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Fission Products (fission + products)
Selected AbstractsChromatographic partitioning of cesium by a macroporous silica-calix[4]arene-crown supramolecular recognition compositeAICHE JOURNAL, Issue 10 2010Anyun Zhang Abstract A macroporous silica-based 1,3-[(2,4-diethyl-heptylethoxy)oxy]-2,4-crown-6-calix[4]arene (Calix[4]arene-R14) supramolecular recognition polymeric composite, (Calix[4]+Oct)/SiO2 -P, was synthesized. It was performed by impregnating and immobilizing Calix[4]arene-R14 and n -octanol into the pores of the macroporous SiO2 -P particles support. n -Octanol was used to modify Calix[4]arene-R14 through hydrogen bonding. The effect of eight typical fission products contained in highly active liquid waste (HLW) on the adsorption of Cs(I), one of the heat generators, was investigated at 298 K by examining the effect of contact time and the HNO3 concentration in a range of 0.3,7.0 M. (Calix[4]+Oct)/SiO2 -P showed excellent adsorption ability and high selectivity for Cs(I) at 4.0 M HNO3 over the tested elements. The partitioning of Cs(I) from a simulated HLW was operated by (Calix[4]+Oct)/SiO2 -P packed column. Cs(I) was able to be effectively eluted by water and separated from the tested metals. It is demonstrated that (Calix[4]+Oct)/SiO2 -P is promising to apply in chromatographic separation of Cs(I) from HLW. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Thermochemistry and Crystallization of Glass-Forming Y-Substituted Sr-Analogues of Fresnoite (Sr2TiSi2O8)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Tae-Jin Park Strontium titanosilicate (Sr2TiSi2O8) is the Sr-analogue of fresnoite (Ba2TiSi2O8). It may provide useful properties due to the unusual five-coordinate titanium in its structure. Sr2TiSi2O8 is also a possible oxide form for the immobilization of short-lived fission products in radioactive waste. Through , decay, strontium decays to yttrium and then to zirconium. Therefore, not only the stability of Sr-loaded waste forms but also that of a potential decay product series with charge-balance in a naturally occurring mineral or ceramic is of fundamental importance. To incorporate the reaction 3Sr2+=2Y3++vacancy in the fresnoite composition, Y-substituted Sr-analogues of fresnoite, (Sr2,xY2/3x)TiSi2O8 (x=0, 0.5, 0.75, 1, 1.25, and 1.5) were prepared by a high-temperature synthesis and were found to form glass upon cooling. The Y-end-member (Y1.33TiSi2O8, x=2) crystallized to a mixture of Y2TiSiO7, TiO2, and SiO2 upon quenching in air. The enthalpies of formation of Y-substituted Sr-fresnoite glasses were obtained from drop solution calorimetry in a molten lead borate (2PbO·B2O3) solvent at 702°C. The enthalpies of formation from constituent oxides were exothermic but become less so with increasing Y content. The enthalpy of vitrification of Sr2TiSi2O8 composition was measured to be 68.5 ± 6.2 kJ/mol. The thermodynamic stability of the Y-substituted Sr-analogue of crystalline fresnoite may become marginal with increasing yttrium content. Their ready glass formation, even in the absence of radiation, suggests that amorphous phases may dominate as the Sr- and Cs-containing waste forms decay. [source] Thermochemistry and Aqueous Durability of Ternary Glass Forming Ba-Titanosilicates: Fresnoite (Ba2TiSi2O8) and Ba-Titanite (BaTiSiO5)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2009Tae-Jin Park Barium titanosilicates are possible oxide forms for the immobilization of short-lived fission products in radioactive waste. Ba2TiSi2O8 (fresnoite) and BaTiSiO5 (Ba-titanite) samples were prepared by a solid-state synthesis. The enthalpies of formation of Ba2TiSi2O8 crystal and glass at 25°C and of BaTiSiO5 glass were obtained from drop solution calorimetry in a molten lead borate (2PbO,B2O3) solvent at 701°C. The enthalpy of formation for fresnoite composition samples from constituent oxides was exothermic and became more exothermic with increasing crystallinity. Differential scanning calorimetry revealed that the crystallization rate of the fresnoite glasses increased with increasing devitrification. A modified Product Consistency Test-Procedure B (PCT-B) was used to collect solubility data on the fresnoite and titanate phases. The tests suggest that both glassy and crystalline fresnoite exhibit favorable aqueous stability and should be explored further as radioactive waste forms for long-term storage. [source] The role of mass spectrometry to study the Oklo,Bangombé natural reactors,MASS SPECTROMETRY REVIEWS, Issue 5 2007J.R. De Laeter Abstract The discovery of the existence of chain reactions at the Oklo natural reactors in Gabon, Central Africa in 1972 was a triumph for the accuracy of mass spectrometric measurements, in that a 0.5% anomaly in the 235U/238U ratio of certain U ore samples indicated a depletion in 235U. Mass spectrometric techniques thereafter played a dominant role in determining the nuclear parameters of the reactor zones themselves, and in deciphering the geochemical characteristics of various elements in the U-rich ore and in the surrounding rock strata. The variations in the isotopic composition of a large number of elements, caused by a combination of nuclear fission, neutron capture and radioactive decay, provide a powerful tool for investigating this unique geological environment. Mass spectrometry can be used to measure the present-day elemental and isotopic abundances of numerous elements, so as to decipher the past history of the reactors and examine the retentivity/mobility of these elements. Many of the fission products have a radioactive decay history that have been used to date the age and duration of the reactor zones, and to provide insight into their nuclear and geochemical behavior as a function of time. The Oklo fission reactors and their near neighbor at Bangombé, some 30 km to the south-east of Oklo, are unique in that not only did they become critical some 2,×,109 years ago, but also the deposits have been preserved over this period of geological time. The long-term geochemical behavior of actinides and fission products have been extensively studied by a variety of mass spectrometric techniques over the past 30 years to provide us with significant information on the mobility/retentivity of this material in a natural geological repository. The Oklo,Bangombé natural reactors are therefore geological analogs that can be evaluated in terms of possible radioactive waste containment sites. As more reactor zones were discovered, it was realized that they could be classified into two groups according to their burial depth in the Oklo mine-site. Reactor Zones 10, 13, and 16 were buried more deeply, and were therefore less weathered than the other zones. The less-weathered zones are of great importance in mobility/retentivity studies and therefore to the question of radioactive waste containment. Isotopic studies of these natural reactors are also of value in physics to examine possible variations in fundamental constants over the past 2 billion years. © 2007 Wiley Periodicals, Inc., Mass Spec Rev 26:683,712, 2007 [source] | ||||||||||