An Investigation into the Oxidation State of Molybdenum in Simplifies High Level Nuclear Waste Glass Compositions

2003 ◽  
Vol 807 ◽  
Author(s):  
R. J. Short ◽  
R. J. Hand ◽  
N. C. Hyatt
Keyword(s):  
Oxidation State ◽  
Nuclear Waste ◽  
Photoelectron Spectroscopy ◽  
Redox State ◽  
X Ray ◽  
Reducing Atmosphere ◽  
Spin Resonance ◽  
High Level Nuclear Waste ◽  
High Level ◽  
Glass Compositions

The redox state of Mo in glasses containing simplified simulated high level nuclear waste (HLW) streams has been investigated using Electron Spin Resonance (ESR) and X-ray Photoelectron Spectroscopy (XPS). Melts performed in highly oxidising or neutral (air) atmospheres contained Mo6+, but our study indicates that the Mo can be at least partially reduced to Mo4+ or Mo3+ by melting in a reducing atmosphere. The implications for glasses containing a full simulated HLW stream are that the formation of detrimental crystalline phases containing Mo6+ upon heat treatment may be avoided by reducing the oxidation state of Mo during melting.

Nepheline Crystallization in High-Alumina High-Level Waste Glass

2015 ◽  
Vol 1744 ◽  
pp. 85-91 ◽  
Author(s):  
José Marcial ◽  
John McCloy ◽  
Owen Neill
Keyword(s):  
Nuclear Waste ◽  
Waste Glass ◽  
High Alumina ◽  
High Level Waste ◽  
Interfacial Conditions ◽  
Waste Vitrification ◽  
Cooling Schedules ◽  
High Level Nuclear Waste ◽  
High Level ◽  
Glass Compositions

ABSTRACTThe understanding of the crystallization of aluminosilicate phases in nuclear waste glasses is a major challenge for nuclear waste vitrification. Robust studies on the compositional dependence of nepheline formation have focused on large compositional spaces with hundreds of glass compositions. However, there are clear benefits to obtaining complete descriptions of the conditions under which crystallization occurs for specific glasses, adding to the understanding of nucleation and growth kinetics and interfacial conditions. The focus of this work was the investigation of the microstructure and composition of one simulant high-level nuclear waste glass crystallized under isothermal and continuous cooling schedules. It was observed that conditions of low undercooling, nepheline was the most abundant aluminosilicate phase. Further undercooling led to the formation of additional phases such as calcium phosphate. Nepheline composition was independent of thermal history.

The Incorporation of Cerium in Zirconolite

1996 ◽  
Vol 465 ◽  
Author(s):  
B. D. Begg ◽  
E. R. Vance
Keyword(s):  
Absorption Spectroscopy ◽  
Nuclear Waste ◽  
Valence State ◽  
Charge Compensation ◽  
Sample Design ◽  
Sintering Atmosphere ◽  
X Ray ◽  
High Level Nuclear Waste ◽  
High Level ◽  
X Ray Absorption

ABSTRACTZirconolite (CaZrTi2O7) is the primary actinide-bearing Synroc phase for the immobilisation of high-level nuclear waste. Using X-ray absorption spectroscopy and microanalysis we have investigated the incorporation of cerium, as a simulant for plutonium, on both zirconolite's Ca and Zr sites under a range of redox conditions. The Ce valence state was found to vary between Ce3+ and Ce4+ depending on the both the sintering atmosphere and temperature. The existence of alternative charge compensation schemes, predominantly cation vacancies, in addition to those used in the sample design was inferred in many of the zirconolites and will be discussed in detail.

Non-Linearity in Glass Composition Dependence of Dissolution Rates: Effect of Solution pH

1993 ◽  
Vol 333 ◽  
Author(s):  
Shi-Ben Xing ◽  
Isabelle S. Muller ◽  
Ian L. Pegg
Keyword(s):  
Nuclear Waste ◽  
Glass Composition ◽  
Ph Dependence ◽  
Solution Ph ◽  
Ph Values ◽  
Waste Vitrification ◽  
High Level Nuclear Waste ◽  
High Level ◽  
Soluble Components ◽  
Glass Compositions

ABSTRACTIn our previous studies on the optimization of glass compositions for high-level nuclear waste vitrification it was found that, over certain composition ranges, PCT leachate concentrations increased dramatically with very small changes in glass composition. The large differences that are observed between the leachate pH values for the “durable” and the “less-durable” glasses is one possible cause for this strongly non-linear glass composition effect; conversely, the pH difference may be merely another symptom. In this study, four simulated nuclear waste glasses (two of the less-durable and two of the durable types), were leached in both zwitterionic and inorganic buffer solutions, at fixed pH-values in the ranges of 7 to 12. The very different leaching behaviors of the two types of glasses persisted and, furthermore, different pH-dependence was found despite their very similar glass composition. This study suggests that the leachate pH difference observed between the less-durable and the durable glasses under uncontrolled pH conditions is not the major cause of the large difference of leaching behavior between those glasses. The normalized release ratios of soluble components (B, Li, Na) to Si show significant differences for the two types of glasses.

Long Term Field Leaching Studies of Simulated Nuclear Waste Glass in Granite and Salt

1991 ◽  
Vol 257 ◽  
Author(s):  
R.L. Schulz ◽  
D.E. Clark ◽  
A.R. Lodding ◽  
G.G. Wicks
Keyword(s):  
New Mexico ◽  
Nuclear Waste ◽  
Waste Isolation Pilot Plant ◽  
Study Results ◽  
High Level Nuclear Waste ◽  
High Level ◽  
Interaction Test ◽  
Glass Compositions ◽  
Term Field

ABSTRACTField leaching studies were carried out in granite at the Stripa site in Sweden and also in salt in the Materials Interface Interaction Test at the Waste Isolation Pilot Plant (MIIT/WIPP) in New Mexico. The goal of these studies is to assess the durability of various glass compositions engineered to isolate high-level nuclear waste from the biosphere. An additional goal of the MIIT study is to determine how the glasses interact with a wide array of proposed materials that may be a part of the multi-barrier waste package. These substances include metals, geological host specimens,, as well as engineered backfill and overpack materials.Two year data on the SRLY (165/TDS) glass compositions has been extracted from both studies (Stripa and WIPP/MIIT) and five year data has recently become available from the MIIT study. Results from SEM/EDS, SIMS and FTIRRS analyses on glass/glass interfaces are presented in this paper.

Molybdenum in Nuclear Waste Glasses - Incorporation and Redox state

2002 ◽  
Vol 757 ◽  
Author(s):  
R. J. Short ◽  
R. J. Hand ◽  
N. C. Hyatt
Keyword(s):  
Heat Treatment ◽  
Nuclear Waste ◽  
Redox State ◽  
Redox Conditions ◽  
Simplified Model ◽  
Glass Melts ◽  
Composition And Structure ◽  
Trivalent Cations ◽  
High Level Nuclear Waste ◽  
High Level

The composition and structure of the mixed metal molybdates that can form in simulated high level nuclear waste (HLW) glass melts have been studied. It was found that molybdates of a tetragonal scheelite type were formed upon heat treatment of the simulated glass samples (representative of the slow cools experienced by the real vitrified product), and that these compounds are capable of incorporating the majority of the mono, di, and trivalent cations that would be present in a real HLW glass. In addition, it has been shown that altering the redox conditions prevailing upon melting can promote or suppress crystallisation in simplified model waste glasses that contain molybdenum. Experiments to investigate the effect of redox conditions during melting of simulated HLW glass on molybdate formation are also reported.

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