[T]he report’s executive summary certainly gets to the heart of their findings.
“The rhetoric from small modular reactor (SMR) advocates is loud and persistent: This time will be different because the cost overruns and schedule delays that have plagued large reactor construction projects will not be repeated with the new designs,” says the report. “But the few SMRs that have been built (or have been started) paint a different picture – one that looks startlingly similar to the past. Significant construction delays are still the norm and costs have continued to climb.”
Because military engineers overengineer these things from the most expensive materials available, and they also perform frequent maintenance on them, which is also expensive.
To add to this: A certain type of Soviet submarine used a lead-bismuth alloy as coolant for their reactor. The coolant solidifies at ambient temperature so it had to be heated indefinitely by some way or another or else it solidified and trashed the reactor. I don’t think any of them exist anymore since Russia wasn’t able to afford sustaining the giant navy after the Soviet collapse.
Just goes to show how insane nuclear submarine engineering is, or was at some point.