I have good news: we have a working nuclear fusion reactor that produces power on the order of 300 septillion watts per second. In their wisdom, its engineers conveniently placed it about 1 AU from the Earth, meaning that all we need to do is catch the energy it's currently transmitting to us.

Presumably 300 septillion Watts (=Joule per second).

And it's true that the sun shines about 100 PW, or 5000x humanity's total energy usage (≈20 TW) on the surface of earth on a nice day.

We are doing that more efficiently with higher levels of CO2

And how would I go about that during Finnish winter?

What do you consider the biggest remaining challenge associated with the nuclear waste problem?

Personally, I think Yucca mountain is a great place to store it in the USA but that will likely never be politically viable. And I'm not sure what solutions exist for nations outside of North America.

I'm also personally still be concerned about transportation accidents resulting in permanently contaminated areas.

Outside the US, Finland's Onkalo repository is on track to be the first operational commercial repository [1]. We have some operating military ones, like WIPP already.

[1] https://www.posiva.fi/en/index.html

As for transportation, this has been a big concern for some time but has pretty rock-solid technical solutions [2]. We regularly ship high-level nuclear waste around (e.g. from nuclear submarines to Hanford) and haven't really had any incidents. I'd claim that the issue is basically solved with these robust containers.

[2] https://www.youtube.com/watch?vW=hlextDSoVkQ

For comparison, we have chemicals like mercury (and much worse) that stay dangerous forever, and we mostly handle them just fine.

There's only a tiny amount of high level nuclear waste.

There aren't technical problems, only political ones.

Yucca mountain has been designated as the long term storage site since 1987 by Congress. Every change of party majority since then has either stopped or restarted work on it.

Hanford has been consuming roughly 10% of the deparment of energy's annual budget for many years and is projected to continue to do so for decades. and the cleanup effort has been fraught with scary mishaps.

Actinide burning reactors are IMHO a better path forward. There are various proposals and research reactors, some using alternate fuel cycles.

The bottom line is the nastiest stuff in spent nuclear fuel are the actinides. They're all naturally radioactive and most of the stuff with long (10,000+ year) half lives that requires long-term storage. You need Yucca Mountain mostly for the actinides. If instead you smash them with fast neutrons you can get them to fission, releasing some energy (though sub-critical) and transmuting them into either much more stable isotopes (little radioactive decay) or really unstable ones (nasty but they decay so fast you only need to hold onto them for a few days/months/years).

The short version is besides reprocessing spent fuel we should be putting the nasty stuff through the sausage grinder again to turn it into much less nasty stuff instead of fighting over where to keep the nasty stuff safe for 100,000 years.

Sure, it doesn't create long-lived waste, but it's a big stretch to assume that fusion reactors will be cheap.

Even if you assume that the fusion part is cheap, you still have to convert the energy to electricity or at a minimum mechanical work (unless you're using the process heat, which is admittedly a possibility for a fair bit of current demand).

Steam turbines aren't exactly cheap to build.

Yes, there are alternative energy conversion possibilities for some possible fusion fuel cycles, but as I understand it those fuel cycles are much more difficult than D-T fusion and therefore are even further away from being a practical power source.