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Comment by sandworm101 | Hacker News Reader

Earthquake-prone japan is in a perfect position for deep disposal. Japan is atop a subduction fault. Drill a deep enough hole into that subducting plate and any waste will eventually be pulled into the mantel. If we are really serious about getting rid of things permanently, ie not having access to them for thousands of years, then miles-deep wells backfilled with concrete are very practical. Any future civilization who is building something that many miles underground, miles under the sea floor, probably has the tech to deal with whatever we have put down there far better than we.

Most disposal ideas these days are premised on the idea that one day, maybe, we might want to get access to the material again. They should really call it storage.

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From your username, you might be biased and might know someone who wants the job. ;)

I mean that's a start, but I would vitrify the waste first, then put it in a subduction zone. Of course, they were talking about vitrification when I was briefly a Nuke E.

When containers get breached, they diffuse through rock and soil and reach the surface. French govt estimated that it would reach the surface 400 years after burial (so, 100 years for a breach and 300 years to swim down and up), diffused enough not to cause harm.

So nuclear waste in a subduction zone would require a zone which dives faster than diffusion goes.

Sweden is storing the stuff in a room 500 meters (.25 miles) inside a hill. That isn't deep disposal. Deep is perhaps 5000 meters down, even 10000 meters, maybe also below the sea floor. Down there the rock is warm and flexible. And not in a room but just in the drilled hole. Diffusion back to the surface won't be a problem.

> French govt estimated that it would reach the surface 400 years after burial (so, 100 years for a breach and 300 years to swim down and up), diffused enough not to cause harm.

What kind of waste are you talking about? Long-term stored high-activity radioactive waste is certainly not going to leak its way to the surface in 400 years.

High activity materials decay much faster than low activity materials. There's only so many protons and electrons you can shed.

Regardless of their activity, long-term stored waste is expected to be vitrified and stored in rock formations that are water-tight (in France's case a specific type of clay) and have not moved for millions of years.

It's hard to imagine anything that would lead to radioactive material leeching to the surface or an aquifer in hundreds of years.

Activity matters a lot actually. And predicting long term geological events is the difficult part. Hundreds of years, yeah, not a problem. Thousands and we start getting fuzzy. But this is why I suggested we "pass the buck" in another comment. Meaning to develop better solutions and let our science advance and take advantage of the fact that we can safely store, with modern methods, for several hundred years.

> When containers get breached, they diffuse through rock and soil and reach the surface.

No? Unless there's some force pulling the waste up the contents of a container, breached or not - will move with the surrounding rock. And in a subduction zone, that rock is getting pulled down deeper into the crust.

If the waste is pulled into the mantle near a volcano, wouldn't that be a problem? Maybe no new volcanoes will form in 100k years.

My understanding is that there’s such a vast amount of mantle and it’s generally a liquid so that after the waste “dissolves” in the mantle only a very tiny fraction of it would be brought back to the surface in future eruptions.

Uranium exists in nature, it's how we mine it; if nuclear waste is distributed around the mantel, it may be distributed in part via volcanos, but likely not in quantities like a nuclear test.

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