Japans second nuclear reactor in the quake-stricken north experienced serious troubles on Sunday after its emergency cooling system failed, triggering a fresh radiation threat, a day after a blast rocked the site following a massive quake and tsunami in which thousands of people are feared dead. The Fukushima power plants operator said pressure was rising inside reactor No. 3 after it lost its cooling system. The development came a day tens of thousands of people were evacuated from the area after a blast and leakage from the No. 1 reactor at Fukushima, 240 km north of the capital Tokyo. The explosion had blown off the roof and walls around the reactor. According to IAEA, the UN nuclear watchdog agency, an estimated 1,70,000 people had been evacuated from the area around the plant. Hourly radiation at the site was measured at 882 micro sievert, in excess of the allowable level of 500, Kyodo news agency reported. The nuclear safety agency also said the Tokyo Electric Company acknowledged that the No. 3 reactor of the Fukushima plant had lost its cooling functions, while at least 22 people are known to have been exposed to radiation near the plant since yesterday. The No. 3 reactor had lost the ability to cool its core and was now in the process of releasing radioactive steam, Chief Cabinet Secretary Yukio Edano said.