scholarly journals Obsidians and Tektites: Natural Analogues for Water Diffusion in Nuclear Waste Glasses

1991 ◽  
Vol 257 ◽  
Author(s):  
James J. Mazer ◽  
John K. Bates ◽  
Christopher M. Stevenson ◽  
C. R. Bradley
Keyword(s):  
Nuclear Waste ◽  
Yucca Mountain ◽  
Water Diffusion ◽  
Molecular Water ◽  
Strongly Correlated ◽  
Savannah River ◽  
Total Water ◽  
Reaction Conditions ◽  
Natural Analogues ◽  
Time Periods

ABSTRACTMolecular water diffusion in natural obsidians and tektite was investigated in vapor hydration tests performed between 75 and 230°C for up to 400 days. Reaction progress was monitored using measurements of the birefringent hydration layer, an alteration feature associated with strain caused by molecular water diffusion in obsidians. The hydration rate constants and temperature dependence of the reaction are strongly correlated with the logarithm of the initial total water content of the glass. These values have been quantified for conditions relevant to the potential Yucca Mountain repository. The low initial total water concentrations of Savannah River Lab nuclear waste glasses produced at the bench-top scale help to minimze the effects of molecular water diffusion in waste glasses. The results of this study indicate that molecular water diffusion does not dominate waste glass reactions under conditions considered in this study. However, it is unknown whether molecular water diffusion will be important under other reaction conditions, especially longer time periods.

scholarly journals Leaching Savannah River Plant Nuclear Waste Glass in a Saturated Tuff Environment

1984 ◽  
Vol 44 ◽  
Author(s):  
N. E. Bibler ◽  
G. G. Wicks ◽  
V. M. Oversby
Keyword(s):  
Stainless Steel ◽  
Radioactive Waste ◽  
Nuclear Waste ◽  
304L Stainless Steel ◽  
Savannah River ◽  
Mass Losses ◽  
Savannah River Plant ◽  
Simulated Waste ◽  
Nuclear Waste Glass ◽  
Time Periods

AbstractSamples of SRP glass containing either simulated or actual radioactive waste were leached at 90°C under conditions simulating a saturated tuff repository environment. The leach vessels were fabricated of tuff and actual tuff groundwater was used. Thus, the glass was leached only in the presence of those materials (including the Type 304L stainless steel canister material) that would be in the actual repository. Tests were performed for time periods up to 6 months at a SA/V ratio of 100 m−1. Results with glass containing simulated waste indicated that stainless steel canister material around the glass did not significantly affect the leaching. Based on Li and B (elements not in significant concentrations in the tuff or tuff groundwater), glass containing simulated waste leached identically to glass containing actual radioactive waste. The tuff buffered the pH so that only a slight increase was observed as a result of leaching. Results with glass containing actual radioactive waste indicated that tuff reduced the concentrations of Cs-137, Sr-90, and Pu-238 in the free groundwater in the simulated repository by 10–100X. Also, radiolysis of the groundwater by the glass (approximately 1000 rad/hr) did not significantly affect the pH in the presence of tuff. Measured normalized mass losses in the presence of tuff for the glass based on Cs-137, Sr-90, and Pu-238 in the free groundwater were extremely low, nominally 0.02, 0.02, and 0.005 g/m2, respectively, indicating that the glass-tuff system retained radionuclides well.

scholarly journals The Role of Natural Glasses as Analogues in Projecting the Long-Term Alteration of High-Level Nuclear Waste Glasses: Part 1

1993 ◽  
Vol 333 ◽  
Author(s):  
James J. Mazer
Keyword(s):  
Nuclear Waste ◽  
Waste Glass ◽  
Molecular Water ◽  
Natural Environments ◽  
Water Contact ◽  
Natural Analogues ◽  
High Level Nuclear Waste ◽  
Common Observation ◽  
High Level

ABSTRACTThe common observation of glasses persisting in natural environments for long periods of time (up to tens of millions of years) provides compelling evidence that these materials can be kinetically stable in a variety of subsurface environments. This paper reviews how natural and historical synthesized glasses can be employed as natural analogues for understanding and projecting the long-term alteration of high-level nuclear waste glasses. The corrosion of basaltic glass results in many of the same alteration features found in laboratory testing of the corrosion of high-level radioactive waste glasses. Evidence has also been found indicating similarities in the rate controlling processes, such as the effects of silica concentration on corrosion in groundwater and in laboratory leachates. Naturally altered rhyolitic glasses and tektites provide additional evidence that can be used to constrain estimates of long-term waste glass alteration. When reacted under conditions where water is plentiful, the corrosion for these glasses is dominated by network hydrolysis, while the corrosion is dominated by molecular water diffusion and secondary mineral formation under conditions where water contact is intermittent or where water is relatively scarce. Synthesized glasses that have been naturally altered result in alkali-depleted alteration features that are similar to those found for natural glasses and for nuclear waste glasses. The characteristics of these alteration features appear to be dependent on the alteration conditions which affect the dominant reaction processes during weathering. In all cases, care must be taken to ensure that the information being provided by natural analogues is related to nuclear waste glass corrosion in a clear and meaningful way.

Experimental Investigation of Hydrous Pyrolysis of Diesel Fuel and the Effect of Pyrolysis Products on Performance of the Candidate Nuclear Waste Repository at Yucca Mountain

1993 ◽  
Vol 333 ◽  
Author(s):  
Kenneth J. Jackson ◽  
Susan A. Carroll
Keyword(s):  
Experimental Investigation ◽  
Nuclear Waste ◽  
Diesel Fuel ◽  
Yucca Mountain ◽  
Nuclear Waste Repository ◽  
Hydrothermal Solutions ◽  
Pyrolysis Products ◽  
Analytical Technique ◽  
Hydrous Pyrolysis ◽  
Waste Repository

It is thought that a significant amount of diesel fuel and other hydrocarbon-rich phases may remain inside the candidate nuclear waste repository at Yucca Mountain after construction and subsequent emplacement of radioactive waste. Although the proposed repository horizon is above the water table, the remnant hydrocarbon phases may react with hydrothermal solutions generated by high temperature conditions that will prevail for a period of time in the repository. The preliminary experimental results of this study show that diesel fuel hydrous pyrolysis is minimal at 200°C and 70 bars. The composition of the diesel fuel remained constant throughout the experiment and the concentration of carboxylic acids in the aqueous phases was only slightly above the detection limit (1–2 ppm) of the analytical technique.

scholarly journals Hydrogen Speciation in Hydrated Layers on Nuclear Waste Glass

1986 ◽  
Vol 84 ◽  
Author(s):  
Roger D. Aines ◽  
Homer C. Weed ◽  
John K. Bates
Keyword(s):  
Nuclear Waste ◽  
Vapor Phase ◽  
Waste Glass ◽  
Hydroxyl Group ◽  
Molecular Water ◽  
Hydroxyl Groups ◽  
Phase Layer ◽  
Nuclear Waste Storage ◽  
Nuclear Waste Glass ◽  
Saturated Atmosphere

AbstractThe hydration of an outer layer on nuclear waste glasses is known to occur during leaching, but the actual speciation of hydrogen (as water or hydroxyl groups) in these layers has not been determined. As part of the Nevada Nuclear Waste Storage Investigations Project, we have used infrared spectroscopy to determine hydrogen speciations in three nuclear waste glass compositions (SRL-131 & 165, and PNL 76-68), which were leached at 90°C (all glasses) or hydrated in a vapor-saturated atmosphere at 202°C (SRL-131 only). Hydroxyl groups were found in the surface layers of all the glasses. In addition, molecular water was found in the surface of SRL-131 and PNL 76-68 glasses that had been leached for several months in deionized water, and in the vapor-hydrated sample. The water/hydroxyl ratio increases with increasing reaction time; molecular water makes up most of the hydrogen in the thick reaction layers on vapor-phase hydrated glass while only hydroxyl occurs in the least reacted samples. Using the known molar absorptivities of water and hydroxyl in silica-rich glass the vapor-phase layer contained 4.8 moles/liter of molecular water, and 0.6 moles water in the form hydroxyl. A 15 micrometer layer on SRL-131 glass formed by leaching at 90°C contained a total of 4.9 moles/liter of water, 2/3 of which was as hydroxyl. The unreacted bulk glass contains about 0.018 moles/liter water, all as hydroxyl.The amount of hydrogen added to the SRL-131 glass was about 70% of the original Na + Li content, not the 300% that would result from alkali-hydronium ion (H30+) interdiffusion. If all the hydrogen is then assumed to be added as the result of alkali-H+ interdiffusion, the molecular water observed may have formed from condensation of the original hydroxyl groups according to:20H = H20 molecular + 00where 00 refers to a bridging oxygen, and OH refers to a hydroxyl group attached to a silicate polymer. The hydrated layer on the nuclear waste glasses appears to be of relatively low water content (4 to 7% by weight) and is not substantially hydroxylated. Thus, these layers do not have many of the properties associated with “gel” layers.

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