On the correct electronic ground state of Tc(<i>g</i>)

Rard, Joseph A.; Rand, M. H.; Thornback, John R.; Wanner, Hans

doi:10.1063/1.460423

Cited by 25 publications

(38 citation statements)

References 13 publications

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“…Using Although our assessment of the published databases for orthophosphate species led us to conclude that the CODATA values are probably the best, they are limited to certain "key" compounds and aqueous species at 298.15 K. The Nuclear Energy has been extending the CODATA effort to include many more compounds and aqueous species [14,21,55], but these newer evaluations are limited mainly to those of relevance to radioactive waste management. These extensions include the aqueous "diphosphate" or "pyrophosphate" ions of various degrees of protonation.…”

Section: Some Effects Resulting From Inconsistencies Between Thermodymentioning

confidence: 99%

The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA

Rard

Wolery

2007

J Solution Chem

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Section: Some Effects Resulting From Inconsistencies Between Thermodymentioning

confidence: 99%

The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA

Rard

Wolery

2007

J Solution Chem

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“…12,13 The leachability of technetium can be greatly decreased by reducing soluble TcO 4 -to insoluble Tc(IV) species by the addition of blast furnace slag (BFS) or other reductants to the grout. The D eff ( 9 9 Tc) values of reducing grouts are much smaller, 3¥10 -11 cm 2 s -1 to 4¥10 -12 cm 2 s -1 , because Tc(IV) how low solubility and readily sorbs to the grout matrix.…”

Section: Manuscript Textmentioning

confidence: 99%

Evolution of Technetium Speciation in Reducing Grout

Lukens

Bucher

Shuh

et al. 2005

Environ. Sci. Technol.

112

182

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Cementitious waste forms (CWFs) are an important component of the strategy to immobilize high-level nuclear waste resulting from plutonium production by the U.S. Department of Energy (DOE).Technetium ( 9 9 Tc) is an abundant fission product of particular concern in CWFs due to the high solubility and mobility of pertechnetate, TcO 4 -, the stable form of technetium in aerobic environments. CWFs can more effectively immobilize 9 9 Tc if they contain additives that reduce mobile TcO 4 -to immobile Tc(IV) species. Leaching of 9 9 Tc from reducing CWFs that contain Tc(IV) is much slower than for CWFs containing TcO 4 -. Previous X-ray absorption fine structure (XAFS) studies showed that he Tc(IV) species were oxidized to TcO 4 -in reducing grout samples prepared on a laboratory scale. Whether the oxidizer was atmospheric O 2 or NO 3 -in the waste simulant was not determined. In actual CWFs, rapid oxidation of Tc(IV) by NO 3 -would be a concern, whereas oxidation by atmospheric O 2 would be of less concern due to the slow diffusion and reaction of O 2 with the reducing CWF. To address this uncertainty, two series of reducing grouts were prepared using TcO 4 -containing waste simulants with and without NO 3 -. In the first series of samples, the TcO 4 -was completely reduced using Na 2 S, and the samples were placed in containers that permitted O 2 diffusion. In these samples, all of the technetium was initially present as a Tc(IV) sulfide compound, TcS x , which was characterized using extended X-ray absorption fine structure (EXAFS) 2 spectroscopy, and is likely Tc 2 S 7 . The TcS x initially present in the grout samples was steadily oxidized over 4 years. In the second series of samples, all of the TcO 4 -was not initially reduced, and the grout samples were placed in airtight containers. In these samples, the remaining TcO 4 -continued to be reduced as the samples aged, presumably due to the presence of reducing blast furnace slag. When samples in the second series were exposed to atmosphere, the lower-valent technetium species were rapidly oxidized to TcO 4 -.KEYWORDS technetium, cement, grout, nuclear waste BRIEFS The speciation of technetium in reducing grout samples was followed using X-ray absorption fine structure spectroscopy. The reduced technetium species were susceptible to oxidation by oxygen, but nitrate had no observable effect over the duration of the experiment. MANUSCRIPT TEXTIntroduction Immobilization of the high-level nuclear waste created during plutonium production by

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“…The electronic configuration of neutral, gaseous technetium atoms in the ground State is [Kr]4t/®5j^ [2] ( Table 1). As a consequence of the lanthanide contraction the atomic radius of 1.358 Ä of technetium [3] proved to be only O.Ol 5 Ä smaller than the radius of rhenium, while the difference between the atomic radii of technetium and manganese amounts to almost 0.1 Ä.…”

Section: Introductionmentioning

confidence: 99%