Another day, another aftershock in Japan, where crews at Fukushima Daiichi managed to continue pumping water into damaged reactors during an earthquake Tuesday but briefly suspended the injection of nitrogen into unit 1.
The 6.3 magnitude aftershock at 2:07 p.m., local time, did not cause further damage to the reactors, and it followed a 6.4 magnitude quake in the same northeastern region that morning and a 5.6 magnitude quake in the center of the country. Tokyo Electric Power Co. did find a small fire at a building near unit 4 in the morning, news agencies reported, but firefighters from Japan’s Self Defense Forces soon put it out.
That evening, workers began pumping 700 tons of highly contaminated water from trenches near unit 2 into the reactor’s condenser, Kyodo reported. The operation is expected to take 40 hours, and afterward crews will begin pumping the remainder of an estimated 60,000 tons of water flooding basements at the reactors into buildings and a large barge en route to the plant.
While the amount of radioactive contaminants escaping the plant has not risen substantially following aftershocks in recent days, Japanese regulators officially upped the accident’s categorization to the highest level on the International Nuclear Event scale Tuesday. The Economy, Trade and Industry Ministry and the Nuclear Safety Commission reported that between 370,000 and 630,000 terabecquerels of radioactive contaminants have escaped from reactors 1, 2 and 3. Currently, regulators estimate the plant is emitting only 1 terabecquerel of radioactive material per hour, but levels spiked on March 15 and March 16, Kyodo quoted regulators as saying. A hydrogen explosion on March 15 is believed to have damaged the suppression chamber in unit 2.
In an ongoing effort to identify the sources of radiation leaking from the plant, TEPCO has taken a small sample of water from the spent fuel tank in unit 4 to determine if its fuel has been damaged. Conflicting reports from the Nuclear Regulatory Commission and TEPCO indicated that decay heat from the fuel rods either caused the tank to generate steam or started a fire last month. The water temperature in the tank, now supplied with water from pumps on the ground, recently was measured at 90 C. Its temperature usually ranges between 20 C and 30 C.