The Nuclear Waste Disposal Problem

What, then, are our options for disposing of nuclear waste? Since our focus is on evaluating fission reactors as a viable source of energy in the future, we will examine the properties of and disposal options for SNF, and ignore storage of defense waste (from decommissioned nuclear warheads, etc.).

One option that nuclear proponents discuss is the use of breeder reactors to recycle the waste. On the surface, recycling sounds like a good choice from an environmental standpoint, as it would reduce the amount of waste that needs to be disposed of, and it would reduce the required amount of environmentally harmful Uranium mining. However, the Carter administration chose in 1977 to ban the use of breeder reactors due to the enhanced risk of nuclear proliferation (breeder reactors produce Plutonium, which is ideal for making nuclear bombs). France uses breeder reactors to recycle their fuel, but I’ve been told by experts at Vanderbilt that breeder reactors are so complex that they frequently break down and have poor safety records [1]), so France has started to decommission their plants. Breeder reactors are not a panacea to the waste disposal problem.

Geological storage is widely considered to be the safest method for storage of SNF [2]. Until recently, the goal was to isolate SNF from the surface environment for at least 10,000 years, which was considered long enough for the total radiation level to decrease to acceptable levels. However, a court ruling in 2006 (?) increased the mandatory safe storage duration to 1,000,000 years. Considering humans have yet to build any structure that has lasted more than 5,000 years, there clearly is no way to guarantee that a HLNW disposal structure could maintain its integrity and confine the waste for one million years.

Yucca Mountain is a logical choice to store SNF because it is so dry. The primary objective of SNF storage is to keep the waste away from water. Why? Because water is the strongest known solvent, and it is mobile. The fear is that water would dissolve the waste and transport it a densely populated area such as Las Vegas, which is where groundwater from Yucca Mountain was originally thought to flow. Yucca Mountain has the lowest water table in the continental U.S.; to get well water there, you would have to drill a well 2,000 feet deep. The idea was to bury the waste 1,000 feet deep so that 1,000 feet of rock would protect it from the groundwater below and any infrequent precipitation events at the surface. Furthermore, it was discovered that Yucca Mountain is in an isolated hydrologic basin, so even in the worst-case scenario where the waste contaminated the groundwater, it would still be isolated within that small, uninhabited basin. Yucca Mountain is located at the edge of the Nevada Test Site, where 928 atomic bombs were detonated between 1951 and 1992, so it is already contaminated by radiation. Finally, the low population density and suitable host rock (volcanic tuff) make Yucca Mountain well suited for disposal of SNF.

Evidence that geological storage of SNF is relatively safe comes from natural analogues such as the Oklo natural reactor in Gabon. In this location 1.7 billion years ago a natural uranium ore deposit formed. At that time natural uranium had a higher proportion of ²³⁵U, the fissile isotope, so the uranium did not have to be artificially enriched like today to generate a self-sustaining nuclear reaction. Isotopic analyses show that the ore body is highly depleted in ²³⁵U, and has the same proportions of isotopes as SNF, so we infer that the ore body acted as a natural fission reactor (http://www.ocrwm.doe.gov/fact/Oklo_Natural_Nuclear_Reactors.shtml). In fact, 15 separate reactors have been discovered at the site. When the reactors were active 1.7 BYBP, groundwater acted as neutron moderator, slowing neutrons so that they could fission ²³⁵U nuclei. The heat released by fission reactions caused the groundwater to boil off, which shut down the chain reaction. Groundwater would then fill up the reactor again, and the cycle repeated. The fission reactions consumed 6 tons of ²³⁵U, producing 15,000 megawatt-years of energy over 500,000 years and heating rocks to ~400°C. Yet in the 1.7 BY since the reactors stopped operating, the original uranium and all of the fission-product nuclides have remained immobile, even though the host rocks are permeable and were likely often filled with flowing water. This is very strong evidence that SNF can be stored safely underground.

Some of my own research can be applied to the problem of safe SNF storage. To answer the question of what material can safely immobilize the components of SNF, geologists look to nature for the answers. They look for minerals that can hold high concentrations of radioactive elements like uranium and thorium for long periods of time. The mineral that holds the longevity record, the Methuselah of all Earth materials, is zircon (ZrSiO₄). The oldest solid material ever found on the surface of the earth is a 4.4 BY old fragment of a zircon crystal. How do we know it is 4.4 BY old? Zircon concentrates uranium in its structure, and once a zircon crystal grows it traps the uranium so that it can’t escape. Over time, the uranium decays to lead at a very low but constant rate, so that today we can measure the proportions of uranium and lead isotopes and estimate the amount of time elapsed since crystallization. This “isotopic clock” works because zircon also traps the lead after it forms from uranium decay, and because zircon does not incorporate any lead when it forms. Zircon can last 4.4 BY because it is very stable and therefore insoluble in natural waters, as shown by measurements made by myself and others. All of this suggests that zircon would be a good “wasteform” for storage of uranium in SNF. The problem is that zircon actually incorporates < 1 wt.% uranium in it structure, and we need something that can incorporate much higher concentrations. Another problem is that over time high radiation levels destroy the zircon structure [3], turning the zircon crystals into glass, which is much more soluble in natural waters and therefore much less effective at immobilizing the uranium [4].

A better candidate for storage of uranium and thorium is the mineral monazite, which is a rare earth element phosphate (REEPO₄). Although the geological evidence suggests that monazite is not quite as durable as zircon, it can hold much higher concentrations of Th (up to 10 wt.% ThO₂) without experiencing significant radiation damage and still last for billions of years. In the laboratory, I have studied the solubility of monazite in natural waters at elevated temperatures and pressures, and found its solubility to be very low at near-neutral pH. In field studies, I have investigated the stability of monazite in rocks, and have developed methods for using monazite to date the infiltration of water into rocks [5]. Although this research was “pure science” because the primary objective was to develop a better understanding of how the Earth works, it has implications for storage of SNF. History shows that most technological advances were enabled by research in pure science, and since it is primarily advances in technology that fuel the economic engine, particularly in the U.S., and that in the future may provide answers to how our society may become sustainable, it would be unwise for the U.S. to stop investing in pure science.

I am confident that further research into durability of crystalline wasteforms and the geology of potential waste disposal sites will give us the technological ability to safely dispose of SNF in the future. However, we do not and may never have the political or societal will to deal with the problem. Even if we as a society face the situation, agree on a site, and fund the building of a facility, it will take too long to make nuclear power a short-term fix to our energy needs. Abandoning Yucca Mt. means that we won't have a SNF disposal site for at least 20 years. Given the possibility that they will be stuck with more SNF in the future, utility companies are less likely to start building new power plants. In addition, since it takes about 20 years to build a new reactor, U.S. capacity to generate electricity through nuclear fission is unlikely to increase for at least 30 years.

To sum up, what are the advantages of nuclear power plants? They have near-zero CO₂ and pollutant emissions. What are the disadvantages? Radiation is released to the environment at every stage of the nuclear fuel cycle. There is a very small but real risk of nuclear reactor accidents (e.g., Chernobyl). Terrorists or hostile countries could steal enriched uranium destined for fission reactors or plutonium from breeder reactors to make nuclear bombs. The U.S. has no safe SNF disposal facilities, and won’t have any for at least twenty more years. We have a limited supply of minable uranium, so nuclear power is a non-renewable energy source (we have enough U ore to deploy 1000 new reactors in the next 50 years and maintain for 40 years [6]). Finally, nuclear power is not cost-effective. In a nutshell, nuclear power is a very complicated, expensive, centralized form of energy production that requires a lot of government involvement (regulation and oversight), has a very vocal opposition, and big potential problems, while decentralized, renewable energy sources pose fewer risks and may be more cost effective.

In general, I am advocating a move from centralized to decentralized, from hard path to soft path, from non-renewable to renewable, and from fossil fuels to alternative energy sources. Nuclear is centralized, and we don't have a solution to the waste problem, so I am not recommending it as an energy source, unless it is the only way we can eliminate fossil fuels.

1. Charman, K., Brave Nuclear World? Part II. World Watch Magazine, 2006: p. 12-18.

2. Macfarlane, A.M. and R.C. Ewing, eds. Uncertainty Underground: Yucca Mountain and the Nation's High-Level Nuclear Waste. 2006, The MIT Press: Cambridge, Massachusetts. 431.

3. Farnan, I., H. Cho, and W.J. Weber, Quantification of actinide [agr]-radiation damage in minerals and ceramics. Nature, 2007. 445(7124): p. 190-193. http://dx.doi.org/10.1038/nature05425

http://www.nature.com/nature/journal/v445/n7124/suppinfo/nature05425_S1.html

4. Grambow, B., Nuclear Waste Glasses - How Durable? Elements, 2006. 2: p. 357-364.

5. Ayers, J.C., et al., In situ oxygen isotope analysis of monazite as a monitor of fluid infiltration during contact metamorphism: Birch Creek Pluton aureole, White Mountains, eastern California. Geology, 2006. 34(8): p. 653-656. http://geology.geoscienceworld.org/cgi/content/abstract/34/8/653

6. Ansolabehere, S.e.a., The Future of Nuclear Power: An Interdiscplinary MIT Study. 2003, Massachusetts Institute of Technology. p. ix-x, 1-16.

Change Your Transportation

Transportation has a huge environmental impact, so society must focus on reducing that impact. Consider the environmental impact of a single automobile that travels an average of 100,000 miles in its lifetime. There is the damage that results from the manufacturing of the car and the mining and processing of the raw materials; from the drilling, transporting, and refining of the oil and gas that it uses; and from the emission of green house gases, NOx that contributes to acid rain, and ozone that causes photochemical smog. There are many other problems associated with automobiles. Driving a car is one of the riskiest activities we engage in, and cars make walking and bicycling much more dangerous on shared roads. Much of our country has been paved over by roads and parking lots, which has increased flooding risks but also uglified our landscape (I love Joni Mitchell’s song “They Paved Paradise and Put up a Parking Lot”). Driving in heavy traffic is very stressful, often leading to episodes of “road rage”. Yes, driving in the countryside without other cars can be very relaxing and enjoyable, but how often does that happen today, and is it worth all of the problems it creates? My prediction is that the most significant lifestyle change in the U.S. in the next two decades will be the abandoning of the car culture. That lifestyle won’t disappear completely, but it will become less prevalent as the price of fuel dramatically increases (due to peak oil and carbon taxes). The change may be traumatic, as 88% of workers in the U.S. travel to work by car, making the U.S. particularly vulnerable to peak oil [1]. People will choose smaller cars, cars that do not run on fossil fuels, or other modes of transportation including moped, bicycle, and mass transit. They will move closer to their jobs to decrease their transportation costs (I hope to buy a home within walking distance of my work before peak oil makes the cost unaffordable). They will take fewer long trips, and they will go to school closer to home. They will travel less for work, as companies try to cut costs. Telecommuting will become even more widespread, and in many cases, videoconferencing will make travel to meetings unnecessary. All of these changes will reduce traffic congestion and pollution, increase our national security by decreasing our dependence on foreign oil, reduce CO₂ emissions contributing to global warming, and I would argue, increase our health (more walking) and quality of life (less time wasted in traffic, better scenery).

Change What You Drive

The technology of automobiles hasn’t changed dramatically over the last 100 years. Most still use a standard internal engine fueled by gasoline. Throughout my life, U.S. auto manufacturers have presented prototypes of cars that were supposed to change the way we drive, but none of them ever came to fruition. Production and leasing of the EV-1 in the 1990’s signaled a potential shift to electric cars, but GM aborted that foray into new technology by confiscating all of the cars and destroying them, as documented in the film “Who Killed the Electric Car?”. However, contrary to general wisdom and the claims of some environmentalists, electric cars currently are not better for the environment. That is because the electricity used to power them comes primarily from the burning of fossil fuels, especially coal. Also, they are inherently less efficient, because any time you convert energy from one form to another you lose some energy. Converting fossil fuels into electricity to fuel automobiles is much less efficient than using them to fuel the car with an internal combustion engine directly. The same argument holds true for the now heralded hydrogen cars, which use electricity to produce hydrogen gas H₂, which in a fuel cell in the car reacts with oxygen gas O₂ to produce H₂O, releasing energy in the process. Although the hydrogen-fueled car emits only water, the process of producing the hydrogen requires lots of energy that usually comes from the burning of fossil fuels, which emits large amounts of CO₂ and other pollutants. So how can we make cars less harmful to the environment? First we must convert our primary source of energy from fossil fuels to renewable forms like wind and solar. Then we should use the electricity that is produced to fuel plug-in gas-electric hybrid cars, or eventually to produce H₂ gas for hydrogen-fueled cars.

Hybrid cars like the Toyota Prius have already raised the bar for energy efficiency. Hybrids have both a gasoline engine and electric motor. They produce electricity through regenerative braking, and automatically shut off the engine when idling. Another promising development is cars that run on biofuels such as ethanol and biodiesel. Flex cars can use ethanol or gasoline, but this is not a new technology, as it dates back to the original flex-fuel vehicle, the Model T, built in the 1910s. Many have concluded that production of ethanol from corn is not energy efficient, with some estimates showing that it requires more fossil fuel energy to produce the ethanol than is obtained from burning it. In addition, use of corn for ethanol production has increased the price of corn worldwide, which is a serious problem for the poor who depend on it for food. An increase in the price of corn causes increases in the price of all products for which corn is used as a feedstock. This problem of using food for fuel can be avoided by producing ethanol using switchgrass and wheat straw, which are also more energy efficient than corn.

So what can you do now? First, make every effort to decrease the number of miles you travel. Combine your errands. Never idle you car. Make sure your car is in tune and properly inflate the tires to maximize gas mileage. Carpool whenever possible. Make purchases online rather than driving to the store. Accelerate and decelerate slowly, and try to maintain a constant top speed. Ask your boss if you can telecommute one day per week. Vacation locally, or consider purchasing carbon offsets for the miles that you travel for vacation [2].

When the time comes to change your ride, buy a fuel-efficient hybrid as soon as you can, or even better, switch to mass transit. Encourage your employer to pay for your mass transit costs (like my employer, Vanderbilt University, they may be willing to do so because it means they will save money by building fewer parking garages). Imagine how much money you would save if you didn’t have monthly car and car insurance payments.

In the future, I envision a decentralized system of energy production for fuel-efficient homes and cars. Picture a windmill in your yard, and solar panels on your roof. The wind and the sun that power these energy sources are free and limitless. The electricity that they produce could be used to power your home and your plug-in electric car, or to produce hydrogen for the fuel cell in your car, all with zero CO₂ emissions or pollution.

1. Brown, L., Plan B 3.0: Mobilizing to Save Civilization. 2008, New York, NY: W.W. Norton & Co., Inc.

2. Jeffery, Y., L. Barclay, and M. Grosvenor, Green Living for Dummies. 2008: For Dummies.

Case study: DuPont Plant, New Johnsonville, TN

For a number of years I took students in my graduate course Aqueous Geochemistry to tour the DuPont Plant in New Johnsonville, TN, about two hours west of Nashville. The plant manufactures Titanium Dioxide TiO₂ by mining the mineral ilmenite FeTiO₃ and reacting it Hydrochloric acid HCl as follows: FeTiO₃ + 2HCl = FeCl₂ (aq) + TiO₂ + H₂O. The Titanium dioxide is a pigment that gives Kilz paint, Oreos, and many types of toothpaste their brilliant white color. There are two problems with this process. One is that the product solution is still very acidic. The other problem is that ilmenite contains many toxic heavy metals that are soluble in the acidic solution. In the 1960’s when people didn’t know better, DuPont was allowed to dispose of hundreds of thousands of gallons of this toxic acid solution directly into the Tennessee River, which of course killed all fish and bottom feeders downstream. Later they switched to the more environmentally friendly but more expensive process of deep-well injection. They drilled wells between 1000-2000 feet deep and then pumped the acidic waste into a confined, deep limestone layer. The thinking was that the limestone (which contains calcite CaCO₃ and dolomite CaMg(CO₃)₂) would neutralize the acid: CaCO₃ + 2H⁺ = Ca²⁺ + H₂O + CO₂. The confining (impermeable) layer above would keep the waste isolated from shallow aquifers that supplied drinking water. Once again, there were two problems with this plan, which my class would remind the DuPont engineers of every year, and every year they would claim ignorance. First, the acidic solution dissolves the limestone, which results in the formation of large caves deep underground. Eventually the weight of the overlying rock layers causes them to collapse, breaking into pieces, falling, and filling the caves. This shatters the confining layer and makes it permeable, so that the wastes can rise up into the aquifers. The other problem is that, as shown in the reaction, limestone dissolution produces CO₂ gas, and the pressure of that gas can build until it shatters the overlying rock and escapes. Either way, it seemed likely that the confining layer would eventually be compromised. So, to their credit, DuPont came up with a new solution that was even more environmentally friendly but (they claimed) even more expensive. Since around the year 2000 DuPont has been reacting the ilmenite with sodium carbonate, and according to the DuPont engineers the only by-product is harmless FeCO₃ (the mineral siderite), which is used to make bricks for construction. However, recently it was learned that this process produces dioxin as a by-product. Pure Dioxin is the strongest poison known to man (it is the neurotoxin in Agent Orange), and the New Johnsonville Plant is the fourth-largest producer of dioxin in the U.S..

This case study illustrates many different points. First, it is difficult to anticipate all of the potential outcomes of a complex industrial process. That is why ecologists advocate the precautionary principle. Second, industrial chemistry sorely needs to be “greened”. Green chemistry is a field just now coming into its own, and it has the potential to reduce greatly the environmental impact of the chemical industry. Third, despite repeated attempts at trying to “green” the chemical process, the production of Titanium Dioxide still causes serious environmental problems. DuPont is being sued by numerous plaintiffs who live near or work at their Titanium Dioxide plant in DeLisle, Mississippi, who claim that dioxin has seriously damaged their health or caused the death of loved ones (http://video.google.com/videoplay?docid=-7693391300780002092). At New Johnsonville, TN, many citizens are afraid to talk about the health risks posed by the DuPont plant because they work for the plant, their livelihood depends on its success, and they fear retaliation (http://www.dupontsafetyrevealed.org/newjohnsonville.htm). This raises many questions: Should we allow chemical companies to manufacture goods like Titanium Dioxide that are nonessential (it is simply used for aesthetic reasons) but that cause great harm to human health and the environment? Or should we close the plants, even if it meant that thousands of people would lose their jobs? The plants in New Johnsonville DeLisle are by far the largest local employers, so closing them would be an economic disaster for those communities. In fact, years ago when DuPont reapplied to the State of Tennessee for a permit for deep well injection, a representative of the Tennessee Environmental Council asked me if I would testify against the application. I refused, saying that deep well injection seemed to be the best of the alternatives known at the time, and that I couldn’t bear the thought of helping to put all of those people in New Johnsonville out of work. Yes, I am pro-environment, so I believe we should always be looking for ways to protect the environment, but the overall benefits of change have to outweigh the overall negatives, and in this case, the economic vitality of New Johnsonville seemed to me to outweigh the potential risks of deep-well injection.

Environmental Risk

Here’s an example of how knowledge can sometimes make life more difficult. In the morning, I am often confronted with the question of whether to empty the water out of the teapot and refill it with fresh water. It seems wasteful to dump the water in the pot down the drain, and furthermore that water has degassed its fluorine (although all fluorine probably degasses during boiling anyway). However, the water may have leached heavy metals from the pot while in contact with it for several days, or perhaps bacteria have begun to grow in the water. Also, I am impatient, and prefer to fill the pot with hot water so it takes less time to boil. So I dump the water out and then run the tap water for one minute before filling the pot because water standing in our pipes overnight may have leached metals from our pipes (this is unlikely to be a problem for us, though, because the practice is designed to avoid lead that leaches from solder that connects Copper pipes, and most of our pipes are galvanized steel). Is it better to save energy by using the water already heated in my hot water heater rather than heating cold water on my stove until it boils? Or is it better to save water by not running it until the water gets hot, which in my house takes roughly one minute? There are so many considerations that go into making such a simple decision, that complex decisions can seem overwhelming. Am I overanalyzing every situation? Wouldn’t life be simpler if I always did what was easiest, but perhaps at a slightly higher level of risk? Are the perceived dangers great enough to warrant my concern? Won’t I become unhappy if I have to assess a list of threats for every decision I make? Thinking about the world this way does make it seem to be a dangerous place.

The best approach to this problem of “too much information” is to only concern yourself with the greatest potential threats. The problem is that human perception of risk in the modern world is notoriously inaccurate. Stone Age humans faced essentially the same risks that their ancestors faced may thousands of years previously. Natural selection caused humans to evolve, preparing them to better deal with these risks and reducing their chances of succumbing to those risks. Also, they could pass on survival strategies orally from generation to generation. My guess is that Stone Age humans’ perception of risks in their environment was largely accurate. However, our society and environment is now changing so rapidly that evolution does not have time to prepare us for the many new risks we are faced with. Furthermore, the risks our generation faces are different from the risks faced by our parents, so the wisdom they impart to us is not sufficient, and we have to rely on other sources of information to adequately deal with these new risks. In this new world, how well do our new coping strategies prepare us for risk? Not very well. A famous study published in Science (*v. 236, 1987) examined the perception of risk by groups such as college students and The League of Women Voters. They were asked to rank risk associated with twenty different activities. Their rankings were then compared with the actual risks, defined as the mortality rate for that activity (number of deaths per year associated with that activity, probably normalized to the number of people participating in that activity *check). These two groups rated “nuclear power” as the highest risk, when in reality it was the lowest risk. Studies like this have led to several generalizations about risk perception:

1. We are genetically predisposed to worry about risks, because worrying about risk increases our chances of survival. However, it is possible to worry too much.

2. We tend to overestimate the risk associated with high-impact, low probability events (e.g., nuclear power plant disasters)

3. Man-made risks worry us more than natural ones (e.g., radiation from power lines & cell phones are less dangerous than radiation from the sun)

4. New (unfamiliar) risks worry us more than old risks.

A good example of point 2 is air travel. Many people are so afraid of traveling on airplanes that they refuse to fly. However, per mile traveled, the risk of dying in an automobile is much greater than in an airplane.

So what are the risks associated with global warming, peak oil, and water pollution? We will examine that question in the following chapters.