I think it's quite plausible that today's dry casks could last several centuries. So, we have a technology that will last as long as it could be intended to. Arguably it's better for our descendants to do this and let them deal with the waste, not needlessly do something much more expensive. Our descendants will not like that we squandered wealth and left them with larger debts or lower growth either. Always consider what else could be done with resources when you advocate their use.

Question 1: How many seconds until its below lethal levels.

Question 2: How many years will it take until the last atom is gone with a probability of 99%?

But sanity checking, we find the same chart on the EPA's website[0] as well as the IAEA's site, which you can then calculate the chain yourself pretty easily (down 2 + left 2 (alpha), diag up left (beta-), diag up left (beta-)).

Maybe you're thinking of U-235, which has a half-life of 7e8yrs? Or U-233 with 1.6e5yrs? These aren't considered stable btw.

[0] https://www.epa.gov/radiation/radioactive-decay

[1] https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html

This is debatable and I don't like to -- especially in a public setting -- give an authoritative answer of "yes" or "no" because truth is that neither of these would be correct.

I'd rather state some of the factors involved and give you the idea that this is complicated and that there are very smart people working on these issues and we have good reason to trust them (rather than trying to reason through the problem entirely by ourselves[0]).

So the question about nuclear safety is not a binary one, and truthfully this is true for any question about safety (or most things!). Instead it is about level of acceptable risk. This can be VERY small and to the point where we just treat it as a binary case (but it isn't!) or certain bounds. This type of risk assessment is quite complex, especially with nuclear, and depends of the __type__ of failure. So this also includes a whole other topic of failure design/engineering (e.g. skyscrapers are __designed__ to collapse in on themselves. Not to make them weaker or to cause them to fail, but to control the way that they fail __if__ they fail. You don't want your building falling over and taking out another building (creating a cascading effect), so if it falls in on itself it is less likely to cause more damage. Bridges are another common example if you want to learn more).

Nuclear safety design is quite complex because of all the ways things can go wrong and our great concern for safety (making this a WELL studied topic and why the nuclear industry is one of the safest, and arguably the safest in terms of power generation. Even including the 3 main disasters). Disasters are complex and I'll bet you most of what you've heard about Chernobyl, Fukushima, and 3 Mile are quite limited in accuracy. This isn't because of dishonesty or malintent, but because of the complexity.

So the big questions about nuclear storage is how long we want to have a high confidence in our storage. Certainly we have a large and abnormal margin of safety in nuclear compared to other industries, but the question is if we want this or not (that's not a question that science answers, that's a public policy question and to answer appropriately we need to be aware of our answers to this question for other comparable industries (which means not assuming or "reasoning your way through it." It means spending time)) There are some people who want the high level waste to be safely stored for tens of thousands of years and under strong conditions such as not necessarily understanding English or our conventional warning signs (there's a whole rabbit hole to go down here![1]). But there are others who think it is fine to have a safety solution that is good for several hundred years and that we should use this as we invent better techniques. With this, we actually have the technology and even use it today. This route would allow us to store waste on site and there's discussion of ways to cheaply and effectively decommission plants ontop of themselves. (FWIW, this is the option I'm in favor of) Part of the reason some want this method is because it's extremely reasonable to believe that we actually want this material and as our technology has advanced in the last 70 years, we've learned how to extract much more energy from our fuel (which means much lower waste products, which means lower length of half-lives on material, which also means we can recycle old fuel and turn it into new fuel. To understand this properly we need to understand how the fuel actually works, but this is another long topic. I'll just say that we use a very small portion of it. And I'll also mention that France gets about 17% of its total electricity from recycled nuclear. Not 17% of nuclear energy, 17% of __total__ electricity[2]).

The last thing I want to say is we have to keep in mind how much material we're discussing here. I think people grossly overestimate this. Here's a picture of __all__ of France's high level waste[3]. All 60 years of it. It could fit in a Costco. This video[4] shows Russia's. Again, all 60 years worth. And it is worth noting that Russia isn't doing the same recycling as France, so all that material is technically still fairly valuable. You should compare this to other industries. This is important when we're considering our risk assessment because the footprint of waste storage is still an environmental concern. And if we're producing 240 metric tons of coal waste every year (many train cars worth), it can put this into perspective because all that needs to go somewhere. While numbers aren't quite that high for renewable sources it is non-zero.

And one more thing I need to stress to people. From the perspective of scientists, there is 0 people pushing for an all nuclear power solutions. That's considered idiotic. It is similarly considered idiotic to push an all solar or all wind solution. The consensus is we need a well diversified portfolio of energy generation and that the right choice depends on where the power is being generated and needed. Also in the opinion of scientists the argument is more often about "should nuclear be on the table or not." (I for one think it should be) But being on the table doesn't mean it has to be used. Given the context of this thread, I'm sure many of you can see that there is likely no reason to build nuclear plants in the American southwest where there is bountiful sunshine and wind[5]. The question is far less obvious if we are talking about the Pacific Northwest or New England. The question also matters when 50% of zero carbon energy in the US comes from nuclear and where in some regions it is the __only__ zero carbon producer of electricity[6] (but that's more complicated, because we can build renewables in those locations, but politics is also an issue. But that is why I keep stressing not pretending to be experts in complex topics because that's how people get deceived. And I'll say that both "nuclear bros" and "anti-nuclear-pro-renewable" crowd often get a lot of things wrong, though their hearts are in the right place. Both typically get the proliferation question wrong as well as the thorium and waste questions wrong. I mean both nuclear and climate are quite complicated subjects, so it's probably unsurprising).

So I don't know if this actually helps answer your question or not.

[0] "our" role on the public side is to decide policy, not science. We can litmus test and should definitely be skeptical of claims but at the end of the day there needs to be some trust somewhere and the question is who you're placing it in. The people that publish tons and tons of papers that aren't actually readable to the average person or the person who writes laws and doesn't know a positron from a neutrino. The world is specialized and we need to make sure we know what our individual limits are.

[1] https://en.wikipedia.org/wiki/Long-term_nuclear_waste_warnin...

[2] https://world-nuclear.org/information-library/country-profil...

[3] https://x.com/Orano_usa/status/1182662569619795968

[4] https://www.youtube.com/watch?v=_5uN0bZBOic&t=105s

[5.0] https://www.nrel.gov/gis/solar-resource-maps.html

[5.1] https://www.nrel.gov/gis/wind-resource-maps.html

[6] https://app.electricitymaps.com/zone/US-SE-SOCO

For the low and intermediate level waste, these probably aren't useful amounts of radiation. Even if you could 100% turn all that energy into electricity. It just wouldn't be that much (the amount to harm your body is actually not that much total energy, because cascading effects. Again, complicated, because type of radiation and where it is plays a significant role (dominating even)).

But for the high energy waste, yes! In fact, France even does this (ironically the US invented the technology). 17% of their total electricity comes from recycled fuel. This is partially why I'm in favor of in situ storage.

But this does get quite complicated. As I've, and others, said, if something is long lasting it probably isn't giving off much radiation. Though, these isotopes typically can be converted into an isotope that will be shorter lived and produce higher energy (in fact, this is part of the whole theory behind nuclear power). In fact, even all that fuel from France that is "spent" is still pretty energetic.

But I should finish by referencing this graph[0]. The differential in y is energy and so you gain energy (electricity) going right to left if you're an element heavier than lead (fission) or left to right if you're lighter (fusion). While the slope is relatively steady, at a certain point it becomes not worth it.

So really there's a lot to consider here but we would need to invent quite a lot of things along the way. Which, is very viable in the next few hundred years (which is how long we believe we can safely store fuel on site).

[0] https://www.britannica.com/science/nuclear-binding-energy

I thought about getting a little bit deeper into the details, but decided to keep it brief. `godelski`s comment expands on the theme for anyone interested.

And all is well!

Don't always assume malicious behavior. We're nerds. Sometimes we just get excited to talk about things we've sunken thousands of hours of our lives learning and get excited thinking others might also be excited with this thing we find cool.

I hope there are things you get a lot of joy thinking about and when given the chance to talk about. I for one always enjoy hearing people talk about their passions (I just hope that passion aligns with dedication).

Essentially, they use optical fiber as radiation sensors on Fukushima. So, while the concern about cloudiness is valid, the reality is that at least some types of optical fibers work okay even there.

Radiation hardening is tricky, there are tradeoffs involved and lots of reasons you might choose different points on the spectrum from "disposable robot" to "robot expected to have a long service life in a radiation environment."