S. Gossé

Towards the determination of the geographical origin of yellow cake samples by laser-induced breakdown spectroscopy and chemometrics

Yellow cake is a commonly used name for powdered uranium concentrate, produced with the uranium ore. It is the first step in the fabrication of nuclear fuel. As it contains fissile material its circulation needs to be controlled in order to avoid proliferation. In particular there is an interest in onsite determination of the geographical origin of a sample. The yellow cake elemental composition depends on its production site and can therefore be used to identify its origin. In this work laser-induced breakdown spectroscopy (LIBS) associated with chemometrics techniques is used to discriminate yellow cake samples of different geographical origin. 11 samples, one per origin, are analyzed by a commercial equipment in laboratory experimental conditions. Spectra are then processed by multivariate techniques like Principal Components Analysis (PCA) and Soft Independent Modeling of Class Analogy (SIMCA). Successive global PCAs are first performed on the whole spectra and enable one to discriminate all samples. The method is then refined by selecting several emission lines in the spectra and by using them as input data of the chemometric treatments. With a SIMCA model applied to these data a rate of correct identification of 100% is obtained for all classes. Then to define the specifications of a future onsite LIBS system, the use of a more compact spectrometer is simulated by a numerical treatment of experimental spectra. Simultaneously the reduction of spectral data used by the model is also investigated to decrease the spectral bandwidth of the measurement. The rate of correct identification remains very high. This work shows the very good ability of SIMCA associated with LIBS to discriminate yellow cake samples with a very high rate of success, in controlled laboratory conditions.

Thermodynamic Modelling of the Destruction of the Surface Cr2O3 on Alloy 230 in the Impure Helium Atmosphere of a Gas Cooled Reactor

Above a given temperature called TA, the chromium rich oxide which has been developed on the surface of Haynes 230® and model NiCrWC alloys at a lower temperature becomes unstable in impure helium: carbon monoxide is released. Actually, oxide is reduced by carbon from the alloy. A thermodynamic model is developed to rationalize the variation of TA as a function of the partial pressure of CO in the gas phase. It was found that, at the early stages of the scale reduction, the relevant reaction occurs at the oxide/metal interface between chromia and carbon from the alloy. The interfacial activity of carbon in the alloy can be calculated based on measurements of the interfacial weight percentage of chromium and using ThermoCalc® software. Excellent agreement is observed between experimental values of TA and theoretical predictions.

Direct measurements of the chromium activity in complex nickel base alloys by high temperature mass spectrometry

Chromium rich, nickel based alloys Haynes 230 and Inconel 617 are candidate materials for the primary circuit and intermediate heat exchangers (IHX) of (Very)-High Temperature Reactors. The corrosion resistance of these alloys is strongly related to the reactivity of chromium in the reactor specific environment (high temperature, impure helium). At intermediate temperature – 900°C for Haynes 230 and 850°C for Inconel 617 – the alloys under investigation are likely to develop a chromium-rich surface oxide scale. This layer protects from the exchanges with the surrounding medium and thus prevents against intensive corrosion processes. However at higher temperatures, it was shown that the surface chromia can be reduced by reaction with the carbon from the alloy [1] and the bare material can quickly corrode. Chromium appears to be a key element in this surface scale reactivity. Then, quantitative assessment of the surface requires an accurate knowledge of the chromium activity in the temperature range close to the operating conditions (T ≈ 1273 K). High temperature mass spectrometry (HTMS) coupled to multiple effusion Knudsen cells was successfully used to measure the chromium activity in Inconel 617 and Haynes 230 in the 1423- 1548 K temperature range. Appropriate adjustments of the experimental parameters and in-situ calibration toward pure chromium allow to reach accuracy better than ± 5%. For both alloys, the chromium activities are determined. Our experimental results on Inconel 617 are in disagreement with the data published by Hilpert [2]. Possible explanations for the significant discrepancy are discussed.

Safest Roadmap for Corium Experimental Research in Europe

Severe accident facilities for European safety targets (SAFEST) is a European project networking the European experimental laboratories focused on the investigation of a nuclear power plant (NPP) s ...

SAFEST ROADMAP FOR CORIUM EXPERIMENTAL RESEARCH IN EUROPE

SAFEST (Severe Accident Facilities for European Safety Targets) is a European project networking the European corium experimental laboratories with the objective to establish coordination activitie ...