Elaine Loi

pH dependence of the aqueous dissolution rates of perovskite and zirconolite at 90 C

Perovskite and zirconolite are two of the major phases of the Synroc titanate mineral assemblage. Their aqueous durability under a range of pH conditions at 90 C has been examined. Solution analysis, electron microscopy and X-ray diffraction have been used to investigate the dissolution behavior of these phases, and a perovskite phase doped with Nd, Sr and Al, using buffered solutions at pH levels of 2.1, 3.7, 6.1, 7.9 and 12.9. After 43 days of leaching, Ca and Ti extractions from perovskite and zirconolite show only a weak pH-dependence. SEM investigation of the samples leached at pH 2.1, 6.1 and 12.9 showed that a titanaceous surface layer formed on the perovskite specimens. XRD analysis of the perovskite samples showed that anatase formed on the leached surface at acidic and neutral pHs, but not under alkaline conditions, and that minor amounts of rutile also formed. In the leached perovskite specimens doped with Nd, Sr and Al, no rule was found by XRD and anatase was only detected in the sample leached at pH 2.1. There were no detectable changes in the leached zirconolite samples examined by SEM and XRD.

Nuclear forensic analysis of uranium oxide powders interdicted in Victoria, Australia

Abstract Nuclear forensic analysis was conducted on two uranium samples confiscated during a police investigation in Victoria, Australia. The first sample, designated NSR-F-270409-1, was a depleted uranium powder of moderate purity (∼ 1000 μg/g total elemental impurities). The chemical form of the uranium was a compound similar to K2(UO2)3O4 · 4H2O. While aliquoting NSR-F-270409-1 for analysis, the body and head of a Tineid moth was discovered in the sample. The second sample, designated NSR-F-270409-2, was also a depleted uranium powder. It was of reasonably high purity (∼ 380 μg/g total elemental impurities). The chemical form of the uranium was primarily UO3 · 2H2O, with minor phases of U3O8 and UO2. While aliquoting NSR-F-270409-2 for analysis, a metal staple of unknown origin was discovered in the sample. The presence of 236U and 232U in both samples indicates that the uranium feed stocks for these samples experienced a neutron flux at some point in their history. The reactor burn-up calculated from the isotopic composition of the uranium is consistent with that of spent fuel from natural uranium (NU) fueled Pu production. These nuclear forensic conclusions allow us to categorically exclude Australia as the origin of the material and greatly reduce the number of candidate sources.

Effects of pH and Uranium Valence State on the Aqueous Dissolution of Brannerite

The dissolution of the thorium analogue of brannerite (ThTi 2 O 6 - I ) and U(IV)/U(V) doped Th-brannerite (Th 0.97 U 0.03 Ti 2 O 6 - II and Th 0.955 U 0.03 Ca 0.015 Ti 2 O 6 - III ) in aqueous media under atmospheric conditions has been studied to elucidate the effects of pH and uranium valence state on the dissolution rate. The dissolution of I is nearly stoichiometric but slightly preferential release of U occurs for II and preferential release of Ca and U occur for III . The V-shape pH dependence previously observed for U-brannerite only occurs for U (not other matrix elements) for II , indicating that the pH dependence is related to the U oxidation state upon dissolution. The normalised U dissolution rates of III are nearly an order of magnitude higher than those of II for pH values over 3, suggesting brannerite is less durable with U(V) doping. TEM examination of specimens after leaching revealed few surface alteration products, which is consistent with the nearly stoichiometric dissolution of thorium brannerite.

Contribution of bulk mass spectrometry isotopic analysis to characterization of materials in the framework of CMX-4

Seven laboratories used the results of bulk uranium isotopic analysis by either inductively coupled plasma mass spectrometry (ICP-MS) or thermal ionization mass spectrometry (TIMS) for characterization of the samples in the Nuclear Forensic International Technical Working Group fourth international collaborative material exercise, CMX-4. Comparison of the measured isotopic compositions of uranium in three exercise samples is implemented for identifying any differences or similarities between the samples. The role of isotopic analyses in the context of a real nuclear forensic investigation is discussed. Several limitations in carrying out ICP-MS or TIMS analysis in CMX-4 are noted.

Dissolution of Synroc in Deionised Water at 150°C

Synroc containing 20 wt% simulated high level waste (HLW) was subjected to two sets of leach tests at 150 C where the leachant was and was not replaced during the test (replacement and non-replacement testing). The leachant was a KH-phthalate buffered solution (pH 4.2). Samples were characterized before and after leach testing using SEM, AEM and SIMS. Elemental concentrations in leachates were measured using ICP-MS. In concert with the findings of (1) a dissolution study of perovskite in a flowing leachant and (2) a previous Synroc dissolution study (wherein Synroc containing 10 wt% simulated HLW was subjected to periodic replacement, leach testing in deionized water at 150 C), the results of this study show that when the leachant replacement frequency is varied from 7 d to the duration of the test, there is no effect on leach rate or leaching mechanisms.

The Effect of Radiation Damage on Zirconolite Dissolution

Polished tiles (7x7x2 mm3) of Nd-bearing zirconolite were fabricated and then some were irradiated on both large faces with 3 MeV or 2 MeV Au2+ ions (total fluence of {approx} 1 x 1015 ions/cm2) in order to render the zirconolite amorphous and so simulate displacement damage caused by alpha decay. Both the irradiated and non-irradiated tiles were then subjected to static dissolution tests in 0.01M nitric solution (pH2) at 90 C, for periods of 0-1, 1-7, 7-14 and 14-28 days. It was found that radiation damage did not affect the dissolution rate of zirconolite as indicated by the elemental leach rates of Nd, Ti, Ca and Al. The results of solution analyses are consistent with those obtained from X-ray Photoelectron Spectroscopy (XPS) in that the Ca, Nd, Ti and Al concentrations in the top surface layer (< 5 nm) all decreased with respect to that of Zr after dissolution testing, and the leached surface composition of the non-irradiated zirconolite is very similar to that of the two irradiated specimens. The implications of these results are discussed in the context of previous work.

Aqueous Dissolution of Rb-Bearing Hollandite and Synroc-C at 90°C

Rb-doped Ba-hollandite and synroc-C samples were prepared for aqueous dissolution studies at 90 ° C in deionized water using MCC-1 protocols. Small amounts of possibly Rb-bearing BaTiO 3 , hibonite and alumina accompanied the major Rb-doped (0.1 formula units) hollandite phase. The Rb loadings in the synroc samples ranged from 0.89 to 2.67 wt%. Rb leached at 2 /d from hollandite samples and 2 d from synroc, with the values decreasing with increasing dissolution time. The variance between the dissolution rates for the different Rb-doped hollandite and synroc samples is discussed, in terms of Rb-bearing minor phases.

Surface Alteration of Titanate Ceramics in Aqueous Media

From elastic recoil detection analysis (ERDA) of 2 MeV He ions and secondary ion mass spectroscopy (SIMS), exposure of Synroc-C to D 2 O at 150°C for ∼ 30 days produced surface deuteration products of a few nm in thickness, with surface roughness after polishing down to 0.25 µm diamond finish not being of critical importance in the thickness determination. Reaction at 250°C produced more extensive deuteration and general surface alteration, over depths of about a micron. SIMS did not show any surface enhancement of rare earths or Zr on Synroc-C surfaces reacted at 90°C for up to 336 days. Pu-doped SynrocC exposed to deionised water at 70°C showed surface depletion of Pu by alpha-spectroscopy. Zirconolite-rich Synroc showed less surface deuteration than Synroc-C after reaction for 3 weeks at 150°C in D 2 O. Admixtures of 0.001 M of fluoride ions to dilute HCI (pH = 2) produced deposits of anatase, ∼ 20 µm thick, on perovskite after a few weeks at 90°C; these deposits were much thicker than those produced by the dilute HCI without the fluoride ions being present.