: didn't some around-the-world racing boats in the 80s use "spent uranium" in their keels because it was denser than lead? What made that safe?

[GaryHLucas]

Yes it is denser than lead, by almost TWICE! DU depleted uranium is slightly radioactive, and I'm guessing with 6 feet of water between the keel bulb and the boat provided quite a lot of shielding. But what really got everyone upset was the huge advantage such a keel provided, at a very high level of racing where every little advantage can count.

[Faster]

Eric Taberly on one of his 'Pen Duick"(?) transatlantic racers.. I seem to recall it was a larger boat.. PD VI.

Being 1.7 times as dense as lead, it was 'outlawed' by the racing authorities of the day. Availability (and access) is obviously an issue. As a national hero the French government facilitated Taberly's access.

It would most certainly be radioactive, but if encapsulated in a lead sheath (which is how we protect and use radioactive sources in process measurement) it would likely be safe as long as it stayed contained and intact. - not sure how you'd get anyone to build you one, though!

I think there was another racing boat, since sunk, that had a keel containing spent Uranium ballast.

[seabreeze_97]

Makes great rounds for the GAU-8 Avenger cannon in the A-10.

[steel]

Except for tungsten, uranium is the most dense naturally occurring element which isn't precious (like gold). It is weakly radioactive. It naturally contains 0.72% of the 235 isotope which has a half life of 4,468,000,000 years and decays in to 231Th The remainder in the 238 isotope with a half life of 703,800,000 years which decays in to 234Th, and so on and so on which creates trace amounts of other elements in with the uranium, like radon gas which comes up and in to your basement. The 235U isotope is used for nuclear reactors and weapons. The 238 isotope is much less radioactive but not a whole lot, as you can see from the half lives. Uranium is also flammable in open air.

Depleted uranium has most of the 235U isotope removed so that only has 0.2% of the 235U remaining, so it's useless for nuclear power and weapons, unless you know how to get the remaining 0.2% out. Since it is cheap it is used for things like counterweights and ammunition. They like to use it as ammunition because it is cheap, dense, and burns when fired which will help detonate the warhead on an incoming missile.

Depleted uranium is something like half as radioactive as the natural 0.7% uranium. In depleted uranium I think the majority of the radiation comes from the 238U isotope. Even if it was 100% depleted it would still be radioactive. Those who use it like to tell everybody it is "depleted" and hope you think that they mean that it is depleted of being radioactive, which it is not.

Since uranium is mildly radioactive, it is pretty harmless since it has a very long half life (it decays very slowly) and when it decays it is mostly alpha and beta decay radiation which is easily stopped (I'm not sure if that's true about beta decay). However, it burns. Then you have uranium oxide dust floating around in the air and it gets in your lungs and your body. Even though alpha decay can be stopped by a piece of paper or your skin, once it's in your body that doesn't matter. It is now very deadly, especially to pregnant women and children. Iraq is becoming a nuclear wasteland now because of this. Turkey is complaining that uranium dust is blowing in to their country. It's a really bad situation and the US doesn't have any incentive to care.

[SlowButSteady]

Depleted uranium and spent uranium are two very different things. Uranium naturally occurs as 238U (~99.3%) and 235U (~0.7%), plus a couple of other isotopes only occurring as traces. Depleted uranium has most of the 235U taken out (for use in bombs, reactors, et cetera), leaving about 99.8% 238U and about 2% 235U. As such depleted uranium is not as radioactive as native uranium, but it still releases about 50-60% of the radiation of the native mix.

Spent uranium usually refers to spent fuel rods from reactor cores. These rods are very radioactive, as they have been capturing neutrons while in the reactor core and have all kinds of very "hot" radioisotopes. In fact, plutonium is synthesized in this manner (as well as most of the short-lived isotopes used in medicine and research).

[heinzir]

Thanks for the clarification.