<p>It also repudiated the widely-held belief that a hydrogen explosion might have occurred at its No. 2 reactor.<br /><br />The Tokyo Electric Power Co's in-house report indicated the utility prepared the manual with a view to dealing with nuclear plant accidents including severe incidents on the assumption that emergency power generators, including diesel generators, would work properly to keep reactor cooling systems functioning.<br /><br />In fact, none of the backup generators worked after the March 11 earthquake and tsunami hit the plant located on the Pacific coast.<br /><br />According to the report compiled by an intra-company investigative committee, the plant operator first recognized that large explosions had been heard at the No. 2 and No. 4 reactors past 6 a.m. on March 15.<br /><br />The utility then confirmed that the air pressure in an area near the containment vessel of the No. 2 unit was falling and also that the upper part of the building housing the No. 4 unit had been seriously damaged.<br /><br />Subsequent analysis of the data led the company to conclude that an explosion had occurred at the No. 4 reactor, but it "erroneously recognized" that something akin to an explosion had possibly taken place at the No. 2 unit, according to the report.<br /><br />In the accident at the Fukushima plant, the buildings housing the No. 1 and No. 3 reactors were damaged due to hydrogen explosions while that of the No. 4 unit, which was idled for a regular inspection at the time of the natural disasters, was also destroyed. The building of the No. 2 reactor still stands.</p>
<p>It also repudiated the widely-held belief that a hydrogen explosion might have occurred at its No. 2 reactor.<br /><br />The Tokyo Electric Power Co's in-house report indicated the utility prepared the manual with a view to dealing with nuclear plant accidents including severe incidents on the assumption that emergency power generators, including diesel generators, would work properly to keep reactor cooling systems functioning.<br /><br />In fact, none of the backup generators worked after the March 11 earthquake and tsunami hit the plant located on the Pacific coast.<br /><br />According to the report compiled by an intra-company investigative committee, the plant operator first recognized that large explosions had been heard at the No. 2 and No. 4 reactors past 6 a.m. on March 15.<br /><br />The utility then confirmed that the air pressure in an area near the containment vessel of the No. 2 unit was falling and also that the upper part of the building housing the No. 4 unit had been seriously damaged.<br /><br />Subsequent analysis of the data led the company to conclude that an explosion had occurred at the No. 4 reactor, but it "erroneously recognized" that something akin to an explosion had possibly taken place at the No. 2 unit, according to the report.<br /><br />In the accident at the Fukushima plant, the buildings housing the No. 1 and No. 3 reactors were damaged due to hydrogen explosions while that of the No. 4 unit, which was idled for a regular inspection at the time of the natural disasters, was also destroyed. The building of the No. 2 reactor still stands.</p>