scholarly journals Comparison of Ceramic Waste forms Produced by hot Uniaxial Pressing and by Cold Pressing and Sintering

1994 ◽  
Vol 353 ◽  
Author(s):  
V. M. Oversby ◽  
E.R. Vance
Keyword(s):  
Production Method ◽  
Activity Level ◽  
Waste Form ◽  
Phase Assemblage ◽  
Waste Streams ◽  
Cold Pressing ◽  
N2 Atmosphere ◽  
Precursor Material ◽  
Simulated Waste ◽  
Cold Pressed

AbstractSynroc C waste form specimens prepared using the Australian-developed technology are uniaxially pressed in stainless steel bellows at 1200°C and 20MPa. This produces a material with high chemical and physical durability and with the radioactivity enclosed inside both the waste form and the bellows. An alternative method of producing the ceramic product is to use cold pressing of pellets followed by reactive sintering to provide densification and mineralization. Depending on the scale of waste form preparation required and on the activity level and nature of the waste streams, the cold press and sinter method may have advantages. To evaluate the effects of production method on waste form characteristics, especially resistance to dissolution or leaching of waste elements, we have prepared two simulated waste samples for evaluation. Both samples were prepared from liquid precursor materials (alkoxides, nitrates, and colloidal silica) and then doped with waste elements. The precursor material in each case corresponded to a basic phase assemblage of 60% zirconolite, 15% nepheline, 10% spinel, 10% perovskite, and 5% rutile. One sample was doped with 25% by weight of U; the other with 10% by weight each of U and Gd. Each sample was calcined at 750°C for 1 hr. in a 3.5% H2 in N2 atmosphere. Then one portion of each sample was hot pressed at temperatures ranging from 1120 to 1250°C and 20MPa pressure in steel bellows. A separate portion of each sample was formed into pellets, cold pressed, and sintered in various atmospheres at 1200°C to produce final products about 2/3 cm in diameter. Samples were then examined to determine density of the product, grain sizes of the phases, phase assemblage, and the location of the U and Gd in the final phases. Density data indicate that sintering gives good results provided that the samples are held at 200°C for long enough to allow trapped gases to escape.

The Development of a Ceramic Waste Form for Immobilisation of Highly Active Wastes from Radical Purex Reprocessing Operations

1996 ◽  
Vol 465 ◽  
Author(s):  
Ewan Maddrell
Keyword(s):  
Fuel Cycle ◽  
Nuclear Fuel Cycle ◽  
Waste Form ◽  
Phase Assemblage ◽  
Waste Streams ◽  
Initial Development ◽  
Ceramic Phase ◽  
Highly Active ◽  
Waste Minimisation ◽  
Optimum Solution

ABSTRACTThe development of novel, Radical Purex, reprocessing technologies, leading to fission product waste streams with high levels of inert constituents, may mean that vitrification is no longer the optimum solution for the immobilisation of highly active wastes at the back end of the nuclear fuel cycle. A ceramic phase assemblage is described which uses the inert constituents of the waste stream as a functional component of the waste form, permitting high waste loadings to be achieved and thus enabling waste minimisation considerations to be satisfied. The initial development of this phase assemblage is presented.

Corrosion of a Plutonium-Bearing Titanate Ceramic

1997 ◽  
Vol 3 (S2) ◽  
pp. 747-748
Author(s):  
E. C. Buck ◽  
T. DiSanto ◽  
A. J. Bakel ◽  
J. K. Bates
Keyword(s):  
Nuclear Weapons ◽  
Laboratory Testing ◽  
Waste Form ◽  
Waste Streams ◽  
Corrosion Resistant ◽  
Cold Pressing ◽  
Ceramic Waste ◽  
Natural Analogues ◽  
Titanate Ceramic

A titanate-based ceramic waste form, rich in phases structurally related to zirconolite (CaZrTi2O7), is being developed as a possible candidate for immobilizing excess plutonium from dismantled nuclear weapons. The waste form is made by cold pressing and sintering of CaO, TiO2, ZrO2, A12O3, BaO, and Gd and Pu oxides. A prototype Pu-loaded ceramic that is being tested contains Pu,Gd-zirconolite-(3T), Pu-bearing brannerite, Gd-zirconolite-(4M), zirconolite-(2M) (see Figure 1), rutile (TiO2), Gd-bearing perovskites, various aluminotitanate phases, and undissolved plutonium oxide. Evidence from laboratory testing and natural analogues of titanates suggests that these phases are extremely corrosion resistant. Zirconolite-rich ceramics have also been considered for the disposal of actinide-bearing waste streams, because zirconolite and related polytypes are able to incorporate at least 20 wt% of actinides. However, since each phase in the multiphase ceramic corrodes at a different rate, the release of any one component or the corrosion of the bulk waste form is difficult to predict

scholarly journals High-Quality Green-Emitting Nanodiamonds Fabricated by HPHT Sintering of Polycrystalline Shockwave Diamonds

2020 ◽  
Vol 15 (1) ◽  
Author(s):  
Vladimir Yu. Osipov ◽  
Fedor M. Shakhov ◽  
Kirill V. Bogdanov ◽  
Kazuyuki Takai ◽  
Takuya Hayashi ◽  
...  
Keyword(s):  
Polycrystalline Diamond ◽  
Particle Beam ◽  
Production Method ◽  
High Energy ◽  
Nitrogen Vacancy ◽  
High Energy Particle ◽  
Paramagnetic Resonance ◽  
Precursor Material ◽  
Mean Size ◽  
Characteristic Features

Abstract We demonstrate a high-pressure, high-temperature sintering technique to form nitrogen-vacancy-nitrogen centres in nanodiamonds. Polycrystalline diamond nanoparticle precursors, with mean size of 25 nm, are produced by the shock wave from an explosion. These nanoparticles are sintered in the presence of ethanol, at a pressure of 7 GPa and temperature of 1300 °C, to produce substantially larger (3–4 times) diamond crystallites. The recorded spectral properties demonstrate the improved crystalline quality. The types of defects present are also observed to change; the characteristic spectral features of nitrogen-vacancy and silicon-vacancy centres present for the precursor material disappear. Two new characteristic features appear: (1) paramagnetic substitutional nitrogen (P1 centres with spin ½) with an electron paramagnetic resonance characteristic triplet hyperfine structure due to the I = 1 magnetic moment of the nitrogen nuclear spin and (2) the green spectral photoluminescence signature of the nitrogen-vacancy-nitrogen centres. This production method is a strong alternative to conventional high-energy particle beam irradiation. It can be used to easily produce purely green fluorescing nanodiamonds with advantageous properties for optical biolabelling applications.

scholarly journals Quality and Antioxidant Properties of Cold-Pressed Oil from Blanched and Microwave-Pretreated Pomegranate Seed

Foods ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 712
Author(s):  
Tafadzwa Kaseke ◽  
Umezuruike Linus Opara ◽  
Olaniyi Amos Fawole
Keyword(s):  
Radical Scavenging ◽  
Total Phenolic ◽  
Yellowness Index ◽  
Cold Pressing ◽  
Microwave Pretreatment ◽  
Radical Scavenging Capacity ◽  
Scavenging Capacity ◽  
Pomegranate Seed ◽  
Cold Pressed

The present research studied the influence of blanching and microwave pretreatment of seeds on the quality of pomegranate seed oil (PSO) extracted by cold pressing. Pomegranate seeds (cv. Acco) were independently blanched (95 ± 2 °C/3 min) and microwave heated (261 W/102 s) before cold pressing. The quality of the extracted oil was evaluated with respect to oxidation indices, refractive index, yellowness index, total carotenoids content, total phenolic content, flavor compounds, fatty acid composition, and 2.2-diphenyl-1-picryl hydrazyl (DPPH) and 2.2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging capacity. Blanching and microwave pretreatments of seeds before pressing enhanced oil yield, total phenolic content, flavor compounds, and DPPH and ABTS radical scavenging capacity. Although the levels of oxidation indices, including the peroxide value, free fatty acids, acid value, ρ-anisidine value, and total oxidation value, also increased, and the oil quality conformed to the requirements of the Codex Alimentarius Commission (CODEX STAN 19-1981) standard for cold-pressed vegetable oils. On the other hand, blanching and microwave heating of seeds decreased the pomegranate seed oil’s yellowness index, whilst the refractive index was not significantly (p > 0.05) affected. Even though both blanching and microwave pretreatment of seeds added value to the cold-pressed PSO, the oil extracted from blanched seeds exhibited lower oxidation indices. Regarding fatty acids, microwave pretreatment of seeds before cold pressing significantly increased palmitic acid, oleic acid, and linoleic acid, whilst it decreased the level of punicic acid. On the contrary, blanching of seeds did not significantly affect the fatty acid composition of PSO, indicating that the nutritional quality of the oil was not significantly affected. Therefore, blanching of seeds is an appropriate and valuable step that could be incorporated into the mechanical processing of PSO.

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.

Validation of a Nuclear Waste Repository Performance Assessment Model:Comparison of Theory With Experiment

1987 ◽  
Vol 112 ◽  
Author(s):  
R. W. Geldart ◽  
B. P. Mcgrail ◽  
K. C. Rhoads ◽  
M. J. Apted
Keyword(s):  
Mass Transfer ◽  
Dissolution Kinetics ◽  
Waste Form ◽  
Nuclear Waste Repository ◽  
Transfer Model ◽  
Mass Transfer Model ◽  
Buffer Solution ◽  
Simulated Waste ◽  
Limited Mass ◽  
Radionuclide Release

AbstractLaboratory tests were conducted to validate a radionuclide mass transfer model. During the experiments, cesium and uranium releases from a simulated waste form embedded in an isotropic medium of quartz sand were measured. A 0.01 M NaH2PO4 buffer solution flowed past the waste form. Downstream concentrations obtained from computer simulations were compared with experimentally measured concentrations of cesium and uranium. Uranium release was found to be controlled by solubility-limited mass transfer, while cesium release was controlled by waste form dissolution kinetics. It was also found that the effects of dissolution on groundwater chemistry must be coupled with solubility-limited mass transfer models to defensibly predict radionuclide release rates under realistic repository conditions.

scholarly journals Quality of wheat germ oil obtained by cold pressing and supercritical carbon dioxide extraction

2013 ◽  
Vol 31 (No. 3) ◽  
pp. 236-240 ◽  
Author(s):  
M.M. Özcan ◽  
A. Rosa ◽  
M.A. Dessi ◽  
B. Marongıu ◽  
A. Pıras ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Wheat Germ ◽  
Alpha Tocopherol ◽  
Fatty Acid Profiles ◽  
Wheat Germ Oil ◽  
Cold Pressing ◽  
Carbon Dioxide Extraction ◽  
Total Fatty Acids ◽  
Cold Pressed

Laboratory-prepared wheat germ oil was obtained by cold pressing and supercritical CO<sub>2</sub> extraction. The main objective was to compare the quality of both oil samples obtained, with emphasis on their fatty acids compositions and tocopherol contents. The percentages of palmitic, oleic, linoleic, and linolenic acids determined in the cold-pressed oil were 15.89, 15.48, 54.88, and 7.34% of total fatty acids, respectively, and those in the oil extracted by supercritical CO<sub>2</sub> were 16.50, 15.05, 54.79, and 7.29% of total fatty acids, respectively. The average proportions of saturated, mono- and polyunsaturated fatty acids calculated for wheat germ oil obtained by cold pressing accounted for 17.15, 17.63, and 62.22% of total fatty acids, respectively, and those calculated for wheat germ oil extracted by supercritical CO<sub>2</sub> were very similar, accounting for 18.14, 17.58, and 62.08% of total fatty acids, respectively. As expected, the fatty acid profiles determined in both oils studied were observed to be almost identical. In contrast, the level of &alpha;-tocopherol in the oil extracted by supercritical CO<sub>2</sub> was found to be considerably higher (1.27 mg/g) than that in the oil obtained by the cold pressing procedure (0.79 mg/g). &nbsp;

Effect of Gallium Oxide on Phase Assemblage in Apatite and Whitlockite Hosts for Waste Immobilization

2008 ◽  
Vol 1107 ◽  
Author(s):  
Lee. A. Gerrard ◽  
Shirley. K. Fong ◽  
Brian. L. Metcalfe ◽  
Ian. W. Donald
Keyword(s):  
Solid Solution ◽  
Gallium Oxide ◽  
Phase Assemblage ◽  
X Ray Diffraction ◽  
Apatite Phase ◽  
Complete Solid Solution ◽  
Total Phase ◽  
Simulated Waste ◽  
Lower Temperature ◽  
Gallium Phosphate

AbstractTo immobilize halide and actinide ions present in specific ILW waste a process has been developed that uses mineral phases as the host material. The mechanism of substitution of gallium into these phases will have a large effect on the phase assemblage. This will inevitably affect the total amount of halide that can be immobilized in to total phase mixture.The full simulated waste stream composition containing varying concentrations (1–40 wt.%) of gallium oxide was studied. Also nominal compositions for gallium doped fluorapatites (Ca10-1.5xGax)F2(PO4)6 (x = 0, 0.25, 0.5, 0.75, 1.0) and gallium doped whitlockites Ca9Gay(PO4)6+y (x = 0.2, 0.4, 0.6, 0.8, 1.0) were prepared at 750–1050 °C.These were studied by powder x-ray diffraction (XRD) to determine the phase assemblage and solid solution limits of gallium in the apatite and whitlockite phases. It was found that a complete solid solution was formed between whitlockite, Ca3(PO4)2, and Ca9Gay(PO4)6+y. In the nominal apatite compositions it was found that gallium did not substitute into the apatite structure but was instead partitioned over Ca9Gay(PO4)6+y, gallium phosphate, and unreacted gallium oxide. At higher temperatures gallium suppressed the formation of the apatite phase and was largely partitioned into the Ca9Gay(PO4)6+y phase whereas at lower temperature the majority was present as unreacted Ga2O3. In the full DCHP compositions it was found that gallium is likely to be partitioned over a number of phases including apatite, cationdoped whitlockite and gallium phosphate.

Comparison of the Leachability of Three TRU Cement Waste Forms

1982 ◽  
Vol 15 ◽  
Author(s):  
Wayne Ross ◽  
Joseph Westsik ◽  
Frank Roberts ◽  
Clark Harvey
Keyword(s):  
Elevated Temperatures ◽  
Waste Form ◽  
Cold Pressing ◽  
Waste Forms ◽  
Leach Test

ABSTRACTCement waste forms prepared by three processes, casting, cold pressing, and FUETAP (Formed Under Elevated Temperatures and Pressure) have been compared for their leachability by using the MCC-1 leach test. The results indicate that releases of plutonium are not controlled by the waste form matrix and that there is no significant overall advantage to any of the three cement processes from a leachability viewpoint.

scholarly journals Thermoelectric Power of YBa2Cu3O7-Xand YBa2Cu4O8Under Pressure

1993 ◽  
Vol 15 (3-4) ◽  
pp. 147-153
Author(s):  
Sheela K. Ramasesha
Keyword(s):  
Single Crystal ◽  
Thermoelectric Power ◽  
Polycrystalline Sample ◽  
Crystallite Orientation ◽  
Cold Pressing ◽  
Broad Maximum ◽  
Cold Pressed

Thermoelectric power (TEP) of YBa2Cu3O7-X(123) and YBa2Cu4O8(124) samples are measured as a function of pressure. The TEP of an as-sintered 123 polycrystalline sample shows a broad maximum around 1.25 GPa whereas that of the cold-pressed sample decreases steadily. The ab-plane TEP of 123 single crystal decreases monotonically and the c-axis TEP exhibits a maximum around 1.5 GPa. Disappearance of the broad maximum in the polycrystalline sample upon cold-pressing is interpreted in terms of the crystallite orientation occurring under pressure. TEP of the 124 polycrystalline sample decreases sharply up to 4.5 GPa and at a lower rate with further increase in pressure, a trend similar to that is observed in the variation of Tcas a function of pressure.

Sign in / Sign up

Export Citation Format

Share Document