Fukashima: The Effect of Sulphuric Acid on Plutonium?

Using acid to dissolve and draw out the nuclear material is a possibility, but there are complications.
The stuff is currently somewhere under a lake of 80,000 tons of water, possibly in blobs at the bottom of the reactor vessels or on the pedestals that hold the reactors. With the site badly contaminated and the water quite loaded with radioactive material, no one as yet has come up with a way to find the core material, much less remove it. It will probably take decades, judging by the Chernobyl example, where that material is still there, with no plans to remove it, more than 25 years after the accident.

 

In general its a lot easier to deal with solid fuel than aqueous (dissolved) fuel. And that's is a huge understatement. When dealing with solutions that contain fissile material, you have to worry about that solution accidentally going critical. Criticality accidents are significantly more common with aqueous fuel than solid fuel. For instance subtle changes could cause the fissile material to precipitate out of the solution, and accumulate until critical mass is achieved. You even have to worry about the change in geometry of the flow due to pumps breaking. When this happens you go from a vortex volume which has a high surface area to volume to cylindrical volume which has a much lower surface area to volume ratio and is more prone to going critical.

On top of that you have to consider the reactor vessel. If you going to start adding acid to dissolve the fuel, that same acid is going to eat away at the reactor vessel. And you run the risk of creating leaks or enhancing any leaks that already exist. And then after all that what do you do with the accumulated radioactive acid?

It is much easier and safer to deal with solid fuel. We were able to clean up three mile island after its core melted. And we can do the same with Fukushima.

 

I would expect that Pu or Pu compound (at Los Alamos) was dissolved in some apparatus that contained the Pu solution in a vessel. The Fukushima units are huge volumes of not only U and Pu, but other transuranics, e.g., Np, Am, Cm, and fission products. The fuel may have melted or otherwise chemically reacted with seawater, so part of the fuel maybe in the form of rubble, part would be particulates, and some is in solution, or may have migrated into the cement/concrete. Attempting to dissolve the volume in the containment vessel would be problematic, and could actually increase the contamination locally.

If the majority of the fuel is in a solid mass, that mostly excludes moderation. So placing that volume in solution would raise concerns of criticality.