Uranium-Plutonium alloy?

Suppose a worker at the nuclear bomb factory was gathering up the leftovers from a production run and noticed he had a sub-critical amount of U-235 and another sub-critical amount of plutonium.

Could he just melt the two metals together and end up with a sufficient amount of fissile material, even though the material isn’t a single pure element?

“Hey … You got Uranium in my Plutonium!”

“Hey… You got Plutonium in my Uranium!”

Plutonium and Uranium — two fissile metals that go great together!


Well…I assume that any worker at a uranium/plutonium refining plant would be under more supervision and have more clearly defined procedures than to simply allow workers to melt stuff togeather as they want.

In any case, in order for a nuclear explosion, you would need a super critical amound of either plutonium-239 or uranium-235 (highly enriched uranium). Regular (natural) uranium and reactor-grade uranium cannot be used to build a weapon. There are other isotopes that can be used for fission, but U-235 and Pu-239 are the commonly used ones.

Just bringing together enough material to be above critical mass does not gaurentee an explosion though. They have to be brought togeather very rapidly and under the right conditions. If a nuclear weapon is destroyed in an explosion or fire, for example, it’s highly unlikely that it would detonate, because in order for it to detonate it woud have to have all ignition points in the explposive initiator detonate in the correct order to create a symetircal implosion effect.

In some cases, if nuclear material is brought togeather in imperfect conditions, such as a flawed weapons design, it will “fissle.” This means that fission begins but the material is blown apart or depleated before a full-sized explosion occures. However, it may cause a small (by nuclear weapon standards) explosion.

Even if you didn’t have a full-scale explosion though, it could easily kill you. I heard a story about a worker during the manhattan project who accidentally brought togeather enough material for it to become supercrtical. Eventhough it fizzled, it instantly killed him by producing a super-intense pulse of neutrons and gamma radiation.

AS far as using uranium and plutonium togeather. Theoretically, you probably could use them both as fission fuel in a mixture for a weapon, though it might yeild difficult to predict results. There are weapons which contain a uranium and a plutonium component, but not in a mixture. (at least not that I know of). For example, the Teller design for the H-bomb contains a plutonium first stage and a fusion stage with a uranium “spark plug” in the middle.

Also, some power reactors have been run on Mixed Oxide Fuel or MOX, which is a combination of plutonium and uranium, but nowhere near weapons grade. Also, any reactor that runs on uranium for long enough will build up some plutonium in the fuel through breeding of U-238. In practice, this plutonium does contribute to the power of the reactor,


What does that article have to do with the OP? No mention of any plutonium is made.

I think that since plutonium is fissile that adding it would increase the rate at which fission takes place and possibly induce criticality. Whether simply melting them together is a possible real-world event is unlikely, but I’m treating this as a thought experiment.

Any hypothetical alloy of U-235 and plutonium will have a critical mass, so the basic answer is yes.

I don’t see any particular reason why a mixture greatly complicates the matter when it comes to any of the physics. For instance - if offhand - it’s fairly obvious how to adjust the standard simple estimates for spherical critical masses to cover a uniform mixture of two fissile components.
One of these cases where the aspects that are straightforward to calculate get marginally harder and those that are messy to predict were, well, messy to handle already.

Yes, that’s correct. But I was kind of thinking of somebody throwing togeather left over random amounts of uranium and plutonium and then using it for a weapon.

Obviously, if you’re using a non-standardized material which you don’t know the exact composition of, it’s going to be difficult to calculate.

Some nuclear weapons have been made using an alloy of uranium and plutonium. A fission chain reaction is caused by neutrons from a fissioning nucleus hitting another fissionable nucleus and causing it to split, releasing more neutrons. Neutrons released by a fissioning uranium atom can induce fission in a plutonium nucleus, and vice versa, so there’s no reason you can’t mix them.

But I think the hypothetical worker mentioned in the OP wouldn’t be very likely to make a satisfactory bomb unless he really knew what he was doing.

The metallurgy of plutonium is very weird and complicated. It has six solid phases at standard pressure. It is also very prone to corrosion. I’m not sure what you would get if you alloyed it with uranium.

Here’s a cite for what I said above about mixtures of uranium and plutonium being used in nuclear weapons cores: http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html#nfaq8.1.5

From that site:

I don’t think a composite pit has to use an alloy of uranium and plutonium. It could be a uranium shell with a plutonium core, or vice versa. I’ve read references to processes being used to bond the two materials in the construction of a nuclear weapon.

Suppose nothing!
It just isn’t done that way.
Any new operation, mixture, etc. is thoroughly studied, tested carefully, and reviewed before doing it on a larger scale.

I’m pretty sure you’re right and that I was wrong when I said “alloy” in my first post. For one thing, that site says “composite” instead of “alloy,” and it also says on another page that uranium doesn’t form alloys with very many other elements and doesn’t mention anything about plutonium being one of them.

So I think the hypothetical worker in the OP wouldn’t have much luck melting the two together.