[cyberax]

It's an extremely stupid idea. Your whole water column is going to be contaminated with fission products. And you won't be able to get any reasonable amount of power out of that contraption.

And even if you are stupid enough to actually do this, the fuel efficiency will be terrible. Your only negative feedback for fission is the Doppler effect and thermal expansion. So you will only be able to utilize a tiny percentage of the fissionable materials.

[rcxdude]

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

[cyberax]

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.

[UltraSane]

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

[tonyedgecombe]

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.

[cyberax]

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

It's even _more_ stupid!

[UltraSane]

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

[cyberax]

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.

[consensus1]

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

[cyberax]

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

[UltraSane]

actually you just pump the water into a tank. You can also pull the reactor up on a cable if needed.