6 Mai 2015
May 5, 2015
A sampling inspection of tanks containing radioactive waste produced during the processing of contaminated water at the Fukushima No. 1 Nuclear Power Plant has found that over 10 percent of them have leaked.
The tanks contain sludge and wastewater produced when removing radioactive contaminants from water with the Advanced Liquid Processing System (ALPS). The plant's operator, Tokyo Electric Power Co. (TEPCO) sampled 105 of 1,354 tanks at the plant, and found that contaminated water had leaked or seeped out of 15 tanks, or about 14 percent of those that were inspected. Each tank measures about 1.5 meters in diameter and 1.9 meters in height and can hold roughly 3 tons of waste.
A TEPCO worker found water had accumulated on the ground under the tanks and on their lids during an inspection in early April. It emerged that wastewater had leaked from holes to let out gas near the tops of the tanks. TEPCO suspects that hydrogen and other gases built up in the wastewater, thereby increasing its volume and forcing it out through the gas holes.
The highest concentration of radioactive cesium in the leaked wastewater was around 9,000 becquerels per liter. The radioactivity of materials emitting beta rays, meanwhile, was particularly high, at around 3.9 million becquerels per liter.
The tanks are shielded within a concrete structure at the Fukushima No. 1 nuclear plant, and TEPCO official Isao Shirai maintains that there have been no leaks outside the plant site. The tanks were drop tested in advance, but no tests using actual wastewater were carried out. TEPCO says the leaks were "unexpected."
An official from the Secretariat of the Nuclear Regulation Authority commented, "The leaked water is the most concentrated contaminated water at the nuclear power plant. Quick countermeasures are needed." Officials will ask TEPCO to thoroughly manage the radiation exposure of workers involving in leak checking and other relevant work.
TEPCO plans to take measures to prevent further leaks, including reducing the amount of wastewater in the tanks by about 10 centimeters. At the same time, as long as ALPS continues operating, it will keep producing sludge and wastewater. As the number of tanks increases, TEPCO will have to secure space for them. It also faces the task of dealing with the waste once the tanks have reached the end of their durable life (about 20 years).
May 05, 2015(Mainichi Japan)