The trouble-plagued water decontamination system at the Fukushima Daiichi nuclear complex is on track to resume operations Tuesday after breaking down last week, the operator of the plant said.
The launch of the system, which combines Japanese, U.S. and French technology, is considered crucial for bringing the plant’s damaged reactors to a cold shutdown and eliminating the release of radiation. About five hours after launching Thursday night, the system stopped early Friday after alarmingly high levels of radiation were detected in its upstream section.
However, a close inspection over the weekend found no major flaws, plant operator Tokyo Electric Power Co. said Monday.
While it was initially feared that the system might have been clogged with sludge, resulting in an accumulation of radioactive material, “the high levels of radiation were due to the radioactivity of the water the system was treating,” Tepco spokesman Junichi Matsumoto said.
Tepco expects the system to resume operations Tuesday after trial runs are conducted.
The system is key to Tepco’s plan of achieving a so-called “cyclic injection” of water into reactors, in which cooling water is recycled.
Under current cooling operations, water that is used to cool the reactors is leaking out from damaged parts of the reactors and is accumulating in the basements of the plant, emitting strong radiation and hampering work to repair the plant. Water is expected to fill up all storage facilities and start overflowing by the end of the month.
The water treatment system has four different components—a Toshiba Corp. oil separator, a cesium removal device developed by Kurion Inc. of the U.S., a decontamination device from France’s Areva SA, and desalination equipment built by Hitachi Ltd. and others. The involvement of so many manufacturers and the need to rush the construction has brought about a system that has been plagued with glitches from the beginning.
On Sunday, for instance, a pressure-relief valve in the Kurion equipment sent false alarms for the second time in four days, forcing Tepco to disable the valves to prevent them from holding up the system.
The Kurion facility has four separate lines, with each consisting of six zeolite-containing cartridges: one for removing oil and radioactive technetium, four for radioactive cesium, and one for iodine.
After the first five hours of operation, Tepco found that the cartridge for removing oil and technetium was absorbing radioactive material far more than initially projected, indicating the need to frequently change the cartridges. Tepco is now working to figure out how the process of removing radioactive material can be evened out among the six cartridges.
Meanwhile, another worker is suspected of having received more than 250 millisieverts of radiation, above the permissible dosage limit for a worker in an emergency situation, bringing the total number of workers who have likely been exposed to above-acceptable amounts of radiation to nine, Tepco said. Many of the most heavily irradiated workers were on the front lines of a battle to bring damaged reactors under control in the immediate aftermath of the March 11 earthquake and tsunami.
Of the of 3,639 workers who worked in the Fukushima Daiichi in March, 3,514 have already undergone whole-body counter checks for internal contamination. Another 46 workers are expected to receive a checkup this month, while the remainder are either overseas or unable to be contacted, according to Tepco.
