Tokyo Electric Power Co. knew there could be an explosion at the No. 3 reactor at the Fukushima No. 1 nuclear power plant the day before it happened, but didn't report the possibility to authorities.
Tokyo Electric Power Co. knew there could be an explosion at the No. 3 reactor at the Fukushima No. 1 nuclear power plant the day before it happened, but didn't report the possibility to authorities.
The failure to notify the central and local governments was revealed in reports submitted by TEPCO to the Nuclear and Industrial Safety Agency (NISA) of the Ministry of Economy, Trade and Industry (METI).
The reports were made available on NISA's website June 24.
From March 11 to May 31, TEPCO provided 11,000 documents to NISA and neighboring local governments by fax based on Article 10 of the special measures law on nuclear disasters.
According to the documents, a hydrogen explosion took place at the No. 3 reactor building around 11 a.m. on March 14, blowing off the upper part of the building.
Before the explosion, however, TEPCO did not submit to NISA data it had showing that an explosion was possible.
According to the data, 300 millisieverts of radiation per hour were detected in the No. 3 reactor building at 1:17 p.m. on March 13, a day before the explosion.
A report written at 2:07 p.m. also stated there was a strong possibility that hydrogen had accumulated in the No. 3 reactor building.
At 5:20 a.m. on March 14, TEPCO's head office ordered officials at the nuclear power plant to again check hydrogen concentrations in the No. 3 reactor building, a document revealed.
The documents indicate hydrogen was being produced because the fuel rods were exposed to air after the earthquake and tsunami destroyed the cooling system.
However, TEPCO did not report these findings to NISA or local governments.
At a news conference in May, NISA spokesman Hidehiko Nishiyama said: "If we had understood the situation in the No. 3 reactor building before the explosion, we would have notified the public. We will look at TEPCO's failure to report the facts to NISA in the course of the full investigation into the explosion."
Regarding the dumping of seawater into the pressure vessel of the No. 1 reactor to cool it, officials at the plant started the injection at 7:04 p.m. on March 12 and continued it without suspension.
However, TEPCO incorrectly told NISA it had suspended the operation for a short time before restarting at 8:20 p.m.
This report was also included in the documents made available on NISA's website.
Based on the inaccurate report, lawmakers held heated discussions in the Diet on whether the suspension was a good idea when in reality the effort to cool the reactor with seawater had never stopped.
(This story was written by Takashi Sugimoto and Eisuke Sasaki.)