And there is often something left behind, at least in the U.S. where there is no long-term repository for spent nuclear fuel. As a result, on each and every decommissioned nuclear power plant site sit some number of concrete and steel casks encasing the used uranium fuel rods. For example, the Humboldt Bay nuclear power plant being torn down in California has a concrete pad with such cylinders sunk into it so they cannot tip over in an earthquake. In addition, the pad is situated on a hill high enough to avoid a tsunami. "The safety briefing is if the tsunami warning goes off, then run to the top of where the spent fuel is because that's the highest ground around," Hickman says.
In the case of Fukushima, it will be years before the uranium fuel rods—if not too melted and deformed—are cool enough to be shifted to such long-term storage. If the fuel rods are more melted, however, the cleanup will be even more challenging, particularly if they have formed a "puddle". "You can't very easily cool it off because you can't get water to the center," notes nuclear physicist Douglas Akers of INL.
That makes it nearly impossible to remove, hence the puddle that sits in the basement of Chernobyl. "Once you get fuel that is deformed or spread like in Chernobyl, the risk to the worker and engineering controls that need to be put in place to protect the worker become very expensive," CH2M HILL's Kehler explains. "If there is a meltdown that is that extreme, then you are looking at an entombment state for a number of years." It remains unclear exactly how melted the fuel in the three damaged reactors and two crippled spent-fuel pools at Fukushima Daiichi are, although U.S. Secretary of Energy Steven Chu estimated that as much as 70 percent of the fuel rods may have melted.
At the same time, the puddle is relatively impervious. "It's ceramic armor surrounding fission by-products," Akers says.
And then there are the sites that are really contaminated, like Hanford in Washington State—some 1,500 square kilometers laced with the residue of U.S. bomb-making operations stretching back to World War II. "You hope that whoever left it for you cleaned it out," says Kehler, whose company is tasked with cleaning the site. "Sometimes they did and sometimes they didn't."
Of course, even unregulated military sites for the production of nuclear weapons often made at least some attempt to contain radioactive material, including some of the most polluted sites in the world, which Soviet technicians contaminated in pursuit of plutonium. That is not the case for unplanned meltdowns, like the ones that ended the use of TMI reactor No. 2, Chernobyl reactor No. 4, and now Fukushima Daiichi reactor Nos. 1, 2 and 3.
TMI was relatively easy to clean, thanks to safety systems that contained most of the radioactive material. "Only 3 to 4 percent of the reactor inventory [of radioactive noble gases*] was released," Akers says, and most of what did escape remained in the reactor buildings. "Effectively, everything producing any off-site damage was all retained in the facility."
But Fukushima and, even more so, Chernobyl saw the failure of such safety systems to contain radioactive material and—in the case of Chernobyl because of a fire—dispersal occurred over a wide area. Cleaning that is impossible: "From a soil standpoint, there really is no [in-place] treatment for radioactive contamination," Kehler explains. "It's either removal or fix-in-place and control the footprint." As a result, the amoebalike contours of the exclusion zone in Ukraine and Belarus stretch out around the remnants of the defunct nuclear power plant in Ukraine.