Six years after the nuclear disaster in Fukushima, engineers remain vexed by a key question: What damage did the massive earthquake cause at the atomic plant before it was hit by the subsequent tsunami?
The answer matters because of the potential implications for the earthquake safety standards of other nuclear reactors in Japan, which sits on the seismically unstable Ring of Fire around the Pacific. The area accounts for about 90% of the planet’s earthquakes, with Japan being shaken by 10% of them, according to the US Geological Survey.
The impact of the quake is “still actually a question mark,” Mitsuhiko Tanaka, a former nuclear equipment engineer for Hitachi Ltd., said at a press conference in Tokyo.
“But I’m also saying that the anti-seismic design of the power stations was inadequate and I’m also saying that without the tsunami the same accident possibly would have occurred. So even excluding the tsunami, just the earthquake alone could possibly cause a major rupture. I’m stressing that one should not neglect or ignore the issue of the earthquake.”
That commission, which had the power to subpoena evidence, differed from other studies by placing a greater emphasis on the potential quake damage. Indeed, its 2012 report said Tepco “was too quick to cite the tsunami as the cause of the nuclear accident and deny that the earthquake caused any damage.”
The panel, which was also scathing about the lax approach of the then regulators, raised the possibility that the quake damaged equipment necessary for ensuring safety and that a small-scale accident involving a loss of coolant occurred in unit 1.
Looking back at the six-month inquiry, Tanaka said: “It is really quite unfortunate that the investigation committee disbanded without really exposing or explaining much after the accident. Much remains unresolved.”