Fukushima update: water processing system hot testing and site isolation work

10 April 2013

To mitigate the water leaks found in underground reservoirs, TEPCO will continue to 'steadily perform' hot testing of the multi-nuclide removal system (ALPS) built to purify contaminated water, TEPCO announced 8 April. Hot tests of that system began in March.

In the early days and weeks after the accident in March 2011, Iodine-133 was the most prevalent radionuclide, but its short half-life (three months) means that it has decayed and is no longer a threat. Longer-term caesium radionuclides, salt and oil have been removed for years through the existing circulating water treatment system. But many other potentially-hazardous radionuclides (including Co-60 and Pu-239) remain in that water. To remove those, TEPCO has been building a new water treatment complex on site to remove 62 radionuclides. The system consists of three redundant trains, each of which has a flow rate of 250m3/day. Contaminated water is pretreated in iron and carbonate coprecipitation facilities, and then run through adsorbent towers. Slurries and spent adsorbent generated by the process is stored in HICs: high-integrity containers that are stored in a new temporary storage facility. The facility is protected from equipment leaks by a series of barriers ranging in height from 100mm-500mm high. Each protected cell has a leak detector.

Hot testing will involve processing between 1000-2000 m3 of water per system to evaluate its capability to remove radionuclides. A second test, to make sure that the system will maintain the radionuclide removal capacity, will run for four months, because that is the length of the longest adsorption replacement cycle. If all goes to schedule, full-scale operation could begin in September.

Trial operation is scheduled to have begun of a groundwater diversion system to prevent groundwater flowing downhill from above the Fukushima site becoming contaminated. A series of 12 pump wells have been drilled upland of the plant. They will pump groundwater to sand filters and then to temporary tanks (in three systems, A, B and C). Stored water will be analysed, and then, if free of contamination, pumped to the sea. Test results from December-March 2012 showed contamination was lower than allowable limits, 1 Bq/L. One consequence of this work is that the water table around the Fukushima Daiichi reactors will gradually drop. That will have an effect on the project to dry out the reactor and turbine buildings; contaminated floodwater pooled in the bottom levels of these buildings is kept lower than groundwater to prevent further contamination. Operational launch of the first system is scheduled for the end of April. Work continues on construction of a piled barrier that isolates the contaminated site from the sea.

TEPCO have published data showing very high levels of radioactive contamination of fish caught in February within the Fukushima Daiichi port. The most contaminated areas unsurprisingly yielded the most contaminated fish. Six samples of Greenling sampled within the water intake area of Fukushima Daiichi had a Cs-137 concentration of 4.8 x10^5 Bq/kg. These were the areas where the seafloor was concreted to reduce the spread of radioactive contamination, which was assumed to deposit on the seafloor; they are also netted off with silt fences. Still, within the port area fish that are highly-contaminated were sampled, including another six Greenling with Cs-137 contamination of 330,000 Bq/kg. Other species had slightly lower contamination levels: a sample of 47 Spotbelly rockfish had a Cs-137 contamination of 99,000 Bq/kg. In February, a gill net was installed across the port inlet. Such contamination appears to be well-contained; for comparison, Greenling samples taken outside of the port up to 20km radius had contamination levels from 15-450 Bq/kg (28 measurements). Data was analyzed by Tokyo Electric Power Environmental Engineering Co., Inc.

Picture: Adsorption tower inside the ALPS facility, with crane for HICs visible behind

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