23 Février 2014
February 22, 2014
TEPCO investigating possible human errors
Tokyo Electric Power Company has yet to determine the cause of a recent leak of radioactive water at the Fukushima Daiichi nuclear plant.
About 100 tons of highly contaminated water leaked from a tank at the number 4 reactor from Wednesday to Thursday.
TEPCO officials at first said the cause may have been mechanical trouble at one of the 3 valves on a pipe linking a treatment facility to the tank. They said contaminated water flowed even though the valve was shut.
However, they later said a photo shows the valve open on Wednesday morning. They also said another valve on a pipe that was to be used to transfer contaminated water was shut at the time but was open after the leak was found.
They now say opening and closing of these 2 valves by someone probably led to the leak.
TEPCO is interviewing workers as to why and how the valves were operated.
The utility is also reviewing ways to supervise engineers who handle valves and monitor water levels in a tank.
This is because the water level was not monitored properly at the time the valves were operated. And tools for closing and opening the valves were not stored properly.
Feb. 22, 2014 - Updated 07:45 UTC
Tokyo Electric Power Co. has determined an unidentified worker at its crippled Fukushima No. 1 nuclear power plant left valves open along a conduit, which resulted in 100 tons of highly radioactive water overflowing from a storage tank, sources said Feb. 21.
While the utility at first said valve malfunctions could not be ruled out, it concluded the cause was human error after examinations of a photo and water level gauge records.
Three valves line a conduit that sends radioactive water into the storage tank that overflowed. Two of them were open and the remaining one was closed when workers spotted the leak at around 11:30 p.m. on Feb. 19.
Radioactive water normally cannot flow into the tank unless all valves along the conduit are open. But water did flow in, leading TEPCO to initially suspect a malfunctioning valve.
However, a photo shot around 11 a.m. earlier on the day as part of a work procedure showed the third valve in the open position. In addition, readings of a water level gauge in the overflowing tank rose around noon on the same day.
These circumstances led TEPCO officials to believe that somebody opened the valve at around 11 a.m.
TEPCO has interviewed people who were working that day but has yet to identify the worker who operated the valves, the sources said.
Human error, not equipment failure, may have caused leak: TEPCO
TOKYO (Kyodo) -- The operator of the crippled Fukushima Daiichi nuclear complex said Friday that human error, not equipment failure, may be responsible for the leakage of about 100 tons of highly radioactive liquid from a storage tank earlier this week.
When Tokyo Electric Power Co. first disclosed the incident Thursday, it said that a faulty valve may have allowed water to flow into the tank that was already nearly full.
On Friday, however, the utility dismissed that possibility, saying 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 told a press conference.
The photos show the valve was in the "open" position at around 11 a.m. Wednesday, but in a "closed" position as of 12:30 a.m. Thursday. Workers noticed the tank leaking water at 11:25 p.m. Wednesday.
Because the valve was open, radioactive water was directed to the wrong tank.
The photos also showed that a lever to operate valves was left attached to the valve in question, which Ono admitted was not desirable.
"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.
TEPCO confirmed early Thursday that water had stopped leaking from the tank. The utility believes the liquid has not flowed into the adjacent Pacific Ocean as there is no drainage nearby.
The incident is another sign TEPCO is struggling to manage a massive amount of radioactive water generated in the ongoing process of cooling three reactors that experienced meltdowns during the nuclear crisis that erupted in March 2011.
The water passes through a facility that can reduce cesium, but it contains high concentrations of radioactive substances such as strontium-90. Strontium 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 radioactive substances, such as strontium, from water accumulating near the tank.
February 22, 2014(Mainichi Japan)
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.
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.