Just how high is the radiation level on the (what used to be) operating floor of Reactor 3? TEPCO has released only one measurement of the Reactor 3 operating floor, and it was on one location only (above the reactor well). While I am still looking for that TEPCO's PDF document, there is an indirect indication of how high it could be.
Kyodo News reporters visited Fukushima I Nuclear Power Plant on April 4, and wrote up a detailed article for the 2nd anniversary of the nuclear accident. The article, judging by the number of retweets, doesn't seem like it's been read widely. But in it, there is a reference to radiation levels of Reactor 4 and Reactor 3, located 100 meters apart.
From Kyodo News "Current situation at Fukushima I Nuke Plant: 2 years after the accident, uncertainty still reigns, guarding against trouble 24/7" (4/8/2013; part):
(On the operating floor of Reactor 4)
"We can't stay here long. Let's go back down." The TEPCO employee who accompanied us called to us. The air dose level on the [Reactor 4] operating floor is 262 microsieverts/hour. The wrecked Reactor 3 building, located north of the Reactor 4 building, has extremely high radiation, and the Reactor 4 building [operating floor] is affected even though it is 100 meters away. On the Reactor 4 operating floor, several workers with full-face masks and protection gear were working quietly.
From the top left of the picture, clockwise:
ALPS: 4.5 microsieverts/hour
Dry cask temporary storage area: 5
Outside the Anti-Seismic Building: 20
Ocean-side of Reactor 3 (beyond the Reactor 3 turbine building): 1300
Plugged hole where the highly contaminated water leaked into the ocean: 250
At the wall to shield ground water: 130
Reactor 4 Operating Floor: 262
Control room for Reactor Cooling System (indoors): 7.4
Kyodo News also has the video news, showing the locations that they visited:
0:20 Anti-Seismic Building, the plant's headquarter for day-to-day operation of the plant "restoration" work
0:55 Construction of walls to block the flow of groundwater, at the water intake for Reactors 1-4, due for completion in April next year
1:10 ALPS (Multi-nuclide removal system) building
1:34 Control room for the reactor cooling system
2:20 Reactor 4 building
2:40 Reactor 4 Operating floor (they went up in an elevator)
3:09 Reactor 4 narrow stairway to descend from the operating floor