What will happen to US Nuclear Power Plants when a massive solar flare burns out the entire US electrical power grid?

This week, flooding along the Missouri River in Nebraska is threatening two nuclear power plants. In one plant, workers accidentally punctured an inflatable levee allowing flood waters to reach and short out the transformers that powered the cooling system that prevents reactor meltdown. The backup diesel system fortunately worked and maintained cooling to the reactors until the plant could be returned to the grid.

But what happens when the power grid is blown out nationwide by a massive electromagnetic pulse from a solar super-storm? Such coronal mass ejections have happened in the past, and it is a safe bet they will happen in the future. A huge coronal mass ejection in 1859 blew out the telegraph network worldwide, causing numerous fires. It also produced displays of the Northern Lights as far south as Rome, Italy; Havana, Cuba; and Hawaii.

There are 150 aging nuclear plants in the USA, and all of them rely on the power grid being available to power cooling pumps except for brief outages in which back-up systems can keep the reactors cool. What plan exists for dealing with the destruction of the entire power grid nationwide, a catastrophe that would take many months to repair?