The final report expected from the United Nations’ International Atomic Energy Agency on the Fukushima Daiichi nuclear power plant accident that occurred in March 2011, says the three-reactor meltdown was due, in part, to the lack of a response to concerns that a tsunami event could hit the plant, Japanese media are reporting.
The Japanese nuclear energy regulator at the time, the Nuclear Industrial Safety Agency, and the operator of the plant, the Tokyo Electric Power Company, were aware of the possibility of an earthquake-triggered tsunami event that put the plant at risk, the report says. But they failed to heed the warnings.
“The Fukushima Daiichi (No. 1) NPP had some weaknesses which were not fully evaluated by a probabilistic safety assessment, as recommended by the IAEA safety standards,” says the report that will not be officially released until September. The Japan Times reported that it reviewed a copy of the report on Sunday.
The report says that postulations as early as 2007 spelled out the possible results of an 8.3-magnitude earthquake, which would trigger a tsunami of about 15 meters high, which would have overwhelmed the main buildings of the facility’s No. 1 plant.
Instead of shoring up the plant’s defenses, the response at the time was to order more studies, the IAEA report says.
“TEPCO did not take interim compensatory measures in response to these increased estimates of tsunami height, nor did NISA require TEPCO to act promptly on these results,” the report says
“The operators were not fully prepared for the multi-unit loss of power and the loss of cooling caused by the tsunami. Although TEPCO had developed severe accident management guidelines, they did not cover such an unlikely combination of events,” the report says.
While the report says TEPCO and the NISA failed to respond to a potential 8.3-magnitude earthquake, the Great East Japan Earthquake that struck on March 11, 2011, was measured as a 9.0-magnitude earthquake, which is a significantly larger earthquake.
Pointing to another culprit last week, TEPCO said that data collected from a robotic exploration of the plant’s damaged No. 2 building in October shows that a disk that was supposed to rupture to vent radioactive steam at a set amount of pressure in an exhaust pipe failed to burst during the accident.
Much like a fuse representing the weak-point in an electrical system, the disk was expected to burst when pressure built up in the containment vessel exhaust piping system, RT reported.
The disc that did not burst is located between a valve and a containment vessel exhaust pipe. However, the robot that collected data in October did not detect increased radiation near the disk, indicating it failed to burst.
As Reactor No. 1 and No. 2 at Fukushima Daiichi used the same exhaust system, it has been postulated that pressure in the system from Reactor No. 1 served to balance the pressure building up in No. 2. This could explain why the disk did not rupture.