A. Chevarier

Nitrogen profiling in nitride films and nitrogen-implanted samples using the 14N(α, α) and14N(α, p) reactions at 6 MeV incident energy

We investigate the nitrogen profiling potentially using incident alpha particles from 5 to 7 MeV. In this energy range the alpha scattering cross sections on light elements are substantially larger than the Rutherford cross sections and therefore lead to competitive sensitivity. Moreover, another advantage is the high mass resolution which allows to profile simultaneously carbon, nitrogen and oxygen. The analysis of TiN, NbTiN films and nitrogen implanted steel are presented. The inclusion, in the simulation program, of the 14N(α, α) and14N(α, p) cross sections allows to get a complete reproduction of the spectra and authorizes to determine accurately the nitrogen profile. Such a dual nitrogen analysis improves profile determination in case of thick analyzed layers. The sensitivity limits connected to the alpha scattered yield on steel substrate are 1016 and 5 × 1016 N atoms/cm2 for the 14N(α, α) and14N(α, p) reactions, respectively.Abstract We investigate the nitrogen profiling potentially using incident alpha particles from 5 to 7 MeV. In this energy range the alpha scattering cross sections on light elements are substantially larger than the Rutherford cross sections and therefore lead to competitive sensitivity. Moreover, another advantage is the high mass resolution which allows to profile simultaneously carbon, nitrogen and oxygen. The analysis of TiN, NbTiN films and nitrogen implanted steel are presented. The inclusion, in the simulation program, of the 14 N (α, α) and 14 N (α, p ) cross sections allows to get a complete reproduction of the spectra and authorizes to determine accurately the nitrogen profile. Such a dual nitrogen analysis improves profile determination in case of thick analyzed layers. The sensitivity limits connected to the alpha scattered yield on steel substrate are 1016 and 5 × 1016 N atoms/cm2 for the 14 N (α, α) and 14 N (α, p ) reactions, respectively.

Zirconium surface modification under fission product irradiation. Application to nuclear fuel cladding tubes

Abstract Nuclear fuel devices of pressurised water reactors are composed of uranium oxide pellets which are enclosed in zircaloy-cylinders. During reactor operation in the contact with the fuel the zircaloy oxidises non-uniformly in depths of the order of some micrometers. Furthermore, energy deposition of fission recoils leads to sputtering of uranium onto the inner surface of the cladding material. Thus, sputtered uranium ions start to migrate outwards. Experiments were performed at Institut Laue Langevin (ILL) on the Lohengrin mass spectrometer in order to simulate the alteration of cladding tubes in contact with the nuclear fuel during irradiation. A thin UO 2 deposition in direct contact with a zirconium foil was put into the ILL high flux reactor (5×10 14 neutrons cm −2 s −1 ). The variation of energy loss of selected fission products in the foil put in evidence a zirconium oxidation whose kinetics constant is deduced from these experiments. Following oxidation the fission product mean kinetic energy is stabilised, but still a broadening of the energy distribution is observed, which is characteristic of uranium diffusion inside the zirconia target. Using Ficks model, a uranium diffusion coefficient in zirconia under irradiation is deduced.

Study of zircaloy-4 fuel cladding corrosion using ion beams.: Application to long-term disposal of nuclear wastes

Abstract In pressurised water reactors the cladding tubes in zircaloy-4 are oxidised up to several micrometres on the internal face by direct contact with the UO2 pellets. At the same time, fission products such as 129I are implanted by recoil. Until 1995, the cladding tube pieces called hulls were embedded in concrete. The concrete medium being very basic, this study simulates the corrosion of hulls in the perspective of a long-term disposal in these severe pH conditions. This paper is dedicated to the study of the partial dissolution of the oxide layer, which is the responsible mechanism for the activity release. In order to follow the solid–liquid interface, europium was implanted into the material surface as a marker. Next, the corrosion induced in autoclave at 300°C, 140 bars and in alkaline water was studied. The determination of europium profiles using Rutherford backscattering spectrometry analysis (RBS) allows to deduce the fraction of dissolved ZrO2. It was shown that this dissolution is not homogeneous in porous zirconia and gives rise to the formation of crevices. Using the nuclear microprobe of Pierre Sue laboratory, a more precise study of the specimen surface was performed.

Zirconium oxidation under high-energy heavy-ion irradiation

This paper concerns the study of zirconium oxidation under irradiation with high energetic Xe ions. The irradiations were performed on the IRRadiation SUD (IRRSUD) beam line at Grand Accelerateur National d’Ions Lourds of Caen. The oxygen partial pressure was fixed at 10−3Pa and two temperature conditions were used, either 480°C reached by Joule effect heating or 280°C due to Xe energy deposition. Zirconia was fully characterized by Rutherford backscattering spectrometry, scanning electron microscopy, and grazing angle x-ray diffraction. Apparent diffusion coefficients of oxygen in ZrO2 were determined from these experiments by using a model which takes into account a surface exchange between oxygen gas and the ZrO2 surface. These results are compared with thermal oxidation data.

Study of iodine migration in zirconia using stable and radioactive ion implantation

Abstract The large uranium fission cross section leading to iodine and the behaviour of this element in the cladding tube during energy production and afterwards during waste storage is a crucial problem, especially for 129 I which is a very long half-life isotope ( T = 1.59 × 10 7 yr). Since a combined external and internal oxidation of the zircaloy cladding tube occurs during the reactor processing, iodine diffusion parameters in zirconia are needed. In order to obtain these data, stable iodine atoms were first introduced by ion implantation into zirconia with an energy of 200 keV and a dose equal to 8 × 10 15 at cm −2 . Diffusion profiles were measured using 3 MeV alpha-particle Rutherford Backscattering Spectrometry at each step of the annealing procedure between 700°C and 900°C. In such experiments a reduced iodine concentration was observed, which correlated to a diffusion-like process. Similar analysis has been performed using radioactive 131 I implanted at a very low dose of 10 9 at cm −2 . In this case the iodine release is deduced from gamma-ray spectroscopy measurements. The results are discussed in this paper.

Iodine release from oxidised Zircaloy cladding in contact with an alkaline solution

Abstract During reactor processing, fission products, among which iodine, are implanted by recoil inside the Zircaloy cladding tube. At the same time, oxidation of the cladding tube occurs, hence in the waste storage phase, zirconia acts as a migration barrier. Before chemical separation, the cladding tubes are sectioned into pieces called hulls in order to release the UO 2 pellets which are rendered soluble in nitric acid. The hulls are collected as a solid waste and were embedded inside a concrete structure until 1995. In the perspective of geological storage, a great interest is given to iodine release processes in order to model and to extrapolate them to large time scales. In order to analyse the mechanisms involved in iodine migration, iodine atoms were introduced in Zircaloy oxidized samples by means of ion implantation. Corrosion tests were performed in order to simulate the impact of infiltrated water in the concrete disposal. Iodine release was measured by Rutherford backscattering spectroscopy. Processes responsible for iodine release are analysed.

Use of RBS to validate europium surface implantation as a marker for the corrosion study of zirconia

This study is related to the nuclear waste management and to the long-term behaviour of radionuclides in deep storage. The aim of this paper is to study the corrosion of zirconium in deep storage. In order to simulate the inner side of zircaloy cladding tubes, the zirconium samples were oxidised in air at 500°C during 3 h. Two hundred keV-implanted europium ions were used as marker to follow the evolution of the ZrO2–liquid interface. In a first step, air annealings were performed in the temperature range 850–950°C. Diffusion profiles were measured using 3 MeV alpha-particles Rutherford backscattering spectrometry (RBS) at each step of annealing. By extrapolation it is shown that at 300°C the europium diffusion in ZrO2 is negligible. In a second step, the specimens were exposed to a basic solution (pH 13.5) at 300°C in autoclave under a 107 Pa pressure. By means of RBS, it was possible to deduce the fraction of dissolved ZrO2. It was shown that this dissolution is inhomogeneous. These results are confirmed by scanning electron microscopy (SEM).

Profiling of carbon, oxygen and argon contamination in sputter-deposited films using nuclear backscattering and nuclear reaction spectroscopy

Abstract Carbon, oxygen and argon contaminations are known to play an important role in modifying the properties of surface coating films. We have profiled such elements using quantitative and non-destructive nuclear analysis techniques. Carbon and oxygen profiling is performed using nuclear backscattering of high-energy α-particles. Measurements of carbon and oxygen contamination on niobium-coated copper RF cavities used in high-energy accelerator technology are carried out. Oxygen and carbon sensitivity limits are respectively 10 15 and 5 × 10 15 atoms/cm 2 while surface depth resolutions are 30 and 25 μg/cm 2 . Argon contamination profiling is performed using the 40 Ar(p, γ) 41 K resonant nuclear reaction at a proton incident energy of 1101.8 keV. Argon profiling in niobium films is studied: the depth resolution is around 5 μg/cm 2 while the sensitivity limit is 10 14 atoms/cm 2 within each depth resolution step.

Ion beam analysis using alpha particles and protons for compositional determination of niobium superconducting compound films

A prospective study of new materials for making superconducting cavities is in progress. In this context (Nb1 − xTix)N films have been deposited on carbon and copper substrates and carefully characterized. In order to determine the film stoichiometry behaviour from the surface up to the substrate film interface, multistep analysis is performed. It includes RBS titanium and niobium profiling, and NBS nitrogen profiling. Moreover, contaminant incorporation (H, C, O, Ar) is checked. Measurements of carbon and oxygen contamination utilize NBS with, respectively, 5.7 and 7.5 MeV helium ions. Profiling of hydrogen contamination is performed using ERDA induced by 2.5 MeV alpha particles. Electron microprobe measurements are used to control argon incorporation. For a film manufactured under given deposition conditions, compositional analysis is then obtained with an accuracy better than 1%. An attempt is made to correlate the element composition and the deposition parameters.

Argon irradiation damage at a Cu/Al2O3 interface for different alumina structures

The evolution of damages at a Cu/Al2O3 device interface after Ar+ irradiation, depending on alumina structure, and the effect of surface roughness on sputtering have been studied. A polycrystalline Cu/Al2O3 bilayer and polycrystalline Cu on amorphous alumina were irradiated with 400 keV Ar+ ion beam at doses ranging from 5 × 1016 to 1017 Ar+/cm2 at room temperature. The copper layer thicknesses were between 100 and 200 nm. RBS analysis was used to characterize the interface modification and to deduce the sputtering yield of copper. The SEM technique was used to control the surface topography. A RBS computer simulation program was used to reproduce experimental spectra and to follow the concentration profile evolutions of different elements before and after ion irradiation. A modified TRIM calculation program which takes into account the sputtering yield evolution as well as the concentration variation versus dose gives a satisfactory reproduction of the experimental argon distribution. The surface roughness effect on sputtering and the alumina structure influence at the interface on mixing mechanisms are discussed.