Events at the Fukushima nuclear power plant in Japan have implications for nuclear power plants elsewhere in the world, including 23 in the United States that are of the same Generation 2 design, says Raymond Orbach, former Undersecretary for Science at the US Department of Energy under George W. Bush, and now director of the University of Texas’ Energy Institute. Orbach spoke today in a well-attended session on nuclear energy at the American Physical Society meeting in Dallas, Texas. He said several issues arising from Fukushima’s operations by the Tokyo Electric Power Company (Tepco) should result in immediate retrofitting and review of practices at Generation 2 reactors elsewhere in the world.
In particular, Orbach questioned why it took Tepco three days after the tsunami to flood the reactor with seawater after diesel generators that power pumps that circulate crucial coolant water failed, as did backup generators. The injection of seawater is a standard step in nuclear power plants to mitigate the risk of a meltdown in an overheating core, although it also permanently destroys the reactor. “Why did they wait so long? Well of course you ruin the reactor when you do it. It’s also a question of the power company not wanting to admit that all else failed,” he told the meeting. Flooding the reactor sooner could have avoided the need to vent radioactive steam caused by overheating of fuel rods and an explosion caused when steam from the overheating water reacted with zirconium cladding that holds fuel pellets in the reactor vessel to produce hydrogen, Orbach said.
He highlighted measures that could be taken now to make many Generation 2 nuclear power plants safer (Generation 2 plants were built in the 1970s, the same time as the reactors at the Fukushima plant):
-There should be a system of passive cooling for spent fuel so that cooling can continue even once electric power fails (in the Fukushima plant, the power failure led to overheating of spent fuel stored in the reactor)
-There could be a method of venting the primary containment that minimizes hydrogen explosion risk
-Meltdown products (sometimes called “corium”) should stay contained in the reactor vessel even if there is a meltdown ( fear of a meltdown and escape of corium is paramount at Fukushima)
-There should be a core-catcher to mitigate any spillage from the vessel and stop “corium” getting into the water table in case of a meltdown
-Spent nuclear fuel should not be stored in the reactor but should be moved away from the reactor site. (At Fukushima there was up to four times as much spent fuel stored on the reactors as existed in the reactors, posing an extra challenge to avoid overheating when power failed.)
Orbach emphasized that the problems at Fukushima were caused not by the magnitude 9.0 earthquake that hit Japan on March 11, but by the tsunami that followed. The plant was built to survive up to an 8.2 magnitude seismic event and shut down safely following the earthquake, but wasn’t able to cope when the tsunami cut the power to diesel generators and destroyed back-up generators too. Orbach says the scope of the events that followed have been more similar to the scale of Three Mile Island accident than the Chernobyl disaster, even though the plant was just 250 kilometers from the epicenter of a quake larger than it was designed to withstand. “I would argue that shows the safety issues of seismic events are quite good,” he says.
For full coverage of the Fukushima disaster, go to Nature’s news special.
Image: Damage following the explosion at the Fukushima Nuclear Power Plant /AP Photo/Japan Defense Ministry