Three Mile Island. Chernobyl. The China Syndrome. And now, Fukushima Daiichi. All are bywords for nuclear disaster. That doesn't even get into the fact we don't know what to do with the waste resulting from fission power. And yet, like it or not, nuclear power is going to at least have to be in the mix if we're going to make a smooth transition into a post-petroleum age. What are we to do?
For starters, the US can start taking the lead in developing new generations of commercial reactors that are safer and produce less waste. If President Obama is serious about creating a green economy, this has to be on the table, no less than improving solar and wind tech.
I've been thinking a lot about this. There are proven reactor designs that are safer and more efficient than the water cooled reactors failing in Japan, and that failed at Three Mile Island and Chernobyl.
For instance, there's the Molten Salt Reactor. This is, in some ways, a very old technology. It was first used as a part of research into the feasibility nuclear propulsion for aircraft. A modified B-36 bomber powered by an experimental molten salt reactor small enough to fit in the plane's bomb bay flew numerous times in the late '50s before the program was ended in 1961. Oak Ridge produced a working experimental reactor of this design in the mid-70s. So the basic concept has been around since our grandparents' time and has been successfully proven.
There are numerous advantages to this design. Using thorium, rather than uranium, as fuel, is cheaper since thorium is about as abundant as lead and the reactor then "breeds" uranium. Using molten salt as a cooling medium allows for a more efficient heat exchange and thus more efficient power production. The fuel is easier to reprocess. Finally, because the salt doesn't need to be kept under pressure which makes this a safer design than a water-cooled reactor.
The primary disadvantage seems to be upkeep. The thorium cycle produces more neutrons, which can cause problems; the nickel alloy used to shield the reactor core can also be corroded by stray neutrons and, in the event of an improper shutdown, the salt itself.
Pebble Bed Reactors
NPR's Morning Edition did a story on safer reactor designs yesterday morning, focusing on the so-called "pebble bed" design. Developed in Germany, this design embeds nuclear material in "pebbles" of graphite of tennis ball size or smaller, in a reactor cooled by inert gas. Due to the design, a pebble bed reactor can't melt down; thanks to an effect called doppler broadening the reaction is self-limiting. As with the molten salt reactor, the system is more efficient at generating power. It is also less complex than current commercial reactors.
The main disadvantages seem to be waste and flammability of the graphite pebbles. Though the waste produced by pebble bed reactors are less radioactive than current reactors, the number of graphite spheres used means there is more of it. Also, there are concerns that if oxygen got into the reactor core the graphite spheres could ignite, releasing radioactive particles into the atmosphere. Germany decided not to pursue this design for its own commercial reactors; but China and South Africa have licensed it, and the Chinese have a working prototype pebble bed reactor.
Fast Neutron Reactors
Like the two designs above, this is a proven concept. It has the safety advantages of Pebble Bed Reactors or Molten Salt Reactors, with (in my opinion) two other major advantages. The greatest is environmental; a fast neutron reactor uses almost all the fissile material in its core, leaving far less radioactive waste and far less overall. To borrow a metaphor from Scientific American magazine, if you imagine a 100-pound block of fuel, a current commercial reactor would use about 2 pounds. A fast neutron reactor would use about 98 pounds. Another big advantage is that there are designs of this type of reactor that cannot produce weapons-grade waste--not a small consideration in light of concerns about nuclear programs in Iran or North Korea. If we could offer them FNRs, we would be assured that they would be put to peaceful use.
The two major disadvantages of FNRs are moderating the reaction and the coolant. The neutrons move so fast that control rods of neutron-absorbing materials like cadmium don't work. And FNRs use molten sodium metal as a coolant. Most of you have seen what happens when someone puts a piece of solid sodium in water in chemistry class; so a coolant breach would be--to put it mildly--problematic.
I'm not a physicist. But if we must use nuclear fission power, we must ensure that safer and more efficient reactor designs become more commercially viable. And that means government funding. And I don't have a problem with that, so long as it's part of a balanced energy policy that includes things like wind and solar, and research into future power sources like fusion. And do we really want to be left behind on this? China and India in particular are pursuing nuclear power with a vengeance. I have no problem with that. Quite the contrary. I just think we shouldn't have to buy Indian or Chinese reactors in the future because we've been sitting on our hands for no good reason.