No, nuclear was never considered a renewable source of energy. It’s low-carbon, maybe.
Look, HN loves nuclear. You’ll find people here who propose running an actual nuclear reactor in every backyard. You’ll find excuses why the Sowjets were obviously incapable of securely running a nuclear plant, but capitalist societies can do it without a hitch. Then, two years later, you’ll have people telling you the Japanese were obviously incapable of running a nuclear plant, but France is obviously different. Plus, the Green conspiracy has somehow thwarted the breakthrough of cold fusion pebble bed thorium reactors, but now it’s just around the corner.
Meanwhile, in reality, it has simply become economically unfeasable to build nuclear reactors. Solar and wind are doing their version of Moore’s law. Batteries, and other storage technologies, are taking a bite out of the storage problem. Smart grids, combining load variability and harnessing end-user storage capacity for grid storage are basically there.
Your suggestion of throwing nuclear waste into the most corrosive substance available in quantity (sea water) nicely demonstrates this naïveté. There’s a post on the front page right now that shows that low-grade radioactive exposure has literally killed hundreds of thousands. Just because you can’t see it, and it was once the darling of science fiction, does not mean it won’t kill you.
Nuclear plants are only economically unfeasable to build because coal plants still are. The world is still building lots of coal plants all over the place (lots in my backyard - China is building lots, and now Japan is planning on replacing their nuclear with coal). If coal plants had to pay for the externalities of their generation you would see more interest in nuclear.
I've always thought the negatives of nuclear were less economic than other factors (though the high fixed capital costs might be an unattractive model in some cases). The worst case scenario for a nuclear accident is pretty frightening to a lot of people. While it may be true that overall fossil fuels are more dangerous in the long run, people tend to overvalue spectacular, high profile failures.
In addition, one negative of nuclear I don't see come up on HN very often, is that nuclear power plants pose an extra risk in regards to nuclear proliferation and terrorism concerns. I do think that some of the recent decline of nuclear is, in part, geopolitical. You don't see groups of nations banding together to stop another nation from building a coal plant.
Speaking of naïveté, it seems that nuclear energy is arguably renewable, and thus “was never considered a renewable source of energy” is at best, naive.
The Japanese reactors were inundated with a beyond-design-basis earthquake and tsunami that killed 30,000 people (zero of whom died from radiation). It'd be tough to argue that they're incapable of running a plant. They just didn't build appropriately for their environment (that plant in particular was designed to be safe from USA tornados...)
Russia, S. Korea, India, & China are building economically feasible reactors right now because they standardized on a design and are building multiple of the same kind. [1,2]
Current batteries are not a feasible solution for leveling large capacity renewables. The 10-day total wind outage that just happened in the US pacific northwest kept 4 GWe of wind offline. The battery to back that would have been 100 stories high on a football field and cost $90B, and would have to be replaced every 20 years or less. Not even 100% renewable superstar Jacobsen [3] (who's suing his scientific critics) suggests using batteries for large-scale load balancing. (He uses hydro with pumped storage, which is actually not a good option due to biogenic methane emissions) [4]
Nuclear waste is a solved problem, technically. You put it in crystalline bedrock, salt deposits, or deep boreholes. The Finns are opening their repository in 2023 [5]. It's a political problem.
There's also very little of it; you're entire lifetime of waste (were you 100% nuclear) fits in a soda can. Nuclear is one of the only energy sources where it's even feasible to consider handling the total waste because of this energy density.
Nuclear is not very renewable since its fuel supply is limited (although very large compared to fossil fuels).
Dumping waste in the ocean is not a great idea, because you can't be sure that fishing grounds won't be contaminated. Nobody wants radioactive fish.
In general, I think the best solution to long-term storage of nuclear waste is to keep it at some facility where it can be continuously monitored. That way, you at least know when something leaks. Unfortunately, energy producers are really good at not paying for that kind of externality.
There is actually a pretty strong case to made to say nuclear is renewable [1]. Basically, there's enough uranium dissolved in seawater that is replenished through runoff and plate tectonics faster than we could ever burn it as a civilization for billions of years. Methods for extracting it economically are very close. See this entire journal issue about the technology [2].
Uranium supply is limited, but there is far more Thorium.
Thorium technology is quite immature at the moment but India and China are developing it, although it'll take quite a while to get to third, or fourth generation level maturity.
There's more Thorium in the crust, there's more Uranium in seawater. With either fuel (plus breeder reactors), the nuclear fuel supply of earth is unlimited on a several billion year timeframe at world-scale.
Here's an entire special issue (from 2016) of Industrial & Engineering Chemistry Research describing progress in extracting uranium from seawater: http://pubs.acs.org/toc/iecred/55/15
Neither does Uranium if you're using breeder reactors. And you have to be using breeder reactors if you're using Thorium because Th-232 is a strong neutron absorber and you can't start a reactor on it at all. You have to breed it up through Pa-233 to U-233 which is fissile. By definition all thorium reactors are breeder reactors. Fertile U-238 can do the exact same thing; instead of U-233 it breeds fissile Pu-239. If you want all the raw details on Thorium check this out [1].
