How do you make safe, cheap modular nuclear reactors? Bury them a mile deep

This is an interesting proposition! I don't remember ever having learnt of such an option. Perhaps, technology has advanced to allow for this.

This article is based on company information. Apparently, the company is in negotiations with national regulators.

How do you service a nuclear reactor deep underground? In general, the information provided by the company appears a bit sketchy or early stage or cagey.

How do you make safe, cheap nuclear reactors? Bury them a mile deep "Startup Deep Fission has come up with a new way to deal with the economic and safety problems of nuclear power that is, to say the least, novel. The idea is to build a reactor that's under 30 inches (76 cm) wide and stick it down a mile-deep (1.6-km) drill shaft."

The base design reactor is 15 MWe. It is fully modular, and boreholes can be spaced close to each other: 10 to provide 150 MWe, or 100 to yield 1.5 GWe. The figure does not show all the boreholes but close-spaced reactors can share a steam generator and condenser. The modular nature allows the reactors to be spread across a military base or a large city.