[morsch]

In a nice bit of symmetry, another RTG is lost in an ocean trench: The fuel cask from the SNAP-27 unit carried by the Apollo 13 mission currently lies in 20,000 feet (6,100 m) of water at the bottom of the Tonga Trench in the Pacific Ocean. This mission failed to land on the moon, and the lunar module carrying its generator burnt up during re-entry into the Earth's atmosphere, with the trajectory arranged so that the cask would land in the trench. The cask survived re-entry, as it was designed to do,[18] and no release of plutonium has been detected. The corrosion resistant materials of the capsule are expected to contain it for 10 half-lives (870 years).[19]

https://en.m.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliar...

[nafizh]

So after 870 years, it begins to pollute the water?

[AdamJacobMuller]

10 half lives means it will have reduced radioactivity to

(1/2/2/2/2/2/2/2/2/2/1)*100 % of original or .19% of its original radioactivity. Also keep in mind radioactive decay is not even. The faster, thus more dangerous, particles inherently decay faster and will be even more degraded, I'm not going to do the math on it, but, probably another order of magnitude or three.

[thombat]

The connection between half life and decay energy isn't so linear. Looking at a table of gamma ray energies [0] one can see that the lowest-energy distinct five have half lives in hours:

    5994
     104
       6
    2904
  482117

with the highest-energy distinct five in hours:

          12.8
          15.0
           3.48
           1.9
  6280920000    (717,000 years!)

However since the output power is the product of the activity and the decay energy it certainly follows a diminishing curve since fewer decays as time advances.

[0] https://application.wiley-vch.de/books/info/0-471-35633-6/to...

[GekkePrutser]

True but plutonium is pretty poisonous too. Luckily the ocean is very big

[azernik]

After it decays, it's no longer plutonium; instead it's uranium-234. Uranium's heavy-metal toxicity is quite well-established, and uranium-234 is more radioactive than the natural isotopic mix, but at the low-single-digit-kilogram scale involved in the SNAP-27 RTG it's not a major concern.

[freeflight]

> Luckily the ocean is very big

As is the planets atmosphere, which for the longest time served as a justification to pump it full with emissions, that now leave us with a run-away problem at a scale that's still difficult for most people to wrap their heads around.

[azernik]

That's a problem because we're still pumping out emissions. RTG losses have been a small number (under 5) accidents that have probably emitted in total under 10kg of material.

[freeflight]

But RTG losses ain't the only emissions of pollutants into the oceans.

Fukushima is leaking into the Pacific to this day even with Tepco collecting vast amounts of it to store in tanks. The US is dumping the majority of its PFAS into the Atlantic completely untreated, large parts of the world use the oceans as their dumpster, for agricultural, industrial, plastic and all kinds of other waste, to such a degree that we are running out of great coral reefs but instead have great garbage patches.

Yet for the longest time we only worried about oil spills, which are also an still on-going issue in addition to all the aforementioned ones, old ones like the vast amounts of munitions dumped into it, which also includes chemical weapons [0] and possibly upcoming ones like deep-sea mining.

It's mind-boggling to me how we as a collective species can be so unbelievably short-sighted to only recognize these problems once they've already run so far away from us that any attempts at solving them are borderline impossible.

[0] https://www.smithsonianmag.com/science-nature/decaying-weapo...

[garmaine]

Source? Other than the radioactivity, plutonium isn’t any more poisonous than other heavy elements, afaik. And it’s not a lot of material.

[klodolph]

I think the comment is referring to the heavy metal toxicity, which is presumed but poorly studied in humans.

[garmaine]

Yeah but we’re talking about a small amount of material. There’s probably more lead in the electronics you use. Dumped in the ocean, it’s nothing.

[bigbubba]

One RTG is nothing, a handful of whole nuclear reactors have been dumped into the ocean before (a few of the accidentally, and a few of the deliberately.)

[WarOnPrivacy]

Adding Fukashima and dozens of nuclear tests. It's like we tried to chemo the ocean for 30 years.

[ac29]

Ocean water already contains 4 billion tons of uranium: http://large.stanford.edu/courses/2010/ph240/gorin2/

[mattr47]

And then we get Godzilla.

[morsch]

Most of it will have decayed into Uranium-234, which will pollute the water. If the container really contains it for that long. Fortunately the ocean is really big.