Publisher Summary An effective strategy for dealing with high-level waste is to partition the short-lived fission product elements from the long-lived actinides, creating separate waste streams. Once there are two waste streams, the properties and durability of the waste form can be designed to a level appropriate to the toxicity and time required for isolation from the environment. With such a strategy the fission product elements may be incorporated into a borosilicate glass and the actinides into more durable crystalline ceramics. Although special glass compositions may be developed for actinide incorporation, their long-term durability is less easily assured, particularly on the time scales required for actinide immobilization and confinement. The final selection of any waste form should depend on its ability to incorporate the radionuclides of interest, its chemical durability, response to a radiation-field, and physical properties as well as the time required for isolation to protect the environment.

Actinide host phases as radioactive waste forms

Crystal chemistry of uranium (V) and plutonium (IV) in a titanate ceramic for disposition of surplus fissile material

Branneritecontaining ceramics were produced by cold pressing and sintering (CPS) and cold crucible inductive melting (CCIM) methods and examined by X-ray diffraction and absorption and by scanning electron microscopy. Brannerite content in the ceramics ranged between ∼20 and 90 vol.%. Uranium is mainly partitioned between brannerite and minor mixed U/RE oxide but since brannerite is a dominant phase, it takes up to 90% of total U. Uranium in the ceramics is present as U(IV) and U(V). In the low-brannerite ceramics U occurs as U(IV) whereas in the ceramics with brannerite as major phase U(V) dominates over U(IV). Ce in the brannerite ceramics is mainly trivalent. The first coordination shell of U in ceramics produced by CPS is split into two sub-shells with U-O distances of 1.7–1.9 A and ∼2.1 A while in the melted ceramics this interatomic distance is 2.1–2.2 A. The next three atoms (Ti) are positioned at a distances of 3.1–3.2 A.

Phase partitioning and uranium speciation in brannerite-based ceramics

Phase compositions, structural features, and element distributions were studied for samples of the compositions REE2(Zr2−x
 Ti
 x
 )O7, which are potential matrices for immobilization of the rare earth-actinide fraction of high-level waste from spent nuclear fuel reprocessing. Samples with x up to 0.8 consist of pyrochlore, and at higher titanium content, of pyrochlore and monoclinic REE titanate with perovskite-type structure. The monoclinic phase becomes prevalent at x > 1.2. With respect to the content of the incorporated waste, it surpasses pyrochlore matrices by 10 wt %. The radiation resistance of this phase is close to that of titanate pyrochlore, but its amorphization dose is lower than for zirconate and titanate-zirconate pyrochlore. To check the suitability of monoclinic titanate for immobilization of the REE-actinide waste fraction, it is necessary to study its behavior in solutions and the effect of amorphization on the actinide leaching. The matrix can be prepared by the cold pressing-sintering method suggested in the United States for the synthesis of pyrochlore matrices with plutonium. High rate of solid-phase reactions in titanate systems allows the equilibrium to be attained at a moderate temperature (1400°C) within short sintering time (the first hours). One more possible procedure for matrix fabrication is cold crucible induction melting followed by the melt crystallization.

Potential matrices for immobilization of the rare earth-actinide fraction of high-level waste in the REE2Zr2O7-REE2Ti2O7 system

Pyrochlore-rich ceramics containing additional zirconolite, brannerite and rutile have been developed for immobilizing excess weapons plutonium. This study reports data for a ceramic containing small amounts of Al and Mo in addition to the major oxide components of Ti, U, Ca, Hf, Gd and Ce. Hafnium and Gd are added as neutron absorbers, Al and Mo represent impurities. Quantitative electron microprobe data demonstrate that UO2 is strongly partitioned into brannerite (45 wt%), which is present as euhedral crystals with inclusions of unreacted UO2. Pyrochlore forms the groundmass and has an average UO2 content of 28 wt%. Zirconolite contains only 15 wt% UO2, but is significantly more effective in accommodating Hf and Gd than both brannerite and pyrochlore. Zirconolite incorporates U together with Hf and Ce in one structural site, whereas brannerite and pyrochlore accommodate U with Gd in a site that is distinct from that occupied by Hf. Incorporation of Gd into zirconolite takes place via a coupled substitution involving Al, thus explaining the high Al2O3 contents (3 wt%). Molybdenum was not detected in the major oxides, and it might be present in the accessory rutile. Although the studied waste form was designed to incorporate Pu, the present dataset is also valuable because immobilization of highly fissile U (e.g., U-233) might need to be considered in the future.

Element Partitioning in a Pyrochlore-Based Ceramic Nuclear Waste form

We report x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectra from the plutonium L{sub III} edge and XANES from the cerium L{sub II} edge in prototype titanate ceramic hosts. The titanate ceramics studied are based upon the hafnium-pyrochlore and zirconolite mineral structures and will serve as an immobilization host for surplus fissile materials, containing as much as 10 weight % fissile plutonium and 20 weight % (natural or depleted) uranium. Three ceramic formulations were studied: one employed cerium as a ''surrogate'' element, replacing both plutonium and uranium in the ceramic matrix, another formulation contained plutonium in a ''baseline'' ceramic formulation, and a third contained plutonium in a formulation representing a high-impurity plutonium stream. The cerium XANES from the surrogate ceramic clearly indicates a mixed III-IV oxidation state for the cerium. In contrast, XANES analysis of the two plutonium-bearing ceramics shows that the plutonium is present almost entirely as Pu(IV) and occupies the calcium site in the zirconolite and pyrochlore phases. The plutonium EXAFS real-space structure shows a strong second-shell peak, clearly distinct from that of PuO{sub 2}, with remarkably little difference in the plutonium crystal chemistry indicated between the baseline and high-impurity formulations.

/pdf/exafs-and-xanes-analysis-of-plutonium-and-cerium-edges-from-4pjazv5x2n.pdf

EXAFS and XANES analysis of plutonium and cerium edges from titanate ceramics for fissile materials disposal.

We report x-ray absorption near edge structure (XANES) and extended x-ray fine structure analysis (EXAFS) spectra from the plutonium Llll and cerium Lm edges in prototype titanate ceramic hosts for disposal of surplus fissile materials. These spectra were obtained using the MRCAT beamline at the Advanced Photon Source (APS). The XANES and EXAFS results are compared with electron loss spectra (EELS) determination of oxidation state from the plutonium MlV,V and cerium MlV,V edges [1,2]. The titanate ceramics studied are based upon the hafniumpyrochlore and zirconolite mineral structures and will serve as an immobilization host, containing as much as 10 weight % fissile plutonium, and 20 weight % (natural or depleted) uranium. Similar formulations were composed using cerium as a “surrogate” element, replacing both plutonium and uranium in the ceramic matrix. We find the plutonium to be present almost entirely as Pu (IV), while the cerium is clearly in a mixed III-IV oxidation state in the surrogate ceramic.

EELS and Xanes Analysis of Plutonium and Cerium Edges From Titanate Ceramics for Fissile Materials Disposal

Titanate ceramics have been selected as the preferred waste form for the immobilization of excess plutonium. Corrosion tests are underway to try to understand the long-term behavior of this material. In this paper, results from PCT-B static dissolution tests are used to provide an explanation of the observed corrosion behavior of a zirconolite-based ceramic. Two important observations are made. First, Ca is released at a constant rate [7 x 10{sup {minus}5} g/(m{sup 2} day)] in PCT-B tests for up to two years. Second, the release rates for Pu and Gd increase with time (up to two years) in PCT-B tests. The first observation suggests that the ceramics continue to corrode at a low rate for at least two years in PCT-B tests. The second observation suggests that the release rates of Pu and Gd are controlled by some process or processes that do not affect the release rate of other elements. Evidence indicates that this is due to the preferential dissolution of brannerite from the ceramic.

/pdf/the-impact-of-brannerite-on-the-release-of-plutonium-and-4kaemlidis.pdf

The impact of brannerite on the release of plutonium and gadolinium during the corrosion of zirconolite-rich titanate ceramics

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

M. C. Hash

Author Tools

Chat about Author

Papers

EXAFS and XANES analysis of plutonium and cerium edges from titanate ceramics for fissile materials disposal.

EELS and Xanes Analysis of Plutonium and Cerium Edges From Titanate Ceramics for Fissile Materials Disposal

The impact of brannerite on the release of plutonium and gadolinium during the corrosion of zirconolite-rich titanate ceramics