Human error, not equipment failure, may be responsible for the roughly 100 tons of highly radioactive water released from a storage tank earlier this week, the operator of the crippled Fukushima No. 1 power plant says.
When Tokyo Electric Power Co. first disclosed the incident Thursday, it said a faulty valve may have allowed water to flow into the tank, which was already nearly full.
On Friday, however, the utility dismissed that possibility and said it found photographs that showed the valve appeared to be operating properly around the time the leak occurred.
“There could have been some (human) error, but we have to check the situation,” Tepco spokesman Masayuki Ono said at a press conference Friday.
The photos show the valve was in the “open” position at around 11 a.m. Wednesday but in a “closed” position at 12:30 a.m. Thursday. The tank leak was noticed at 11:25 p.m. Wednesday.
Because the valve was open, the radioactive water was directed to the wrong tank.
Early Thursday, Tepco confirmed the leak had been stopped.
The photos also show that a lever used to operate the valves was left attached to the valve in question, which Ono said was undesirable.
“Usually, a lever should not be left attached to a valve so that someone does not accidently touch the lever when passing and change the valve’s status,” he said.
The utility doesn’t think any of the liquid got into the adjacent Pacific Ocean because there is no drainage nearby.
The incident is another sign of Tepco’s ongoing struggle to manage the radioactive water being generated by the cooling operations of the three reactors hit by the triple meltdown in March 2011.
After cooling the fuel rods, the tainted water is pumped through a facility that extracts most of the cesium. But it still contains high concentrations of other radioactive substances, such as hazardous strontium-90, which tends to accumulate in bones and is thought to cause bone cancer and leukemia.
Tepco said Thursday it detected 240 million becquerels per liter of beta ray-emitting substances, such as strontium, from water accumulating near the tank.