9 workers (5 TEPCO employees, 4 from TEPCO affiliate companies) entered the reactor building to do measurements and inspections in order to prepare for the nitrogen injection into the Containment Vessel. They spent about 30 minutes, surveying about half the floor, getting exposed to 5.88 to 7.98 millisieverts of radiation for their work.
96 millisieverts/hour radiation at the staircase going down to the basement, at the southwest corner (circled in red).
Blowup of the photo at the location (3), where 100 millisieverts/hour radiation was measured: