Radionuclide Incorporation and Long Term Performance of Apatite Waste Forms

AbstractCurrent trends in modelling waste package performance are reviewed mainly from the perspective of the Swedish SKB studies. Examples are given, which illustrate the approaches for modelling different waste forms, i.e. HLW glass and spent nuclear fuel, and candidate canister materials, such as copper and steel. The relative importance of thermodynamics, reaction kinetics and near-field transport are discussed.

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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.

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The National Research Council, Study of the Isolation System for Geologic Disposal of Radioactive Wastes

MRS Proceedings ◽

10.1557/proc-26-461 ◽

1983 ◽

Vol 26 ◽

Cited By ~ 2

Author(s):

Thomas H. Pigford

Keyword(s):

Individual Dose ◽

Spent Fuel ◽

Geologic Repository ◽

Isolation System ◽

Waste Forms ◽

The Individual ◽

Long Term Performance ◽

Term Performance ◽

Environmental Releases

ABSTRACTThis study was conducted for the U. S. Department of Energy by the Waste Isolation Systems Panel appointed by the National Academies of Science and Engineering. The panel was charged to review the alternative technologies available for Isolating of radioactive waste in mined geologic repositories, evaluate the performance benefits from these technologles as potential elements of a waste Isolation system, and identify appropriate technical criteria for satisfactory long-term performance of a geologic repository. Conceptual repositories in basalt, granite, salt, and tuff were considered. Site-specific data on geology, hydrology, and geochemical properties were evaluated and used to define parameters for estimating long-term environmental releases, supplemented when necessary by generic properties.The technology for solid waste forms and waste packages was reviewed and evaluated. Borosilicate glass and unreprocessed spent fuel are the waste forms appropriate for further testing and for repository designs. Testing in a simulated repository environment is necessary to develop an adeauate prediction of the long term performance of waste packages in a geologic repository. Back-up research and development on alternative waste forms should be continued. The expected functions of backfill placed between the rock and waste package need clearer definition and validation.The overall criterion to be used by federal agencies in designing a geologic waste-isolation system and in evaluating its nerformance has not yet been specified. As a guideline, the panel selected an average annual dose of 10-4 sieverts to a maximally exposed individual at any future time, if the exposure is from expected events such as the slow dissolution of waste solids in wet-rock repositories and the groundwater transport of dissolved radionuclides to the biosphere. Risks from unexpected events such as human intrusion were not evaluated.Calculations were made of the long-term isolation and environmental releases for conceptual repositories in basalt, granite, salt, and tuff. The major contributors to geologic isolation are the slow dissolution of key radioelements as limited by solubility and by diffusion and convection in groundwater surrounding the waste solids, long water travel times from the waste to the environment, and sorption retardation in the media surrounding the repository. Dilution by surface water can reduce the individual radiation exposures that can result from the small fraction of the waste radioactivity that may ultimately reach the environment. Estimates of environmental releases and individual doses were made both for unreprocessed spent fuel and for reprocessing wastes.Accelerated dissolution of waste exposed to groundwater during the period of repository heating was also considered. Long-term environmental releases of radioactivity from some repositories were calculated to cause doses to maximally exposed individuals that are several orders of magnitude below the Individual dose criterion of 10-4 Sieverts per year. Other conceptual repositories were found to not meet the individual dose criterion, although these repositories could still meet the radioactivity release limits in the standard proposed by the Environmental Protection Agency.The technology for geologic waste disposal has advanced to the state of a preliminary technical plan, suitable for testing, verification, and for pllot-facility confirmation. The waste Isolation program needs a reliable prediction of long-term performance that will serve as a basis for final design, construction, licensing, and waste emplacement.

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Alpha-Decay Damage and Annealing Effects in Natural Pyrochlores: Analogues for Long-Term Radiation Damage Effects in Actinide, Pyrochlore, Structure Types

MRS Proceedings ◽

10.1557/proc-127-253 ◽

1988 ◽

Vol 127 ◽

Cited By ~ 5

Author(s):

G. R. Lumpkin ◽

R. C. Ewing

Keyword(s):

Pyrochlore Structure ◽

Alpha Decay ◽

X Ray Diffraction ◽

Final State ◽

X Ray ◽

Waste Forms ◽

Annealing Effects ◽

Long Term Performance ◽

Term Performance

ABSTRACTCubic pyrochlore structure types, A2-mB2O6(O, OH, F) i-n*pH2O, and their derivatives (e.g., monoclinic zirconolite) are important actinide-bearing phases in polyphase, ceramic waste forms (e.g., SYNROC). These waste form phases may typically accumulate alpha-decay doses of 1025 alpha-events/m3 in 1, 000 years or 1026alpha-events/m3 in one million years (i.e., for SYNROC with 20 wt. % HLW). Natural pyrochlores have calculated doses ranging from 1024 to 1027 alpha-events/m3 (= 0.02 to 50 dpa) which have accumulated over ten to a thousand million years. Actinide doping experiments typically reach doses of 1025 alpha-events/m3over periods of several years. Detailed x-ray diffraction analysis of natural samples reveals that the alpha-decay dose at which there is an initial loss of crystallinity (i.e., transition from crystalline to the aperiodic, metamict state as a result of alpha-decay damage) increases as a function of the geologic age of the sample. The increase in the calculated alpha-decay dose which is associated with a specific degree of damage (e.g., loss of x-ray diffraction intensity) is attributed to annealing of isolated alpha-recoil tracks back to the original, crystalline structure. Based on a model of gradual track fading, the alpha-recoil tracks in natural pyrochlores have mean lives on the order of 108 years. In contrast, minerals which remain crystalline (e.g., uraninite, UO2) despite doses of over 1027 alpha-events/m3 have mean alpha-recoil track lives of approximately 104 years. This demonstrates that the microstructure of alpha-decay damaged materials depends not only on the total alpha-event dose, but also on the annealing kinetics of alpha-recoil track fading. Therefore, the prediction of the long-term performance and final state of crystalline phases in ceramic nuclear waste forms requires the determination of alpha-recoil damage annealing as a function of time and temperature.

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Preparation and characterization of multiphase ceramic designer waste forms

Scientific Reports ◽

10.1038/s41598-021-84014-1 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Braeden M. Clark ◽

Priyatham Tumurugoti ◽

Shanmugavelayutham K. Sundaram ◽

Jake W. Amoroso ◽

James C. Marra

Keyword(s):

Fixed Ratio ◽

Chemical Durability ◽

Waste Form ◽

Ceramic Waste ◽

Waste Forms ◽

Plasma Sintering ◽

Long Term Performance ◽

Term Performance ◽

Elemental Release

AbstractThe long-term performance, or resistance to elemental release, is the defining characteristic of a nuclear waste form. In the case of multiphase ceramic waste forms, correlating the long-term performance of multiphase ceramic waste forms in the environment to accelerated chemical durability testing in the laboratory is non-trivial owing to their complex microstructures. The fabrication method, which in turn affects the microstructure, is further compounding when comparing multiphase ceramic waste forms. In this work, we propose a “designer waste form” prepared via spark plasma sintering to limit interaction between phases and grain growth during consolidation, leading to monolithic high-density waste forms, which can be used as reference materials for comparing the chemical durability of multiphase waste forms. Designer waste forms containing varying amounts of hollandite in the presence of zirconolite and pyrochlore in a fixed ratio were synthesized. The product consistency test (PCT) and vapor hydration test (VHT) were used to assess the leaching behavior. Samples were unaffected by the VHT after 1500 h. As measured by the PCT, the fractional Cs release decreased as the amount of hollandite increased. Elemental release from the zirconolite and pyrochlore phases did not appear to significantly contribute to the elemental release from the hollandite phase in the designer waste forms.

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