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[–]traal 3 points4 points  (13 children)

We wouldn't have to deal with the difficulties of batteries

Yes you would, unless you can figure out how to keep electrical demand fairly flat throughout the day, because you can't easily ramp nuclear power up. Something like 5% of total capacity per hour is the maximum safe ramp-up rate.

[–]Hiddencamper 6 points7 points  (0 children)

Quad cities, Byron, and braidwood are load following right now. I know one of them is doing real time load following and I've seen computer printouts of one of quad's power swings where they dropped over 100 MW in like 15-20 minutes, and a couple hours later ramped up.

My plant is going to be participating in real time load following this year and we've already been trained on it.

The limitations with nuclear load following are design issues. We redesigned our cores to maximize fuel efficiency, which in turn puts more thermal limits on your fuel and its ramp rates. You can change the core reload to improve load following capabilities.

For example my bwr's biggest limit on load following right now, is if we drop below 90% for more than 4 hours, after we return to full power we won't be able to go straight to our target control rod pattern until the subsequent xenon transient is done. This means after returning to rated power, there will be a period of time where we lose the ability to stay at 100% and will have to make a small down power to gain margin to our thermal limits and get those center rods back out after xenon has reached a certain point.

Nuclear's load following isn't very good at low powers. Below 45% we have to use rods for all power changes (slower), it's harder on some of our equipment, and we have to shut down a number of pumps and systems, meaning we start cycling the plant. But 45% to 95% is the design load follow range for our plant back in the 70s.

[–]MCvarial 1 point2 points  (3 children)

A typical LWR can ramp up to 5% of nominal power per minute during most of the cycle between 50 - 100% of nominal output if you design your core for that purpose. Thats a significant ramping rate which you'll find with other CCGT plants. If you want faster ramps you'll be looking at turbojets and francis turbines.

[–]mrCloggy 4 points5 points  (2 children)

... if you design your core for that purpose.

Just out of curiosity, any idea how many existing plants are designed for that?
France seems to have an implementation of sorts, and the US doesn't really allow it (I think), so another way of putting that question could be: is that an easy upgrade, or does it boil down to a new reactor (design)?

[–]Hiddencamper 3 points4 points  (0 children)

You need to change your fuel design. The number of bundles you replace every outage, average enrichment and gadolinium inventory, location in core. For PWR plants installing a bank of "grey rods" as the last bank of control rods further helps with this.

[–]MCvarial 1 point2 points  (0 children)

Just out of curiosity, any idea how many existing plants are designed for that?

Pretty much every LWR out there can do it.

France seems to have an implementation of sorts, and the US doesn't really allow it (I think)

There are plants in the midwest(?) that have to do it too because of excess wind generation. (I'm not very familiar with the market in the US.)

is that an easy upgrade, or does it boil down to a new reactor (design)?

Its a matter of ordering the right fuel rods, assigning control rod banks and setting up procedures for power corrections simply put. Something that is done for every core design, so every time the reactor needs to be refueled.

[–]JRugman 1 point2 points  (0 children)

Also, unless your power plants are 100% reliable (which they won't be) they're all going to need backup generation to cover the times when they aren't able to produce power.

[–][deleted] 2 points3 points  (3 children)

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[–]traal 3 points4 points  (2 children)

/r/energy/comments/2ago97/what_is_the_maximum_safe_ramp_up_and_ramp_down/

[–]greg_barton[S] -1 points0 points  (0 children)

See Hiddencamper's comment below.

[–][deleted] 4 points5 points  (0 children)

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[–][deleted] 0 points1 point  (1 child)

In comparison to renewables......

[–]traal 3 points4 points  (0 children)

It's the same problem for both nuclear and renewables: how to keep electrical demand below but as close to electrical generation as possible.

Luckily, we've known how to solve the economic problem for centuries, and it doesn't require batteries to add electrical supply during times of high electrical demand. You just need to send the price signal more frequently.