TEPCO used “quake-prone” circuit breakers at Fukushima Daiichi for decades despite warnings

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The total loss of power at Fukushima Daiichi after the March 11th earthquake was worsened by a receiving circuit breaker of Okuma Line which despite being deemed “quake-prone” in 1978 remained installed and in use for more than 30 years.

The circuit breaker at the plant was located at the Switchyard, collapsed in the magnitude 9.0 earthquake, reports have said.  The  outside electric power supply was completely lost as the outside electric power supply facilities, circuit breakers, cables, steel power lines and such like got damaged or were destroyed due to this earthquake, not the tsunami.

After it fell, the subsequent tsunami hit the site, submerging all alternating current (AC) electrical power to the cooling systems for the reactor and reactor fuel ponds, including that from backup diesel generators (although one remained able to operate for Reactor Unit 6 and then Reactor Unit 5), triggering the dreaded “station blackout.”

A diagram of the Fukushima Daiichi electrical switchyards

The Fukushima Disaster has long been characterized as a “beyond-design-basis accident”, however many of the fundamental weaknesses have been simple lapses or complete failures in oversight and judgment related to safety-related decisions.

Officials neglected and ignored previous historical and geological information related to earthquake and tsunami activity and potential in the region, and even lowered the site prior to construction.

The plant was built on a 4.3-6.3 m (14-23 foot) high cliff which offered some natural protection against tsunamis, but the tsunami wave experienced on March 11th, was over 15-25 meters high at points at and around Fukushima Daiichi.

According to TEPCO’s calculations, the maximum probable tsunami at Fukushima was a mere 5.7 meters, and the site therefore was protected by a 6 m protective wall.  The utility had been delaying the publication of new research which had significantly increased the potential threat, but which was still minimal when compared to the actual experienced tsunami on March 11th.

The 1978 report by members of a panel at the Electric Technology Research Association said that the structure supporting the circuit breaker in question was not strong enough and pointed to many cases of damage caused by past temblors.

The members, including officials of TEPCO and the Natural Resources and Energy Agency as well as experts, recommended that utilities install a more quakeproof device, which housed major equipment in a tank.

The faulty circuit breakers will likely still be overlooked, the disaster will be deemed as inevitable, the Nuclear and Industrial Safety Agency already says most of the nuclear plants in Japan have introduced the newer more earthquake resistant tank-shaped devices.

A photo of the broken ceramic insulators at Fukushima Daiichi after the 1978 earthquake

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