[madaxe]

Espionage is not exploration, no matter what your congressman tells you.

The plutonium is for RTGs on benthic listening buoys, which are moored deep in the water column, or anchored directly to the sea floor. They have very sensitive hydrophones, and powerful burst ELF transmitters. This allows triangulation of targets.

They're made of steel and are never intended to be recovered - so we can look forward to plutonium salts in the oceans.

[raverbashing]

If I'm not mistaken the casing of it is very, very hard (even for space missions, where it's designed to whithstand a failed launch and reentry) and takes a very long time to degrade

[madaxe]

Saltwater, astounding pressure and marine organisms make for a far harsher environment than the vacuum of space, or even a botched re-entry.

That said the argument I heard was that by the time they fall apart, the Pu has all but decayed.

[nate_meurer]

The argument you heard is correct. The casings are likely made of something that is completely unaffected by saltwater, the pressures involved are neither astounding nor even interesting in this context, and... marine organisms? Which ones? Harsher than a botched re-entry?

[madaxe]

The casings are steel, the rtg is in a ceramic capsule. You'd be amazed at what barnacles and such can pry wide open given time.