Gov't agency to resume probe into cause of Fukushima nuclear accident

5 September 2019

The central government's Nuclear Regulation Authority confirmed at its meeting in Tokyo on Sept. 4 that it will resume investigation at Tokyo Electric Power Co.'s Fukushima Daiichi plant that was crippled by the 2011 accident in a fresh bid to identify what caused the disaster.

Based on findings obtained through progress in the work to decommission the plant, the NRA will analyze the process of dispersion of radioactive fallout as well as the loss of electrical power sources that led to the accident, seeking to draw up a more detailed interim report in 2020. The agency came up with an initial interim report in 2014 but it failed to cover some matters due to high levels of radioactivity at the plant. It will deepen the analysis of factors behind the mishap through the additional investigation and use findings from the probe to help prevent severe accidents.

The investigation will focus on buildings that house nuclear reactors, including those facilities where radiation dosages have declined following cleanup operations. The NRA will analyze factors and developments that resulted in the accident on the basis of new findings from decommissioning work such as the status of debris of melted nuclear fuel, the distribution of radioactive dosages, and damage to facilities and equipment. It intends to shed light on where and through which routes radioactive substances leaked from containment vessels, the conditions of equipment related to the cooling of reactors, and the mechanism of hydrogen explosions, among other factors.

The planned fresh investigation will be conducted after approval at the NRA's next or later regular meeting. It will include on-the-spot surveys, collection of sample materials and various analyses, to be undertaken in cooperation with the utility and Japan Atomic Energy Agency. The outcome of the probe will be discussed by a panel of experts such as NRA members and outside intellectuals toward compiling a new interim report.

"The question is whether we will be able to learn lessons that should be reflected (in nuclear plant regulations) without ending up just grasping specific phenomena (at the time of the accident)," NRA Chairman Toyoshi Fuketa told reporters after the meeting.

Investigation committees set up separately by the government, parliament and other parties concerned after the March 2011 nuclear accident differed in their views over some points, including the course of events that unfolded in the disaster. In response, the NRA examined challenging issues at study panel meetings and produced the first interim report in October 2014, which blamed the loss of a power source of the No. 1 nuclear reactor not on vibrations caused by the temblor preceding the nuclear accident but on tsunami triggered by the quake. No panel meeting has since been held.

(Translated by Kyodo News)