Eli5: Why do nuclear plants need external power? Couldn’t they just siphon off some of the power the plant makes to accomplish the same tasks (like an alternator running the electrical components in a car)?

Question

Eli5: Why do nuclear plants need external power? Couldn’t they just siphon off some of the power the plant makes to accomplish the same tasks (like an alternator running the electrical components in a car)?

In: 2

Answer 1

Yes, they can and do.

But if there’s a failure they still need power. Need to power valves, control systems, cooling water etc. They also need power just to start up.

For obvious reasons you don’t want things to stop working in a nuclear plant if there’s a failure inside, so they need backup power.