Earthquake in Japan: How to avoid nuclear meltdowns.

The Hive
Collective wisdom.
March 28 2011 5:50 PM

How To Fix the Nuclear Crisis in Japan

A physicist breaks down the best reader ideas for how to fix Fukushima.

Fukushima nuclear power plant. Click image to expand.
The Fukushima nuclear plant

Within days of the devastating tsunami that struck northeast Japan, the situation at the damaged Fukushima I nuclear power plant had become a crisis of nearly unthinkable proportions. Widespread failure in the primary and backup cooling systems forced engineers to resort to increasingly desperate and creative measures to avert an unmitigated nuclear catastrophe. In that spirit, Slate solicited ideas from readers for what to do next.

To help evaluate the responses, we enlisted the aid of University of Virginia physicist Lou Bloomfield. Here are his thoughts on the most popular entries, in order of increasing viability. (Submissions have been edited for clarity.)

1. Inflatable Dome, by Victor Lyatkher
The area around the nuclear station is encircled by a six-meter-wide concrete wall. A plastic inflatable dome with a convex roof is built to surround the station.  This inflatable "pool" is filled with five-or-more meters of water. At the same time, pressured air is injected into the plastic dome in a tangential direction, creating a stream vortex—like a tornado—inside the dome. That will create a deep pressure decline in the center. The pool-dam will continue to have sides raised up to 1000 meters with a roof on top of it that will condensate boiling water. The roof on top of the dome is chilled by high winds and should have controlled windows with filters to allow it to release pressure if needed. To prevent allowing radiation into groundwater, the concrete road should be surrounded by wells filled with concrete.

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Many readers responded positively to this solution, though others estimated that it would take far too long to be effective. But either way, Bloomfield saw some problems:

"If I've interpreted this story correctly, then it's not realistic. Without sealing the bottom of the pool, the water is going to work its way downward and carrying radioactive materials downward with it. Those materials will contaminate the groundwater. The higher the walls and the deeper the pool of water becomes, the more pressure there will be at the bottom of the pool and the faster water and radioactive junk will seep into the ground and groundwater. Swirling the water to depress the height of water near the middle of the pool and raise the height of water near the walls would require enormous power because viscous interactions in the water and at the walls will dissipate energy rapidly. Moreover, swirling would increase the pressure at the wall surfaces and necessitate thicker walls."

2. Drop the fuel rods in the ocean, by user GoneToPlaid.
Most of the localized radiation is emanating from the fuel rods in the storage pools. This prevents technicians from working at the reactors for any extended period of time. Using helicopters with long cables or large mobile cranes shielded with steel cladding and thick lead windows, hook onto the fuel rod cages, haul them out, and drop them into the sea fairly nearby. This is only a temporary solution, but it would rapidly cool the fuel rods, quickly reduce radiation levels, and prevent any possibility of criticality if the fuel rod bundles melt and slump to the bottom of the storage pools. When the local radiation levels plummet, much longer shifts of workers will be able to do what is necessary in order to restore power to the reactors in order to run the pumps and prevent core meltdowns.

But Bloomfield says: "I don't think that anyone can get near those fuel rods, let alone airlift them out. Ground-based cranes would probably be more reasonable, just because that removes all the complications of operating a helicopter with precision and trying to shield the pilots from the serious radiation involved. (Shielding a helicopter with lead or steel is likely to make that helicopter too heavy to fly.)

"Even with cranes, though, access to those fuel rods requires opening up the containment vessels," he continues "I don't think that anyone wants to open the entire top of one of those vessels. If the fuel storage pools have boiled away and exposed fuel rods to overheat and melt, then any movement is likely to disperse more radioactive junk far and wide. I also don't think that anyone wants to put them in the sea, where the radioactive constituents in the breached fuel assemblies can then leach out into the oceans. The oceans are big, but if this were a really good solution for disposing of nuclear waste, wouldn't we already be doing it? All the fuss about Yucca Mountain would have been avoidable."

3. Sand, By user SmagBoy1
We need to inject something into the core of any non-exposed fuel that will be able to absorb most of the neutrons that are given off via fission. Even under perfect conditions, the uranium in the fuel will fission due to natural decay, but the material we add could keep that occasional event from cascading. What material? Water is the obvious choice. But, when heated, it boils off. And there's a continued health risk to those applying more water to the fuel (either via helicopter, hoses, etc.). Plus, unless the vessel is complete enough to hold the water that dropped or injected, it will all run out of the core, producing a need for continued application. As such, what we need is a less viscous, equally or superiorly neutron absorbent material. What is that material? Sand. Pure, simple sand. It's almost as abundant as water and can absorb neutrons just as well. Plus, it's far less viscous, and, if wet, will not run out of the area in which it's placed.

But Bloomfield says: "The problem with the fuel rods isn't uranium. It's the uranium daughter nuclei created by fissions of the past (while the fuel was being used in the reactors). Those fuel rods are now rich in shorter-lived, highly radioactive isotopes of more prosaic elements, including cesium and iodine. They aren't being heated by fission chain reactions, they're being heated by their own intense spontaneous radioactivity. Only time will reduce that self-heating. Until that time, they have to be cooled and contained. Water slows neutrons and absorbs heat, but that water has to be cooled as well so that the radioactive fuel rods don't heat it to boiling. Using sand in place of water would slow the neutrons, but something would have to keep the sand cool (the fuel rods will heat the sand until the whole mixture melts).

"If the water in one of those fuel storage pools was replaced by sand, I would expect the fuel rods to eventually heat the sand so hot that bad things would start to happen. The fuel rods would begin to leak and gaseous radioactive junk would probably begin to volatilize out of the sand. Sand does melt, at about 1700 C, but the resulting quartz glass is so viscous that it wouldn't circulate much and it would instead get hotter and hotter. It would probably start to vaporize, along with aspects of the fuel rods. I don't know what reactions would occur, but I would not be surprised if the cladding on the fuel rods interacted badly with molten quartz (liquid silicone can actually oxidize some metals, notably aluminum—lass factories are paranoid about aluminum because if one aluminum can gets into their molten glass furnace, they'll have useless, contaminated glass for a day.

"I think that glass encapsulation of radioactive waste is one of the viable long-term confinement concepts. But I'm pretty sure that that glass encapsulation requires much, much more dilute radioactive waste. Packing a small amount of glass or sand chock-full of fuel rods is going to produce a lot of heat in a hurry and the glass probably won't be able to handle the heat flow without terrible consequences."

4 . Cheap robots, by Gunnar Helliesen
Use remote control vehicles to enter the stricken plant and gather data, bring fire hoses to bear, and start the initial dumping of concrete, if it comes to that. What is very important here is to apply the KISS principle: Use sturdy, cheap and simple vehicles, not complex and expensive ones. Use the remote controlled mini-tank called the Ripsaw. Do NOT use prototype walking humanoid robots filled to the brim with electronics that will just fail anyway. Build a full-sized helicopter to be remote controlled, so it can go much closer to the plant, hover, and precision-dump water or concrete. Never mind that it might crash, just build 10 or 20 of them. It's still cheap compared to the cleanup costs of a full-scale meltdown.

Slate's Will Saletan recently reported that several prototypes of such robots have been built, but none have become widely used.

Bloomfield says: "I think that this idea is reasonable. I suspect that many of the people working on the disaster wish that they had more and better unmanned vehicles  for working in the high radiation zones. It seems like a good plan for the international nuclear poer community to develop a collection of such remotely controlled machines—water delivery machines, remotely piloted helicopters, and even remotely control data acquisition machines. It would be nice, for example, just to have robots that could go take a look at the fuel storage pools and report back the water levels in those pools. There have been competitions in the past for self-guided vehicles that travel across the desert or through urban environments. In the present case, we don't even need the self-guided sophistication—remotely guided would be good enough and much easier to do. I could imagine a competition for remotely guided nuclear disaster robots. It would be great and lots of fun to watch."

Chris Wilson is a Slate contributor.

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