That’s because U-238 is also radioactive, though only about one-seventh as much as U-235.
According to Matweb, Uranium compares poorly with a decent steel alloy. It’s slightly less hard, has significantly worse tensile strength, and has almost no ability to elongate without breaking. This, along with the much greater density, makes for a poor choice for a sword; it’ll be much more likely break if you actually use it to hit something.
The Matweb site doesn’t state if the properties given are for natural, depleted or enriched uranium, but it probably doesn’t matter. Having the same electron valences and nearly the same weight, U235 and U238 should have nearly identical chemical and mechanical properties.
But, if the hero had already mutated from contact with radioactivity, there’d be no additional problem.
When people ask me why I love the SDMB, this is exactly the sort of thing I mean. The strangest, silliest questions provoke the most interesting and thoughtful discussions. Where else would an inquiry about a sword made out of — heh — uranium — heh heh — provoke such a technically detailed roundtable?
Sorry to gush. Please continue. 
Amen. I couldn’t get this thread open fast enough. I’ve been wondering about the possibility ever since I read an adventure/fiction/potboiler novel, where the solution was a bit like Colonel Mustard in the Library with a hot sword. I can’t think of a way of naming the book without spoiling it, but wondered if the OP had a novel in mind when he asked the question.
Depleted uranium most assuredly does not have the properties we need. The OP wants the sword to be radioactive. He wants to be able to start up a nuclear reactor by sliding the sword into a slot. If we didn’t want a radioactive sword, we’d just use steel and be done with it.
The real question is how effective we want this thing to be as a sword. Is the protagonist going to be regularly engaging in heavy swordfights, or is he just going to draw it and everyone cowers in fear? The latter isn’t too implausible… It would be very easy for a radioactive weapon to develop a reputation for being cursed. Additionally, in the event that it breaks in combat, would the mystique of the scenario allow for the blade to be re-forged? It’d still be uranium, so all of the “interesting” properties would be maintained.
Nit pick - that’s a longsword. 
Depleted uranium used in a rotor:
http://www.cartercopters.com/High%20Technology%20Gyroplane.htm
(scroll about half way down, or search on uranium)
I’ve lifted said rotor (one blade), it is doable, but required effort.
Brian
Well, they called it a Bastard Sword…
Noodling around elsewhere in that site, I find that our uranium bastard/long-ish sword would weigh about as much as a two-handed sword, so it would definitely be wieldable, it would just be a bit short for normal two-handed maneuvers and tactics.
I also see that I screwed up one of the links in my earlier post. The source asserting uranium as the second hardest common metal is here.
Well a great sword can weigh from 5 to 8 lbs, so yes, it would come in at the top of the scale there. BUT the reason such weapons are easily wielded is due to their point of balance and blade shape.
That much weight on a smaller sword might make it unwieldly even if it does weigh the same as a greatsword. Most likely the blade geometry and shape, probably the whole design would have to change.
I assure you a 3ft 8inch sword is well into the Hand-and-a-half range unless you’re Shaqile O’Neil.
Hence, why it is a longsword.
Longsword (langeschwert, spadalonga, etc) is a long blade with a full hilt that accomodates two hands.
The bastard sword is smaller and usually posseses a hilt that accomodates 1 and a half hands It’s a tight fit for two-hands. It’s basically an arming sword for either 1 or two-hands. Usually the blade tapers sharply into a point at the end.
You might be getting your definition of ‘longsword’ from D&D or role-playing.
I’d envisioned the sword—well, swords, for a reactor—as being something like a holy or royal relic (kind of like the Sword of Temporal Justice or it’s siblings, held in the Tower of London) It wouldn’t be the hero’s normal sword, just one that he was ferrying from one place to another. Though he might draw it to use in combat in a a desperate situation—like if he was caught off guard, without his own sword. Or even if he wanted to make a point of overawing someone. But he wouldn’t even know was radiation was, much less that that was the danger the sword presented.
And, that being said…could a special shielded (with Lead, or maybe even Gold?) scabbard to keep the Uranium sword in, to help protect one from the radiation? Or would a scabbard built hefty enough to provide meaningful radiation protection just be too heavy to carry?
And Cervaise, koeeoaddi? Double amen to that. Triple, even. Thanks for the replies, all!
No, there is no such real thing as a “longsword”. I have found no contemporary account in Europe that anywhere describes a longsword. And modern commentary is decidedly mixed. That particular length is built such that it could be swung by one hand, if I understand correctly, but it’s designed to be used by two for most people. Which is the definition of a bastard sword. The specific length of the hilt is irrelevant - ones intended for use in battle would probably have been built for a given user, anyway. There is no absolute gospel about swords.
[QUOTE=smiling bandit]
No, there is no such real thing as a “longsword”.
[QUOTE]
Incorrect. The term was commonly used to describe the weapon I mentioned during the middle ages and the renaissance by fencing masters during these periods. I’m tempted to say master Lichteneur and Ringeck and all the others knew what they were talking about.
It is true that through out time the term was applied to any weapon with a long blade. The Roman’s calvary sword (very basically a larger version of the gladius hispanicus) were termed ‘longswords’.
Then you are not looking hard enough. In my studies as a historicla fencer I’ve come accross the term (Spadalonga, langeschwert, etc) many a times. I have trained to use the weapon, I’d be very embarrassed if I couldn’t even use the correct term for it.
It is true that swords varied widely in design and length as well as other factors were sometimes tailored to the intended user. But the general terms for these weapon still applies as a way to identify them, their method of use, and their purpose on the battlefield.
A longsword, as I explained (and is pictured here: http://www.schwertkampf-ochs.de/willkommen.html) are well defined in the fechtbuchs or fencing manuals of the high middle ages. The sword was used two-handed but could also be used one-handed when mounted.
Here’s an exmaple of a bastard sword: http://www.armor.com/2000/catalog/item081.html Notice the blade shape, and the hilt, which accomodates 1 hand and a half.
Capulet probably shouldn’t have called his wife “Ho”…
Doh! Sorry for the sloppy coding.
Argh! not only sloppy coding but the wrong link. This is a bastard sword: http://www.atar.com/pics/Bastard1.JPG
The ‘bastard sword’ I linked to originally is actually a german longsword. Whicih goes to show that not every armorer knows what their talking about. And that although some terms may be interchangeable, some aren’t.