Tokyo Electric Power Co. indicated Sunday another thermometer may be malfunctioning at the bottom of the No. 2 reactor vessel at the tsunami-crippled Fukushima Daiichi nuclear power complex as the plant operator observed abnormal temperature readings the previous day.
The thermometer was deemed unavailable for use when it showed an abnormally high electrical resistance level following a sudden increase of temperatures to 60 C on Saturday morning, leaving only one temperature measurement device working properly at the bottom of the reactor vessel, the utility said.
In February, another of the three thermometers at the bottom of the vessel was found to have malfunctioned after showing a surge in temperatures.
“We are able to check temperatures at the vessel’s bottom with the remaining one and assess whether a cold shutdown is maintained by monitoring all thermometers, including those at other locations,” Tokyo Electric officials said.
A stable cold shutdown is achieved when the temperature inside the reactor is kept below 100 C. The latest incident left unavailable 18 of 36 thermometers placed to measure temperatures at the reactor vessel.