Interpreting Uranyl Mineral Diffraction Patterns

Secondary phases that form during the corrosion of nuclear waste forms may influence both the rate of waste form dissolution and the release of radionuclides [1]. The identification of these phases is critical in developing models for the corrosion behavior of nuclear waste forms. In particular, the secondary uranyl (VI) minerals that form during waste form alteration may control uranium solubility and release of radionuclides incorporated into these phases [2].The U6+ cation in uranyl minerals is almost always present as a linear (UO2)2+ ion [3]. This uranyl (Ur) ion is coordinated by four, five, or six anions (ϕ) in the equatorial plane resulting in the formation of square (Urϕ4), pentagonal (Urϕ5), and hexagonal (Urϕ6) bipyramids, respectively [3]. These bipyramid polyhedra may polymerize to form complex infinite sheet structures. The linking of Urϕ5 is observed in a number of uranyl minerals formed during waste glass and spent fuel corrosion [2,4], such as weeksite [Na,K(UO2)2(Si205)3*4H2O] and β-uranophane [Ca[(UO2)(SiO3OH)]2*5H2O].

Download Full-text

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.

Download Full-text

The Long-Term Performance of Nuclear Waste Forms: Natural Materials - Three Case Studies

MRS Proceedings ◽

10.1557/proc-294-559 ◽

1992 ◽

Vol 294 ◽

Cited By ~ 3

Author(s):

Rodney C. Ewing

Keyword(s):

Case Studies ◽

Nuclear Waste ◽

Experimental Results ◽

Waste Form ◽

Short Term ◽

Waste Forms ◽

Long Term Performance ◽

Term Performance ◽

Nuclear Waste Forms

ABSTRACTNatural materials may be used to advantage in the evaluation of the long-term performance of nuclear waste forms. Three case studies are presented: (I) radiation effects in ceramic waste forms; (II) corrosion products of U02 under oxic conditions; (III) corrosion rate of nuclear waste glasses. For each case, a natural phase which is structurally and chemically analogous to the waste form is identified and used to evaluate the long-term behavior of a nuclear waste form. Short-term experimental results are compared to the observations made of analogous natural phases. The three case studies illustrate that results may range between providing fundamental data needed for the long-term evaluation of a waste form to only providing qualitative data of limited use. Although in the most rigorous view the long-term behaviour of a phase cannot be predicted, the correspondence between short-term experimental results and observations made of natural phases provides confidence in the “predicted” behavior of the waste form. The strength of this approach rests with the degree to which a mechanistic understanding of the phenomenon is attained.

Download Full-text

Leaching Studies of Crystalline Sodium Phases in Nuclear Waste Forms

MRS Proceedings ◽

10.1557/proc-6-163 ◽

1981 ◽

Vol 6 ◽

Cited By ~ 1

Author(s):

E.R. Vance ◽

T. Adl

Keyword(s):

Surface Area ◽

Nuclear Waste ◽

Waste Form ◽

Waste Forms ◽

Nuclear Waste Forms

The immobilization of non-radioactive Na in nuclear waste has not been given much attention. However since Na compounds are normally very soluble, Nabearing phases may render a waste form more susceptiible to leaching of radionuclides. The Na-phases may incorporate radionuclides and also, leaching of soluble Na phases will increase the surface area of the waste form. The crystalline Na-bearing phases which might occur in tailored ceramic formulations for nuclear waste are nepheline [1,2], magnetoplumbite [3] and sodalitetype materials [4]. Other Na phases which might occur in titanate-tailored [2,5] or titanate-encapsulated [6,7] forms are perovskite [8,9], Na2Ti3O7 (especially in titanate-encapsulated materials) and Na2TiSiO5 or Na2Ti2Si2O9, etc., if the waste contained sand or zeolites [10].

Download Full-text

Corrosion Behavior and Microstructure Influence of Glass-Ceramic Nuclear Waste Forms

CORROSION ◽

10.5006/2449 ◽

2017 ◽

Vol 73 (11) ◽

pp. 1306-1319 ◽

Cited By ~ 5

Author(s):

R. Matthew Asmussen ◽

James J. Neeway ◽

Tiffany C. Kaspar ◽

Jarrod V. Crum

Keyword(s):

Corrosion Behavior ◽

Nuclear Waste ◽

Glass Ceramic ◽

Waste Forms ◽

Nuclear Waste Forms

Download Full-text

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

Download Full-text

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.

Download Full-text