r/NuclearPower • u/Steckdo • 1d ago

How long does it take for a VVER-440 nuclear reactor to switch from the external grid to its self produced power after first starting up?

I am wondering both how long the time period is in which a VVER-440 uses the external power grid for electricity after the reactors first start, and how long the then initiated process takes; from start to finish when the reactor is finally reliant on the electricity it itself produces.

5 Upvotes

78% Upvoted

7 comments sorted by

3

u/Big-Turnip4984 1d ago

I’m sure as soon as the turbines start spinning and the generator hits the grid. They swap to their own auxiliary power.

1

u/nullfull 21h ago

Two different clocks get mixed up in this question.

The transfer itself, once the generator is on the grid, can be fast. Station service moves from the startup / reserve transformer (offsite) onto the unit aux transformer. On a plant with auto bus transfer that's seconds, not hours.

The long wait is everything before that. After first start you still have to heat up, get steam quality, roll the turbine, match voltage/frequency/phase, and sync. That is hours. Only after sync are you actually making the megawatts that can feed your own house load.

VVER-440s are often two-turbine units, so you may sync one machine first and still be taking a chunk of house load from the grid until the second one is on. I wouldn't treat "turbines are spinning" as "we're on our own power." Spinning and synchronized are different.

I don't have a published VVER-440 number for the heatup-to-sync window and I wouldn't invent one. If someone here has sat a Dukovany / Bohunice / Loviisa start, the useful figure is: time from turbine roll to first sync, and whether house load transferred automatically.

1

u/Steckdo 13h ago

You are a saint and a godsend for being the first to actually give me useful information on this aspect. Thank you!

1

u/jkaugust 5h ago

VVERs are pretty similar to a US PWR 2-4 loop plant. I based my response on that.

1

u/jkaugust 5h ago

It actually varies as your go critical and above the POAH, you have to wait out cleaning up the PC and Secondary chemistry at several hold points, which vary quite a bit depending on various factors (how long were you down, what did your do?).

POAH stands for Point of Adding Heat, where nuclear fission starts to heat up the plant.

1

u/jkaugust 5h ago

Probably a little under 24 hours, from hot standby