RCC-MRX code context, overview, on-going developments

International audienceRCC-MRx Code is the result of the merger of the RCC-MX 2008 developed in the context of the research reactor Jules Horowitz Reactor project, in the RCC-MR 2007 which set up rules applicable to the design of components operating at high temperature and to the Vacuum Vessel of ITER. This code has been issued in French and English versions by AFCEN (Association Francaise pour les regles de Conception et de Construction des Materiels des Chaudieres Electro-nucleaires) in 2012, and a new edition will be published at the end of 2015.A significant work has been performed for this edition to improve the code in order to facilitate its use and understandability, and also to have a better fit with the feedbacks of the users. In parallel, in compliance with the EC's objectives and its own policy of openness, AFCEN proposes to make its codes evolve, taking into account the needs and expectations of European stakeholders (operators, designers, constructors, suppliers) threw a workshop called CWA phase 2. This paper gives an overview of the realized work and also will identify the work to be done for an opening of a standard such as RCC-MRx code

Identification and characterization of a new zirconium hydride

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Nanoscale Precipitation, Recovery and Grain Growth in ODS Steel Particles

International audienc

Nanoscale Precipitation, Recovery and Grain Growth in ODS Steel Particles

International audienc

On ball-milled ODS ferritic steel recrystallization: From as-milled powder particles to consolidated state

International audienceRecrystallization of a ball-milled ferritic ODS steel is studied towards its evolution from as-milled powder to consolidated state. This characterization has been made possible by using a combination of X-ray Diffraction (XRD) and an innovative method based on an Automated Crystallographic Orientation Mapping (ACOM) tool attached to a Transmission Electron Microscope (TEM). Focus Ion Beam preparation has been essential to obtain a thin section of the ODS steel powder particle and perform the ACOM-TEM study. Relevant temperatures regarding recovery and recrystallization during the heat treatment had first been identified with XRD profile analysis. Selected states were further characterized using ACOM-TEM that provides key information on microstructure, i.e. grain size and morphology, crystallite size, local texture and distortion. ACOM-TEM cartographies have revealed for the first time that the microstructure of as-milled ODS ferritic steel particles consists in very anisotropic grains containing undistorted domains and dislocation walls. This is in agreement with the nanosized crystallites measured by XRD results. The mutual benefits of XRD and ACOM-TEM methods to analyse and describe the microstructure are discussed as well as the reliability of dislocation density measurements provided by ACOM-TEM misorientation measurements. In addition, of the ACOM-TEM results, the microstructural evolution during the processing route is interpreted in terms of a competition between recovery, recrystallization, grain growth and precipitation

The effect of Sn on corrosion mechanisms in advanced Zr-cladding for pressurised water reactors

The desire to improve the corrosion resistance of Zr cladding material to allow high burnup has resulted in a general trend among fuel manufacturers to develop alloys with reduced levels of Sn. While the detrimental effect of Sn on high temperature aqueous corrosion performance is widely accepted, the reason for it remains unclear. High-Energy synchrotron X-ray diffraction was used to characterise the oxides formed by autoclave exposure on Zr-Sn-Nb alloys with tin concentrations ranging from 0.01 to 0.92 wt.%. The alloys studied included the commercial alloy ZIRLO® and two variants of ZIRLO with significantly lower tin levels, referred to here as A-0.6Sn and A-0.0Sn. The nature of the oxide grown on tube samples from each alloy during autoclave testing at 360°C was investigated by cross-sectional Scanning and Transmission Electron Microscopy (SEM & TEM). Non-destructive synchrotron X-ray diffraction analysis on the oxides revealed that the monoclinic and tetragonal oxide phases display highly compressive in-plane residual stresses with the magnitudes dependent on both phase and alloy. Additional in-situ Synchrotron X-ray diffraction experiments during oxidation at 550°C provided further confirmation of the trends seen for autoclave tested samples and demonstrated the presence of elevated levels of tetragonal phase in the initial stages of oxidation. In-situ and ex-situ measurements demonstrate unambiguously that the amount of tetragonal phase present and, more importantly, the degree of transformation from tetragonal to monoclinic oxide both decrease with decreasing tin levels, suggesting that tin stabilises the tetragonal phase. It is proposed that in Zr-Nb-Sn alloys with low Sn, the tetragonal phase is mainly stabilised by very small grain size and therefore remains stable throughout the corrosion process. By contrast, in alloys with higher tin levels larger, stress stabilised, tetragonal grains can form initially, but then become unstable as the corrosion front progresses inwards and stresses in the existing oxide relax

Studies regarding corrosion mechanisms in zirconium alloys

Understanding the key corrosion mechanisms in a light water reactor primary water environment is critical to developing and exploiting improved zirconium alloy fuel cladding. In this paper, we report recent research highlights from a new collaborative research programme involving 3 U.K. universities and 5 partners from the nuclear industry. A major part of our strategy is to use the most advanced analytical tools to characterise the oxide and metal/oxide interface microstructure, residual stresses, as well as the transport properties of the oxide. These techniques include three-dimensional atom probe (3DAP), advanced transmission electron microscopy (TEM), synchrotron X-ray diffraction, Raman spectroscopy, and in situ electro-impedance spectroscopy. Synchrotron X-ray studies have enabled the characterisation of stresses, tetragonal phase fraction, and texture in the oxide as well as the stresses in the metal substrate. It was found that in the thick oxide (here, Optimized-ZIRLO, a trademark of the Westinghouse Electric Company, tested at 415°C in steam) a significant stress profile can be observed, which cannot be explained by metal substrate creep alone but that local delamination of the oxide layers due to crack formation must also play an important role. It was also found that the oxide stresses in the monoclinic and tetragonal phases grown on Zircaloy-4 (autoclave testing at 360°C) first relax during the pre-transition stage. Just before transition, the compressive stress in the monoclinic phase suddenly rises, which is interpreted as indirect evidence of significant tetragonal to monoclinic phase transformation taking place at this stage. TEM studies of pre- and post-transition oxides grown on ZIRLO, a trademark of the Westinghouse Electric Company, have used Fresnel contrast imaging to identify nano-sized pores along the columnar grain boundaries that form a network interconnected once the material goes through transition. The development of porosity during transition was further confirmed by in situ electrochemical impedance spectroscopy (EIS) studies. 3DAP analysis was used to identify a ZrO sub-oxide layer at the metal/oxide interface and to establish its three-dimensional morphology. It was possible to demonstrate that this sub-oxide structure develops with time and changes dramatically around transition. This observation was further confirmed by in situ EIS studies, which also suggest thinning of the sub-oxide/barrier layer around transition. Finally, 3DAP analysis was used to characterise segregation of alloying elements near the metal/oxide interface and to establish that the corroding metal near the interface (in this case ZIRLO) after 100 days at 360°C displays a substantially different chemistry and microstructure compared to the base alloy with Fe segregating to the Zr/ZrO interface