The Fukushima Daiichi meltdown was the worst nuclear accident since the Chernobyl catastrophe in 1986. A tsunami struck the coast of Japan that caused three nuclear reactors to melt to their cores at the Fukushima power plant. Less widely known is how much worse the catastrophe could have been: Fukushima had a sister power plant, the Fukushima Daini, which barely escaped a nuclear meltdown.

The Fukushima Daini plant is located about six miles south of Fukushima Daiichi. The traditional rule book for decision making went out the window when the tsunami blasted Japan’s coast. Nevertheless, the site superintendent, Naohiro Masuda, along with the rest of the 400 employees, survived the chaos without triggering an explosion or nuclear meltdown.⁽¹⁾

So how did Daini avoid the fate of the northern Fukushima power plant? The magnitude 9.0 earthquake produced waves three times higher than what Daini was designed to withstand. Only one diesel generator and a power line remained intact. Fortunately, that one power line was able to supply electricity to control rooms, which monitored water level, temperature and pressure.

Assessing the damage

Nevertheless, three of the four reactors didn’t have enough electricity to maintain their cooling systems. The inability to cool the reactors is what led to the nuclear meltdown at the Fukushima power plant. To keep the reactors cool, Masuda and his team had to figure out a way to connect those reactors to a single power line.

Before Masuda could start connecting the reactors to the power line, he had to persuade people to act. Let’s not forget that they were in the midst of a natural disaster of almost biblical proportions. In particular, Masuda had to figure out how to coax his peers to deny the basic primordial instinct of self-preservation.

The lights went out at the power plant. In order to get an estimate of the damage, Masuda had to convince his team to go examine the field. “I was not sure if my team would go to the field if I asked, and if it was even safe to dispatch people there,” Masuda said.⁽¹⁾

Masuda started writing down numbers on a white board, including the frequency and magnitude of the aftershocks. He was trying to tally a chart that reflected decreasing danger. “It was not convincing at all,” he later admitted, “but I needed them to be convinced.”⁽¹⁾

By 10 PM, Masuda requested four of the ten team leaders to go out and survey the damage. To Masuda’s relief, no one refused.⁽¹⁾

A crucial decision

The workers reported back to Masuda after surveying the damage. Masuda devised a plan to keep the reactors cool based upon the data gathered, which had to be revised several times as new challenges emerged.

Among the revisions was a crucial choice to change priorities. The night before the earthquake, engineers had calculated how much energy was necessary to power the reactors. Unit 2 was originally given top priority, since its pressure was the highest; however, hours later, Unit 1’s pressure exceeded Unit 2’s pressure.⁽¹⁾

This dilemma required officials to reroute a cable to power the reactors. Almost two days after the disaster, workers finished laying down a six-mile cable through the site. Two hours before Unit 1 was expected to reach its threshold, its cooling system came back online. By contrast, on the morning of March 15, the Fukushima Daiichi power plant was dealing with its third explosion.

What ultimately saved Fukushima Daini was a miraculously sustained power supply, whereas Fukushima Daiichi lost all of its power. While the Fukushima catastrophe was the worst nuclear disaster since Chernobyl, had Daini collapsed, the two debacles combined would have produced the worst nuclear meltdown in human history.

Sources include:

(1) HBR.org