Question

When the heat wave passes and temperatures become mild, electrical demand decreases. What needs to be done to reduce electricity output in response to this decreased demand?


Left: An enclosed square has 4 orange bars, with green bars between them. Right: the green bars have been partially removed from between the orange bars, which are now glowing red and yellow.

Answer 1

You need to reduce the reactor’s fission rate and/or the turbine steam flow so the generator produces less power.

In the picture you described the green bars are control rods (neutron absorbers) between fuel assemblies. Pulling them out increases reactivity and makes the fuel assemblies heat up. To lower output you do the opposite:

- Insert the control rods further into the core (or add soluble neutron poison where applicable) to absorb neutrons and slow the chain reaction.
- That reduces core heat, steam production and thus turbine/generator output.
- Simultaneously the turbine/governor and feedwater systems are adjusted to reduce steam admission smoothly, avoiding thermal/mechanical stress.
- All changes are done gradually and coordinated with the grid operator following plant procedures for load-following or shutdown.

(For non‑nuclear plants the equivalent actions are reducing fuel/air flow to boilers or gas turbines, throttling steam valves, or curtailing generation.)