Yes, ingesting plutonium can cause serious problems. I’m surprised that the Indian Government hasn’t commissioned an exhaustive, multi year search for this device. Maybe the snow is too deep? But I can’t see why one couldn’t carefully skewer into the snow, tessellate the whole mountain with such probes and see if it picks up any radioactivity.
Since the stuff could well have melted itself into the snow and ice very slowly, and might have moved laterally considerably, I guess you'd effectively have to skewer a giant, largely vertical glacier down to the rock below, with rocks of all sizes peppered in, using heavy machinery that doesn't exist yet, at high altitude where just surviving at all is a challenge, with lots of very extreme weather, avalanches, rockfall, crevasses, icefall... in a remote area that is hard to access in the first place. That's absolutely herculean. That would almost certainly cost lives. That would be ridiculously expensive. Chances are that Pu won't become a big issue during your term, and it's just one of what must be hundreds or thousands of gambles any Indian (or any other) government must be taking on issues that possibly might become huge liabilities with some small-ish likelihood. Meanwhile, launching such an endeavor because of a few kg of poison at the very end of the world, because it might somehow endanger 200 millions, that's going to be brutally tough. That's a danger that is very far from intuitive. There are legitimate reasons to argue against the endeavor being worth the cost. Probably not the hill PM Modi wants to die on.
Wouldn't thermal vision be better at finding it? Presumably the thing is hot (especially compared to ambient) and should be visible with some advanced thermal imaging solutions?
Indeed. Either this was some sort of fission device (utterly implausible, IMHO - where's the moderator, for just one thing), or the "wave of heat" mentioned in the article is, shall we say, embellishment.
It sounds like the device was being transported in pieces. Each piece would be warm. Assemble it and you have far more concentrated heat. RTGs also work on temperature differential--when operating there's going to be a system to eject that heat to get a maximum temperature gradient. I can easily picture something like a fan blowing air over a radiator to maximize the power output--and there's your "wave of heat".
I take your point about it warming up after assembly, though I doubt it was fan-cooled. This was a SNAP-19C device, primarily used for Nimbus satellites, where, of course, fans could not be used. A manual is available [1], where it mentions an operating temperature of 380°F (193°C) in space, and 260°F (127°C) in the atmosphere (presumably in an environment around standard sea level temperature and pressure; the air near the top of Nanda Devi is less dense but also colder, and presumably it is often windy.) I guess it would be like standing next to an operating stove (though, of course, in mountaineering clothing.)
The manual also warns, when checking it out, against letting the temperature change too fast: no more than 35°F (19.5°C) in 15 minutes. And don't have it assembled without an electrical load, or it will overheat.
Then there's the question of whether the electronics were fan-cooled, but an RTG is so thermally inefficient that its own waste heat must dominate that dissipated by any device it powers.
Yes, this was an RTG. An RTG is not a fission device. An RTG uses the heat from the radioactive decay (alpha decay, in this case, with some contribution from the beta decay of the daughter nuclides, once they have formed) of the fuel. As khuey said above, this cannot be started or stopped.
