Transportable nuclear reactors for remote power applications were build during the Cold War by both the United States and the Soviet Union, with more recent projects underway. The combination of a nuclear heat source, heat pipe and Stirling engine has been tested at small scale with the DUFF (Desktop Using Flattop Fissions) experiment in 2012.

This version uses a liquid , communicating vessels and an air pump to regulate the criticality of the core. If the scram valve is opened, the air pressure equalizes and the drains into the reserve tank.