Research Program to Investigate the Fundamental Chemistry of Technetium. 1998 Annual Progress Report
Book Synopsis Research Program to Investigate the Fundamental Chemistry of Technetium. 1998 Annual Progress Report by :
Download or read book Research Program to Investigate the Fundamental Chemistry of Technetium. 1998 Annual Progress Report written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Technetium ([sup 99]Tc, [beta] emitter, half-life 2.1 x 10[sup 5] years, spA= 1.7 x 10[sup -2] Ci/g) is one of the radionuclides of major concern because of regulatory considerations for radioactive waste disposal. The propensity of Tc as pertechnetate, TcO[sub 4][sup -], to migrate in the geosphere necessitates its safe, long-term immobilization. Technetium is found in the nuclear waste storage tanks at the Hanford and at the Savannah River sites in highly alkaline environments along with multi-molar concentrations of nitrate, nitrite, and Na ions and lesser amounts of organic complexants, phosphate, sulfate chloride, fluoride, and carbonate. It has been assumed that technetium is present in the waste tanks as the pertechnetate ion but a recent study has suggested that at least in part, technetium is present in another form. There is a lack of information on Tc chemistry in oxidation states III-V with simple inorganic (OH[sup -], CO[sub 3][sup 2-], PO[sub 4][sup 3-], SiO[sub 4][sup 4-]) and common organic ligands (EDTA, citrate, oxalate) under alkaline conditions. This is essential information needed for pretreatment schemes, processing, and the assessment of stability of Tc in waste form materials. Further complicating the Tc waste tank chemistry is the added effect of an intense radiation field originating from[sup 137]Cs and[sup 90]Sr. The interactions of the ionizing radiation with water, nitrate, nitrite, and other minor components create highly reactive species that can strongly perturb the oxidation-reduction conditions. The stability of Tc in waste form materials is of paramount importance for long term storage concerns and the solid state chemical properties of many candidate Tc compounds are unknown. There have been few systematic studies of Tc stability in lower valent solids with the exception of TcO[sub 2]. Thus, it is not possible at present to assess the long term stability of many Tc compounds relevant to proposed waste form materials. This experimental research program addresses the characterization of the chemistry of technetium pertinent to the waste tank environment and to various waste forms. The solution and solid state chemistry of this element will be studied in aqueous solutions as a function of pH with the various salts added such as nitrate and nitrite, and as a function of radiation dose. The second part of this program is a search for stable, lower valent Tc materials which may prove useful for waste storage. This report summarizes the results after nine months of a three year project.
