Tokyo Electric Power Co. saw signs that a hydrogen explosion was possible at the No. 1 reactor of the Fukushima No. 1 nuclear power plant the night before the explosion occurred on March 12, but did not immediately inform the central government, according to a report published by the Nuclear and Industrial Safety Agency (NISA).
Tokyo Electric Power Co. saw signs that a hydrogen explosion was possible at the No. 1 reactor of the Fukushima No. 1 nuclear power plant the night before the explosion occurred on March 12, but did not immediately inform the central government, according to a report published by the Nuclear and Industrial Safety Agency (NISA).
TEPCO also withheld similar information when the same buildup of hydrogen occurred in the No. 3 reactor, despite being obligated under government safety regulations.
The report says TEPCO detected 290 millisieverts of radiation per hour--a level that prohibits entry into the reactor building--at the No. 1 reactor building at 9:51 p.m. on March 11.
Such a high radiation level indicates the strong possibility of radiation and hydrogen leaks inside.
TEPCO's post-explosion analysis indicated a large amount of hydrogen gas was present before the explosion, indicating it had leaked into the reactor's containment vessel, along with radioactive materials.
Nonetheless, TEPCO delayed until around midnight on March 11 informing NISA for the first time about a possible radiation leak at the No. 1 reactor.
At 11 p.m. on March 11, the company again assessed radiation levels at the reactor and concluded that levels were rising inside the turbine building, and TEPCO was still trying to identify the causes.
But TEPCO waited until 5:14 a.m. on March 12 to clearly state there was radiation leak in its report to NISA. The explosion occurred at 3:36 p.m. that day.
Junichi Matsumoto, a senior TEPCO official, defended the delay, saying the company was not required to report all data showing the possibility of a radiation leak under the government's regulations.