Japan's Nuclear and Industrial Safety Agency (NISA) said March 12 that the explosion at the Fukushima Daiichi No. 1 nuclear plant could only have been caused by a meltdown of the reactor core, Japanese daily Nikkei reported. This statement seemed somewhat at odds with Japanese Chief Cabinet Secretary Yukio Edano's comments earlier March 12, in which he said "the walls of the building containing the reactor were destroyed, meaning that the metal container encasing the reactor did not explode."
NISA's statement is significant because it is the government agency that reports to the Agency for Natural Resources and Energy within the Ministry of Economy, Trade and Industry. NISA works in conjunction with the Atomic Energy Commission. Its role is to provide oversight to the industry and is responsible for signing off construction of new plants, among other things. It has been criticized for approving nuclear plants on geological fault lines and for an alleged conflict of interest in regulating the nuclear sector. It was NISA that issued the order for the opening of the valve to release pressure — and thus allegedly some radiation — from the Fukushima power plant.