In-situ Formation of Bismuth-Based Iodine Waste Forms
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1043-T12-05
In-situ Formation of Bismuth-Based Iodine Waste Forms Tina Nenoff1, James L. Krumhansl2, and Ashwath Rajan2 1 Surface and Interface Science, Sandia National Laboratories, PO Box 5800, MS 1415, Albuquerque, NM, 87185-1415 2 Geochemistry, Sandia National Laboratories, PO Box 5800, MS 0754, Albuquerque, NM, 87185-0754 ABSTRACT We investigated the synthesis of bismuth oxy-iodide and iodate compounds, in an effort to develop materials for iodine recovery from caustic waste streams and/or final waste disposal if repository conditions included ambient conditions similar to those under which the iodine was initially captured. The results presented involve the in-situ crystallization of layered bismuth oxide compounds with aqueous dissolved iodine (which resides as both iodide and iodate in solution). Although single-phase bismuth oxy-iodide materials have already been described in the context of capturing radioiodine, our unique contribution is the discovery that there is a mixture of Bi-O-I compositions, not described in the prior work, which optimize both the uptake and the degree of insolubility (and leachability) of iodine. The optimized combination produces a durable material that is suitable as a waste form for repository conditions such as are predicted at the Yucca Mountain repository (YMP) or in a similar type of repository that could be developed in coordination with iodine production via Global Nuclear Energy Program (GNEP) production cycles. INTRODUCTION 129
I is one of the longer-lived fission products (1.6x107 years) produced from the generation of nuclear energy. Although produced in relatively small quantities, 129I is one of the radionuclides that has attracted considerable public concern because of its potential to become concentrated in the human body. Historically, 129I was simply discharged to the atmosphere as a means of disposal. However more recently, iodine was discharged to the ocean (principally the seas around Europe) where isotopic dilution with the natural iodine in seawater renders it harmless. With the growth of the Global Nuclear Energy Program (GNEP) in the United States, there are strong interests in the development of new separation and waste form technologies for all radionuclides that are present in the developing nuclear cycles. This includes the separation of radiological iodine (I2) and development of inherently stable waste forms. Whether wastes are slated for above ground storage or underground burial the primary concern is that the radionuclides (129I in our case) be sequestered in inherently stable chemical forms which will not appreciably dissolve, should water gain access to the site. A second major consideration is that the wastes not exist as powders, since an accident during storage or processing could produce a cloud of radioactive dust with the potential for causing widespread contamination. A number of research groups have investigated the complex crystal structures of layered bismuth oxyiodide compounds. [1-6] In particular, the researchers focused on the s
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