Uraninite-Water Interactions in an Oxidizing Environment

1996 ◽  
Vol 465 ◽  
Author(s):  
M. Fayek ◽  
T. K. Kyser ◽  
R. C. Ewing ◽  
M. L. Miller
Keyword(s):  
Isotope Fractionation ◽  
Theoretical Calculations ◽  
Uranium Mineralization ◽  
Chemical Compositions ◽  
Uranium Deposits ◽  
Oxygen Isotope Fractionation ◽  
Water Oxygen ◽  
High Level Nuclear Waste ◽  
High Level ◽  
Phase Chemistry

ABSTRACTExceptionally low δ 18O values of primary uraninite and pitchblende (i.e. -32 per mil to -19.5 per mil) from Proterozoic unconformity-type uranium deposits in Saskatchewan, Canada, in conjunction with theoretical uraninite-water oxygen isotope fractionation factors suggest that primary uranium mineralization is not in oxygen isotopie equilibrium with clays and silicates. The low δ 18O values have been interpreted to have resulted from the recrystallization of primary uranium mineralization in the presence of modern meteoric fluids having low δ 18O values of ca. -18 per mil. The absence of apparent alteration in many of the uraninite and pitchblende samples requires that the uranium minerals exchange oxygen isotopes with fluids, with only minor disturbances to their original chemical compositions and textures. However, experiments on the interaction between water and natural uraninites, from these deposits, and detailed electron micro-probe analyses of natural uraninite and pitchblende indicate that, in the presence of water, old uraninite rapidly alters to curite (Pb2U5O174H2O). The hydration of uraninite to curite releases uranium and calcium into solution and becquerelite (Ca(UO2)6O4(OH)6H2O) is precipitated. In the presence of Si-saturated waters, uranium silicate minerals, soddyite ((UO2)2(SiO4)2H2O) and kasolite (Pb(UO2)SiO4H2O are precipitated in addition to, curite and schoepite ((UO2)8O2(OH)12(H2O)12). The mineral paragenesis observed in these experiments is similar to sequences observed in oxidized zones in uranium deposits and UO2-water experiments. Therefore, it is unlikely that natural uraninite and pitchblende can simply exchange oxygen with an oxidizing fluid without a concomitant change in phase chemistry or structure, nor will oxidation of uraninite lead to the formation of U3O7. as predicted by theoretical calculations used in natural analogue studies for the disposal of high level nuclear waste.

New mineralogical data on uranophane and β-uranophane; synthesis of uranophane

1993 ◽  
Vol 57 (387) ◽  
pp. 301-308 ◽  
Author(s):  
Fabien Cesbron ◽  
Philippe Ildefonse ◽  
Marie-Claude Sichere
Keyword(s):  
Nuclear Waste Repository ◽  
Uranium Deposits ◽  
Physico Chemical ◽  
Natural Analogues ◽  
High Level Nuclear Waste ◽  
Polymorphic Forms ◽  
Uranyl Silicates ◽  
Xrd Patterns ◽  
High Level

AbstractUranyl-silicates are widespread minerals in oxidised parts of various uranium deposits, and they frequently contain associations of the polymorphic forms of uranophane. In several recent works devoted to the study of uranium deposits as natural analogues of high-level nuclear waste repository (HLNWR), uranophane is frequently mentioned but without determination of the exact polymorphic species. The existence of two polymorphs presenting different stabilities has to be taken into account when considering the long-term behaviour of these minerals and the use of thermodynamic models for predicting the radionuclide migration in HLNWR. We present here new crystallographic data on betauranophane, and preliminary results of synthesis experiments of uranyl silicates. XRD patterns and calculated parameters of beta-uranophane from a Mexican U-deposit are presented. Synthesis experiments succeeded in crystallising uranophane (alpha form) at different pH, Si-, Ca- and Na activities, but beta-uranophane was never obtained. The controlling physico-chemical parameters responsible for the occurrence of these two polymorphic forms are still unknown.

Calibration of the phosphate δ18O thermometer with carbonate–water oxygen isotope fractionation equations

2013 ◽  
Vol 347 ◽  
pp. 217-226 ◽  
Author(s):  
Christophe Lécuyer ◽  
Romain Amiot ◽  
Alexandra Touzeau ◽  
Julie Trotter
Keyword(s):  
Oxygen Isotope ◽  
Isotope Fractionation ◽  
Carbonate Water ◽  
Oxygen Isotope Fractionation ◽  
Water Oxygen

A comparison of radiation effects in crystalline ABO4-type phosphates and silicates

2000 ◽  
Vol 64 (2) ◽  
pp. 185-194 ◽  
Author(s):  
A. Meldrum ◽  
L. A. Boatner ◽  
R. C. Ewing
Keyword(s):  
Damage Accumulation ◽  
Radiation Effects ◽  
Ion Irradiation ◽  
Ion Beam ◽  
Chemical Compositions ◽  
Transmission Electron ◽  
Host Materials ◽  
High Level Nuclear Waste ◽  
High Level

AbstractThe effects of ion irradiation in the ABO4-type compounds were compared by performing experiments on four materials that include the most common crystal structures (monazite vs. zircon) and chemical compositions (phosphates vs. silicates) for these phases. Pure synthetic single crystals of ZrSiO4, monoclinic ThSiO4, LaPO4 and ScPO4 were irradiated using 800 keV Kr+ ions. Radiation damage accumulation was monitored as a function of temperature in situ in a transmission electron microscope. The activation energies for recrystallization during irradiation were calculated to be 3.1–3.3 eV for the orthosilicates but only 1.0–1.5 eV for the isostructural orthophosphates. For the ion-beam-irradiated samples, the critical temperature, above which the recrystallization processes are faster than damage accumulation and amorphization cannot be induced, is >700°C for ZrSiO4 but it is only 35°C for LaPO4. At temperatures above 600°C, zircon decomposed during irradiation into its component oxides (i.e. crystalline ZrO2 plus amorphous SiO2). The data are evaluated with respect to the proposed use of the orthophosphates and orthosilicates as host materials for the stabilization and disposal of high-level nuclear waste. The results show that zircon with 10 wt.% Pu would have to be maintained at temperatures in excess of 300°C in order to prevent it from becoming completely amorphous. In contrast, a similar analysis for the orthophosphates implies that monazite-based waste forms would not become amorphous or undergo a phase decomposition.

Mcc Corrosion Tests at Reference Testing Conditions for A27 Cast steel in Hanford Ground Water

1986 ◽  
Vol 84 ◽  
Author(s):  
M.D. Merz ◽  
F. Gerber ◽  
R. Wang
Keyword(s):  
Pacific Northwest ◽  
Pressure Vessel ◽  
Static Pressure ◽  
Cast Steel ◽  
Statistical Treatment ◽  
Testing Conditions ◽  
Corrosion Tests ◽  
Corrosion Rates ◽  
High Level Nuclear Waste ◽  
High Level

AbstractThe Materials Characterization Center (MCC) at Pacific Northwest Lab- oratory is performing three kinds of corrosion tests for the Basalt Waste Isolation Project (BWIP) to establish the interlaboratory reproducibility and uncertainty of corrosion rates of container materials for high-level nuclear waste. The three types of corrosion tests were selected to address two distinct conditions that are expected in a repository constructed in basalt. An air/steam test is designed to address corrosion during the operational period and static pressure vessel and flowby tests are designed to address corrosion under conditions that bound the condi ring the post-closure period of the repository.The results of tests at reference testing conditions, which were defined to facilitate interlaboratory comparison of data, are presented. Data are reported for the BWIP/MCC-105.5 Air/Steam Test, BWIP/MCC-105.1 Static Pressure Vessel, and BWIP/MC-105.4 Flowby Test. In those cases where data are available from a second laboratory, a statistical analysis of interlaboratory results is reported and expected confidence intervals for mean corrosion rates are given. Other statistical treatment of data include analyses of the effects of vessel-to-vessel variations, test capsule variations for the flowby test, and oven-to-oven variations for air/steam tests.

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