As testimony to how fleeting progress is and how quickly things can go to pot at the plant, NHK reports that steam, along with a biologically unacceptable amount of radiation is now present in part of the reactor 1 building, so much so that they are sending Packbots in again instead of humans. From NHK:
Tokyo Electric Power Company inspected the inside of the No.1 reactor building on Friday with a remote-controlled robot.
TEPCO said it found that steam was rising from a crevice in the floor, and that extremely high radiation of 3,000 to 4,000 millisieverts per hour was measured around the area. The radiation is believed to be the highest detected in the air at the plant.
TEPCO says the steam is likely coming from water at a temperature of 50 degrees Celsius that has accumulated in the basement of the reactor building.
The company sees no major impact from the radiation so far on ongoing work, as it has been detected only within a limited section of the building.
The No.1 reactor is believed to have suffered a meltdown after the March 11th earthquake and tsunami.
Steam is a most unwelcome development within the reactor 1 building. With recently reported basement water concentrations of Cs-137 in the millions of Bq/cc, you can imagine what will happen if the steam persists for an extended period of time. It will permeate the entire floor and the water may evaporate away, but the residue containing isotopes remains - on the ceiling, walls, equipment - everything.
It's this sort of contamination that is extremely difficult to address, with the potential to greatly elevate readings within the entire floor.