Could one make a Enriched Uranium...sword?

[Ranchoth]

There’s no easy way to put this, so I’ll just say it…could I make a sword out of enriched Uranium?

Say, we’re making a typical “bastard sword,” just with HEU in lieu of Steel for the blade.

Would it be too radioactive to handle safely? If not, would it feel warm to the touch?

How much heavier than a Steel sword would it be? Could an average person even lift it, much less wield it?

Even if it was non-radioactive and light weight enough—which I doubt—to wield, could the metal even stand up to the punishment of combat? Would it be too brittle, or inflexible?

Finally…could you build a working reactor that would use several of these swords as fuel rods? (I’m thinking that fuel rod insertion would be manual…kind of like a reverse “Sword in the Stone” deal.)

So…any thoughts? Aside from that I shouldn’t come up with “smart” ideas after watching anime steampunk?
Well, thanks for your patience,

Ranchoth

[Mangetout]

Heavier metals tend to be quite malleable; I can’t find any plain English information on the structural properties though.

[Desmostylus]

@Ranchoth

How much heavier than a Steel sword would it be? Could an average person even lift it, much less wield it?

Uranium is about 2.4 times as dense as iron. So if your steel sword weighed say 10 kg, the uranium sword would weigh 24 kg.

@Ranchoth

Would it be too radioactive to handle safely?

Yes, but the answer really depends on exactly how radioactive it was, which depends on how enriched the uranium was, how much of it there was, what shape it was, and what other materials were close to it or built into it. And “safely” is not an objective measure anyway. I certainly wouldn’t want one anywhere near me, but the hero in a novel may well take the risk if he’s only going to be holding it for say a few minutes.

@Ranchoth

…would it feel warm to the touch

You could make one so that it was warm to the touch. It wouldn’t be a good idea to be anywhere near it, because it would mean that you had a critical mass, i.e. a self-sustaining chain reaction. That’s a very dodgy proposition, because you could accidentally bring your sword close to a moderator material, e.g. charcoal, which could make your sword supercritical: meltdown or “boom”.

@Ranchoth

Finally…could you build a working reactor that would use several of these swords as fuel rods? (I’m thinking that fuel rod insertion would be manual…kind of like a reverse “Sword in the Stone” deal.)

Definitely.

[kanicbird]

Think of the weight of a lead sword. You would have trouble lifting it. Also using depleated Uranium would be a healthier choice.

[Achernar]

@Desmostylus

Yes, but the answer really depends on exactly how radioactive it was, which depends on how enriched the uranium was, how much of it there was, what shape it was, and what other materials were close to it or built into it. And “safely” is not an objective measure anyway. I certainly wouldn’t want one anywhere near me, but the hero in a novel may well take the risk if he’s only going to be holding it for say a few minutes.

24kg of U-235 has 6.1e25 atoms for an activity level of 1.9e9 Bq = 52 mCi. U-235 produces 4.7MeV alpha particles, so if you absorbed 10% of this radiation, that’s 0.0014 J/s. If you massed 80kg, that’s 1.8 millirads/sec, or 35 millirems/sec. One hour would give you 126 rems of exposure, which will have biological effects. A few hours would be fatal.

However, I’m thinking that there should be some sort of reduction factor since it’s only alphas. Did I leave out a step?

[Mangetout]

@Desmostylus

You could make one so that it was warm to the touch. It wouldn’t be a good idea to be anywhere near it, because it would mean that you had a critical mass, i.e. a self-sustaining chain reaction. That’s a very dodgy proposition, because you could accidentally bring your sword close to a moderator material, e.g. charcoal, which could make your sword supercritical: meltdown or “boom”.Definitely.

I thought a moderator had the opposite effect of, well, moderating (i.e. restricting or slowing down) nuclear reactions.

[Desmostylus]

No. Neutrons from fission are fast moving. Those fast neutrons are less likely to be absorbed by another uranium nucleus than neutrons that have been absorbed and re-emitted by a moderator (in the sense of go-between or interface) and slowed down in the process.

[swansont]

@Achernar

24kg of U-235 has 6.1e25 atoms for an activity level of 1.9e9 Bq = 52 mCi. U-235 produces 4.7MeV alpha particles, so if you absorbed 10% of this radiation, that’s 0.0014 J/s. If you massed 80kg, that’s 1.8 millirads/sec, or 35 millirems/sec. One hour would give you 126 rems of exposure, which will have biological effects. A few hours would be fatal.

However, I’m thinking that there should be some sort of reduction factor since it’s only alphas. Did I leave out a step?

Alphas tend not to penetrate, so they shouldn’t be a risk for external exposure. You’d be depositing the energy in you outer layer of dead skin, or clothing. If you’re a sword swallower, though, it would be trouble.

[swansont]

@Desmostylus

It wouldn’t be a good idea to be anywhere near it, because it would mean that you had a critical mass, i.e. a self-sustaining chain reaction. That’s a very dodgy proposition, because you could accidentally bring your sword close to a moderator material, e.g. charcoal, which could make your sword supercritical: meltdown or “boom”.

I think a single sword is so far from a good geometry that there isn’t much risk of criticality, though if you were wielding it, you are already close to a moderating material - the human body, and all of its water.

As for “boom,” frankly, no. Making a bomb just isn’t as easy as all that.

[Desmostylus]

@Achernar

However, I’m thinking that there should be some sort of reduction factor since it’s only alphas. Did I leave out a step?

Where did you get the alphas from? The U235 goes to two daughters (or more) and some neutrons. It’s conceivable that a daughter could be an alpha. There’s no reason to assume that there are no neutrons emitted and that one daughter must always be an alpha.

[Desmostylus]

@swansont

As for “boom,” frankly, no. Making a bomb just isn’t as easy as all that.

That’s a fairly silly statement. Making something that will explode, if you already have the U235, is very easy.

In an uncontained reaction, like with the sword we’re discussing, everything depends on the mass of uranium involved, the shape and the moderators. At the minimum, your sword turns to molten slag, because the energy being generated by the chain reaction is sufficient to do so. At a slightly higher rate of energy release, the sword gets blown to pieces. At still higher rates, we get Hiroshima.

You could argue that a sword wouldn’t make a good bomb, because it required too much uranium for a given explosive yield, or because it was too dangerous, or whatever. You couldn’t argue that it wouldn’t make a bomb at all.

[Achernar]

@Demostylus

Where did you get the alphas from? The U235 goes to two daughters (or more) and some neutrons. It’s conceivable that a daughter could be an alpha. There’s no reason to assume that there are no neutrons emitted and that one daughter must always be an alpha.

I think maybe we’re thinking about different things. I was talking about the radioactive decay of U-235, not fission.

I realize that 24 kg is well over critical mass for U-235, but I was just using that as example; in practice it would have to be much, much lighter. 10kg is a huge overestimate for the mass of a steel bastard sword.

[swansont]

@Desmostylus

That’s a fairly silly statement. Making something that will explode, if you already have the U235, is very easy.

In an uncontained reaction, like with the sword we’re discussing, everything depends on the mass of uranium involved, the shape and the moderators. At the minimum, your sword turns to molten slag, because the energy being generated by the chain reaction is sufficient to do so. At a slightly higher rate of energy release, the sword gets blown to pieces. At still higher rates, we get Hiroshima.

You could argue that a sword wouldn’t make a good bomb, because it required too much uranium for a given explosive yield, or because it was too dangerous, or whatever. You couldn’t argue that it wouldn’t make a bomb at all.

I think you can argue that it wouldn’t make a bomb at all. Geometry is very important. Nuclear reactors, with a much more efficient geometry, aren’t candidates for nuclear explosions because of this. Even if you had prompt supercriticality, once the material starts to melt, the geometry changes, and all bets are off. Bombs depend on the reactions happening very quickly. Neutron leakage needs to be minimized. You don’t get that with a sword.

Now, if you want to re-cast the sword in a different geometry, then you can start talking bomb, but that’s a different argument.

[smiling_bandit]

Uranium is about 2.4 times as dense as iron.

You could certainly lift it. A good sword can eigh as little as two pounds. Strange but true: they’re not really that heavy. You could even lift a big German Zweihaender.

[AndrewL]

What about the mechanical properties? Does uranium hold an edge well? Is it malleable, brittile, or tough? If you whack something with your uranium sword, will it hold up like a steel sword would, or will it bend or shatter? This will help determine the minimum weight for the sword - part of the reason good swords can be made suprisingly lightweight is because they’re made from very good, high strength-to-weight steel alloys.

[MikeS]

Uranium shavings are pyrophoric, meaning that they have an annoying tendency to burst into flame when exposed to air. This site seems to imply that the same thing will happen if the surface is allowed to oxidize (which it apparently does quite readily.)

On the other hand, a sword that spontaneously bursts into flame might be kind of cool, too.

[Pop1]

@MikeS

Uranium shavings are pyrophoric, meaning that they have an annoying tendency to burst into flame when exposed to air. This site seems to imply that the same thing will happen if the surface is allowed to oxidize (which it apparently does quite readily.)

On the other hand, a sword that spontaneously bursts into flame might be kind of cool, too.

I don’t know about that. We had some pieces of depleted Uranium sitting in stock where I used to sell specialty chemicals. We never had any problems with them bursting into flame.

Depleted Uranium is used as shielding for tanks and such, and so I doubt it would be brittle. Things that break apart easily make poor armor.

I can’t say what kind of edge it would hold, though.

[Wesley_Clark]

Depleted uranium would be a better method. its obviously easier to come across than enriched uranium, and its also 2.5x as dense as steel. Plus depleted uranium is already used in weapons.

[Umbriel]

Here’s a sample Bastard Sword, with weight given as 3.1lbs (1.4kg). A Uranium sword would therefore weigh approximately 7.4lbs (3.4kg). Probably very awkward for a real swordsman, but nothing you couldn’t get accustomed to with training. It wouldn’t make for very deft parrying, though. Mighty barbarian warriors or evil Witch Kings (loved that morning star in ROTK, BTW), of course, wouldn’t be unduly inconvenienced.

This source asserts that U238 is normally slightly softer than steel, which is at odds with this site, which asserts that it is the second hardest common metal known, after Tungsten. Even given that the depleted uranium used in projectiles is subjected to a classified hardening process, it seems to be an open question just how hard the enriched uranium sword would be.

Of course, a sword slightly softer than steel would still be a pretty effective weapon. The Romans and Greeks did fine with iron and bronze, after all. Moreover, the increased mass of the uranium sword would make it cleave that much more effectively. If, as a natural characteristic or due to alloying or hardening, the uranium sword is also harder than steel, it’d likely perforate armor wonderfully.

The pyrophoric quality of depleted uranium only kicks in at about 500C. It enhances the effect of high velocity projectiles, which easily reach that temperature on impact, but would not make much difference to a sword. Granulated uranium’s pyrophoric qualities are accentuated, presumably because of increased oxygen exposure, and even friction. A sword would likely develop a “patina” that would limit further reactivity. However…

Another quality that makes depleted uranium desirable in projectiles is “adiabatic shear banding”. I.e., it’s self-sharpening. A uranium sword might therefore hold a wicked edge. Moreover, the pyrophoric qualities of particles lost on impact with an enemy’s sword or armor would make for a nicely showy spray of sparks, beyond what a sword fight would normally produce.

I’ve heard that even depleted uranium is slightly warm to the touch, so I expect that an enriched uranium sword would be as well, even if no fission activity was going on. All in all, I’d say go for it! Just be sure to wear a lead codpiece.

[BlackPheonix]

@AndrewL

What about the mechanical properties? Does uranium hold an edge well? Is it malleable, brittile, or tough? If you whack something with your uranium sword, will it hold up like a steel sword would, or will it bend or shatter? This will help determine the minimum weight for the sword - part of the reason good swords can be made suprisingly lightweight is because they’re made from very good, high strength-to-weight steel alloys.

Lets stick to depleted uranium. It already has the properties we need.

Ok, just read a lot about it and here’s what I’ve found:

Using uranium would be incredibly stupid, depleted would be excellent. Aside from being absurdly heavy your sword would be considerably stronger and tougher than steel. You’d probably want some sort of alloy just for weight concerns. Any wounds inflicted on your foe might be toxic and definitely radioactive but I’m not sure what affects would be with so little exposure.

On a side note, if you were wearing DU armor you would be virtually unstoppable… presuming you could move. Any kind of DU cross-bolt or arrow (not sure how well the latter would work) would be a formidable armor-piercing weapon.