Two months before it was made public that fuel melted in three reactors at the Fukushima No. 1 nuclear power plant, a team at the Nuclear and Industrial Safety Agency deduced it but nothing was done with the sensitive information.
Two months before it was made public that fuel melted in three reactors at the Fukushima No. 1 nuclear power plant, a team at the Nuclear and Industrial Safety Agency deduced it but nothing was done with the sensitive information.
The team concluded in a report that meltdowns occurred at the No. 1 to 3 reactors as of 2:45 p.m. on March 18, a week after the Great East Japan Earthquake, according to documents that The Asahi Shimbun obtained through a freedom-of-information request.
But the NISA did not publish the team's analysis because it was a provisional organization hastily assembled of about 10 officials, including from the industry ministry and the Japan Nuclear Energy Safety Organization.
Eiji Hiraoka, the NISA’s vice director-general, said he did not prioritize the analysis because there were no rules on incorporating work by provisional organizations.
“We must reflect on that we failed to establish (the team) within the formal organizational structure,” Hiraoka said.
The plant’s operator, Tokyo Electric Power Co., acknowledged a meltdown at the No. 1 reactor on May 15 and those at the No. 2 and 3 reactors on May 24, two months after the plant was crippled by the March 11 earthquake and tsunami.
The NISA acknowledged the meltdowns only after TEPCO’s announcement. The team’s analysis was not utilized for explanations to the public or other initial responses to the nuclear disaster.
The ad hoc team started its activities on March 14 within the NISA’s Emergency Response Center.
The NISA’s policy planning and coordination division requested the group's formation to obtain level-headed evaluations at a time when conventional divisions responsible for analyses were preoccupied with emergency responses.
The team analyzed data on water levels and pressure, as well as readings of the Containment Atmospheric Monitoring System, which measures radiation dose rates in the reactors’ containment vessels. All data were sent from TEPCO on an around-the-clock basis.
On March 15, radiation levels sharply rose at the No. 1 and 2 reactors, suggesting that melted fuel had fallen to the bottom of the containment vessels.
Despite the meltdowns, the team’s report said stable conditions continued as long as water was pumped in from the outside because melted fuel, accumulated at the bottom, was largely submerged.
But the analysis was treated only as a reference because the team was not formally placed within the NISA’s organizational framework.