Kinetic study of the oxidation by oxygen of a zirconium based alloy: ZrNbO. Differences between the pre- and post-transition stages

International audienceThe oxidation by oxygen of a zirconium based alloy, M5TM (which is a ZrNbO alloy, containing 1% of Nb) has been studied. The M5TM alloy, like many zirconium alloys, undergoes a kinetic transition. The aim of the present work is to achieve a better understanding of the oxidation in the pre-transition stage, and to clearly identify the differences between the pre- and post transition stages from the kinetic point of view. The oxidation of M5TM was followed by isothermal gravimetry at 490°C, under a controlled partial pressure of oxygen (in the range 7 to 200hPa). First, we have verified the steady state assumption, by coupling thermogravimetry and differential scanning calorimetry (DSC) : it is shown that the system is in a steady state from the beginning of the oxidation, in the pre- and post-transition stages. Then, the existence of a rate-limiting step was verified in the pre-transition stage using an experimental method based on temperature or pressure jumps; this assumption is no more verified in the post-transition stage, which means that the oxidation does not proceed in the same way as in the pre-transition stage. Finally, we have obtained the variations of zirconia growth reactivity with the oxygen pressure, in the pre-transition stage (using the pressure jump method). The oxygen pressure has a slightly accelerating effect, which cannot be interpreted by the diffusion of oxygen vacancies through a dense oxide layer (in that case no effect of the oxygen pressure would be observed). In the post-transition stage, the oxygen effect is more important

Modelling of the kinetic transition in zirconium based alloys: Application to the oxidation of Zircaloy-4 by water vapour

International audienceThe kinetic curves of oxidation of Zircaloy-4 exhibit a transition, which is a sharp increase in the oxidation rate when the oxide thickness reaches a critical value. The pre-transition stage is controlled by the diffusion of oxygen vacancies in the oxide layer. In the post-transition stage, oxygen or water vapour have an accelerating effect on the oxidation (whereas they have no influence during the pre-transition) and the oxide layer is damaged, with large cracks parallel to the metal/oxide interface and connected to the gaseous atmosphere by pores. Consequently, it is clear that the post-transition stage cannot be accounted for by the same mechanism as in pre-transition. In this paper, we propose a geometrical modelling allowing to describe the progressive transformation of the oxide layer during the transition. This model is based on a random appearance of pores (connected to the external surface) which leads to the transformation, from a pre-transition stage to the post-transition stage, of small sections s0 of the oxide layer (analogy with the models of thermal transformations of powders, involving the processes of nucleation and growth of a new phase). The model allows to describe the kinetic curves obtained for the oxidation by water vapour of Zircaloy-4

M5_Framatome cladding high temperature oxidation behavior during simulated LOCA transients

International audienceDemonstrating the satisfying cladding oxidation behavior in LOCA conditions and predicting accurately breakaway occurrence is of importance for the cladding producer and its customers. FRAMATOME developed a dedicated facility at his PAIMBOEUF plant in order to perform one- and two-sided oxidation tests in steam, with a tight monitoring (temperature, steam flow). M5Framatome claddings were oxidized at temperatures from 800 to 1100°C for at least 5000 s. Parabolic kinetics, protective oxides and a lack of significant hydrogen pick-up were observed. These tests confirmed the M5Framatome excellent behavior and the absence of breakaway in these conditions. Metallography and SEM observations allowed us to quantify the layers’ thicknesses of the oxide the oxygen-stabilized alpha phases. The metal/oxide interface roughness as well as the oxide porosity were also estimated by image analysis, and are shown to depend on the oxidation temperature. In parallel, Finite Element Modeling of the oxidation and the addition elements’ diffusion was developed. Diffusion equations take into account the evolution of the chemical potentials of the elements, computed thanks to the THERMOCALC software and the FRAMATOME ARTABAZ thermodynamic database. Calculated diffusion profiles are compared to experimental data and discussed

LHC1: a semiconductor pixel detector readout chip with internal, tunable delay providing a binary pattern of selected events

The Omega3/LHCl pixel detector readout chip comprises a matrix of 128 X 16 readout cells of 50 mu m X 500 mu m and peripheral functions with 4 distinct modes of initialization and operation, together more than 800 000 transistors. Each cell contains a complete chain of amplifier, discriminator with adjustable threshold and fast-OR output, a globally adjustable delay with local fine-tuning, coincidence logic and memory. Every cell can be individually addressed for electrical test and masking, First results have been obtained from electrical tests of a chip without detector as well as from source measurements, The electronic noise without detector is similar to 100 e(-) rms. The lowest threshold setting is close to 2000 e(-) and non-uniformity has been measured to be better than 450 e(-) rms at 5000 e(-) threshold. A timewalk of < 10 ns and a precision of < 6 ns rms on a delay of 2 mu s have been measured. The results may be improved by further optimization

Observation of vertex factorisation breaking in central pp interactions

Central \pipi events produced in pp interactions are studied in terms of correlations between the outgoing protons. It is observed there is more $\rho^{0}$(770) and \fmeson production in reactions where the outgoing protons %fastest and slowest particles in the laboratory frame are on opposite sides of the beam. This effect is not attributable to the trigger or the experimental acceptance, and suggests that the vertices do not factorise

Severe early onset preeclampsia: short and long term clinical, psychosocial and biochemical aspects

Preeclampsia is a pregnancy specific disorder commonly defined as de novo hypertension and proteinuria after 20 weeks gestational age. It occurs in approximately 3-5% of pregnancies and it is still a major cause of both foetal and maternal morbidity and mortality worldwide1. As extensive research has not yet elucidated the aetiology of preeclampsia, there are no rational preventive or therapeutic interventions available. The only rational treatment is delivery, which benefits the mother but is not in the interest of the foetus, if remote from term. Early onset preeclampsia (<32 weeks’ gestational age) occurs in less than 1% of pregnancies. It is, however often associated with maternal morbidity as the risk of progression to severe maternal disease is inversely related with gestational age at onset2. Resulting prematurity is therefore the main cause of neonatal mortality and morbidity in patients with severe preeclampsia3. Although the discussion is ongoing, perinatal survival is suggested to be increased in patients with preterm preeclampsia by expectant, non-interventional management. This temporising treatment option to lengthen pregnancy includes the use of antihypertensive medication to control hypertension, magnesium sulphate to prevent eclampsia and corticosteroids to enhance foetal lung maturity4. With optimal maternal haemodynamic status and reassuring foetal condition this results on average in an extension of 2 weeks. Prolongation of these pregnancies is a great challenge for clinicians to balance between potential maternal risks on one the eve hand and possible foetal benefits on the other. Clinical controversies regarding prolongation of preterm preeclamptic pregnancies still exist – also taking into account that preeclampsia is the leading cause of maternal mortality in the Netherlands5 - a debate which is even more pronounced in very preterm pregnancies with questionable foetal viability6-9. Do maternal risks of prolongation of these very early pregnancies outweigh the chances of neonatal survival? Counselling of women with very early onset preeclampsia not only comprises of knowledge of the outcome of those particular pregnancies, but also knowledge of outcomes of future pregnancies of these women is of major clinical importance. This thesis opens with a review of the literature on identifiable risk factors of preeclampsia

Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan

This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good

Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle of the West African Monsoon

The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. In the Sahel, the magnitude of rainfall anomalies is comparable to that obtained by other authors using SST anomalies confined to the proximity of the Atlantic Ocean. The mechanism connecting the Pacific/Indian SST anomalies with West African rainfall has a strong seasonal cycle. In spring (May and June), anomalous subsidence develops over both the Maritime Continent and the equatorial Atlantic in response to the enhanced equatorial heating. Precipitation increases over continental West Africa in association with stronger zonal convergence of moisture. In addition, precipitation decreases over the Gulf of Guinea. During the monsoon peak (July and August), the SST anomalies move westward over the equatorial Pacific and the two regions where subsidence occurred earlier in the seasons merge over West Africa. The monsoon weakens and rainfall decreases over the Sahel, especially in August.Peer reviewe

Measurements of the pp → ZZ production cross section and the Z → 4ℓ branching fraction, and constraints on anomalous triple gauge couplings at √s = 13 TeV

Four-lepton production in proton-proton collisions, pp -> (Z/gamma*)(Z/gamma*) -> 4l, where l = e or mu, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb(-1). The ZZ production cross section, sigma(pp -> ZZ) = 17.2 +/- 0.5 (stat) +/- 0.7 (syst) +/- 0.4 (theo) +/- 0.4 (lumi) pb, measured using events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60 4l) = 4.83(-0.22)(+0.23) (stat)(-0.29)(+0.32) (syst) +/- 0.08 (theo) +/- 0.12(lumi) x 10(-6) for events with a four-lepton invariant mass in the range 80 4GeV for all opposite-sign, same-flavor lepton pairs. The results agree with standard model predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZ. couplings at 95% confidence level: -0.0012 < f(4)(Z) < 0.0010, -0.0010 < f(5)(Z) < 0.0013, -0.0012 < f(4)(gamma) < 0.0013, -0.0012 < f(5)(gamma) < 0.0013