Ultra Safe Nuclear

Ah, the old "it hasn't happened yet, therefore it can't happen" argument. I'm sure if you honestly think about it you can realize why that argument is nonsense.

> (3 out of the 4 can be intermittent/dependant on environmental conditions and are not reliable).

We're talking here about power for hydrogen production. Intermittency doesn't matter much for that (it requires the electrolysers be cheap, but their costs have plummeted recently, so that's no longer an obstacle.)

> Perhaps I'm unaware of some technological breakthrough which can produce hydrogen using little energy?

Perhaps you could stop using strawman arguments? Hydrogen doesn't have to be produced with little energy in order for hydrogen storage to be viable. The energy that is used just needs to be sufficiently cheap. You know, like that $0.013/kWh power from large scale PV in the UAE? And that's only the latest in a constant string of record low bids.

> Nuclear is great once up-front costs are paid.

Yes, if you can get the Nuclear Fairy to wave a magic wand and make the power plant appear for free, it's much less expensive (but even then, the operating costs will be much higher than renewables). In the real world where real money has to be paid to build nuclear power plants, not so much.

> I have pondered whether it would be possible to generate hydrogen more cheaply via concentrating solar or geothermal.

Neither of these are competitive with PV now. Hell, it's now cheaper to make domestic solar hot water with PV and a resistive heater than it would be to use solar thermal collectors (although a heat pump water heater would be cheaper still). PV has gotten THAT cheap.

About land area: you said this "I'm making the claim because it is painfully obvious that unless you're making calculations about spherical cows there's nowhere near enough resources, surface, and specifically predictability to have renewables be more than marginal for a long time." If land area (which I assume is what you meant by "surface" there) isn't a showstopper, why did you list it? But thanks for admitting now that it isn't a showstopper. I consider the point conceded and that part of your claim retracted.

> Ad hominem

Argument from authority can be met by impeaching the credibility of the authority.

> So you ignore the IPCC reports?

Show me in the IPCC report where it supports your claim "it is painfully obvious that unless you're making calculations about spherical cows there's nowhere near enough resources, surface, and specifically predictability to have renewables be more than marginal for a long time." I'll wait.

> No. In a fast reactor the prompt neutron multiplication time is an order or magnitude faster than in a thermal reactor, but still several orders of magnitude slower than in a weapon.

One could still have prompt supercriticality. So, even if the neutrons are slower than in a weapon, they are still much faster than in a thermal reactor, so the doubling time could be much shorter. There's also the possibility that, because the core contains tons of plutonium, the rearrangement driven by the supercriticality could cause the arrange to become MORE reactive, not less (this may be unlikely, but it's very hard to rule out in any possible accident.) Edward Teller famously warned about this issue back in the 1960s.

For this reason I suspect that nothing but a fast MSR could be licensed in the west.

You will note that the French have now abandoned Astrid, which was to be their next attempt at a prototype fast reactor. It's so distant now that it's not worth keeping the expertise around.

Renewables have only recently become competitive (or more than competitive). This has happened so fast that existing generating capacity is still largely the old technology. Those old technologies will only be ripped out when their OPERATING costs are greater than the full cost of installing renewables to replace them.

That this old technology is still there doesn't mean it's competitive on a clean sheet basis, it just means it's not worth ripping it out yet.

The rapid decline in renewable prices leads to some interesting contrasts. In the UAE, for example, they are now bringing some Korean reactors online that were green lighted about a decade ago. They will produce power for somewhere around $.08/kWh, perhaps a bit higher. At the same time, contracts have been signed for a large PV field there that will sell power for $0.013/kWh. If they had waited on those nuclear plants and just built PV now they would have come out ahead.

What you want to look at is where new money is going, when new generating capacity is needed (and remember, power demand has been flat in the US for a decade). Renewables are taking a large share of that, and would take a larger share (in the US) with nonzero CO2 taxes.

But more importantly, my comment was about how there are a lot of emission factors outside energy production that matter a lot in the discussion of climate change and ignoring that makes it difficult to solve the problem.