Would the fuel efficiency be sufficiently bad to make the fuel costs relevant to the cost of running the plant, though?

Yes, it would. Fuel is around 2-4% of the total costs for a regular nuclear power plant, but that's because regular reactors can burn it deeply. This reactor will only burn a couple of percents of the available fuel, so the fuel costs will probably be around 10-20 times higher.

BTW, this tradeoff can be acceptable for some very specific applications. Kilopower ( https://en.wikipedia.org/wiki/Kilopower ) is designed to use passive regulation.

The water column is isolated fron the fuel. The weight of the water column just allows for a cheaper enclosure.

https://www.nrc.gov/docs/ML2419/ML24191A372.pdf

Presumably once you are finished with it you could just fill it with concrete.

Or partially fill it and drop another reactor on top.

The only projects that overrun more than nuclear is nuclear waste disposal. This kills two birds with one stone.

So it's a regular reactor BUT IN A MINESHAFT!! The reactors yearn for the mines!

It's even _more_ stupid!

No. Being at the bottom of a mile deep hole in bedrock makes a very effective isolation.

Isolation from _what_? If you reactor melts down, it will contaminate the water column above it. And by having it inside the shaft, you won't be able to do any maintenance on it.

It's a stupid idea designed to filter out investors who are stupid enough to fall for it.

How does your reactor melt down if it is submerged in coolant?

It boils off the coolant, creating a vapor lock, then water-zirconium reaction happens. Then it explodes and ruins the shaft. So you'll have to drill a rescue well, and then defuel the reactor to avoid any possible contamination.

Again, this is a monumentally stupid idea for no reason whatsoever.

And modern reactors are already passively safe. Even if the core melts down, it'll be contained in a core catcher: https://en.wikipedia.org/wiki/Core_catcher

It boils off a 1 mile deep water column? And you don't need a core catcher when you are already 1 mile deep in bedrock. It just goes to the bottom of the hole.

> It boils off a 1 mile deep water column?

Yes?

> And you don't need a core catcher when you are already 1 mile deep in bedrock.

Yes, you do. Because if the shaft explodes or gets blocked near the top, the fission products can travel up the water column.

So this thing is just boiling off water from the mile deep water column, and nobody things "hey maybe we could add some more water"? How does a shaft "explode"? What is generating the explosive force?