Water sampled from a well at the crippled Fukushima No. 1 nuclear plant has been found to contain levels of radioactive tritium that exceeds the limit for dumping it into the Pacific, operator Tokyo Electric Power Co. said.
The discovery was the first report of over the limit tritium in groundwater at the wells since Tepco began discharging water into the ocean last week.
In samples taken from one of the 12 wells on Monday, 1,700 becquerels per liter of tritium was detected, exceeding the maximum limit of 1,500 becquerels, the utility said on Tuesday.
Tritium levels in samples taken last month also topped the limit.
Tepco stopped pumping water from the well on Tuesday night, and said it plans to step up groundwater monitoring.
The utility is now releasing groundwater from the 12 wells into the sea after temporarily storing it in tanks and checking radiation levels.
Tepco hopes to use the wells to block the inflow of groundwater to the reactor buildings of the plant’s wrecked reactors, and to minimize the amount of highly toxic water building up on-site, by starting to dump water into the sea.
Also Tuesday, Tepco said it had confirmed water was leaking from a pipe in the reactor containment vessel inside the plant’s No. 1 reactor building. The utility used a camera-mounted remote-controlled robot in the operation. It was determined last November that water was leaking from the vessel’s bottom near the pipe, at a rate of up to 3.2 tons per hour.
In the No. 1 to No. 3 reactor buildings, highly contaminated water leaking from the vessels has amassed, preventing work to remove nuclear fuel from the vessels.