"By 20:56 [15:26 GMT], [the reactor] has been brought to the minimum controlled power level. The physical launch phase was therefore completed. We are now moving to the power launch phase," the source said.
Minimum controlled reactor power is a level sufficient to control the self-sustaining nuclear chain reaction. This is one of the final stages necessary to launch the reactor. The reactor has yet to undergo a series of tests before it can start generating electric power.