TEPCO took this photo when they sent carbon-based workers on June 29 to the 5th floor of the Reactor 4 reactor building. They released other photos on June 30 as part of press handouts but this had to wait a day.
It looks like a nice radon hot spring water, doesn't it?. The temperature is rather high for comfortable bathing, at constant 85 degrees Celsius (185 degrees Fahrenheit).
Here's what they released separately as the press handout on June 30:
The fuel pool valve is totally rusted, probably from seawater.
The radiation level turned out to be "benign" for the plant, and TEPCO says the workers can now go up there for the work of installing the cooling system for the Spent Fuel Pool.