High radiation levels and technical difficulties continue to stymie full-scale operations of key decontamination equipment at the Fukushima No. 1 nuclear power plant even though tests started more than a year ago.
High radiation levels and technical difficulties continue to stymie full-scale operations of key decontamination equipment at the Fukushima No. 1 nuclear power plant even though tests started more than a year ago.
The multi-nuclide removal equipment, called ALPS (advanced liquid processing system), began trial runs in March 2013 to reduce levels of 62 kinds of radioactive substances in contaminated water, such as strontium, to below detectable limits.
But Tokyo Electric Power Co. has been forced to repeatedly suspend operations, having discovered holes from corrosion and
Cloudy water was found at the B channel of the ALPS system in March. Two months later,
TEPCO, operator of the embattled nuclear plant, concluded that the packing to fill gaps had deteriorated due to radiation exposure and
High radiation readings have not only damaged the system, but have also prevented workers from spending long hours near ALPS for inspections and repairs.
Radioactive water to be processed contains various impurities derived from seawater and concrete, and chemical agents are necessary to remove them. An elaborate pipe arrangement also makes it difficult for workers to handle ALPS.
The ALPS system consists of two facilities: preprocessing and absorption.
The system first removes materials that can hamper radioactive substance removal procedures at its preprocessing facility. At this stage, mud and metal in contaminated water stored in tanks are precipitated with chemical agents. Then calcium and magnesium are filtered out by adding sodium carbonate and other chemicals to the water.
The deteriorated packing was found at a filter used at the last stage of preprocessing.
After all preprocessing procedures are complete, the water is transferred to the absorption facility, where radioactive materials will be absorbed by particles 0.5 millimeter in diameter and removed. A total of 15 devices of seven types can remove 62 kinds of radioactive substances.
But one of the three ALPS channels has been found to fail to significantly decrease levels of four radioactive materials.
As of May 27, about 360,000 tons of highly contaminated water remain stored in tanks on the plant site to be processed with ALPS.
While the decontamination equipment has processed just 85,000 tons of water since the start of trial runs, TEPCO and the government expect all the water on the premises to be processed by the end of the fiscal year.
To achieve that goal, the utility plans to double ALPS’ current processing capacity of up to 750 tons per day by this fall.
The government is also expected to provide funding to introduce a similar system with the capacity of up to 500 tons per day in the near future.
However, even after readings for the 62 types of radioactive substances fall to well below detectable limits, radioactivity levels of those materials in the processed water will likely remain at several hundreds of becquerels per liter in total.
In addition, ALPS cannot remove tritium, raising radioactive levels in the processed water by several hundreds of thousands of becquerels per liter. Those levels of tritium are not allowed to be released into the sea.
It is possible that contaminated water on the premises contains radioactive materials other than the 62 kinds. The Nuclear Regulation Authority has told TEPCO to re-examine the water to decide if it includes additional radioactive substances.
TEPCO intends to replace current bolted storage tanks for radioactive water with ones made of welded steel plates to prevent water leaks. But if the start of ALPS’ full-scale operations is delayed even further, it will likely become difficult for the utility to continue storing contaminated water at the plant site alone.