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{sup 99}Tc is a major fission product from nuclear reactors. Because {sup 99}Tc has few applications outside of scientific research, most of this technetium will ultimately be disposed of as nuclear waste. The radioactive decay of {sup 99}Tc to {sup 99}Ru produces a low energy {beta}{sup -} particle, but because of its fairly long half-life of t{sub 1/2} = 2.13 x 10{sup 5} years, {sup 99}Tc is a major source of radiation in low level waste. Technetium forms the soluble TcO{sub 4}{sup -} anion under oxic conditions and this ion is very mobile in groundwater, but technetium is reduced to less soluble Tc(IV) hydrolyzed species under anoxic conditions. Geochemical modeling of the dissolution of nuclear waste, and of the solubility and speciation of the dissolved radionuclides in groundwaters, is an integral part of the Performance Assessment of the safety of a nuclear waste repository, and this modeling requires a critically-assessed thermodynamic database. Such a database for technetium was published in the book Chemical Thermodynamics of Technetium, with literature coverage through 1998. This database is described herein, along with more recent relevant studies. Gaps in the knowledge of the chemical and thermodynamic properties of technetium are pointed out, and recommendations aremore » made for measurements that are needed to eliminate these gaps.« less

Current Status of the Thermodynamic Data for Technetium and Its Compounds and Aqueous Species