"has been fully operational" is correct and can be used in written English.
You can use it when you are discussing a period of time during which something has been available to use and running normally. For example: The new airport has been fully operational since October, providing much needed access to the region.
PPS was developed in 1996 and has been fully operational since January 1997.
The SCT has been fully operational throughout all data taking periods, delivering high quality tracking data.
VERITAS consists of an array of four 12 m-diameter atmospheric Cherenkov telescopes that has been fully operational since September 2007.
Coming into force in 2002, the ICC has been fully operational for a mere 8 years--a child in relation to other permanent global institutions.
The Dakota Access Pipeline, which runs from North Dakota to southern Illinois and sparked months of protests, has been fully operational since June after the Trump administration approved the last phase of its construction.
But under the New York Immigrant Family Unity Program, which has been fully operational for the last three years, the city itself pays to provide lawyers to immigrants in detention who can't afford them.
Nevertheless, CICIG had been fully operational for barely a year when Rosenberg was killed, and the case threatened some of the country's most untouchable figures.
Even if it had been fully operational, that alone would not account for all the increase in response time, which depends on a number of human, strategic and technological factors.
Russian firm Zvyozdochka, which refitted the submarine, said the vessel had been fully operational when it was returned to India in January.
The GPS and GLONASS satellite systems have played a central role in the journal simply because these have been fully operational for a long time.
So, he was later surprised when results came back with Enterococcus levels below 10. (He noted that the plant might not yet have been fully operational).
