According to TEPCO, twenty workers at Fukushima Daiichi spent two and a half hours in the Unit 1 reactor building collecting water and sediment for sampling analysis from the accumulated water in the torus room. Workers collected water samples from the top of the water surface and from the bottom of the torus room.
Workers also collected sediment they reported appeared to look like sand. Radiation levels on the outside of the container holding the sediment registered at 4 millisieverts per hour.
Source: TEPCO
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