How Does Nuclear Failure Figure Into the Energy Future?
Friday, March 25, 2011 at 4:36PM 
The wreckage of the nuclear reactors at the Fukushima facility, as of 3.21.11 Image Courtesy NHK WorldNuclear energy just isn’t like any other form of energy generation that we have. Not because the mode of action is all that different. Essentially, most forms of energy generation that we have use fuel to create an exploitable heat differential. In other words, you need one area that is hot (the motor, the geothermal loop, the reactor) and another area that is cool (the radiator, the cooling loop, the generation cycle). You can exploit this temperature difference to, for instance, contain and channel multiple explosions into producing mechanical energy without melting the engine, or it can be used along with the amazing ability of heated water to expand in size to create force in the form of pressure, and use turbines to convert this energy into electricity. Most coal, nuclear and gas power plants are essentially large steam engines, using heat sources to create steam or supercritical water and drive turbines with it. Nuclear reactors, especially light water reactors like the ones at the Fukushima plant, generate lots of heat, and so usually have a secondary loop of coolant, often river or seawater, which is either used purely for cooling and expelled from the plant again as a hot liquid back into its source, or to generate power by using supercritical water to heat water into steam, which is then run through the turbines and expelled from a cooling tower. But this leads to the big difference between nuclear energy and other ways of heating things up; you can’t just cut off the throttle. It’s a chain reaction, not simple combustion, and turning it off is a process, and is not instantaneous. So, every nuclear reactor has safety systems built in to make sure that the process can be throttled down successfully. In theory. But recent events suggest that our ability to anticipate is often outstripped by our ability to engineer.
Now the possibility arises that the spent fuel pond may have evaporated, and without that coolant even well spaced spent fuel rods can overheat and melt down. The Japanese are attempting to execute brave but desperate plans to cool the reactors with water drops from helicopters and water cannons from fire trucks at the time of this writing. I wish the heroes that are fighting this the best of luck. Hopefully the better understanding of the health effects of radiation that we have today will lead to fewer deaths amongst them than amongst the people who tried to arrest the Chernobyl disaster, even if the worst should occur. These grim tidings bring to mind another major difference between nuclear energy and other power sources. If your solar panel fails, you are out of a few thousand dollars. If your windmill breaks down, you can usually fix it. If your engine pops a gasket, you are inconvenienced for a few days. But if your nuclear power plant really goes south and loses control of the chain reaction, large areas of the land will be rendered uninhabitable and thousands upon thousands of heroic people will die in the process of halting the chain reaction. It’s a whole different level of risk upon failure. Given what is known even now, it’s not premature to lay some blame for this catastrophe.
Tsunami. The word means “harbor wave” in Japanese. Think about that for a moment; why is a Japanese word the one generally used, world over, for the phenomena of large ocean waves crashing ashore with disastrous consequences? The reason for this quirk of language is that Japan has experienced more tsunami than any other place in the world. Around 200 tsunami have occurred there in recorded history, with some being really extreme events such as a ~20 meter tsunami that hit the the Sanriku region of Japan in 1896, killing tens of thousands of people. Most deaths from that tsunami occurred in Miyagi prefecture. Which also happens to be where the Fukushima power plant is located, right on the coast. Placing the critical backup generators on one of the lower levels of the structure, right on the coast in the one area on Earth that is most prone to tsunami is criminal negligence. These structures need to last for centuries and, despite the fact that they were absolutely critical to preventing a series of catastrophic nuclear chain reactions in not one but five reactors, the backup generators were sitting ducks to a common phenomena in the area. Once a diesel engine has been flooded with sea water. . well, it’s not a fixable inconvenience. The generator, and all of it’s associated electrical equipment, are very vulnerable to salt water, and once corroded all of those critical and hard to replace components are junk. The engineers and managers at Tokyo Electric Power and GE who were responsible for this decision in the 1970′s should be publicly ridiculed as incompetent, deprived of employment or pension and possibly prosecuted. I really can’t stress enough how much of a fantastic engineering failure the placement of the backup generators was. This fatal design flaw, in light of the history of Japan, should not have made it into the final design.
The other group I need to lay blame upon are not around in any numbers to accept it; the leaders of the post war era, both west and east. Rather than invest money in intrinsically safe reactor designs that produce waste that is less radioactive than the starting components, such as the traveling wave reactor design, you guys decided it was a swell idea to invest in breeder reactors that produce waste that is more radioactive than the fuel that goes in. Why do something that seems so stupid? One good reason is that reactors of this sort can create some of the fuel they consume, especially after reprocessing. But I would argue that the reprocessing step is the real reason that our leaders pushed for this design; it allows for the extraction of highly enriched uranium and even plutonium, and you know what that is good for. To build nuclear weapons, of course! Why use another system for generating power when the system developed for military purposes already does that, and allows you to build glittering racks of weapons that can be used to annihilate the entire human race as a bonus! Now this design is entrenched, and most nuclear electricity generation is accomplished in boiling water reactors or pressurized water reactors, both of which enrich fuel which requires reprocessing. Our leaders that arose from the trauma of World War II were driven mad with fear for one another, and so made a lot of mistakes. We will be paying for their mistakes in their place for a long time.
Looking forward, we are looking at an era of energy scarcity unless we invest now in new forms of energy generation. Nuclear can be a part of the energy future, even a big part, but first we need work out a design that is intrinsically safe, generates less dangerous waste, and can be mass produced. Accomplishing those three goals might seem pie in the sky, but that’s only because of our experience in the past 40 years with the flaws of breeder reactor designs. Ironically, it’s the military itself which has driven development of safer nuclear reactors for power generation. Most nuclear powered ships are currently steam turbine reactors, similar to land based reactors, except smaller. However, the maintenance issues with these reactors have prompted the development of metal cooled reactors, which are cooled with a liquid metal such as lead or sodium. This design change doesn’t provide complete safety, but it does allow for a much longer buffer of time to asses a situation and fix it than a water cooled reactor, and it allows the reactor to run unmoderated. This design is not perfect; a similar design on land leaked non-radioactive sodium in Japan in 1995. But it’s a step forward.
In the past few decades, a lot of fuss has been made about another design; pebble bed reactors. These sort of reactors use a breeder reaction to heat coolant in much the same way as a standard nuclear reactor, but the nuclear fuel is in the form of tennis ball sized pebbles rather than in the form of fuel rods. These pebbles are composed of tiny fragments of a uranium intermixed with a graphite matrix, coated with silicon carbide. In this way, the pebbles make up the fuel source, the nuclear moderator, and the fission product barrier, which makes the design much more simple than a conventional nuclear reactor. Additionally, the coolant is usually some form of noble gas that does not readily absorb neutrons, so there are no radioactive fluids to leak. The pebbles can be added and subtracted from the pebble bed, which allows for easy moderation of the reaction. And, as an additional bonus, the reactor should be resistant to melt down, as it can be cooled by natural circulation of the coolant even during an extended power loss, and the graphite matrix is highly resistant to heat. However, there are some major problems with this design. The graphite has many great qualities for use in a nuclear reactor, except for one; it is flammable. If there is no oxygen present, this is never a problem, but there is potential for a catastrophic fire that would spread radioactivity into the atmosphere if there should be a loss of coolant. Also, the silicon carbide coating, which in theory should resist fire and most forces quite well, is not very resistant to shear forces, and this has caused a few accidents. In one case in a West German research reaction in 1986, an attempt to remove a pebble lodged in the shoot shattered it, releasing radioactivity into the environment. After decommissioning, that same reactor was found to be contaminated with large amount of highly radioactive Strontium and Caesium dust. Pebble bed technology is very promising; it can not melt down even if all of the coolant is lost, it produces no radioactive fluids that must be stored as waste, and the workers are even exposed to less radiation than they are in conventional designs. But until the pebble technology itself is developed a bit further, in order to reduce breakage and dust creation, this technology can’t be considered an intrinsically safe solution.
Another new nuclear technology is the thorium breeder reactor. Thorium 232 is very common compared to uranium, and if it’s bombarded with neutrons it will enrich into uranium 233. This element can be used as nuclear fuel, and it produces a lot of electronics scrambling gamma rays, so it can’t be easily used in nuclear weapons. And the amount of energy that can be derived from a pound of thorium is considerably greater than the amount that can be derived from a pound of uranium, due to it’s complex transmutation from Thorium 232 to Thorium 233 to Protactinium 233 to Uranium 233. So, are there downsides? Yes. It’s worth reading through this interview with one of the people at the forefront of the development of this technology in the IEEE journal if you are really interested in the technology. In fact, the reactor Dr. Ratan Kumar Sinha describes in this piece has recently been finished and put up for review. At any rate, one thing that must be kept in mind is that while Thorium may be a relatively common and innocuous substance, and the wastes from the reactor at the end of it’s cycle much less dangerous than those produced by current systems, but while the reactor is running there is uranium and plutonium in attendance, and starting the thing up currently requires the use of these two elements too. In a way, this could be considered a valid method for the disposal of these highly enriched substances. However, in a truly catastrophic disaster scenario, in which the coolant is drained from the reactor, there is still the possibility for a melt down. On the upside, if there is no coolant loss, this design does allow for passive circulation, without the pumps being continuously powered, which is a vast improvement in safety over the 40 year old design that is repeatedly exploding on the Japanese coast right now. Perhaps we can look to Thorium as a way to solve our energy problems, if this technology proves to be safe and reliable in the Indian test reactor. We shall see.
Nuclear technology is a trade off. We can indeed create of massive amounts of energy with nuclear power, but we can also engender massive amounts of suffering if something goes wrong. At this point, simply assuming that nothing will go wrong cannot be considered a valid strategy when it comes to nuclear power. Recent events have made that abundantly clear. I would like to stress that pretty much any modern reactor is better prepared for disaster than the 40 year old design that is falling to pieces in Japan, and even that facility would be in much better shape were it not for a few fatal design flaws. But there are plenty of those old facilities sprinkled around the planet to become a reoccurring headache unless we make some effort to clean them up and safely store all of the waste. The fact that we are still storing dangerous reactor waste inside reactor buildings where so much can go wrong simply because we have no better place to put it should give us pause. The cost of storing these extraordinarily dangerous substances for thousands of years is never considered in the upfront cost of a new nuclear plant, and even where to store it is complicated by the difficulty in safely transporting such things to a permanent repository. As a result, our leaders have chosen to do nothing, and just let the waste sit perched, vulnerably, atop the reactors that created it. There are technical hurdles for other new energy technologies, such as solar and wind, particularly in regard to providing uninterrupted power regardless of the vagaries of the weather. However, we must bear in mind that these technologies are unlikely kill us if something goes wrong, and their potential to pollute the Earth doesn’t even bear comparison. It may be that the nuclear trade off between safety and massive uninterrupted power is a Faustian bargain, and that investments in safer energy technologies that pose less of a safety and maintenance concern are a better long term solution to our energy problems.
Crossposted on FailDrill
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It's good that you mention Liquid Metal Sodium reactors aka IFR or Gen IV. Barry Brook does a great job showing how IFR is by far the best solution on his bravenewclimate website. All the criticisms about proliferation, safety and waste associated with current nuclear plants are thoroughly discussed there. I highly recommend anyone wanting to be more informed about nuclear check out the Integral Fast Reactor design which appears to be the best solution for our future energy needs.
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