Kyodo News (2/18/2012):
Regarding the thermocouple that exhibited abnormal temperatures at the bottom of the Reactor 2 Pressure Vessel at Fukushima I Nuclear Power Plant, TEPCO announced on February 18 that the company had decided to pick another thermocouple at the same height as representing the temperature at the RPV bottom. The official RPV bottom temperature was now about 30 degrees Celsius, the company said.
TEPCO explained that "the new thermocouple is also located at the bottom of the RPV, and it has been confirmed to be working".
There are three thermocouples at the bottom of the RPV at the same height, surrounding the RPV. The temperature at the thermocouple that had been used as official temperature gauge for the RPV bottom [of Reactor 2] started to rise sharply in early February. TEPCO has determined that it is the instrument failure in which the wires have been nearly severed.
The new and improved official thermocouple for the RPV bottom is "69H2", as of 5PM on February 17, 2012 when "69H1" exhibiting -3 degrees Celsius was unceremoniously ditched. (See TEPCO's plant parameters for Reactor 2 RPV temperature as of 2/19/2012 11AM.) The ever-incurious TEPCO also stopped measuring the Reactor 2 RPV temperatures every hour.
The temperature at the CRD Housing is now 212.6 degrees Celsius, after it started the steady rise on February 14 from 112 degrees Celsius. Conveniently, the thermocouple there is also suffering the instrument failure.
On the other hand, the temperature at the "RPV Drain Pipe Upper Part" has plunged from about 50 degrees Celsius in mid January to -0.3 degrees Celsius on February 19, but it is not considered the instrument failure.
Nothing to see here, move on, say TEPCO and the government.