The water decontamination system at the crippled Fukushima No. 1 nuclear power plant resumed operations on Oct. 4, after a warning sounded and automatically shut down the equipment earlier in the day.
The ALPS (advanced liquid processing system), which removes radioactive materials from contaminated water stored at the plant site, was out of action for 12 hours.
Officials of plant operator Tokyo Electric Power Co. said no water leaked from the ALPS equipment. The system has been plagued with problems. Operations were temporarily suspended in August after a leak was discovered and again in late September due to a blockage.
TEPCO officials said the warning sounded around 6:45 a.m. At that time, work had begun in a tank within the pre-processing equipment that is designed to remove heavy metals and other materials from the contaminated water. A signal was sent to close the valve at the entrance to the equipment, but another signal was sent simultaneously to open the valve so contaminated water could be pumped in from another tank.
A TEPCO official said, "The reason the warning sounded was because conflicting signals were sent at the same time instructing that water be flushed out but also not allowing other water to enter."
After an inspection of the equipment, processing resumed around 6:30 p.m.
In order to cool melted nuclear fuel in the reactors at the Fukushima No. 1 plant, 400 tons of water is circulated into the reactors daily. However, because groundwater also seeps into the reactor buildings at a pace of 400 tons daily, the overflowing contaminated water is being moved to and stored in tanks on the plant site.
As of Oct. 1, about 294,000 tons of highly radioactive water awaited processing.
The ALPS equipment is designed to absorb and remove 62 radioactive contaminants from the water, including strontium. The aim of removing the contaminants is to lower the danger should a leak occur. The ALPS unit has three channels, called A, B and C, and each has a daily capacity to process 250 tons of water.
If the contaminated water cannot be processed, there will be no reduction in the volume of highly radioactive water that is stored in the tanks. However, the ALPS system cannot remove all radioactive elements. For example, tritium, a radioactive isotope of hydrogen, remains in the water after processing so the water must continue to be stored on the plant site.
A trial run began in late March on Channel A. Soon after a trial run began on Channel B in June, contaminated water was found leaking from a tank within the Channel A equipment.
The trial runs were eventually stopped to look into the cause of the leak as well as to repair the equipment.
The trial run on Channel C finally began on Sept. 27, but that had to be stopped the same day because it could not discharge mud. The cause of that problem was the failure to remove a rubber pad from the tank, leading to a blockage in the system.
(This article was written by Shunsuke Kimura and Daisuke Sudo.)
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