after pumping the largest amount of water since March 11, 2011, the temperature at the RPV bottom went from 72.2 degrees Celsius at 5AM on February 7 to 66.7 degrees at 5AM on February 8.
According to TEPCO's handout for the press on February 7, 2012, TEPCO has been injecting the water at the rate of 13.5 cubic meters (or tonnes)/hour in the Reactor 2 Pressure Vessel:
The amount of the core spray system injection water was increased from 3.7 m3/h to 6.7 m3/h at 4:24 am on February 7.
The amount of the continuing feed water system injection is 6.8 m3/h.
On February 1, the total amount of water being injected to the Reactor 2 RPV was 9 cubic meters/hour.
By the way, Mainichi Shinbun reported (2/7/2012) that the margin of error of the thermometers on the RPV may be 20 degrees Celsius:
Thermometers exhibited the maximum 20 degrees Celsius error after the March 11, 2011 accident. Since the definition of a cold shutdown state is "to keep the temperature at the bottom of the Reactor Pressure Vessel at 100 degrees Celsius and below", TEPCO's safety regulation specifies that the local municipalities are to be notified when the temperature exceeds 80 degrees Celsius given the maximum margin of error. TEPCO's Matsumoto said in the press conference on February 6, "The reactor is sufficiently cooled, and there is no need to revise the judgment of the cold shutdown state."
So, the current temperature of 66.7 could be as low as 46.7, or as high as 86.7. That's comforting.
The ever-incurious TEPCO and the overseeing agency NISA simply pump more water into the RPV, instead of ever wondering what may be causing the temperature to rise.