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Comment by Muromec | Hacker News Reader

Well, shutting down nuclear reactor is not a simple process — it has to be actively cooled for weeks after being disconnected, which requires power, which you don’t have because you shut it down. So there should be either on-site generators (burning fuel) or external power . That’s why power stations usually have multiple reactors which are serviced on schedule, so it always has some generation happening.

None of it can be relied on during the war.

Shutting down and not having power to cooldown is how Fukushima happened. Emergency shutdown drill is how Chornobyl’ happened

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> Emergency shutdown drill is how Chornobyl’ happened

And not being informed of well-known (in higher Soviet echelons) serious reactor flaws, like the grafite on the rods being inserted into the reactor core initially spiking the fission process significantly.

Shutting down is a much safer condition than operating. The decay heat decreases massively over time (huge difference between minutes / hours / days /weeks) and gets safer the longer it has been off.

Also if it's online, the electricity needs to go somewhere: any disruption to the electrical grid and it'd have to go off - probably at a bad time. Better to go through the shutdown in a planned manner while the outside situation is (relatively) stable.

What would happen if the grid connection was severed by bombing? Is there no emergency shutdown mechanism where the output is just dumped into some artificial load?

Then again, a 5700MW resistor might require a bit of cooling.

Stoo the turbines and dump the st team/heat into the lake instead?

It's reactor heat -> (heat exchanger) -> steam -> (steam turbine) -> electricity.

If you disconnect the load, you need to stop putting steam through the turbine and dump it somewhere else (i.e. a condenser). All steam turbine plants (including coal) have something similar.

First, reactor protection systems will start reducing power down to 40% nominal if the turbogenerator load disappears (search for URB in https://inis.iaea.org/collection/NCLCollectionStore/_Public/...).

The power would not be dumped into a resistor: the power would be dumped in form of heat with the turbogenerator disconnected from steam. I expect that you can "just" dump it in the condenser and use the standard cooling of the condenser to dump it into the local body of water. If that's insufficient, one can dump steam from the secondary loop into atmosphere (which necessitates adding water there). You can play with a vver-1000 simulator and see how many of these things work; the simulator whose manual I'm citing above can be easily found on the internet.

I was about to mention that reactors often have fuel generators but I remember that the invading force is famous for selling the gas from their tanks to pocket the money…

Given the quality of Russian supply planning and execution it seems as if the biggest danger could be emergency generator fuel supplies getting forcefully repurposed. Good luck doing a safe shutdown...

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