The catastrophic events that crippled the Fukushima No. 1 nuclear power plant were mainly due to a tsunami that was off the charts.
Nobody foresaw such towering tidal waves hitting with such force.
But that was not the only factor. The problems were exacerbated by safety design for important equipment as well as inadequate emergency procedures, according to people associated with Tokyo Electric Power Co., the plant's operator.
"There were problems with safety design of equipment at the Fukushima No. 1 nuclear power plant," said a nuclear engineer who once worked for TEPCO.
A key design flaw, according to the engineer, centered on the location of vital pumping equipment used to bring in seawater to cool the reactor cores. The equipment was located near the coast.
The tsunami triggered by the March 11 Great East Japan Earthquake wrecked both the equipment and its emergency generators. That led to a failure to pump in cooling water to the core.
While the pumping equipment had a cover, it was "almost totally exposed," according to the engineer.
In comparison, the pumping equipment and emergency generators at the Fukushima No. 2 nuclear power plant, situated some 12 kilometers south of the Fukushima No. 1 plant, are installed within a roofed building, although they also lie by the ocean.
A senior official in TEPCO's nuclear power division acknowledged that "a major problem with the pumping equipment was that it was exposed, unlike the Fukushima No. 2 plant where it was installed within a building."
The engineer also referred to piping that is connected to turbine buildings at the No. 1 plant.
"From the time of construction, there were many rough points in terms of safety as the piping was buried underground (without any covering)," the engineer said.
While improvements had been made over the years, such as covering the piping with concrete, the engineer said, "There were sections where the work did not keep up, and the pumping equipment was one example of that."
The four reactors at the Fukushima No. 2 plant all automatically shut down as intended after the earthquake. While there were initial problems in the cooling system pumping in seawater, the cooling mechanism began operating through an external power source.
By March 15, all four reactors had reached the cold shutdown stage, with core temperatures under 100 degrees.
Slowness in responding to upgraded anti-quake guidelines also contributed to the extensive damage at the No. 1 plant.
The difference is evident in a comparison with the Tokai No. 2 nuclear power plant operated by Japan Atomic Power Co. in Tokai, Ibaraki Prefecture.
While the tsunami also battered the Tokai No. 2 plant, protective walls that were constructed after a review of anti-quake guidelines ensured that a power source was maintained.
According to Japan Atomic Power officials, the Tokai No. 2 plant automatically shut down after the earthquake. Because its outside power source was lost, emergency diesel generators began operating to continue cooling the core.
In the blink of an eye, a tsunami some 5 meters high smashed into the plant and flooded part of the complex.
A seawater pump used for cooling purposes that relied on emergency generators was located on the northern side of the plant. It, too, was flooded and malfunctioned.
However, the pump on the southern side of the plant was not flooded so the emergency generator continued operating, allowing for the cooling process to continue.
When the anti-quake guidelines for nuclear power plants were reviewed in 2006, Japan Atomic Power factored in the possibility of a 5-meter tsunami striking the plant.
To cope with such an eventuality, the company decided to construct side walls to cover the pumps that are connected to the emergency generators. The plant already had a protective wall against tsunami.
Construction of the side walls was completed last September.
Because related work on the northern side wall was not completed, the pump on that side was flooded. However, the southern side wall protected the pump on that side.
TEPCO conducted safety checks of its various reactors after the anti-quake guidelines were updated, but the company's focus was on dealing with shaking from quakes rather than tsunami, according to sources.
The process of implementing new measures was still continuing when the twin disasters struck, creating a third, and potentially more horrific, nuclear catastrophe.
TEPCO's failure to consider that an outside power source would not be restored for a protracted period may have also compounded problems at the Fukushima No. 1 plant.
When one of the reactors shut down, water began to be pumped into the core, according to TEPCO sources. But when the water reached a certain height, the supply was automatically turned off as is supposed to happen. This is because major problems can occur if the core is filled with water and it overflows into the turbine.
However, the monstrous tsunami cut off the power source to the reactors, stopping the pumps and leading to a lengthy period when the reactor cores could not be cooled.
When asked whether the reactor cores should have been immediately immersed in water, a mid-level TEPCO official said, "I personally feel that should have been done."
The official said the decision was likely not taken because of a general sense that an outside power source would be restored within hours.
There are procedures and training exercises to deal with a situation in which all outside power sources are lost.
However, a TEPCO source said, "In hindsight, (the function to protect the turbine) had a negative effect."
The mid-level official said: "In the few minutes (until the tsunami hit), there may have been someone who thought, 'Bring the water level up to totally cover the core.' But I don't know if anyone would have made the decision to go ahead with that move."
Experts blamed TEPCO for not taking measures sooner.
Keiji Miyazaki, professor emeritus of nuclear reactor engineering at Osaka University, said the failure to immerse the cores in water immediately after the earthquake was evidence of a lack of foresight.
"If the cores had been flooded with water, damage to the fuel rods might have been avoided," Miyazaki said. "Another question is why the valves to release pressure from the pressure container and containment vessel were not opened immediately."
Kiyoshi Sakurai, a commentator on technology issues, pointed to a number of safety problems at the Fukushima No. 1 nuclear power plant.
"No careful design was conducted for the pumping equipment or emergency generators," Sakurai said. "Placing the emergency diesel generator in the basement of the turbine building was a mistake because the building has lower anti-quake standards than the building housing the reactor core."
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