Nuclear Waste Disposal And The Role Of Science In Decision Making

Bruce Robinson, LANL
 

Ever since mankind unleashed the awesome power of the atom, the world has been confronted with both the tremendous promise and great threat posed by nuclear power. In his landmark Atoms for Peace speech in 1953, President Eisenhower set the nation on a course that led to the widespread, beneficial use of atomic power. Today, the U.S. generates 19% of its electricity from nuclear power reactors; internationally, the percentage in many developed countries is much higher. Nuclear reactors provide a constant, reliable source of power that feeds our electricity grid day and night, rain or shine, in windy or calm weather. Nuclear energy is safe and cost competitive with other major energy sources. Nuclear power plants emit almost no chemical or radioactive pollutants, and virtually no carbon dioxide to the atmosphere. Thus, as we work to make renewable energy options practical on a large-scale nuclear power is a viable alternative to fossil fuels, which are one of the biggest contributors to CO2 and other pollutants in the atmosphere. Nuclear power therefore ought to be a part of our energy future, especially in the first half of the 21st century. However...
 
Ever since nuclear power emerged as a major energy source, we have grappled with what to do with nuclear waste. In the normal operation of a nuclear reactor, unwanted radioactive elements are formed by the energy-generating fission reactions as well as neutron capture reactions. These radioactive elements decay over time frames ranging from minutes to millions of years, and pose a threat to human health. After energy generation, nuclear fuel rods and associated hardware are highly radioactive. Right now, the used or spent nuclear fuel rods are placed in storage pools on the individual reactor sites. These pools provide shielding from radioactivity and cooling to remove the heat generated by radioactive decay. Years later, after the most intense decay heat has tapered off, the fuel rod bundles can be removed and stored safely for long periods in shielded containers (this is called dry cask storage). However, these temporary storage solutions do not solve the problem of permanent disposal, they simply allow us to buy time until a better solution can be found.
 
The concept of permanent disposal of radioactive waste in underground geological formations has a history that is almost as long as nuclear power itself. In 1957, the National Academy of Sciences concluded that storage in mined geologic repositories was the preferred option for solving the nuclear waste disposal problem. Subsequently, different geologic formations and rock types were considered, including salt, volcanic tuff, and granite. After much scientific study, and much political wrangling, the U.S. decided to characterize the volcanic tuffs of Yucca Mountain, located about 100 miles northwest of Las Vegas, Nevada, to determine its suitability as a waste repository site. For the past 20 years, we have been studying the geologic formations, the movement of water, and the geochemistry of the rocks and fluids to determine the ability of the geologic strata to reduce the movement of radioactive elements should they escape the repository. The ultimate question is: would it be safe to bury radioactive waste beneath the surface of Yucca Mountain?
 
Predicting with high precision the future of an engineered system in a natural environment over a period of many thousands of years is beyond our capability. Realizing this, regulatory agencies with responsibility to protect human health and safety have established criteria for evaluating the suitability of a waste repository based on the concept of probabilities and risk. Probability is a measure of how likely it is that some event will occur. Risk is the potential negative impact that might arise from that event and is calculated based on the probability and the potential losses caused by the event. Each of us accept risk in our everyday actions because we believe that the risk of a negative event is much smaller than the positive benefits of those actions. Repository science leads to the calculation of a range of plausible outcomes, rather than a single prediction. Thus, there is a finite probability of an individual in the far distant future receiving a dose from a leaking repository. If the models suggest that the risk of an individual receiving a high radioactive dose is acceptably small, then the repository could be constructed, and waste could be buried there. The definition of acceptably small is made by the regulator in the form of a dose standard. Our role as scientists studying Yucca Mountain is to determine if our analyses show that the repository meets or exceeds that standard. Our studies of Yucca Mountain suggest that yes, the risk is lower than the dose standard set by the regulator.
 
So, even if we think that the repository will eventually leak, as long as the risk is low enough, we as a society will bury the waste there. Are you comfortable with the concept of risk being used in this way? Would your answer change if you lived close to the proposed repository site? Does it matter that the individuals who might receive a dose are people who will be born thousands of years from now? What if I told you that the additional dose that these individuals might receive from a repository is much lower than the levels we receive from normal background radiation due to natural processes? Should these risks be viewed in isolation, or should we compare these risks with risks associated with other energy sources, such as the risk of dramatic climate change precipitated by carbon dioxide buildup in the atmosphere due to fossil fuel burning? Maybe we should just put the problem off, hoping that future generations can resolve the nuclear waste issue for us. Would that choice be ethical?
 
Clearly, nuclear waste disposal is an issue with many dimensions, including scientific, political, and philosophical. It is therefore not surprising that the issue is controversial. What is the role of science in this process? Simply put, our job as scientists is to put relevant facts on the table so that decision makers can decide a course of action. I have my own opinion on what decision should be made regarding Yucca Mountain: I believe the best choice is to bury radioactive waste there. However, for a decision like this to be legitimate, it must reflect our collective value judgments, played out in a socio-political setting in which all citizens have a right to be involved. My hope as a scientist is that my work informs the decision making process by providing objective information that can be used so that we can arrive at the best possible decision.