Black Rock Processing Control Bridge. First head to Central Maintenance using the sector elevator. Go back a bit go up the stairs and run into the room with the turbines.
Once youre at the plant sprint around the perimeter of the domed area until you. Go into the third room and pick up the key. Fast travel to the Upper Panopticon Control Point and head across the bridge to Fortified Unit.
Find a Black Rock Prism.
How to get to Black Rock Processing in Control. Go into the third room and pick up the key. Head through the door to Black Rock Processing deal with the goons inside the security room and instead of going through the door with the chasm head into the Turbine Room. Find a Black Rock Prism in Control.