The temperature levels at Fukushima Daiichi Reactor 2 are forcing workers at Fukushima Daiichi to undertake special measures to verify the accuracy of readings plant workers are using to maintain a state of cold shutdown. On February 22nd, TEPCO found that one thermometer in the lower part of the Reactor Pressure Vessel was trending differently than the other gauges.
TEPCO tested the wires connecting the emergency control control room to the thermometers in the containment and could find no evidence of faulty or broken wires, but in fact confirmed that the DC resistance became higher than the previous tests had shown. Since there is the potential that the temperature readings could be a consequence of the dispersion of the meltdown fuel or because one or more of the thermometers has a defect, TEPCO will develop new tests to evaluate the soundness of the readings, and in the meantime will continue to monitor the level of Xenon-135 in the reactor which would indicate recriticality.
As of February 24th, only 3 temperature readings still labeled as “accurate” by TEPCO have not had temperature levels trending upward in the last 48 hours. The Upper Control Rod gauges have dropped from a 208.8 degree Celsius reading on 2-23, to -5.8 degrees Celsius as of 11:00 am February 24th, the SRV, Feedwater Nozzle, bottom part and upper part of the RPV temperature levels have all risen over the last 48 hours.