13 Février 2012
TOKYO (Kyodo) -- Thermometer readings at the bottom of the No. 2 reactor at the damaged Fukushima Daiichi nuclear plant rose further Monday to exceed 90 C for the first time since it attained a cold shutdown in December, reaching a new high of 93.7 C as of 11 a.m., Tokyo Electric Power Co. said.
While concerns are mounting that the reactor may be reheating, TEPCO said it was likely the thermometer was malfunctioning. The device in question had fluctuated between 75 C and 90 C within a short time, while readings from two other thermometers also at the bottom of the reactor vessel have remained around 35 C.
Earlier in the morning, nuclear disaster minister Goshi Hosono said at a parliament budget committee, "The device's movements are perplexing. At this stage, however, it is not necessary to change the judgment that (the reactor is) in a state of cold shutdown."
TEPCO reported on Sunday to the Nuclear and Industrial Safety Agency of the Economy, Trade and Industry Ministry that the temperature exceeded the limit of 80 C designated by the company's safety regulation for maintaining a cold shutdown. The temperature readings first began rising on Feb. 1.
The utility said it believes sustained nuclear reactions were not taking place in the reactor as no radioactive xenon has been detected inside the containment vessel. To prevent the possibility of the reactor going critical, it has increased the amount of water injected as coolant by 3 tons per hour and poured in 1 ton of boric acid on Sunday.
Junichi Matsumoto, spokesman of the plant operator, told a news conference Monday, "It is likely the thermometer is malfunctioning."
Meanwhile, Fukushima Gov. Yuhei Sato urged the nuclear safety agency to investigate the reason behind the temperature rise and demanded that information be disclosed to the public to ease residents' concerns.
A stable cold shutdown is achieved when the temperature inside the reactor is kept below 100 C. TEPCO considers it desirable to keep the temperature below 80 C, assuming a margin of error of 20 C for the thermometers.
The Nos. 1 to 3 reactors at the Fukushima Daiichi plant in northeastern Japan experienced meltdowns as a result of the loss of key cooling functions in the wake of the devastating earthquake and tsunami on March 11 last year. Melted fuel is believed to have gathered at the bottom of the reactors' pressure vessels.
TEPCO carefully monitoring No.2 reactor
The operator of the Fukushima Daiichi nuclear plant is carefully monitoring the No. 2 reactor one day after the reading of one of its thermometers topped the critical safety threshold of 80 degrees Celsius.
The reading of the thermometer at the bottom of the containment vessel shifted between 80 and 90 degrees even after plant workers increased the amount of water injected into the reactor to about 17 tons per hour.
As of 10 AM on Monday, the reading stood at 91.2 degrees.
The Tokyo Electric Power Company says the thermometer could be malfunctioning, as 2 other thermometers at the same height are showing temperatures of around 33 degrees.
It says 3 other thermometers about 1.5 meters below the others show that temperatures inside the reactor are falling.
TEPCO adds it will continue to carefully monitor the reactor, as it has yet to confirm that the thermometer is malfunctioning.