A fuel cell powerplant system comprises a fuel cell that houses in an airtight containment vessel a cell stack formed from many layers of individual fuel cells, a cooling water loop that cools the fuel cell, and a steam separator that is disposed on the side of an outlet of a fuel cell of the cooling loop and that discharges steam, and wherein one portion of the steam discharged from the steam separator is introduced via a purge steam line to the containment vessel or the cathode of the fuel cell for the purpose of purging containment vessel.