scholarly journals Research Needs in Cement-Based Waste Forms

1990 ◽  
Vol 212 ◽  
Author(s):  
E. W. McDaniel ◽  
R. D. Spence ◽  
O. K. Tallent
Keyword(s):  
Mass Transfer ◽  
Waste Disposal ◽  
Cost Effective ◽  
Waste Form ◽  
Research Needs ◽  
Effective Screening ◽  
Waste Forms ◽  
Fundamental Understanding ◽  
Disposal Options ◽  
Improved Design

ABSTRACTCement-based waste forms are one of the most widely used waste disposal options, yet definitive knowledge of the fate of the waste species inside the waste form is lacking. A fundamental understanding of the chemistry and microstructure of the waste forms would lead to a better understanding of the mass transfer of the waste species, more confidence in predicting and extrapolating waste-form performance, and improved design of waste forms. Better and cheaper leach tests would lead to quicker and more cost-effective screening of waste-form alternatives, cement-based and otherwise. In addition, assessment of durability may be important to predicting waste-form performance in the field over periods of decades and centuries.

scholarly journals Radioactive wastes and disposal options

2018 ◽  
Vol 189 ◽  
pp. 00014 ◽  
Author(s):  
Bernhard Kienzler ◽  
Horst Geckeis
Keyword(s):  
Nuclear Waste ◽  
Waste Disposal ◽  
Waste Treatment ◽  
Nuclear Waste Disposal ◽  
Radioactive Wastes ◽  
Waste Forms ◽  
Disposal Options ◽  
Treatment Procedures ◽  
Host Rocks

This paper provides for a summary of facts which are indispensable for nuclear waste disposal. Information is presented on types of radioactive wastes and the origin, the waste treatment procedures and some characteristics of the waste forms. Finally the various host rocks and the international disposal concepts are discussed and the procedures for safety analyses are shortly described.

Prediction of Waste Performance in a Geologic Repository

1983 ◽  
Vol 26 ◽  
Author(s):  
Paul L. Chambre' ◽  
Thomas H. Pigford
Keyword(s):  
Mass Transfer ◽  
Steady State ◽  
Radioactive Decay ◽  
Time Dependent ◽  
Waste Form ◽  
Radionuclide Transport ◽  
Convective Mass Transfer ◽  
Geologic Repository ◽  
Concentration Boundary ◽  
Waste Forms

ABSTRACTThe rate of dissolution of low-solubility species from waste forms in a geologic repository can be calculated from a theoretical analysis of the time-dependent rate of mass transfer by diffusion and convection Into the groundwater surrounding the waste, assuming a concentration at the waste-form surface eanal to the solubility of the radioelement. The analytical solutions for time-dependent mass transfer are reduced to asymptotic steady-state approximations valid over specified ranges of repository conditions. The predicted steady-state dissolution rates are considerably below those observed in laboratory leaching experiments with borosilicate glass and with other waste forms, indicating that the solid-liquid chemical reaction rates measured in the laboratory experiments are greater than the rates of diffusive-convective mass transfer in the concentration boundary layer surrounding the waste form in a geologic repository. It is shown that the time to reach steady-state dissolution can be as short as a few years, if convective mass transfer in the concentration boundary layer is important, to many thousands of years, If mass transfer is mainly by diffusion in the groundwater. The steady-state mass transfer rate can be Increased, and the time to reach steady state decreased, by sufficiently short half lives of the dissolving species. The theory has been extended to Include the effect of backfill on the steady-state mass transfer from the waste-form surface into moving groundwater.The mass-transfer theory has been extended to include the effect of time-dependent solubilities, diffusion coefficients, and retardation coefficients, which provides a means of calculating the time-dependent dissolution of lowsolubility species from waste exDosed to groundwater during the Period of repository heating. The effects of timetemperature transient dissolution on far-field concentrations and cumulative release are calculated.The transient and steady-state diffusion of radionuclides through a finite backfill layer separating a finite waste solid and porous rock has been analyzed, Including the effects of radioactive decay. Previous backfill analyses have neglected radioactive decay and have assumed an infinite amount of backfill. The results show that the break-through time and rate of radionuclide release depend on properties of the backfill and surrounding rock and on the waste form dimensions.Laboratory tests have been designed to validate these theoretical analyses of diffusive-convective mass transfer with solubility-limit boundary conditions. Preliminary tests are now underway at the Battelle Northwest Laboratory.Peak far-field concentrations of more soluble radionuclides such as cesium-135, with suitably long radionuclide transport times and sufficiently large axial dispersion, are shown to he insensitive to dissolution rate. Equivalent phenomena occur in fracture-flow radionuclide transport.

Uncertainty in air stripping tower design: implications of the air-to-water ratio

2001 ◽  
Vol 1 (4) ◽  
pp. 177-184
Author(s):  
B.I. Dvorak ◽  
J.W. Schauble
Keyword(s):  
Mass Transfer ◽  
Removal Efficiency ◽  
Cost Effective ◽  
Air Stripping ◽  
Henry's Constant ◽  
True Value ◽  
Risk Of Failure ◽  
Process Failure ◽  
Removal Efficiencies ◽  
Water Ratio

Environmental engineers are frequently faced with uncertainty in making design decisions because the true value of many process parameters is unknown. In this study, the design of countercurrent air stripping towers was modeled using fuzzy numbers, taking into account uncertainties in mass transfer and Henry's constant. It was found that, in addition to cost, the risk of failure is an important design consideration for stripping tower design. A significant over-design is both cost-effective and results in less risk of design failure. The air-to-water ratio that yielded the least risk of failure switched from low to high as the removal efficiency of the tower increased. An important result is that at lower removal efficiencies, tower design and operation is most sensitive to uncertainties in mass transfer and at higher removal efficiencies, tower design and operation is most sensitive to uncertainties in Henry's constant . The implication is that low air-to-water ratios are best when the regulatory target removal efficiency is low and/or when the uncertainty in the value of the contaminant's Henry's constant is larger than the uncertainty in the mass transfer coefficient value. Otherwise a high air-to-water ratio results in the least risk of process failure.

Host Phases for Actinide Elements in the Metallic Waste Form

2002 ◽  
Vol 757 ◽  
Author(s):  
D. E. Janney
Keyword(s):  
Stainless Steel ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Transmission Electron Microscope ◽  
Waste Form ◽  
Dissolution Behavior ◽  
Release Rates ◽  
Waste Forms ◽  
Transmission Electron ◽  
Simulated Waste

ABSTRACTArgonne National Laboratory has developed an electrometallurgical process for conditioning spent sodium-bonded metallic reactor fuel prior to disposal. A waste stream from this process consists of stainless steel cladding hulls that contain undissolved metal fission products such as Tc, Ru, Rh, Pd, and Ag; a small amount of undissolved actinides (U, Np, Pu) also remains with the hulls. These wastes will be immobilized in a waste form whose baseline composition is stainless steel alloyed with 15 wt% Zr (SS-15Zr). Scanning electron microscope (SEM) observations of simulated metal waste forms (SS-15Zr with up to 11 wt% actinides) show eutectic intergrowths of Fe-Zr-Cr-Ni intermetallic phases with steels. The actinide elements are almost entirely in the intermetallics, where they occur in concentrations ranging from 1–20 at%. Neutron- and electron-diffraction studies of the simulated waste forms show materials with structures similar to those of Fe2Zr and Fe23Zr6.Dissolution experiments on simulated waste forms show that normalized release rates of U, Np, and Pu differ from each other and from release rates of other elements in the sample, and that release rates for U exceed those for any other element (including Fe). This paper uses transmission electron microscope (TEM) observations and results from energy-dispersive X-ray spectroscopy (EDX) and selected-area electron-diffraction (SAED) to characterize relationships between structural and chemical data and understand possible reasons for the observed dissolution behavior.Transmission electron microscope observations of simulated waste form samples with compositions SS-15Zr-2Np, SS-15Zr-5U, SS-15Zr-11U-0.6Rh-0.3Tc-0.2Pd, and SS-15Zr-10Pu suggest that the major actinide-bearing phase in all of the samples has a structure similar to that of the C15 (cubic, MgCu2-type) polymorph of Fe2Zr, and that materials with this structure exhibit significant variability in chemical compositions. Material whose structure is similar to that of the C36 (dihexagonal, MgNi2-type) polymorph of Fe2Zr was also observed, and it exhibits less chemical variability than that displayed by material with the C15 structure. The TEM data also demonstrate a range of actinide concentrations in materials with the Fe23Zr6 (cubic, Mn23Th6-type) structure.Microstructures similar to those produced during experimental deformation of Fe-10 at% Zr alloys were observed in intermetallic materials in all of the simulated waste form samples. Stacking faults and associated dislocations are common in samples with U, but rarely observed in those with Np and Pu, while twins occurred in all samples. The observed differences in dissolution behavior between samples with different actinides may be related to increased defect-assisted dissolution in samples with U.

The Availability of Sharps Disposal Bins: A Survey of Airports in California

2021 ◽  
pp. 193229682110398
Author(s):  
Jennifer Y. Zhang ◽  
Trisha Shang ◽  
Edward Krisiunas ◽  
Dorian Liepmann ◽  
David C. Klonoff
Keyword(s):  
At Risk ◽  
Waste Disposal ◽  
Published Data ◽  
Self Monitoring ◽  
Average Percentage ◽  
Current State ◽  
Disposal Options ◽  
Safe Mechanism ◽  
Survey Responses ◽  
Question Survey

Background: Sharps waste, especially medical sharps waste, can put those who come into contact with it at risk for injury and exposure to blood-borne pathogens. Options for self-injectors to dispose of their sharps while traveling vary greatly – from sharps containers in limited locations in some public restrooms to large kiosks centrally located to no containers at all. Currently, there is a lack of published data on sharps disposal bins in commercial airports. We surveyed commercial airports in California to assess the current state of sharps waste disposal. Many people with diabetes routinely use sharps every day for injecting medications or for self-monitoring glucose concentrations and these people, along with others who self-inject medications, must have a safe mechanism for sharps disposal when travelling by air. Methods: A five-question survey was sent to 30 commercial airports in California. Responses were collected and then analyzed based on the following three metrics: (1) the percentage of airports that responded and indicated that they had any sharps disposal bins, (2) the percentage of airports that responded and indicated that they had sharps disposal bins in over half their restrooms, and (3) the average percentage of bathrooms that have available sharps disposal bins in airports that responded to our survey. Results: Out of 30 commercial airports in California, we received survey responses from 13 airport representatives and direct email responses from 5 airport representatives. Out of 18 total responses, 11 airports (61.1%) reported that they had some form of available sharps disposal options. Out of the 13 survey responses, 6 airports (46.2%) reported that they had sharps disposal in over 50% of their restrooms. Conclusion: There is a lack of consistency in sharps waste disposal options among commercial airports in California. While many commercial airports in California offer sharps waste disposal options, not all commercial airports have sharps waste disposal options in all their public restrooms. There is room for improved availability of sharps disposal bins in California’s commercial airports.

scholarly journals Motion – Screening and Surveillance of Barrett’s Epithelium Is Practical and Cost Effective: Arguments against the Motion

2002 ◽  
Vol 16 (8) ◽  
pp. 541-545 ◽  
Author(s):  
Naoki Chiba
Keyword(s):  
Cost Effective ◽  
World Health ◽  
Endoscopic Screening ◽  
Effective Screening ◽  
Screening And Surveillance ◽  
Screening Protocol ◽  
Surveillance Programs ◽  
Prolongation Of Life ◽  
Health Organization ◽  
Very High

The issue of whether to screen individuals for Barrett’s esophagus (BE) to prevent esophageal adenocarcinoma (EAC) is highly controversial. Important considerations are that BE is not highly prevalent in the general population and that not many patients with BE develop or die from EAC. Studies that suggest an improved prognosis from surveillance programs are susceptible to lead-time bias. Most of the principles for effective screening, as outlined by the World Health Organization, are not met by endoscopic screening and surveillance protocols. The diagnosis of BE (and dysplasia) is often unclear. Most patients with BE are not identified by screening, and few deaths would be prevented by surveillance. A decision analysis found that the most cost effective screening protocol would be every five years, but the costs associated with prolongation of life are very high, even if a group at high risk for EAC could be identified.

Aging Studies of Pu-238 and -239 Containing Calcium Phosphate Ceramic Waste-forms

2013 ◽  
Vol 1518 ◽  
pp. 73-78 ◽  
Author(s):  
Shirley K. Fong ◽  
Brian L. Metcalfe ◽  
Randall D. Scheele ◽  
Denis M. Strachan
Keyword(s):  
Calcium Phosphate ◽  
Accelerated Aging ◽  
Waste Form ◽  
Calcium Phosphate Ceramic ◽  
Ceramic Waste ◽  
Waste Forms ◽  
Aging Studies ◽  
Flow Through ◽  
Pyrochemical Reprocessing

ABSTRACTA calcium phosphate ceramic waste-form has been developed at AWE for the immobilisation of chloride containing wastes arising from the pyrochemical reprocessing of plutonium. In order to determine the long term durability of the waste-form, aging trials have been carried out at PNNL. Ceramics were prepared using Pu-239 and -238, these were characterised by PXRD at regular intervals and Single Pass Flow Through (SPFT) tests after approximately 5 yrs.While XRD indicated some loss of crystallinity in the Pu-238 samples after exposure to 2.8 x 1018 α decays, SPFT tests indicated that accelerated aging had not had a detrimental effect on the durability of Pu-238 samples compared to Pu-239 waste-forms.

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