You're correct that the 1970s construction isn't the same as modern construction though. During the 1970s, series of the same reactor designs were built. As opposed to most modern construction, which are typically the only reactors of a given kind built in a given country. Serial production is much cheaper than one-off production.
Electrifying railways and other transportation is going to increase electricity usage, not decrease it. Only about a third of total energy consumption is electric, and most of the rest needs to be electrified as a prerequisite to decarbonization. So assuming that electricity consumption is going to decrease is a very dubious prospect.
I just watched the latest Technology Connections video about heat pumps[1] where he talks about the total energy savings in replacing gas stoves with heat pumps to provide residential heating, with total energy savings up to 5 times. This goes to show my previous point about how “[w]e don’t need to replace carbon power 1:1 if we patch up the inefficiencies of our current energy use.”
So to answer your concern that:
> Electrifying railways and other transportation is going to increase electricity usage, not decrease it.
All else being equal, yes. However we are not going to replace the energy consumption 1:1. Electrical railways have the potential to be far more efficient in the energy use. Especially if you consider the potential increase in traction allowing better track usage which will pull super inefficient cars and lorries from the road and onto the tracks.
Also a minor correction:
> So assuming that electricity consumption is going to decrease is a very dubious prospect.
No, I don’t assume that. However I am hopeful that we can easily decrease our total energy consumption as we electrify. Meaning that if we are still pumping gas to put into our newly electrified infrastructure and consumer systems, there is a potential that we need to pump less of it for the same benefits because of how much more efficient these new electrified systems are over the old fossil fuel powered ones.
Even if total energy consumption goes down, huge amounts of fossil fuel usage in transportation and industry needs to be electrifed. The fact that they may be more efficient doesn't change the fact that they are totally unrepresented in current electrical energy usage. I stand by my point: decarbonization means our electricity usage is going to grow significantly as existing fuel-based energy is converted to electrical energy input.
The labor and logistics situation is also completely different from today then it was in the 70s. Today’s megaprojects tend to go way over budget and suffer significant delays. Land acquisition is more complicated (and again that is a good thing as many building project back then tended to displace a lot of minority residents) and a much smaller proportion of our labor pool are construction engineers. This leads to a longer and more expensive building process. As an example the only two reactors currently under construction have gone at least $10 billion over budget and are 6-7 years behind schedule. And these are reactors in the existing Plant Vogtle in Georgie. I imagine a whole new power plant would suffer even worse logistics problems.
> Plans to decarbonize through renewables assumes that hydrogen storage, thermal batteries, or something else will provide effectively free energy storage.
This is only partially true. Plans also include a significantly more efficient energy usage. People are pressuring governments to significantly increase investments in green infrastructure. This includes more robust energy grid, electrifying railways and ferry terminals, increased building standards for efficient power usage and retrofitting old buildings to similar standards. We don’t need to replace carbon power 1:1 if we patch up the inefficiencies of our current energy use. There are also hopes for better battery technology and carbon capture. A carbon capturing gas burning power plant is not an unrealistic advancement, nor is solid state and molten salt batteries (all of which exist today at varying levels of economic feasibility; none less feasible then new new nuclear). Meaning that we can bridge that ~40% without emitting more greenhouse gasses and without new nuclear.