Pressure inside one of six boiling water reactors at the Fukushima Daiichi plant is rising after Japan’s massive 8.9-magnitude earthquake knocked out primary and backup power to its cooling system.
Shutdown reactors remain very hot and must continue to be cooled to keep them from superheating steam and ultimately melting into radioactive slag if water levels fall to the point the reactor core itself is uncovered.
Because Japan is earthquake-prone, its 55 nuclear plants are built to very stringent seismic design requirements, said John Luxat, professor and NSERC industrial research chair in nuclear safety analysis at McMaster University’s Department of Engineering Physics. More importantly, unlike Chernobyl in Ukraine, Japanese nuclear power plants also have hardened containment structures over them.
“If cooling is not re-established, then, over time, the fuel in the reactor vessel becomes uncovered and you will get damage similar to what happened at Three Mile Island” in a Pennsylvania nuclear power plant accident in 1979.
It’s relatively easy to re-establish cooling, he said, even if it takes time because it can take many hours before enough water boils away to uncover the core.
“You could get some radioactive releases in the plant and just about all of those will be contained within the containment structure, and there could be some controlled release of gaseous activity.”
Japan’s nuclear safety agency says pressure inside the disabled No. 1 reactor is now 1.5 times normal pressure and officials may vent slightly radioactive water vapour into the atmosphere to lower pressure. The agency says the release would not harm humans or the environment. The U.S. has sent equipment and personnel to assist with restoring cooling to the plant.
“The containment structures are extremely strong reinforced concrete containment structures and I would anticipate they have not experienced much damage.”
In the worst-case scenario, the core becomes uncovered and begins to superheat the steam in the chamber.
“At some point, you can then initiate oxidation of the cladding of the fuel which adds additional chemical heat. You get a progressive heat-up, and then after a number of hours, you could start to get melting of the fuel,” which will fall down into the pool of water below it.
“You could get more and more molten material forming, but that is a relatively slow process.”
Meanwhile, a top McMaster University mathematician who studies quantum and ocean waves was in California for a meeting Friday when the earthquake-generated tsunami that had crossed the Pacific Ocean with the speed of a jumbo jet struck North America’s West Coast.
“A tsunami is not a breaker multiplied by 100,” said Walter Craig, Canada research chair of mathematical analysis and its applications at McMaster University. “It’s like a tide —and a tide is a wave which comes up in six hours and goes down in six hours.”
A tsunami is generated when an earthquake displaces the sea bottom, which in turn displaces the water, transferring tremendous energy.
“Water is raised, and then it moves away,” at a peak speed of up to 800 km/h, depending on how much the ocean floor moved.
The earthquake that caused the Indian Ocean tsunami that killed 230,000 people in late 2004 thrust the sea bottom upwards about 60 centimetres, which was not particularly high, Craig said. The devastation happened because the upward thrust occurred in a line over hundreds of kilometres.
The waves caused by the earthquake in Japan struck the California coast with enough power to crush boats in Crescent City, 500 kilometres north of San Francisco. But along Japan’s eastern coast near the earthquake’s epicentre, the tsunami struck with even more force.
The wave looks like a rise in the level of the seawater of maybe five metres, but because it’s moving fast, and the water doesn’t have a chance to catch up, it will have a hydraulic jump in the front.
It’s like you’re on dry ground, and coming toward you are five metres of water and behind it, it’s three metres deep. It’s not like a breaker, it’s like the tide coming in, except it’s in one minute, not six hours.