Physically Explaining Japan’s Natural Disaster

Amidst a rush of news stories covering the recent triple-disaster in Japan, it is often hard to fully understand all of what has happened merely from reading about it in popular publications. Three physics faculty members held a special forum to discuss the recent disaster in Japan, and specifically the ongoing nuclear crisis at the Fukushima plant.

Assistant Professor of Physics Josh Grossman explained what happens to the Earth and water during an earthquake and tsunami. All earthquakes are caused by pressure buildup as plates of the Earth’s crust push against each other and become stuck. An earthquake is what happens when these plates suddenly become unstuck and move around. On March 11, that compressed energy was violently released in the form of a magnitude 9.0 earthquake, moving Japan and North America eight feet closer to each other.

“A lot of the time it’s hard to wrap our heads around the way a tsunami behaves,” explained Grossman. A tsunami isn’t just a giant wave that heads for shore. It starts out as a barely-perceptible bulge in the ocean, though underneath a shock wave of water is traveling at hundreds of miles an hour, almost as fast as a jet plane. As that shock wave reaches the shore, the sea floor bottom compresses the shock wave into those towering waves that we all think of as a tsunami.

“When the quake hits, the power plants shut down, as a basic safety measure,” explained Assistant Professor of Physics Erin De Pree in her talk about the responses to the disaster. “Then the tsunami hit. This was a problem.”

The tsunami knocked out Fukushima’s backup generators. Four hours after the earthquake and tsunami had struck,  the plant was forced to switch to battery power. The most important thing that electricity did at the power plant was keep chambers filled with waste, called spent fuel pools, properly cooled. After the backup generators were lost, all the energy from the batteries was spent keeping the spent fuel pools from overheating.

“It was scarier than Three Mile Island, because the power shut off in the control room to conserve electricity for cooling the reactor,” said De Pree. The control room was dark, and operators could not read any direct readouts from sensors in the reactor. After less than a day, these backup batteries ran out of power and there was nothing to keep the spent fuel from overheating except the pools of water that surrounded the spend fuel — which began to boil. Since then, all efforts that the Japanese government and Tokyo Electric have made have involved keeping these spent fuel pools from boiling away all the water and risking a nuclear meltdown.

The Fukushima crisis was not the same as the crises at Three Mile Island or Chernobyl. “This is the first time spent fuel pools have been newsworthy since the 1950s.”

Why use nuclear energy at all then, if it’s so dangerous? “If you use one gram of Uranium-235 (U-235) you have 1 megawatt for a day,” said Professor of Physics Katsunori Mita. For the same amount of energy in coal, explained Mita, you would need 2.6 pounds, over a thousand times more in weight. Plus, using U-235, the spent fuel will be converted into Plutonium 239 – which is usable as a nuclear power source. “An amazing thing about nuclear energy [is] you can make more fuel than it consumes,” said Mita.

On top of that, nuclear energy is normally not so dangerous. “When the splitting of the nucleus occurs, enormous amounts of power are released, [but] the reactor cannot become a bomb. That’s impossible. There is not enough uranium,” concluded Mita.

 

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