P. Trocellier

Preliminary results on the leaching process of phosphate ceramics, potential hosts for actinide immobilization

Abstract A mixed zirconium–lanthanum phosphate La 1/3 Zr 2 (PO 4 ) 3 , noted LaZrP, is studied as a potential host for actinides issued from high-level nuclear wastes. Chemical durability is evaluated and compared with two other phases: a monazite phase LaPO 4 , noted LaP, and a mixed oxide phase La 0.1 ZrO 2.15 , noted LaZrO. Leaching tests are performed and followed by solution and solid analyses. Static tests are performed with a low ratio between surface of ceramic and volume of solution, S / V (about 0.1 cm −1 ). For LaZrP, the phosphate release rate decreases from 10 −2 to 10 −3 g / m 2 / day , while zirconium and lanthanum releases remain very low ( −5 g / m 2 / day ). For the LaP phase, the phosphate release is about 10 times lower than for LaZrP and remains stationary, while the rate of the lanthanum release is below 10 −6 g / m 2 / day . Tests performed at high S / V (about 20 cm −1 ) reveal that the lanthanum release rates after 2 weeks were, respectively, at 10 −9 , 10 −6 and 10 −4 g / m 2 / day for LaP, LaZrP and LaZrO phases. It is shown that NZP or monazite type ceramics are highly resistant to the leaching process.

Nature and distribution of chemical species on oxidized pyrite surface: Complementarity of XPS and nuclear microprobe analysis

Abstract The coupling of X-ray photoelectron spectroscopy (XPS) and nuclear microprobe analysis (NMA) using resonant reactions 16 O ( α , α ) 16 O and 12 C ( p , p ) 12 C at 3.05 and 1.725 MeV, respectively, is particularly adapted to the characterization of thin oxidation layers onto pyrites. XPS permits to determine both oxidation state and chemical environment of S and Fe. NMA gives an information about spatial distribution and chemical composition heterogeneity of oxidation products. Pyrites oxidized in acidic medium produce few solid components. Only FeII sulfate is detected on the oxidized pyrite surface. In carbonate medium, oxidation layer is more complex. Iron is mainly with a (+II) oxidation state under siderite or FeII sulfate form. As illustrated by the comparison of Fe3p and Fe2p3/2 peaks, iron has an (+III) oxidation state to a minor extent under α-FeOOH and FeIII sulfate forms from the first oxidized pyrite layers. Sulfur oxidation induces intermediate species (polysulfides and sulfoxyanions as S2O32− also evidenced in solution) indicating that oxidation occurs at solid state. NMA has shown that oxidation occurs only on localized points of pyrite surface, with oxidation layers showing spatial distribution and thickness heterogeneities.

Dissolution of UO2 in Boom clay water in oxidizing conditions : an XPS study

The solubility behavior of uranium dioxide was studied under oxidizing conditions in the Belgian Boom clay water at 25°C up to 323 days. X-ray photoelectron spectroscopy analyses reveal that both U(VI) and U(IV) oxidation states are present in the altered layer. The U(VI)/U(IV) ratio in this altered layer increases up to 43 days and then remains constant throughout the whole test. In the leachate the uranium concentration also increases up to 43 days and then stabilizes. It is rather unlikely that the altered layer formed on the surface controls thermodynamically the uranium solubility. It is rather probable that the system has reached a pseudo-equilibrium governed by kinetics.

Study of hydrogen in melt inclusions trapped in quartz with a nuclear microprobe

Abstract Elastic recoil spectrometry induced by a 3 MeV 4He microbeam has been used to determine the hydrogen distribution within melt inclusions trapped in quartz. These minerals were selected from different geological environments: Guadeloupe (West Indies), Pantelleria Island (South Sicily, Italy) and San Pietro (South Sardinia, Italy). Bulk hydrogen contents are calculated (H assumed to be in H2O form). The knowledge of hydrogen distribution assists both in a better understanding and in the establishment of volcanic dynamism hypotheses. Finally, hydrogen-rich fluid inclusions are evidenced, the H concentration profile was obtained from simulation of the data and reported for the first time in a glass inclusion.

Nuclear reaction microanalysis and electron microanalysis of light elements in minerals and glasses

Abstract Electron microprobe analysis (EMA) and nuclear microanalysis (NMA) have been used to determine light elements (Z ⩽ 30) in minerals and glasses. Optimum NMA reaction conditions for the detection of various elements are presented and detection limits are estimated for both micro- and macrobeams. A comparison is made between results of EMA and NMA analyses for several elements. Peculiarities of both methods are emphasized. While EMA is convenient in fast routine measurement for most elements in the periodic table above Na, with analytical sensitivities ranging from 100 to 1000 wt. ppm, NMA in charged-particle or prompt gamma-ray nuclear reaction analysis (NRA) mode allows the analysis of all the isotopes between 1H and 19F (except 4He and 20Ne), with a sensitivity often better than 50 ppm. In addition, proton-induced gamma-ray emission (PIGE) enables the determination of heavier elements (from Na to Zn) with relatively good performances. Furthermore, depth profiling and local isotopic ratio measurements constitute some new interesting applications for NMA.

Study of hydrogen content in solids by ERDA and radiation induced damage

Abstract A simulation-optimisation algorithm (GABY code) is used for hydrogen determination in elastic recoil detection analysis (ERDA) induced by 1.8—3 MeV 4He ions. The scattering cross section and the effect of straggling, multiple scattering and geometrical spreading are taken into account in the simulation. The capabilities of this absolute method (in transmission geometry) are briefly described in terms of sensitivity, probing depth and depth resolution. The hydrogen measurements are interpreted in relation to the damage induced by the 4He microbeam. We show that the hydrogen distribution can change during the He irradiation, depending on the local structure of the target material. The influence of large doses and the dose rate are discussed. This procedure has been applied using a nuclear microprobe to study the hydrogen distribution in thin polymer films irradiated by high energy heavy ions (Kr 230 MeV) and natural glasses.

Comparative study of crystalline, amorphous and organic materials using a nuclear microprobe: Theoretical and practical considerations

Abstract This paper is devoted to comparison of theoretical and practical requirements for nuclear microprobe investigations of crystalline, amorphous and organic materials in terms of elemental losses induced by the microbeam irradiation. Five topics are successively considered: sputtering effects, migration of ionic species, temperature increase, bond breaking and atomic displacements.

Stability and distribution of lithium and boron in minerals

Abstract Nuclear muprobe analysis (NMA) was used to study lithium and boron stability and distribution in minerals and synthetic glasses. Beam current densities up to 20 pA/μm 2 for deuterons and less than 25 pA/μm 2 for protons do not alter the composition of the studied materials. Phyllosilicates, pyroxenes, glasses and tourmalines were quantitatively characterized and found to exhibit a certain degree of depth inhomogeneity. The analytical capabilities for lithium and boron isotopic ratio measurements by NMA are then discussed.

Nuclear microprobe study of the composition degradation induced in polyimides by irradiation with high-energy heavy ions

Abstract The hydrogen profile is determined in polyimide films (kapton-H from Dupont) previously irradiated by 50 MeV 32 S ions. Results from elastic recoil detection analysis show the existence of high hydrogen concentration zones located more than 3 μm beneath the surface of the irradiated kapton. Deuteron-induced nuclear reaction analysis is also performed to determine C, N and O distributions. The N and O losses and C content variations are discussed in terms of the irradiation dose. These experimental data do not support suggestions that molecular damage invariably results in loss of volatile species and consequent reorganization of the organic skeleton leading to the formation of carbon-enriched material. Rather they indicate that the molecular rearrangement is influenced by H trapped within the degraded organic matrix.

Applications of new surface analysis techniques (NMA and XPS) to humic substances

This paper illustrates the potentialities and the innovative character of surface analysis techniques such as nuclear microprobe analysis (NMA) and X-ray photoelectron spectroscopy (XPS) in the research field of humic substances (HS), in particular to characterize HS/trace elements association. NMA showed its potentialities to characterize HS/ trace element associations at the microscopic scale and quantification of trace elements scavenged by humic acids (HA) and distribution and thickness of HA films sorbed onto silica surfaces after sorption tests. XPS was used to determine the chemical environment of iodine in natural HS. These techniques enabled us to establish association between HS colloids and numerous trace elements (both cations and anions, especially I) and to evidence a strong affinity of the smallest HA colloids (< 15 nm) for these elements. Moreover, associations between HS and I were clearly evidenced by NMA, through the study of the ternary system (SiO 2 /HA/I), as well as of natural HS. Chemical bonds implied in these associations may be of covalent character, as seen from XPS data. Combination of these techniques with Ion Coupled Plasma Mass Spectrometry (ICP-MS) was also necessary to analyze the aqueous solutions in contact with HS.