3 ms·

Interesting! I was unaware of the limitations of scaling down nuclear reactors. I had never considered that a surplus of energy is actually a "bad thing" but I

Interesting! I was unaware of the limitations of scaling down nuclear reactors. I had never considered that a surplus of energy is actually a "bad thing" but I suppose without the means to store it its just useless work, or am I missing something? I wonder if the new modular reactors allow to better micro-manage the amount of capacity you are adding to any grid.

pbmonster 3y ago
> a surplus of energy is actually a "bad thing" but I suppose without the means to store it its just useless work, or am I missing something It's more complicated than that. Let's say you have just one reactor powering one city, nothing else. What happens as everyone goes to bed and turns of their appliances? The number of consumers goes down and the amount of electrical power consumed drops. What does that mean in terms of the electrical circuit between the city and the steam turbine? The electrical current drawn by the city decreases. Less current flowing out of the generator connected to the turbine means there is less back-action pushing against the turbine shaft. But the reactor is still producing the same amount of heat/steam - which means the turbine immediately speeds up. Because the turbine is spinning faster, the generator is now spinning faster, so the AC power is not 60Hz anymore but also increasing. With higher RPM on the generator, the voltage also increases. So the city now gets higher frequency at higher voltage. Both are very bad. Long before the frequency reaches 60.1 Hz, grid operators would normally switch on storage facilities or drop powerplants that can easily just shut down (all renewables and fast cycling natural gas turbines can throttle down or just go offline in seconds, but the other fossil fuel plants and nukes take hours). If you can't do that, you need to dump large amounts of power in other ways. And that's not easy. There are load resistors, that just turn electricity into heat. But you can easily burn those with a gigawatt plant, its not easy to get rid of a couple of unwanted megawatt. In theory you could also vent steam before the turbine to prevent it from accelerating. Just turn more of the nuclear energy into waste heat instead of electricity. But that's a really bad idea in a nuclear reactor, because you need to keep the reactor cool at all costs and messing with where the heat flows seriously threatens not enough heat flowing away from the primary cooling cycle - after all, this entire thing is designed for around 30% of the energy flowing to the generator. So doing something like that would mean engaging the emergency systems of the reactor.

pbmonster 3y ago

> a surplus of energy is actually a "bad thing" but I suppose without the means to store it its just useless work, or am I missing something It's more complicated than that. Let's say you have just one reactor powering one city, nothing else. What happens as everyone goes to bed and turns of their appliances? The number of consumers goes down and the amount of electrical power consumed drops. What does that mean in terms of the electrical circuit between the city and the steam turbine? The electrical current drawn by the city decreases. Less current flowing out of the generator connected to the turbine means there is less back-action pushing against the turbine shaft. But the reactor is still producing the same amount of heat/steam - which means the turbine immediately speeds up. Because the turbine is spinning faster, the generator is now spinning faster, so the AC power is not 60Hz anymore but also increasing. With higher RPM on the generator, the voltage also increases. So the city now gets higher frequency at higher voltage. Both are very bad. Long before the frequency reaches 60.1 Hz, grid operators would normally switch on storage facilities or drop powerplants that can easily just shut down (all renewables and fast cycling natural gas turbines can throttle down or just go offline in seconds, but the other fossil fuel plants and nukes take hours). If you can't do that, you need to dump large amounts of power in other ways. And that's not easy. There are load resistors, that just turn electricity into heat. But you can easily burn those with a gigawatt plant, its not easy to get rid of a couple of unwanted megawatt. In theory you could also vent steam before the turbine to prevent it from accelerating. Just turn more of the nuclear energy into waste heat instead of electricity. But that's a really bad idea in a nuclear reactor, because you need to keep the reactor cool at all costs and messing with where the heat flows seriously threatens not enough heat flowing away from the primary cooling cycle - after all, this entire thing is designed for around 30% of the energy flowing to the generator. So doing something like that would mean engaging the emergency systems of the reactor.