- waste mgmt
- safety
- proliferation risk
(for uranium-/plutonium-based reactors,
not so much for thorium-based reactors)
- outrageous construction costs
- heat pollution (heat discharge into local waters)
- baseload-only
- slow to blackstart
Thorium reactor designs solve the first three issues only (unless they can be blackstarted soon after a blackout -- do thorium reactors suffer from poisoning?), in which case they'd solve four of the above problems. Or perhaps thorium reactors can be cheap to build? (I'll believe that when I see it, but only then will nuclear [fission] begin go be appealing.)
The only good things about nuclear are that the fuel is cheap (maybe) and it has no air pollution (barring accidents). That's not enough to justify the issues.
There's one more problem: cost per kwh. It might be competitive in the current market (though arguably it actually isn't). But to stay competitive in the future it will need to keep up with mass produced solar/wind continuing to drop in price. It seems solar + storage bids are continuing to break records and are already underbidding nuclear, even before considering subsidies. IMHO, prices will continue to drop over the next years/decades. Bids are currently going as low as 2 cents per kwh in some areas and prices dropping to below a cent might actually happen at some point.
Energy storage is much less of an issue if you can simply produce more than you need to offset e.g. cloudy days and use the excess energy to synthesize any of a wide range of fuels that can be stored, top up batteries, pump water to some reservoir, or power any of the many ways in which we can store energy. People are getting creative when it comes to energy storage. Energy storage cost is dropping rapidly as well.
Nuclear doesn't just need to get safer, it also needs to get vastly cheaper to keep up with this. IMHO if you are not designing for half a cent or less per kwh, you might as well not bother. My understanding is that current designs are off by factor 10 at least. At those prices, even the security needed to protect the facilities will be prohibitively expensive.
Safer designs are the result of safety regulations, if you lift those regulations you will get less safe reactors. They might be cheaper but also less safe.
I think you misinterpret what I was saying. An actively cooled core needs lots of safety measures in place in order to make sure that the water pumps never fail, or if they do there are backup systems in place, and backup systems for those backup systems, etc. There's a physical cost to making all those mechanisms. Furthermore there is a regulatory and administrative cost to ensuring that those mechanisms would work across the entire industry.
On the other hand, something like the NuScale design takes an all-passive approach: it places a smaller fission core directly in a massive swimming pool that has enough water to passively cool the design all the way down. There are no moving parts to switch on in the case of failure. The way you handle a catastrophic failure is: you do nothing. It solves itself.
No moving-part safety mechanisms to install, just a big tank of water. No fallback mechanisms for those safety mechanisms, etc. Inspection is pretty easy: did the water level remain in range? Yes/no.
Cutting costs of safety inspections due to an inherently safer design doesn't mean a less-safe outcome.
For reactors built here a significant part of cost is plain mismanagement, corruption and/or profiteering. This results in costly and less-safe reactors.
Partially this is certainly true and it is easy, since everybody assumes that the costs will increase, nobody is surprised that the reactor which should have costed 3 billion euros will cost over 10 billion euros in the end.
For a technology where the prices are decreasing, this is harder to do.
The only good things about nuclear are that the fuel is cheap (maybe) and it has no air pollution (barring accidents). That's not enough to justify the issues.