----------------------------------------------------------------- Our Energy Future Human Energy Plausible arguments have been made, by Jared Diamond and others, that we enjoyed happier, healthier lives before we came to rely on farming. Since few paleolithic records survive we may never know for sure. But we've kept better records in our misery, and looking back, at least one thing has dramatically improved life since then: industry. Though it's hardly been a uniform success (and has plenty of its own problems) it is by far the brightest feather in our farmer's hats. A growing body of research (as well as common sense) tells us that industry moves in lockstep with the availability of energy. The steam engine began the industrial revolution and oil increased it in the 20th century. We also learned that oil, like all fossil fuels, comes with a terrible price: pollution, even to the point of altering the climate of the entire planet. Moreover, the richest fossil deposits are now nearing exhaustion. To continue using this form of energy we will have to tap ever larger areas, leaving wider destruction (oil sands underlie the magnificent Boreal forest) for less net gain (EROI or EROEI).^1 Two generations ago it was thought that fossil fuels would be replaced by atomic power. That didn't happen, both because oil remained ridiculously cheap and because we didn't trust ourselves with such a concentrated form of energy. Now we are waking up the next morning to find that fossil fuels are like the mortgage we can't afford. Many believe we can 'refinance' by doing things more efficiently -- insulating homes, telecommuting, driving electric cars, urbanizing -- with wind and solar power making up the difference. Unfortunately, the math is not on their side. Efficiency improvements are a good idea not only because they save energy, but because they improve the dignity of society. There is no dignity in consumer goods made of toxic plastics that break and must be thrown out after a year of use. There is no dignity in cold, drafty homes, or sitting in traffic. All such problems should be fixed, but doing so can reduce energy consumption by at most a factor of two or three. Progress in developing nations will increase demand more than this over the next few decades. Wind and solar are appealing technologies that we should continue to develop. But they tap energy sources that are inherently more dilute than fossil fuels. Consider: * A 2010 Honda Accord weighs about 3500 lbs. Imagine replacing all the steel in the car with composites to cut this weight in half. Replace the engine with a 100% efficient motor and cover the entire surface of the car with magic solar cells that are 100% efficient. On average, it would take 2 minutes to collect enough energy to accelerate the car to 60mph. On level ground, in a vacuum, with no friction.^2 * An Apple iPhone consumes about 1 W when in use. If a magic 100% efficient windmill the size of the phone were held in a constant 10mph wind, about 1/4 W could be provided.^3 Running our society on such energy sources will probably make life harder, or at best allow us to maintain current global levels of prosperity. They can not fire engines of innovation, as proponents of the 'green economy' imagine. The Atomic Age Nuclear reactors provide about 15% of the electricity in the United States today. The reactors responsible have been steadily chugging away for more than 30 years, since no reactors have been built in America since the 1970s. They are all of the same design, known as the Light Water Reactor (LWR). The name refers to the fact that they are "moderated" by ordinary water. As distinct from a design prevalent in Canada, which uses heavy water as a moderator, and again from the design of the infamous reactor at Chernobyl, which used graphite. You are probably wondering what a moderator is to a nuclear reactor, and we will explain this by first noting that all three designs mentioned above are thermal-spectrum reactors. This means they use slowly-moving neutrons to split atoms. "Split" is a colorful term that is, like most colorful terms used to describe nuclear physics, slightly inaccurate. The process is less like splitting wood and more like serving Mr Creosote a wafer-thin mint.^4 First, a fissile atom must be convinced to eat a neutron. Only then does it realize its eyes were too big for its stomach and break into smaller atoms, called fission products (releasing useful energy, and more neutrons, in the process). If the wafer-thin neutron is moving too fast though, the fissile atom will simply pay its bill and walk out. In a chain reaction, neutrons for fission must come from prior fissions (free neutrons are much too expensive otherwise).^5 Unfortunately, freshly-barfed neutrons move too quickly to be caught and eaten by other, intact fissile atoms. Hence, no chain reaction can occur without a moderator -- a material that slows down neutrons. On the other hand this isn't unfortunate at all, since it gives us a way to control nuclear reactors: add more moderator to increase the reaction; remove moderator to stop it. We all know that water expands when hot, and it happens that it also moderates neutrons. These two facts endow LWRs with a "negative temperature coefficient of reactivity". This means the reaction is self-limiting. If it intensifies for some reason, the water heats up and expands. This makes it less dense, so it can stall fewer neutrons. More neutrons miss their targets, the reaction rate decreases, and the water cools. This feedback loop keeps the reaction stable. Generation IV The reason reactors haven't been built in the US since the '70s is, of course, Three Mile Island. Here an LWR did melt, though not from a runaway chain reaction as at Chernobyl. What went wrong? The answer is something called "decay heat". Even after fission is halted, fresh fission products in the reactor will continue to emit radiation and heat. Coolant must be pumped through the reactor to remove this heat or the metal bottles containing the fission products can melt. At TMI, operators wrongly believed coolant was flowing when it wasn't. Over a period of hours, decay heat melted parts of the reactor and some radioactive gasses were released into the atmosphere. People living within 10 miles of the reactor got a dose of radiation roughly equivalent to a chest X-ray. If you've recently driven a car made in the 1970s you might wonder if we couldn't build a better kind of reactor today. In fact there are several promising designs, collectively known as "generation-four reactors". One of the most promising is LFTR (Liquid Fluoride Thermal Reactor, pronounced "lifter"). It is type of MSR (Molten Salt Reactor). The "liquid" part refers to liquid fuel (dissolved in molten salt) which is continuously pumped through the reactor. As in an LWR, the liquid expands as the reaction intensifies, reducing its density and thus the rate at which fission can occur. Unlike an LWR however, LFTR can passively handle decay heat. No action is needed -- either from humans or machines -- to keep things cool. The fuel salt is a solid at room temperature. At the bottom of the reactor core (tank) there is a refrigerated drain pipe in which some of the fuel is made to freeze, plugging it. If the reactor ever gets hotter than it's supposed to, this frozen salt melts and the contents of the reactor drain into a wide, shallow pan at the bottom, where there is enough surface area to safely radiate decay heat without any liquid coolant. If the entire plant should lose power, the refrigerator in the drain pipe will stop and the core will again drain into the pan. There are many other benefits to using liquid fuel. It allows the reactor to be continuously refueled, whereas LWRs must be shut down about every 18 monthsfor refueling. This means there's never a need to put more fissile material in the reactor than needed for immediate consumption (LWRs must be loaded with enough fuel to last the 18 months). "Fluoride" refers to the type of salt used. Fluoride salt readily dissolves nuclear fuels like Thorium and Uranium, and the homogeneous mixing of fuel makes for very high neutron efficiency, which contributes to LFTR's overall efficiency -- it can generate vastly more power per pound of ore dug out of the ground than an LWR. The fluoride can also handle very high temperatures, which means it can drive a turbine much more efficiently than water. "Thorium" refers to the fact that LFTR burns Thorium instead of natural Uranium. Thorium itself isn't fissile, but turns into a rare form of Uranium when fed a diet of neutrons (essentially managing to keep down one wafer-thin mint and then attempting another). This is important because Thorium is a very plentiful mineral. There's enough for 10 billion people to sustain American levels of energy consumption for thousands of years. The particular Uranium isotope to which Thorium converts is lighter than the isotope found in Uranium mines and burned in LWRs. This means it has to manage to digest many more neutrons without bursting before it can become Plutonium. LFTRs should make 1,000 times less Plutonium per MWh than LWRs. Essentially, only fission products are produced, which remain radioactive for about 300 years. LWR waste remains radioactive for 50,000 years or more (of course Mercury and other poisons released from burning coal remain toxic forever, as do the Cadmium and Arsenic used in some types of solar cells). The Future Our stories, from ancient epics and imaginary starship voyages to the true story of our journey out of Africa across the earth, tell us that we are a people whose great flaws are redeemed by our capacity for change. We are always changing. These days we have an unprecedented view into both our past and future. It's a good time to consider big changes. Here, we gave some thought to improving the project of industry. Notes ^1 The EROI of an energy source ultimately determines its cost, or availability to society. ^2 1/2 * 1750lbs * (60mph)^2 ~~ 9m^2 * 300W/m^2 * 2min ^3 1/2 * 1.275kg/m^3 * 72cm^2 * (4.5m/s)^3 * 0.593 ~~ 0.25W ^4 http://www.youtube.com/watch?v=BlK62rjQWLk&#t=4m5s ^5 The National Ignition Facility at Lawrence Livermore is working on a project called LIFE. The idea is to use inertial confinement fusion as a neutron source for subcritical fission. Previous subcritical fission proposals have been accelerator- based, but those neutrons are very expensive. ICF generates so many neutrons it can fission almost anything: natural uranium, weapons-grade uranium and plutonium, spent fuel... even depleted uranium. You load it once with enough fissile material for 40 or 50 years and keep it going with a constant stream of fusion "shots" (~ 10/s). At the end they claim 99% burnup of the fissile material. NIF is supposed to achieve ICF break-even for the first time in 2010. Unfortunately the laser used will be able to fire at best a few times a day -- far short of the 10Hz required for LIFE.