A remote-controlled decommissioning robot has discovered contaminated water flowing into a drainage culvert on the northeast side of the first floor of Fukushima Daiichi unit 3, near the main steam isolation valve. TEPCO said that this was the first time that this area had been inspected.
The water is confirmed to be flowing to the basement of the Reactor Building where water still accumulates. TEPCOreports that the leaked water is not flowing out of the building, and no significant changes in monitoring data have been noticed.
The water is assumed to be flowing out from the Primary Containment Vessel. Its temperature, measured on 19 January, was 20°C, 13°C warmer than the surrounding area and that of the water injected for cooling. A sample of the water showed contamination levels of 24,000 Bq/cm3 of all beta radiation, 1700 Bq/cm3 of caesium-137, 700 Bq/cm3 of caesium-134 and 25 Bq/cm3 of cobalt-60. TEPCO said that it would continue to investigate the source of contamination.
The finding is significant because the medium-term decontamination & decommissioning plan for Fukushima Daiichi 1-4 is to flood the units' primary containment vessels with water; this cannot be done until the leaks that continue to feed contaminated water to the units' basements are found and sealed. So far two small leaks have been identified in unit 1's suppression chamber.