We’ve all experienced the economic booms and busts, the ups and downs, and the feeling that sustained growth is something of the distant past never to be experienced again. Some would argue that it’s better that it not be experienced again because the more the economy grows, the faster we destroy our environment.
These assumptions are both not necessarily true. I mean that literally, they perhaps are true the current way we’re going about things, but they aren’t necessarily true if we do things more intelligently. It used to be common wisdom that organisms would multiply to consume the available food supply and that humans were no exception. Thus if you improved the economic conditions in impoverished regions of the world, their population would multiply as food supply permitted, until they were again impoverished.
More recent studies have shown that, where good economic conditions exist, people have fewer children, and in the United States, were it not for immigration from more impoverished regions, we would have negative population growth.
I would argue that another way that poverty hurts our environment is that it results in desperate measures to survive. The future seems less important if we are in immediate danger of starving to death.
Right now the US economy, and to a large degree, the global economy, is limited by energy production. As the economy grows, it reaches a point where it is consuming energy faster than it can be produced, the price of energy soars, and clamps economic growth. Thus we are locked in this cycle of economic oscillation around energy supplies.
This not only locks us in a cycle of unnecessary misery and suffering, but it also results in unnecessary environmental harm. When energy prices go through the roof, highly polluting sources like coal or fracking for hydrocarbons become appealing. We’re willing to dirty the air or water table in order to meet our immediate needs and avoid starvation.
There are long term clean solutions. If we analyze where all of our energy ultimately comes from, it is either hydrogen fusion, or to a lesser degree radio-active decay and fission, and even to a lesser degree than that, energy from the gravitational collapse that created the Earth. Energy that we release through burning fossil fuels is energy stored that was originally created through fusion of hydrogen in our Sun. When we build a Geo-thermal plant, we are using heat that is both generated from radio-active decay, some fission, and left over heat from gravitational collapse. Wind farms capture energy that originated from hydrogen fusion on our sun.
Releasing the stored carbon in fossil fuels results in millions of tons of carbon dioxide entering our atmosphere. When the Earth last had an atmosphere that was mostly carbon dioxide, the Sun was hotter but smaller so it’s effective radiation less. The additional carbon dioxide kept the Earth from being a frozen ice ball but it didn’t provide for an ozone layer that blocked ultraviolet light. That’s why early life on Earth was under water. Under a few feet of water was the only place where ultraviolet light didn’t immediately destroy it. Returning Earth to that environment wouldn’t be healthy for existing life forms, including humans, but now with the Sun a larger more mature star giving off more heat than it did in it’s early days, the Earth would also be much hotter, approaching Venus like temperatures.
Clearly, we need an alternative to fossil fuels, and going to the sources of the stored energy, nuclear fusion and nuclear fission, are the most promising solutions. We can collect solar energy as it arrives at the Earth. The problem there is that it is diffuse. Solar energy when it strikes the surface at 90º, which only happens within 23º of the equator, and then only for a small fraction of the year, amounts to about 900 watts / square meter at sea level. Still, this is enough for the rooftops of many homes to provide sufficient energy for that homes electrical needs. Wind and hydroelectric power are basically using nature to concentrate energy collected over a larger area into a smaller area to harvest. Germany and The Netherlands both derive a substantial portion of their electrical needs from wind power.
A more concentrated form of energy is desirable, that derived directly from releasing a portion of the nuclear binding energy in atoms, either in the form of nuclear fission or fusion. Nuclear fission thus far has been an unreliable and extremely dangerous technology which produces a hazardous waste which must be stored 100,000 years before it decays back to a level which is safe. Nuclear fusion hasn’t yet produced a watt of commercial power. But there have been promising developments in both fields.
In the area of nuclear fission, a type of reactor which rather than putting the fuel in solid rods, suspends it in liquid salts, called a molten salt reactor, promises to change the nuclear industry in ways that would make it compatible with people, both in terms of safety and in terms of radioactive waste. Conventional pressurized water and boiling water reactors have solid fuel in fuel rod assemblies. The solid fuel is usually in the form of uranium oxide and sometimes plutonium oxide is also used as a portion of the fuel.
The Uranium used is a combination of U-235 (the fissile material) and U-238 (the fertile material). Natural uranium is around 99.3% U-238 and .7% U-235. It has to be isotopically enriched to around 3-5% U-235 for use in most commercial power reactors (Canadian CANDU reactors can operate with as little as 2% enrichment).
In a newly fueled reactor, if an emergency occurs and control rods are used to shut down the reaction, the fuel quickly cools because the natural decay rates do not provide large amounts of heat. After a reactor has been operating a while, several things happen, U-235 is split into fission products, atomic fragments, many of which are unstable and have short half-lives. Uranium also captures neutrons and forms transuranic elements (elements heavier than Uranium) some of which have short half-lives and some very long half-lives. Now, if an emergency occurs and the reactor is shut down, these fission products and short-lived transuranics, continue to decay emitting a large amount of heat which is sufficient to melt the fuel and the reactor vessel in the absence of active cooling. This is what makes these reactors so dangerous, even if they’re shut-down, that doesn’t stop them from melting down.
The long term transuranic elements, especially plutonium, are what make the radioactive waste from these reactors such a problem. Because it takes 100,000 years for this mix to decay to the point where they are safe, it creates a storage problem that no civilization including ours can hope to solve. On the other hand, the fission products are mostly short-lived and within a couple hundred years will decay to a safe level, making them a less tractable storage problem. Because conventional uranium fueled reactors produce one particular isotope of plutonium, Pu-239, in preference to others, and that isotope is ideally suited for making bombs, conventional reactors are also problematic in the area of nuclear proliferation.
Since conventional reactors hold their fuel in solid fuel rods, the fission products are also held in those same rods. Many of those fission products absorb neutrons efficiently and poison the nuclear chain reaction. As a result, these rods must be removed and reprocessed when only a small portion of the fuel is “burned”. The fuel has to be stored in on-site ponds until the radiation level cools to the point where it can be transported and reprocessed.
New molten salt design reactors address all of these problems. The fuel is suspended in molten salt rather than in solid fuel rods. This allows waste products to be continuously removed so that they do not continue producing heat if the reactor is shut down. Reprocessing takes place on-site so there is no need to store fuel rods or to transport them offsite for processing. This reduces the potential for accidents and terrorist actions.
The molten-salt reactor naturally has a negative temperature coefficient, which means, as the temperature increases, the reaction rate decreases. This is caused by two physical effects. As the temperature rises, the salts the fuel is suspended in expand, and as they expand, it moves the fissile atoms farther apart decreasing the reaction rate. The second effect is related to Doppler shifting of the neutron energy level. Only neutrons of a specific energy level are readily absorbed by fissile atoms creating a fission. As temperatures increase, the relative movement on one atom nuclei to another increases, causing the energy spectrum of the neutrons emitted by one atom as seen by another to be broader, and as a result, a smaller percentage of neutrons fall within the energy window where they can be efficiently absorbed maintaining the chain reaction.
If the temperature rises too high, a melt plug in the bottom of the reaction tank melts allowing fuel to drain into a much larger holding tank. The geometry of the holding tank is such that fuel is dispersed over a much larger area by gravity. It can no longer maintain the reaction, and since it’s not carrying a large amount of fission products with it, quickly cools and solidifies. This makes the molten salt reactor an inherently safe design in that, if cooling is lost, it shuts itself down and contains the fuel.
The molten salt reactor, in addition to being able to burn uranium fuel, can also function with a thorium fuel cycle. Thorium, which is four times as abundant on the Earth’s surface as uranium, also does not produce large quantities of Pu-239, and does provide many other isotopes which render it’s transuranic produces much less suitable for bombs than uranium fueled reactors. In addition, molten salt reactors can be configured as “burners” rather than “breeders”, using fast rather than thermal neutrons, to burn transuranic waste products produced in other reactors, leaving only short lived fission products and transforming the 100,000 year nuclear waste problem into a more manageable 200 year problem. It is estimated that we could provide for 70-100 years of the worlds electricity needs by using existing waste alone and not mining another gram of uranium. Just to be clear, you can’t run a molten-salt reactor on just transuranics (except for Pu-239), because, with the exception of Pu-239, other transuranics have a less than 50% probability of fissioning after absorbing a neutron so they won’t sustain a chain reaction alone. They can only be used mixed with U-235, U-233, or Pu-239 fuel.
The problem we face with nuclear fission isn’t a scientific problem, it’s a political and economic problem. With all of the problems we’ve had with conventional reactors, there is significant resistance to building more conventional plants. This makes investors less willing to back something new, but something new is really necessary, not only to address our energy problems but also to clean up the huge mess that we’ve already made.
Are molten salt reactors completely safe with no potential problems? Well, no, plumbing still breaks. Anytime you have something mechanical, things break. Putting that much energy into a small area stresses materials, things break. But they can be designed to be passively safe, that is, lose active cooling, electricity, and not melt down or release fuel or fission products into the surrounding environment. Bottom line though, I think there is a viable sane route to using fission for electricity production, it’s just not the one we’re on now.
In the arena of fusion interesting things are happening. Skunk Works Program Manager Charles Chase has outlined their plan for creating a 100 MW Fusion prototype by 2017. What we aren’t being told is the specifics of how he plans to do this other than it is a scaled down fusion reactor, around 100MW. This is exciting news if it is true except that the question of whether or not this technology will be available for civilian purposes remains since Skunk Works develops technology under military contracts and thus under military restrictions and controls, it’s possible this technology may never see civilian light.
Then there are some exciting developments in the arena of cold fusion at NASA and elsewhere. It’s no longer marginally reproducible, and it’s more complex than simple fusion, the most recent incarnations also transmuting nickle into copper in the process. The energy to weight ratio is on the order of 1000 times better than gasoline.
Personally, I’m betting on the Chinese to be the first to bring fusion online for commercial power generation owing to their willingness to put the necessary resources into developing it, and their willingness comes out of necessity, they’re currently choking on coal emissions and they’re still struggling to provide for the energy needs of industry and also rural electrification. But there does seem to be quite a lot of promising developments in this field.