Comment by PaulHoule

It seems obvious that nuclear can not compete against natural gas when natural gas is priced cheaply and the pollution caused by fossil fuel is put on society rather than the operator. A combined grid of renewables and fossil fuels has been the primary strategy in most European countries and was working very well in keeping prices low until Russia invaded Ukraine.

The big problem is that energy prices are set based on the most expensive unit that needs to be turned on to meet demand. Renewables do not tend to be that during periods of low supply, as low supply of energy in the eu market generally means sub-optimal weather conditions for renewables. It is going to be either fossil fuels, nuclear, or battery. If we take out fossil fuels then that leaves battery or nuclear. Neither is very economical without subsidies. Governments (and tax paying citizens) are however very keen on grid stability and thus willing to spend a lot of money to keep it running.

Your reference for [1] just states that bypassing the turbine is a thing, not that it's normally used.

First, reactors are in a stable equilibrium when operating, so one will actually increase their power by increasing the rate at which heat is removed (and v.v.). Alas, that's workable only within some small range.

A reason[1] load-following with PWRs was originally difficult is that traditionally PWRs use boron concentration in primary loop to regulate power and that can be decreased only slowly. The reason it's done that way is that it's the easiest way to ensure that power is adjusted uniformly throughout the core; if instead some control rods were partially inserted, the top part of the core would operate at lower power (and thus lower fuel burn-up) than the bottom part, which would cause compounding control issues later on.

France is using their PWRs in load-following mode by (a) having additional less absorptive control rods ("gray rods") that can be inserted fully to adjust power by smaller increments (b) more complicated schemes to decide which combination of available actuations to use to change power. See https://hal.science/hal-01496376/document for a paper that tries to optimize control designs so that power changes are more possible (and describes how the control schemes work).

Note that the total heat capacity of even just the primary loop in usual reactors is quite large: in PWRs it usually requires ~0.5s of full power output of the reactor to warm it by 1degC, so this can easily cover, say, ~5% variations for something like a minute.

[1] Another is that reactors are not stateless due to xenon poisoning.

I am skeptical that renewables are cheaper than nuclear when one factors in the impossible amounts of energy storage required to make them meet the same reliability guarantees that nuclear (and fossil) can meet - indeed, as far as I know, there exists no proven, cheap, scalable technology to store power at grid scale at all.

Nit: the steam is not released to atmosphere, it is sent directly to the condensers. Treated water to use in boilers and turbines without leaving deposits and damaging them is precious, so it is a closed cycle and not vented to atmosphere whenever possible

Not if the market provides incentives to curtail, which it does with negative pricing. If other energy sources can curtail enough at the same price, they’ll do it. Otherwise nuclear will. The costs you’re alluding to can’t be avoided, but they’ll be spread across the system.

This is all predicated on the market operator actually having the systems in place to signal the need for curtailment effectively, of course. That’s a whole different question.

A nuclear power plant can't just "keep spinning without a load" - all that energy has to go somewhere! If a nuclear plant is disconnected from the grid (tripped), the nuclear reaction must be stopped (eg: by inserting control rods into the core).