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Rising heat at Fukushima plant poses chain reaction danger
Bloomberg News - February 8, 2012
The temperature of the No. 2 reactor was 68.5 degrees Celsius as of 4 p.m. on Tuesday, a decline from 72.2 degrees at 5 a.m., said Osamu Yokokura, a spokesman for the utility.
A reactor temperature must be below 93 degrees to be classed as in cold shutdown, or safe state, which Tepco said was achieved in December.
Nuclear engineers have questioned whether cold shutdown can apply at Fukushima because it's a process used when reactors are shut for regular maintenance or other purposes. In Fukushima, three of the reactors' uranium fuel cores have melted down.
"It was too early to say the plant is safe in December. They declared cold shutdown even though nobody is sure about the location of melted fuel," said Tetsuo Ito, head of the Atomic Energy Research Institute at Kinki University in western Japan. "A similar incident will probably occur again," he said of the rise in reactor temperatures.
Since Feb. 1, temperatures at the bottom of the No. 2 reactor vessel have risen by more than 20 degrees Celsius, according to the company's data.
Tepco said it increased the rate of cooling water being injected into the unit to 13.5 cubic meters per hour from 10.5 cubic meters per hour at 4:24 a.m. on Tuesday. "Tepco is in a dilemma," Ito said, because as it injects more water, more radioactive water will accumulate in the basements of plant buildings.
The disaster caused cooling system failures that led to the reactor fuel meltdowns, release of radiation and the evacuation of about 160,000 people.