Japan has started looking into the causes of the nuclear crisis at the Fukushima Daiichi power plant, with an independent panel of experts holding their first gathering today in Tokyo. The meeting of the panel, led by Yotaro Hatamura, a researcher on human error, marks the beginning of a comprehensive investigation and verification of the country's worst radiation-leaking nuclear accident about three months after it was triggered by the March 11 megaquake and tsunami. Prime Minister Naoto Kan called on the members to make “firm judgments as a panel independent from the government,' and said he is willing to be questioned as part of the panel's investigation process. The panel, entitled to question people concerned, including officials of the plant operator Tokyo Electric Power Co., related Cabinet members and government bureaucrats, would also study the steps taken by the utility and the government'sinitial response to deal with the disaster. The country's nuclear safety regulatory system is also expected to be examined amid criticism over whether it is appropriate to have the nuclear regulatory agency under the wing of the industry ministry that promotes nuclear power. Hit by the magnitude 9.0 earthquake and tsunami waves more than 14 metres high, the six-reactor nuclear complex lost nearly all of its power sources, leading the cooling functions of the reactors and spent nuclear fuel pools at the Nos. 1 to4 units to fail. The Nos. 1 to 3 reactors' cores are assumed to have suffered meltdowns, although the melted fuel is now believed to be kept cool at the bottom of each reactor pressure vessel because water is being injected into the vessel as an emergency measure. The remaining Nos. 4 to 6 reactors were under maintenance at the time of the earthquake and the No. 4 unit has all the fuel in the spent fuel tank. The Nos. 5 and 6 reactors achieved a state of cold shutdown, helped by one emergency diesel generator which escaped being flooded.