[Lewis Thomson (OP)]

Stefan asks:

Why not drop nuclear waste (i.e. fuel rods) into an active volcano for immediate destruction/reduction to elements, rather than encasing in concrete and burying it for the next 40 000 years?

What do you think?

[chiralSPO]

Because obliterating and dispersing the fuel rods is the opposite of what we want to do?

[Janus]

Stefan asks:

Why not drop nuclear waste (i.e. fuel rods) into an active volcano for immediate destruction/reduction to elements, rather than encasing in concrete and burying it for the next 40 000 years?

What do you think?

Because is the elements themselves that are radioactive, and dropping them into a volcano would not change this.

[Kryptid]

An eruption blowing a radioactive dust cloud into the sky would be pretty bad.

[evan_au]

Dropping radioactive fuel rods into the top of a volcano is bad news - it would melt the hermetic seal that encloses the fuel rods, releasing the contents in molten or vapor form.

Some of the more dangerous elements are:
- radioactive Iodine, which is absorbed by the thyroid. It boils into a vapor at 184C
- radioactive Cesium which is absorbed into bone and boils at 671C
- radioactive Radon, which is a gas, breathed into the lungs
- Even particles that aren't vaporized by the high temperatures of lava can be carried into the air by hot updrafts.

It is much safer to drop fuel rods into the bottom of volcanoes, by drilling them into the bottom of subduction zones - deep ocean trenches. There they will be covered by sediment, and drawn down into the mantle - only to come out the volcano after millions of years, after much of the radioactivity has decayed.

I guess the main risk here is that a major earthquake/tidal wave like the one that struck Fukushima may crush and disperse the radioactive material into the ocean, rather than gently burying it deeper in the crust.

See: https://en.wikipedia.org/wiki/Subduction

But nuclear fuel rods are a valuable resource - a nuclear reactor can only break down a fraction of the fuel before the buildup of decay products start acting like neutron absorbers, and slow down the desired nuclear fission reaction. It would be like only using half a tank of fuel, then dumping the remainder down the drain, and refilling the fuel tank with new fuel.

Nuclear fuel reprocessing is a dangerous occupation which requires great attention to safety. It also needs good accounting safeguards to ensure nuclear fuel can't be diverted and refined into weapons-grade material. But it offers the potential to extract far more energy from the same amount of ore.

See: https://en.wikipedia.org/wiki/Nuclear_reprocessing