The temperature at the No.2 reactor of the Fukushima Daiichi nuclear power plant keeps rising even after the injection of more cooling water on Saturday night. The plant operator, Tokyo Electric Power Company, or TEPCO, says a thermometer at the bottom of the reactor registered 78.3 degrees Celsius at 10 AM on Sunday. The reading began to rise in late January to around 70 degrees. TEPCO pumped in more water to push down the temperature, but it rose again on Saturday night to 74.9 degrees, according to Japan''s (NHK WORLD) website. The temperature continued to climb on Sunday morning to hit its highest level since last December, when the government and TEPCO declared all the reactors were at a state of cold shutdown, with their temperatures below 100 degrees. TEPCO denied the possibility of nuclear criticality, saying two other thermometers at the bottom of the reactor show temperatures at around 35 degrees. It adds that continuous nuclear fission would generate radioactive xenon, but gas samples collected from near the reactor found the element below the detection limit. TEPCO is set to dump in boric acid to prevent any nuclear criticality later on Sunday and increase the volume of cooling water by 3 tons per hour. Under new guidelines, the company must keep reactor temperatures at 80 degrees or below, given thermometers'' margin of error of up to 20 degrees.