What, roughly, are the characteristics of nuclear power in grid management?

Question

Electric grids are volatile: As there's close to no storage capacity, power in must equal power out all the time. One part of the management toolset is the various power sources attached to a grid. For the most part, it's relatively straight forward to find some "characteristics" governing these:

• Predictable cycles, like day/night for solar. (or tides, winter/summer, dry/wet seasons, etc.)
• Irregular patterns with some degree of forecasts, like wind for wind power and clouds for solar.
• Short therm buffering, like heat in thermal power plants.
• Quick response ramping up and down, like hydroelectric power with magazines and diesel generators.

What these have in common is that they are intuitive and governed by readily accessible physics. Nuclear power is not intuitive. While it's certainly possible to read up, it quickly becomes a journey down the rabbit hole of isotope burnoff, half-lives and an endless sea of details so deep there's little hope of understanding what the end result of it all is.

Nevertheless, I have tried to extract some general "characteristics" from what I have read:

• Some nuclear power plants can do "load following", adjusting power production within minutes or even seconds. Those are apparently more costly to develop, and the majority of existing power plants are not capable of this.
• Most reactors can ramp production up or down over single and double digit hour periods, adapting to for example peak daytime demands.
• Nuclear powerplants are thermal power plants, so they can make use of the same short-thermal buffering of heat.
• There are significant technological differences between nuclear power plants, so their characteristics may be varied.

I am looking for characteristics at the most coarse level such as these (if they are even correct?)

Answer 1

In the US, Nuclear is used to base load the grid.

As implemented in the USA, Nuclear energy has very high fixed costs and relatively low variable cost. So it is in the utility's interest to run their nuclear capacity as close to 100% as they can.

This may be different in places (France?) with a more significant investment in nuclear or other electrical sources that are even cheaper, like hydro. As you said, different plant types have different characteristics, but expect a plant in the US to run full out as often as it can.

As to your specific questions, the only one I can answer is that there is very little thermal capacity in the plant if you turn the neutrons off. The primary plant will cool off extremely quickly if steam is extracted after shutdown.

Answer 2

Re: load following, from Wikipedia

Modern nuclear plants with light water reactors are designed to have maneuvering capabilities in the 30-100% range with 5%/minute slope. Nuclear power plants in France and in Germany operate in load-following mode and so participate in the primary and secondary frequency control. Some units follow a variable load program with one or two large power changes per day. Some designs allow for rapid changes of power level around rated power, a capability that is usable for frequency regulation.[6] A more efficient solution is to maintain the primary circuit at full power and to use the excess power for cogeneration.[7]

While most nuclear power plants in operation as of early 2000's were already designed with strong load following capabilities, they might have not been used as such for purely economic reasons: nuclear power generation is composed almost entirely of fixed and sunk costs so lowering the power output doesn't significantly reduce generating costs, so it was more effective to run them at full power most of the time.[8][9] In countries where the baseload was predominantly nuclear (e.g. France) the load-following mode became economical due to overall electricity demand fluctuating throughout the day.

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Others with this ability include AP1000 (US), CAP1400 (China), VVER1200 (Russia), APR1400 (Korea)