Melted uranium fuel in one reactor at the stricken Fukushima No. 1 nuclear facility can now be monitored more closely, after the plant operator fitted a thermometer inside the containment vessel in the hope of getting a clearer picture of conditions inside.
Tokyo Electric Power Co. said Oct. 3 it had fitted the device to the No. 2 reactor because five of six thermometers at the bottom of its pressure vessel failed after the disaster in March 2011.
Three reactors at the plant are believed to have gone into meltdown, the process by which uranium rods overheat and molten fuel and other debris slump to bottom of the pressure vessel.
TEPCO has been trying to keep the temperature at the bottom of the pressure vessels of the No. 1-3 reactors at 80 degrees or lower, which is within the definition of cold shutdown. Thermometers help to monitor that.
It is the first time since the disaster that a new thermometer has been installed inside the No. 2 reactor.
Engineers prepared for the operation by fitting a cylinder to a pipe leading to the containment vessel. That pipe injects a boric acid solution.
Workers then inserted the thermometer and extended it about 10 meters inside the containment vessel. They believe it now rests near the bottom of the pressure vessel.
TEPCO said the gauge was functioning.
In December 2011, the government declared that the three reactors were in the state of cold shutdown. However, at the time of the announcement just one of six gauges at the bottom of the No. 2 pressure vessel was functioning, TEPCO said.
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