Apart from the regulatory/safety issues, it's not surprising that if it's hard to miniaturize the system (turbine, condenser if closed loop, control system, etc

Apart from the regulatory/safety issues, it's not surprising that if it's hard to miniaturize the system (turbine, condenser if closed loop, control system, etc.) in an economical way. There do exist smaller nuclear batteries which use another principle for power generation though: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge... They output around 40-100W/kg