JAPAN | Water treatment system at Fukushima plant stops for 7.5 hours, cause unknown

Posted on August 8, 2011

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JAPAN | MAINICHI | 8 August 2011

In this June 1, 2011 file photo released by Tokyo Electric Power Co. (TEPCO), workers inspect equipment inside the cesium absorption tower, part of the radioactive water processing facilities at the Fukushima No. 1 Nuclear Power Plant in Okuma, Fukushima Prefecture. (AP Photo/TEPCO)

Tokyo Electric Power Co. (TEPCO) said a radioactive water treatment system at the Fukushima No. 1 Nuclear Power Plant stopped operating for 7.5 hours shortly after 8 a.m. on Aug. 7, prompting the Nuclear and Industrial Safety Agency (NISA) to instruct the utility to come up with preventative measures.

While the water treatment system was out of operation, processed water was used to cool down reactors, TEPCO, the operator of the crippled nuclear power station in Fukushima, said on Aug. 7. According to the utility, the trouble occurred in a water decontamination device developed by France’s Areva SA. It said one of the pumps used in two separate water treatment systems to inject chemicals aiding precipitation of radioactive cesium stopped operating. In a similar development, another pump also stopped operating due to a glitch on Aug. 4.

Internal investigations found that the pump stopped operating on Aug. 7 because sticky chemicals injected into it had put too much of a load on it. The pump’s operations resumed at around 3:30 p.m. on Aug. 7, after the amount of chemicals in each injection was reduced while the frequency of injections was increased. TEPCO suspects that the other pump may have stopped operating for the same cause on Aug. 4.

Each of the two water treatment systems has one pump for operations under normal conditions and a backup pump for use in times of trouble. The backup pumps in the two systems failed to operate on Aug. 4 and 7, respectively. Engineers are checking the system for the cause of the trouble.

Following a string of problems with the pumps, NISA instructed TEPCO to investigate the causes of the mishaps. The agency urged the utility to work out and submit preventative plans as well as to report a list of troubles other than those with the pumps.

In this photo taken on June 22, 2011 and released on Thursday, June 23, 2011 by Tokyo Electric Power Co. (TEPCO), workers in protective suits set up temporary pressure gauges in the Unit 2 reactor building at the tsunami-damaged Fukushima No. 1 nuclear plant in Okuma, Fukushima prefecture. (AP Photo/Tokyo Electric Power Co.)

In this photo taken on June 22, 2011 and released on Thursday, June 23, 2011 by Tokyo Electric Power Co. (TEPCO), workers in protective suits set up temporary pressure gauges in the Unit 2 reactor building at the tsunami-damaged Fukushima No. 1 nuclear plant in Okuma, Fukushima prefecture. (AP Photo/Tokyo Electric Power Co.)

At the same time, TEPCO for the first time started operating newly installed equipment to evaporate and concentrate saltwater within two of its eight water-treatment systems. The equipment is used to reduce the volume of highly concentrated saltwater that comes from a desalination device within the water treatment system. The volume of highly concentrated saltwater coming from the desalination device is about 1.5 times as much as that of desalinated water. The volume of highly concentrated saltwater is said to be reduced to about 30 percent by using the newly installed equipment.

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