Tokyo Electric Power Co. plans to insert a thermometer through a pipe into the pressure vessel of the No. 2 reactor at the crippled Fukushima nuclear plant to get more accurate readings of interior temperatures.
One of the thermometers affixed to the bottom of the No. 2 reactor pressure vessel went awry and gave abnormal readings of up to 400 degrees in February, causing much anxiety among parties monitoring the situation at the Fukushima No. 1 nuclear power plant.
The Nuclear and Industrial Safety Agency instructed TEPCO to come up with new measurement methods.
TEPCO said 12 of the 59 thermometers affixed to the No. 2 reactor are in disorder.
Although TEPCO presented a number of alternative methods, the most viable approach is to use a pipe that links the exterior of the reactor containment vessel to the interior of the pressure vessel. According to the plan announced on March 2, a thermometer will be inserted, together with an endoscope for visual inspection, from a pipe cutoff.
However, the pipe, which spans 20 meters, is not straight and bends at 90-degree angles along its route. Its diameter is 6.4 millimeters at its narrowest point.
The measurements, expected to begin as early as in July, may face some difficulties.
"We will (test the device) at the No. 5 reactor and other facilitiess to confirm the ability to insert a thermometer," said Junichi Matsumoto, acting general manager of TEPCO's Nuclear Power and Plant Siting Division.
TEPCO is also considering another method to determine temperatures in case the insertion plan fails.
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