Reactor Engineers
Concept · Stellaris 4.5.2
Reactor Engineers in the Stellaris encyclopedia: Reactor Engineers produce Energy Credits
Reactor Engineers in the game's words
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Reactor Engineers produce 
Energy Credits
Aboard their masters' vessels, indentured engineers were often assigned the lowliest and most dangerous jobs. This hardship only sharpened their skills.
Entries that mention Reactor Engineers
Source: common/game_concepts (concept_low_tech_technician) and localisation/english, Stellaris Cygnus v4.5.2 (9776).