President, Members of the Mineralogical Association of Canada and
An author is always pleased to have a paper recognized as a “best paper” – and I am certainly no different; however, I acknowledge the very subjective process by which a “best” paper is selected. Other papers published during 2001 certainly reached a higher level of science or required greater effort and skill. Still, even with these humbling qualifications, I am particularly pleased that this paper was selected, because I think the subject, nuclear materials, is so critically important. The fate of nuclear materials, consumed and generated in nuclear reactors, will determine the future of nuclear power.
Twenty percent of the world’s electricity is generated from approximately 400 nuclear reactors. The use of nuclear power as a replacement for carbon-based sources of energy reduces carbon emissions by an estimated 600 million metric tons per year. However, these same nuclear power plants, as well as reactors used to produce bomb materials, have left the world with a legacy of 150,000 metric tons of used nuclear fuel stored in 36 countries to varying degrees of care. The global production of used nuclear fuel is on the order of 10,000 metric tons per year, containing 100 metric tons of plutonium. The global inventory of plutonium is over 1,400 metric tons of which approximately 450 metric tons have been separated by reprocessing (250 metric tons are used for weapons). The bare critical mass of 239
Pu is less than 10 kg. The fate of plutonium, and other fissile nuclides such as the much more abundant 235
U, is a critical environmental and nuclear weapons proliferation concern. Any significant increase in the use of nuclear power will result in substantial increases in the amount of spent nuclear fuel.
What is the role of geoscientists? If we consider the nuclear fuel cycle as the source term, then the geologic repository is the intersection of the nuclear fuel cycle with geologic cycles, as illustrated by the cartoon in Figure 1. Although the cartoon greatly simplifies the scientific issues, it does illustrate some of the important aspects of the problem. The nuclear fuel cycle operates on a scale of tens of years, and the geochemical or hydrologic cycles operate on scales of hundreds to millions of years. From the nuclear engineering perspective, environmental impact can be lessened by careful design of the fuel cycle. From the geologic perspective, the most important step is in the selection of a repository site. Once the site is selected, the principal geologic means of protecting the environment will by a reduction in the release and transport rates combined with dilution. The science that supports the performance assessment of a site requires an analysis that couples atomic-scale processes, such as spent fuel and waste package corrosion, to crustal-scale processes, such as volcanic activity and climate change, that extend over temporal scales of thousands, if not tens of thousands, of years. The challenge for geoscientists is in modeling these complex, highly-coupled, large-scale geologic systems over extended periods.
Mineralogist can play an exceptionally important role in this process. On the nuclear side of the cycle, there is considerable interest in designing new fuels, inert matrix fuels that “burn up” excess actinides. This is just mineralogy plus neutrons. On the materials science side, the design, evaluation and selection of nuclear waste forms is a job tailor-made for mineralogists. Nuclear waste forms of high chemical durability that are resistant to radiation damage provide the first and most important barrier against release to the environment. There is already considerable insight on the long-term behavior of such materials, many of them minerals, but much remains to be done in developing special waste forms for specific waste streams.
I believe that by recognizing this paper, the Mineralogical Association of Canada has focused the attention of the next generation of mineralogists on one of the major environmental issues of this century. Thank you for selecting this paper for the Hawley Medal.
Figure 1. Cartoon illustrating the intersection
of the nuclear fuel cycle and hydrologic and geochemical cycles. The
geologic repository is the interface between these cycles. Natural
sources of radiation dominate human exposure.