[ Adding more hours of operation just means having a larger or hotter reservoir of the molten salt, rather than adding additional arrays of giant batteries
LFTR: http://liquidfluoridethoriumreactor.glerner.com/2012-what-is-a-lftr/
]
The perfect power source for a Underground Colony.
Actually perfect for anyplace except for the American regulatory state, which makes such technology illegal. This is not new technology. See Wikipedia:
Aircraft Nuclear Propulsion
The General Electric program, which was based at Evendale, Ohio, was pursued because of its advantages in simplicity, reliability, suitability and quick start ability. Conventional jet engine compressor and turbine sections were used, with the compressed air run through the reactor itself to be heated by it before being exhausted through the turbine.
The US Aircraft Reactor Experiment (ARE) was a 2.5 MW thermal nuclear reactor experiment designed to attain a high power density for use as an engine in a nuclear-powered bomber. It used the molten fluoride salt NaF-ZrF4-UF4 (53-41-6 mol%) as fuel, was moderated by beryllium oxide (BeO), used liquid sodium as a secondary coolant and had a peak temperature of 860 °C. It operated for a 1000-hour cycle in 1954. It was the first molten salt reactor. Work on this project in the US stopped after ICBMs made it obsolete. The designs for its engines can currently be viewed at the EBR-I memorial building at the Idaho National Laboratory.
https://youtu.be/tyqYP6f66Mw