Lawrence Livermore plutonium weld observation

Tom shown a weld cross-section with no visible heat affected zone. Material concealed; Tom pinned them down after asking four or five times. Answer: plutonium, very low thermal conductivity. Used to illustrate that HAZ size scales with thermal conductivity.

I once was at Lawrence Livermore National Lab and they showed me a picture of a weld. We were talking about convection in weld pools and stirring of the metal, and they showed me a cross-section of a piece of metal where the weld had no heat affected zone. I said, what type of material is this? I don't see the heat affected zone. They just kept on talking. I asked the question four or five times, they kept on talking, and finally I pinned them down. They said, well, it's plutonium. Plutonium has very low thermal conductivity, so the heat doesn't soak into the plutonium like it does into steel or aluminum. The heat affected zone will be deeper in aluminum or copper, which have good thermal conductivity. Something with almost no thermal conductivity, an insulator, will have a very small heat affected zone. So next time you're welding plutonium, remember you don't have to worry as much about the heat affected zone.