Dissolution of Technetium From Nuclear Waste Forms

ABSTRACTThe immobilization of 99Tc in both ceramic and borosilicate glass waste forms and the mechanism of dissolution of technetium from these waste forms are complicated by the range of technetium valence states. Metallic Tc,ionic Tc4+ oxides, and volatile molecular species containing Tc7+ all occur within the stability field of water. Tc4+ will substitute readily for Ti4+ in titanatebased ceramics in such phases as perovskite (CaTiO3) and spinel (Mg2TiO4). Tc4+ can be homogeneously distributed in borosilicate glass by re-melting the glass under closed system conditions to prevent the re-oxidation of technetium. The dissolution of technetium from both glass and ceramic waste forms follow similar kinetic behavior although the dissolution rate from the titanate is two orders of magnitude lower. Dissolution under highly reducing conditions is too slow to measure on the time scale of the experiments.

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The Use of Hot-Isostatic Pressing to Process Nuclear Waste Forms

ASME 2009 12th International Conference on Environmental Remediation and Radioactive Waste Management, Volume 1 ◽

10.1115/icem2009-16253 ◽

2009 ◽

Author(s):

Martin W. A. Stewart ◽

Sam A. Moricca ◽

Tina Eddowes ◽

Yingjie Zhang ◽

Eric R. Vance ◽

...

Keyword(s):

Electrical Conductivity ◽

Nuclear Waste ◽

Borosilicate Glass ◽

Hot Isostatic Pressing ◽

Processing Technology ◽

Nuclear Wastes ◽

Isostatic Pressing ◽

Waste Forms ◽

Nuclear Waste Forms ◽

Glass Viscosity

ANSTO has developed a combination of tailored nuclear waste form chemistries coupled with the use of flexible hot-isostatic pressing processing technology to enable the successful incorporation of problematic nuclear wastes into dense, durable monoliths. This combined package also enables the design of waste forms with waste loadings well in excess of those achievable via baseline melting routes using borosilicate glass, as hot-isostatic pressing is not constrained by factors such as glass viscosity, crystallisation and electrical conductivity. In this paper we will discuss some of our experiences with problematic wastes, namely plutonium wastes, sludges and HLW such as the Idaho calcines.

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Ion Implantation Studies of Nuclear Waste Forms

MRS Proceedings ◽

10.1557/proc-6-667 ◽

1981 ◽

Vol 6 ◽

Cited By ~ 2

Author(s):

Clyde J. M. Northrup ◽

George W. Arnold ◽

Thomas J. Headley

Keyword(s):

Nuclear Waste ◽

Borosilicate Glass ◽

Alpha Decay ◽

Lead Ions ◽

Waste Form ◽

Elastic Recoil ◽

Elastic Recoil Detection ◽

Waste Forms ◽

Basic Studies ◽

Nuclear Waste Forms

ABSTRACTThe first observations of physical and chemical changes induced by lead implantation damage and leaching are reported for two proposed U.S. nuclear waste forms (PNL 76–68 borosilicate glass and Sandia titanate ceramics) for commercial wastes. To simulate the effects of recoil nucleii due to alpha decay, the materials were implanted with lead ions at equivalent doses up to approximately 1 × 1019 a decays/cm3 . In the titanate waste form, the zirconolite, perovskite, hollandite, and rutile phases all exhibited a mottled appearance in the transmission electron microscope (TEM) typical of defect clusters in radiation damaged, crystalline solids. One titanate phase containing uranium was found by TEM to be amorphous after implantation at the highest dose. No enhanced leaching (deionized water, room temperature, 24 hours) of the irradiated titanate waste form, including the amorphous phase, was detected by TEM, but Rutherford backscattering (RBS) suggested a loss of cesium and calcium after 21 hours of leaching. The RBS spectra also indicated enhanced leaching from the PNL 76–68 borosilicate glass after implantation with lead ions, in general agreement with the observations of Dran, et al. [6,7] on other irradiated materials. Elastic recoil detection spectroscopy (ERD), used to profile hydrogen after leaching, showed penetration of the hydrogen to several thousand angstroms for both the implanted and unimplanted materials. These basic studies identified techniques to follow the changes that occur on implantation and leaching of complex amorphous and crystalline waste forms. These studies were not designed to produce comparisons between waste forms of gross leach rates.

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Understanding the Stability of Salt-Inclusion Phases for Nuclear Waste-forms through Volume-based Thermodynamics

Scientific Reports ◽

10.1038/s41598-018-32903-3 ◽

2018 ◽

Vol 8 (1) ◽

Cited By ~ 2

Author(s):

Emily E. Moore ◽

Vancho Kocevski ◽

Christian A. Juillerat ◽

Gregory Morrison ◽

Mingyang Zhao ◽

...

Keyword(s):

Nuclear Waste ◽

Waste Forms ◽

The Stability ◽

Nuclear Waste Forms

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A Flow Model for the Kinetics of Dissolution of Nuclear Waste Forms; A Comparison of Borosilicate Glass, Synroc and High-Silica Glass

MRS Proceedings ◽

10.1557/proc-11-57 ◽

1981 ◽

Vol 11 ◽

Author(s):

Pedro B. Macedo ◽

Aaron Barkatt ◽

Joseoph H. Simmons

Keyword(s):

Nuclear Waste ◽

Borosilicate Glass ◽

Flow Model ◽

Release Rates ◽

Waste Forms ◽

High Silica ◽

Kinetics Of Dissolution ◽

Kinetics Of ◽

Nuclear Waste Forms

A model has been developed to predict the long-term leach or release rates of various waste-form materials under repository conditions.

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Stability of I and SR Radiophases in Cement Matrices

MRS Proceedings ◽

10.1557/proc-6-147 ◽

1981 ◽

Vol 6 ◽

Cited By ~ 1

Author(s):

M.W. Barnes ◽

B.E. Scheetz ◽

L.D. Wakeley ◽

S.D. Atkinson ◽

D.M. Roy

Keyword(s):

Nuclear Waste ◽

Complete Understanding ◽

Waste Forms ◽

Diffusion Controlled ◽

The Stability ◽

And Diffusion ◽

Nuclear Waste Forms ◽

Aluminate Cement ◽

Short Times ◽

Curing Cement

ABSTRACTThe following study is a portion of a comprehensive research program that is examining the stability of a variety of nuclear waste forms. In addition to the bulk waste forms, important individual radiophases are being studied to obtain a more complete understanding of the behavior of the components of complex multiphase radwaste systems. The stability of the strontium radiophase in supercalcine and an iodine-radiophase will be discussed.The strontium radiophase in this study was Sr-powellite and the iodine radiophase was I-sodalite. Each radiophase was incorporated into bulk compositionally adjusted portland and aluminate cements. Two processing variables were studied: curing at 60°C and warm pressing at 150°C and 345 MPa.Sr-powellite in portland cement leaches incongruently; a combination of dissolution and diffusion-controlled exchange of Ca for Sr is demonstrated. In the warm-pressed aluminate cement these reactions are masked by reactions with the curing cement. I-sodalite leaching data indicate dissolution, dominant at long times, combined with diffusion, dominant at short times.

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Ion Implantation Damage in Silicate Glasses

MRS Proceedings ◽

10.1557/proc-15-423 ◽

1982 ◽

Vol 15 ◽

Cited By ~ 1

Author(s):

George W. Arnold

Keyword(s):

Ion Implantation ◽

Nuclear Waste ◽

Silicate Glasses ◽

Glass Waste ◽

Leach Rate ◽

Implantation Damage ◽

Waste Forms ◽

Long Term Behavior ◽

Nuclear Waste Forms

ABSTRACTIon implantation is a rapid technique for simulating damage induced by α-recoil nuclei in nuclear waste forms. The simulation has been found to be quite good in TEM comparisons with natural α-decay damage in minerals, but leach rate differences have been observed in glass studies and were attributed to dose-rate differences. The similarities between ion implantation and recoil nuclei as a means of producing damage suggest that insights into the long-term behavior of glass waste forms can be obtained by examination of what is known about ion-implantation damage in silicate glasses. This paper briefly reviews these effects and shows that leaching results in certain nuclear waste glasses can be understood as resulting from plastic flow and track overlap. Phase separation is also seen to be a possible consequence of damage-induced compositional changes.

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The Formation and Modeling of Colloids from the Corrosion of Nuclear Waste Forms

10.1557/proc-1124-q11-01 ◽

2008 ◽

Author(s):

Edgar Buck ◽

Rick S. Wittman

Keyword(s):

Nuclear Waste ◽

Waste Forms ◽

Nuclear Waste Forms

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Ab Initio Investigation of Helium Mobility in La2Zr2O7 Pyrochlore

Crystals ◽

10.3390/cryst11060667 ◽

2021 ◽

Vol 11 (6) ◽

pp. 667

Author(s):

Yanxia Lu ◽

Qing Peng ◽

Chenguang Liu

Keyword(s):

Nuclear Waste ◽

Density Functional ◽

Minimum Energy ◽

Elastic Band ◽

Waste Forms ◽

Band Method ◽

And Migration ◽

High Level ◽

Migration Pathways ◽

Nuclear Waste Forms

The α-decay of incorporated actinides continuously produces helium, resulting in helium accumulation and causing security concerns for nuclear waste forms. The helium mobility is a key issue affecting the accumulation and kinetics of helium. The energy barriers and migration pathways of helium in a potential high-level nuclear waste forms, La2Zr2O7 pyrochlore, have been investigated in this work using the climbing image nudged elastic band method with density functional theory. The minimum energy pathway for helium to migrate in La2Zr2O7 is identified as via La–La interstitial sites with a barrier of 0.46 eV. This work may offer a theoretical foundation for further prospective studies of nuclear waste forms.

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