That with full recycling, including partitioning and transmutation. In a once-through cycle it takes more like 10,000 years.

https://www.iaea.org/publications/7112/implications-of-parti...

It might be using different measures of radioactivity (e.g. Curies instead of Watts). I did calculations myself long ago, while studying nuclear power in a university, and it indeed was 300-500 years depending on fuel type.

I'll try to re-do calculations and see what I get.

I'm a professional nuclear engineer (Ph.D. & PE) with 20 years of experience in advanced reactors and fuel cycle. I promise you it's not 300-500 yrs unless you do full recycle with minor actinide partitioning and transmutation.

The publication above shows the graph vs. time in terms of radiotoxicity, which is widely considered to be the key metric.

What'd you use for the calculations? Generally you need to use something like ORIGEN to get it right.

Perhaps I was a bit unclear. The waste will _definitely_ be dangerously radioactive for tens of thousands of years. No questions here.

But in aggregate, it will be less radioactive than the uranium (and its natural daughter products in secular equilibrium) that was expended to produce the waste.

We're aligned on that metric. I'm using the 'less radioactive than the ore from which it was mined' as the metric here as well. It's between 10,000 and 100,000 years.

Though couldn't you get under 'less radioactive than the ore from which it was mined' by just mixing your waste with a big enough quantity of eg ocean water?

No, because this metric is normalized as radiotoxicity per tonne of heavy metal. You could dilute it with lots of tonnes of natural or depleted uranium, I suppose, to game it.

Interesting, thanks!

I guess that specific metric would make heavy water infinitely radioactive?

Don't most of these techniques wind up producing a fair amount of highly enriched products which could easily be used for nuclear weapons? Seems like a big downside at the scales we're talking about.

That's certainly what Jimmy Carter was worried about when he cancelled the USA's national breeder reactor project, the Clinch River Breeder. He then banned reprocessing entirely, but Reagan unbanned it in 1981, so it is at least legal now.

This has been an ongoing debate though. Scientists have developed more sophisticated reprocessing processes that keep all the actinides together rather than pulling out Plutonium on its own. And in any case, the plutonium is reactor-grade rather than weapons grade, (but super-sophisticated weapons designers can make bombs out of any-grade plutonium).

George Bush Jr. tried something called the Global Nuclear Energy Partnership, where existing weapons states would run a bunch of reprocessing plants and contribute fuel to an international fuel bank. Non-weapons countries could reliably get fuel from it and give the spent fuel (aka nuclear waste) back for further recycling/reprocessing/treatment. It wasn't super popular among the 'have not' countries, who didn't want to be beholden to some random fuel bank.

I'd trust Carters opinion on this a lot more. He is a nuclear expert and even personally led a team that cleaned up a meltdown in a reactor in Canada.

It's a very long stretch to say he was a nuclear expert. Actual nuclear experts do not consider him one of us. His policies were pretty damaging to the industry. His hope was that of the US didn't recycle nuclear fuel, then maybe other countries wouldn't. But that was not the case. The UK, France, Japan, Russia went ahead with nuclear fuel recycling anyway.

https://atomicinsights.com/jimmy-carter-never-served-nuclear...

According to this it is true: https://www.snopes.com/fact-check/jimmy-carter-nuclear-meltd...

I suppose a lot of this is still embedded in top secret red tape :(