On the Suitability of Lanthanides as Actinide Analogs

Mater. Res. Soc. Symp. Proc. Vol. 1104 © 2008 Materials Research Society http://www.mrs.org/s_mrs/index.asp 1104-NN04-01 On the suitability of lanthanides as actinide analogs Kenneth Raymond, and Geza Szigethy Chemistry Department, University of California, Berkeley, C A , 94720-1460 and Lawrence Berkeley National Laboratory, Berkeley, CA 94720 ABSTRACT With the current level of actinide materials used in civilian power generation and the need for safe and efficient methods for the chemical separation of these species from their daughter products and for long-term storage requirements, a detailed understanding of actinide chemistry is of great importance. Due to the unique bonding properties of the/-elements, the lanthanides are commonly used as structural and chemical models for the actinides, but differences in the bonding between these 4f and 5f elements has become a question of immediate applicability to separations technology. This brief overview of actinide coordination chemistry in the Raymond group at UC Berkeley/LBNL examines the validity of using lanthanide analogs as structural models for the actinides, with particular attention paid to single crystal X-ray diffraction structures. Although lanthanides are commonly accepted as reasonable analogs for the actinides, these comparisons suggest the careful study of actinide materials independent of their lanthanide analogs to be of utmost importance to present and future efforts in nuclear industries. INTRODUCTION The current primary use of actinide elements globally is as fissile material for civilian power plants, an industry that generates tons of spent nuclear material annually. Undoubtedly, the benefits of utilizing a carbon-free power source in an ever-industrializing world are clearer in the light of the uncertainty of global oil resources and the growing awareness of the effect of greenhouse gasses on the global climate. However, the inherent dangers associated with the actinide waste materials from this industry and their proper treatment procedures has been an area of intense interest and heated debate in both the scientific community and general public. While some countries such as France have employed well-established solution chemistry extractions such as the P U R E X process to separate the fission daughters from actinide material in spent fuel, countries such as the United States decide instead to store their radioactive waste materials in geological repositories to avoid the proliferation of pure transuranium elements that can be attained cleanly from many solution separation techniques. The projected necessary lifetime of geological repository containment integrity is on the order of 10,000 years, making the leaching of nuclear material into the environment and subsequent human exposure to radioactive material a significant safety concern. In order to anticipate the chemical behavior of actinide-bearing materials for so long a lifetime the detailed chemistry of actinide elements must be understood in great detail so that proper storage materials are used to avoid the potential for radiation leaks. In case there is exposure of the environment to these materials, however, as well as to address already-existing clean up efforts, there must also exist well-understood protocols for the removal of actinides from contaminated systems, whether environmental, inorganic, or biological in nature.