Can Carbon Sequestration Help Solve the Climate Crisis? Lessons from Nuclear Waste Disposal
BY ALLISON MACFARLANE
To address the climate change crisis we need both short term and long term solutions that will reduce the emissions of greenhouse gases, in particular carbon dioxide (CO2). At the same time, there is a growing global need for more energy resources to provide for development of many of the world’s population. Secure resources are even more valuable. The question is, which resources will be used over both the short and long terms and how will they impact climate change?
Because it is geographically well distributed and therefore provides a sure and secure resource for many countries, coal will likely continue to play an important role in electricity production. For example, China is building the equivalent of two 500 megawatt (MW) coal power plants every week. Coal consumption was five billion tonnes in 2003, and in 2006 the Energy Information Administration projected that number to double by 2030. India similarly will continue to increase its use of coal as it develops further.
Coal is unfortunately here to stay; therefore, we must find ways to ensure that the CO2 from burning coal does not enter the atmosphere. One promising technology in this regard is carbon capture and sequestration (CCS). CCS is a three-stage process whereby CO2 is captured before or after combustion, converted to a liquid and transported via pipelines to a site where it is sequestered—either deep underground in rocks or deep in the oceans on the continental shelf. Carbon capture and sequestration can be used for most any point source that produces CO2, such as coal, natural gas, and biomass power plants.
The remainder of this paper will focus on the sequestration portion of CCS, which, politically, is the most difficult part of the overall process, because it includes siting of sequestration facilities. The idea behind geologic sequestration is to ensure that CO2 remains underground for at least a thousand years if not significantly longer. Thus, sequestration will be a project more like that of nuclear waste disposal.
Most experts agree that the best solution for the disposal of the spent nuclear fuel and high-level nuclear waste produced by nuclear energy and nuclear weapons production is disposal in a geologic repository. Though nuclear power has been in use fifty years, a geologic repository for high-level nuclear waste has yet to open. Despite technical challenges, the problem has been in large part political. The experience of attempting to site nuclear waste repositories and the regulation of such facilities should provide valuable lessons for those interested in successfully and rapidly siting carbon sequestration facilities.
WHAT IS CARBON SEQUESTRATION?
The basic idea behind carbon sequestration is that liquid CO2 is injected deep into rock where it displaces the fluids (gases or liquids) that occupy the pore space in the rock. At great depths CO2 is a supercritical fluid, meaning that it will be much denser than it is at the surface. Nonetheless, it will still be buoyant in comparison to the fluids present, and therefore it will rise to the top of the rock unit that contains it. To ensure that the CO2 remains below the surface, a cap rock or impermeable layer is needed on top of the reservoir into which it is emplaced. CO2 can also be trapped by reacting with the existing fluids and the rock itself to form new minerals. Another method of CO2 trapping is by adsorption onto coal or organic-rich shales where the CO2 replaces methane (CH4).
As a result, CO2 can be stored in three different geologic settings: depleted oil and gas deposits—in which the fossil fuels have been already removed—unmineable coal deposits, and deep saline formations. This technology to emplace CO2 below the surface is not new. In the oil industry reinjecting extracted CO2, a process called enhanced oil recovery (EOR), has been done for a number of years to increase the output of their wells. The remaining questions about sequestration concern the behavior of CO2 over time as it interacts with available fluids and rock (see Friedmann, 2007 and IPCC, 2005 for a discussion).
A few demonstration sequestration projects already exist. The oldest and one of the largest is the Sleipner project on the North Sea run by Norway. Here they have been injecting CO2 into a saline formation at a rate of 3000 tonnes (t) per day since 1996 with plans to store up to twenty megatonnes of CO2 (MtCO2). The In Salah project in Algeria has been injecting CO2 at a similar rate into a gas field since 2004. The Weyburn, Canada, project has been injecting CO2 as EOR since 2000 (IPCC, 2005). Both oil and gas field projects intend to store similar volumes as Sleipner.
The IPCC (2005) issued a conservative estimate of global CO2 capacities in geologic formations of 200 gigatonnes of CO2(GtCO2), saying that there were likely 2,000 GtCO2 capacity available for exploitation. Considering that global carbon emissions from coal burning were twelve GtCO2 in 2006 and are only expected to rise, large capacities will be needed. Individually, deep saline formations likely have the largest capacities, which may be somewhere between 1,000 – 10,000 GtCO2. Next are the depleted oil and gas fields, with 675 – 900 GtCO2 potential capacity, and then the unmineable coal seams, with between 3 – 200 GtCO2 potential capacity.
Like all energy projects, carbon sequestration is not without risks, the main one of which is leakage. On the global level, leakage of CO2 may exacerbate the climate warming problem. On the local level, CO2 leakage may affect groundwater, ecosystems, and humans. Leakage is not such a significant problem in global terms if either the leak is a slow one or doesn’t manifest for about thousand years. Because the lifetime of CO2 in the atmosphere is on the order of 100 years, and if the globe can significantly reduce CO2 emissions over the next century, then sequestered CO2 need only remain so on the order of 500 – 1000 years.
The local risks pose more of a problem. The danger to humans from catastrophic release of CO2 (“blowout” in the oil and gas industry) is significant, but is already managed on a daily basis in the oil and gas industry. In the worst-case scenario, slow leakage of CO2 from a reservoir could affect drinking water supplies or result in soil acidification. To prevent against these types of occurrences, close monitoring of all sequestration facilities must be required.
SITING A SEQUESTRATION FACILITY
So far, most of the expert discussion about establishing sequestration facilities has focused on property rights and liability. Who owns the land—the surface area—to be used, who owns the pore space to be occupied, who owns the CO2 itself, and who owns the local groundwater that may be affected? All of these questions tend to be governed by state laws, though some federal laws may be applicable too, especially if CO2 is considered a waste (Gerrard, 2008).
Many of these issues were resolved in the case of high-level nuclear waste disposal by selecting land already owned by the federal government. Nonetheless, it is likely that many sequestration facilities will be needed because of the large volume of CO2 that requires disposal and to reduce the length of pipeline required to transport liquid CO2 from capture facilities. As a result, these issues will have to be sorted out before construction of sequestration facilities begins in earnest.
Equally important is the issue of criteria by which to establish and develop sequestration facilities, but so far, this matter has received almost no attention. Here, the experience of siting nuclear waste repositories comes in handy. Not only are siting criteria important, but the process by which the site is established is significant and will bear on the success of the site, as we can see from the nuclear waste experience.
Both the US and the German experience with nuclear waste disposal has advice to offer. In the 1982 Nuclear Waste Policy Act (NWPA), the U.S. Congress tried to ensure a step-wise process in site selection: the Act required that five sites be selected for initial investigation, to be reduced to three for in-depth investigation. These three sites were to include two different rock types to ensure a good comparative assessment of geologic settings. The process established in the 1982 NWPA was never followed fully though, because the Act was amended in 1987 to focus solely on one site, Yucca Mountain, Nevada.
Germany recently rethought its nuclear waste repository selection and established a five-step process, that included (1) excluding sites based on geologic criteria, (2) identifying sites with favorable geology based on a set of weighted criteria, (3) selecting three to five sites for surface exploration and at the same time allowing affected communities to reject the sites, (4) selecting two sites for underground exploration while involving the local communities in decision-making about the sites, and (5) selecting a site (see Macfarlane, 2006). The importance of communicating with the local affected public cannot be overemphasized, as this had led to success in Finland’s siting of its nuclear waste repository (see Vira, 2006).
Thus, both a strong technical and politically-informed set of siting criteria as well as a process that requires public consultation will be necessary for successful carbon sequestration. These will ensure that the public is assured that the siting process was fair and just, and that it has selected sites that are technically suitable and safe.
REGULATION OF A SEQUESTRATION FACILITY
Carbon sequestration will require regulation, as does nuclear waste disposal. In the case of nuclear waste, the Environmental Protection Agency initially established regulations for all potential nuclear waste repositories (and the 1982 NPWA established that at least two would be built), but this was later amended to regulations specifically for the Yucca Mountain site. Because different geologies will be considered, it may be necessary to have regulations that address the different types of sites, instead of one single set of regulations for all sequestration facilities.
A word of caution in setting regulations, though: the numerical radiation dose standards applied to Yucca Mountain have created a situation whereby the only way to evaluate whether the site meets the standard is to use an extremely complex, opaque computer model of how the repository will behave over the next million years, as the standard requires compliance for that long. Validating models of complex earth processes, like the Yucca Mountain model, is not possible, as we cannot know all the features, events, and processes that will affect the system over time (see Macfarlane, 2006). The same will be true for carbon sequestration and this should be kept in mind when developing standards for these sites.
NEXT STEPS
What should be the next steps in developing carbon sequestration? First, a siting decision process should be established that evaluates the importance of different technical criteria. Additionally, thought should be given to how standards should be developed for these sites. These tasks may best be done by a diverse committee, established by the Department of Energy, which includes technical experts, policy experts, representatives of potentially affected communities, and legal experts. Only if all sides of the issue are addressed will carbon sequestration be a potential solution for part of the climate change catastrophe that faces us all.
Allison MacFarlane (amacfarl@gmu.edu) is Associate Professor in the Department of Environmental Science and Policy at George Mason University (http://esp.gmu.edu). Her research focuses on environmental policy and international security.
REFERENCES
S. Julio Friedmann, 2007, Geological Carbon Dioxide Sequestration, Elements, v. 3, pp. 179-184.
Michael Gerrard, 2008, Carbon capture, sequestration raises myriad legal issues, New York Law Journal, Vol. 239, No. 100, www.nylj.com.
Intergovernmental Panel on Climate Change, 2005, Carbon Dioxide Capture and Storage, Cambridge, UK: Cambridge University Press.
Allison Macfarlane, 2006, “Uncertainty, models, and the way forward in nuclear waste disposal”, in A. Macfarlane and R.C. Ewing, editors, Uncertainty Underground: Yucca Mountain and the Nation’s High-Level Nuclear Waste, Cambridge MA: MIT Press, pp. 393-410.
Juhani Vira, 2006, Winning citizen trust: the siting of a nuclear waste facility in Eurajoki, Finland, innovations, Vol. 1, No. 4, pp. 67-82.
