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This paper presents simulations of the xM3 power ramp with the fuel performance code ALCYONE performed during an international simulation exercise organized within the Organisation for Economic Co-operation and Development/Nuclear Energy Agency Power to Melt and Maneuverability project. The xM3 test involved a large-grain UO2 fuel from Mitsubishi Heavy Industries cladded with Zirlo and pre-irradiated in a Spanish pressurized water reactor up to an average burnup of 27 GWd/tU−1. It was then submitted to a staircase ramp protocol in the R2 reactor at Studsvik (Sweden) with 10 successive steps of 5 kW·m−1 up to a ramp terminal level of 70 kW·m−1. The fuel rodlet did not fail, and detailed post irradiation examinations performed during the Studsvik Cladding Integrity Project II evidenced recrystallization of the pellet center around a central hole, interpreted as signs of fuel melting. In this paper, simulations with ALCYONE of the xM3 power ramp, including an advanced model for fuel melting based on thermodynamic equilibrium calculations, are detailed. The model relies on the determination of the liquid fuel fraction evolution with temperature that is used to obtain a continuous description of the material properties during phase change. In consequence of the incorporation of rare earths and actinides in the bulk of the fuel, distinct solidus and liquidus temperatures are estimated. It is shown that the observed central hole and recrystallized central part of the pellet could be the consequence of totally melted fuel (liquidus is reached), partially melted fuel (solidus is reached), or pore migration only. [ABSTRACT FROM AUTHOR]

This paper presents the results of the Power To Melt and Maneuverability (P2M) Simulation Exercise on past fuel melting irradiation experiments, organized within the Organisation for Economic Co-operation and Development/Nuclear Energy Agency Framework for IrraDiation ExperimentS (FIDES) framework by the Core Group (CEA, EDF, and SCK‧CEN) and open to all FIDES members. The exercise consisted in simulating two past power ramps where fuel melting was detected: (1) the xM3 staircase power transient [ramp terminal level (RTL) 70 kW‧m−1, average burnup 27 GWd‧tU−1], carried out in 2005 in the R2 reactor at Studsvik (Sweden), where the rodlet maintained its integrity, and (2) the HBC4 fast power transient (RTL 66 kW‧m−1, average burnup 48 GWd‧tU−1), carried out in 1987 in the BR2 reactor at SCK‧CEN (Belgium), where the cladding failed during the experiment. The exercise was joined by 13 organizations from 9 countries using 11 different fuel performance codes. In this paper, the main results of the Simulation Exercise are presented and compared to available postirradiation examinations (PIE) or on-line measurements during the power ramps (fuel and clad diameters, rod elongation, pellet-clad gap, and fission gas release). Since the focus of the Simulation Exercise is on fuel melting assessment, determination of the boundary between melted/nonmelted fuel and the consequent definition of a melting radius from PIE are first discussed. During the HBC4 ramp, fuel melting was predicted by most of the codes despite differences in the melting models. Higher discrepancies were observed for the xM3 rod that can be attributed partly to power uncertainty and partly to the limited capability of the models to describe partial melting of the fuel during this ramp. Finally, possible code developments to improve simulation results are presented. [ABSTRACT FROM AUTHOR]

This paper presents 2D(r, $\it \theta $ θ) simulations of the HBC-4 power-to-melt experiment performed with the fuel performance code ALCYONE. The HBC-4 experiment is one of the two test cases selected for the simulation exercise on past fuel melting experiments of the Power to Melt and Maneuverability (P2M) project. The ramp terminal level (RTL) at peak power node (PPN) has been estimated at 66 kW·m−1 by gamma scanning and 70 kW·m−1 based on online measurements of thermal fluxes. The fuel burnup at PPN was close to 60 GWd/tU−1. The cladding failed during the short holding time at a RTL of 40 s. Fuel melting took place at the pellet center, and in particular, in front of clad cracks. In this paper, simulations of the HBC-4 power-to-melt experiment are performed using an updated version of the 2D(r, $\it \theta $ θ) scheme of ALCYONE where half of the fuel pellet is described. This configuration allows for the modeling of clad failure by iodine stress corrosion cracking and of its consequences on fuel pellet deformation. The modeling of fuel melting relies on thermochemical equilibrium calculations performed with the OpenCalphad Gibbs Energy Minimizer and the Thermodynamics of Advanced Fuels International Database. The simulation without clad failure indicates that the solidus is reached during the HBC-4 experiment but not the liquidus. The simulation with clad failure leads to a small increase in the fuel temperature that is sufficient to reach the liquidus at the pellet center, in agreement with postirradiation examination (PIE). The impact of water ingress in the rod and vaporization at the pellet surface is discussed, showing that it could explain the pronounced swelling of the fuel pellet reported from the PIE. [ABSTRACT FROM AUTHOR]

Abstract This paper presents 3D simulations of power ramps in pressurized water reactors with the fuel performance code ALCYONE, which is part of the computing environment PLEIADES. The code has been upgraded to couple the description of irradiated fuel thermochemistry already available with oxygen transport taking into account thermodiffusion. The impact of oxygen redistribution during a power transient on irradiated fuel thermochemistry in the fuel and on chemically reactive gas release from the fuel (I (g) , I 2 (g) , CsI (g) , TeI 2 (g) , Cs (g) , Cs 2 (g)) is studied. The simulations show that oxygen redistribution, even if moderate in magnitude, leads to the reduction of metallic oxides (molybdenum dioxide, cesium molybdates, chromium oxide) at the fuel pellet center and consequently to the release of a much greater quantity of gaseous cesium. Pellet-Cladding Interaction failure propensity is shown to decrease in consequence of the thermodynamically favourable reaction of iodine with released cesium in the free volume of the rod. [ABSTRACT FROM AUTHOR]

The present study describes the in-situ electrochemical modifications which affect irradiated PWR UO 2 fuels in the course of a power ramp, by means of in-situ oxido-reduction indicators such as chromium or neo-formed chemical phases. It is shown that irradiated fuels (of nominal stoichiometry close to 2.000) under temperature gradient such as that occurring during high power transients are submitted to strong oxido-reduction perturbations, owing to radial migration of oxygen from the hot center to the cold periphery of the pellet. The oxygen redistribution, similar to that encountered in Sodium Fast Reactors fuels, induces a massive reduction/precipitation of the fission products Mo, Ru, Tc and Cr (if present) in the high temperature pellet section and the formation of highly oxidized neo-formed grey phases of U 4 O 9 type in its cold section, of lower temperature. The parameters governing the oxidation states of UO 2 fuels under power ramps are finally debated from a cross-analysis of our results and other published information. The potential chemical benefits brought by oxido-reductive additives in UO 2 fuel such as chromium oxide, in connection with their oxygen buffering properties, are discussed. [ABSTRACT FROM AUTHOR]

In this paper we study the brittle behavior of UO 2 nuclear fuel. Firstly, we present the interpretation of bending tests with three different approaches to assess rupture parameters (critical stress and surface energy). Secondly, we present Vickers’ indentation tests on fresh UO 2 fuel. The comparison between bending and indentation tests on fresh fuel allows us to assess the parameters necessary to derive the critical stress and the surface energy from indentation tests. Vickers’ indentation is then used to evaluate rupture parameters of irradiated fuels. At the end, we present some applications to fuel rod modeling taking into account the different rupture mechanisms. [ABSTRACT FROM AUTHOR]

• This paper presents simulations of four tests performed on medium to high burnup fuel during the VERCORS and VERDON experimental programs. • The simulations are performed with the fuel performance code ALCYONE where irradiated fuel thermochemistry and fission gas release are coupled. • The simulated release curves of various volatile and semi-volatile Fission Products (Xe, I, Te, Cs, Mo and Ba) are compared successfully to on-line measurements. • The impact of the radial burnup and Fission Product (FP) profiles within the fuel pellet on the FP release from the sample during the Severe Accident sequences is studied. • It is shown that the Fission Product release from the fuel pellets is not significantly increased by the consideration of the burnup and Fission Products radial profiles. This paper presents simulations of four tests performed on medium to high burnup fuel during the VERCORS and VERDON experimental programs. The tests are representative of a Severe Accident (SA) sequence with a temperature increase up to fuel-clad melting and oxidizing/reducing conditions within the furnace. The simulations are performed with the fuel performance code ALCYONE where irradiated fuel thermochemistry and fission gas release are coupled. In this paper, the impact of the radial burnup and Fission Product (FP) profiles within the fuel pellet on the FP release from the sample during the SA sequence is studied. Simulations of the fuel sample behavior during nominal irradiation in commercial reactors are first performed to assess the initial state of the fuel. The simulations of the SA sequences include a burnup dependent fission gas release model. The simulated release curves of various volatile and semi-volatile FPs (Xe, I, Te, Cs, Mo and Ba) are compared successfully to on-line measurements. The impact of the burnup and FP radial profiles on both the thermochemical equilibria within the pellet and the FP release kinetics is discussed. It is shown that the FP release from the fuel pellets is not significantly increased by the consideration of the burnup and FP radial profiles. This conclusion is due to the limited radial extension of the peaked burnup radial profile in the fuel pellet and to the uniform temperature of the fuel samples. [ABSTRACT FROM AUTHOR]

This paper presents the coupling of the fuel performance code ALCYONE with the thermochemical code ANGE and its application to Iodine-Stress Corrosion Cracking (I-SCC). The coupling is illustrated by a 3D simulation of a power ramp. The release of chemically active gases (CsI(g), Tex(1

Studies that estimate indoor aeroallergen exposure typically measure a pre-selected limited range of allergens. In this study, inhalable aeroallergen particles were quantified using the halogen immunoassay ( HIA) to determine the contribution of fungal and non-fungal aeroallergens to total allergen exposure. Bioaerosols from 39 homes of fungal-allergic subjects were sampled using inhalable fraction samplers and immunostained by HIA using resident subject's immunoglobulin E (IgE) to detect allergen-laden particles. Fungal aerosols as well as particles carrying mite, cat, and cockroach allergens were identified and enumerated by HIA. Reservoir dust-mite (Der p 1), cat (Fel d 1), and cockroach (Bla g 1) allergen concentrations were quantified by ELISA. Fungal particles that bound subject's IgE in the HIA were 1.7 (bedroom)- and 1.4 (living room)-fold more concentrated than Der p 1, Fel d 1, and Bla g 1 allergen particles combined. Predominant fungal conidia that bound IgE were derived from common environmental genera including Cladosporium and other fungi that produce amerospores. Airborne mite, cat, and cockroach allergen particle counts were not associated with reservoir concentrations determined by ELISA. This study demonstrates that inhalable fungal aerosols are the predominant aeroallergen sources in Sydney homes and should be considered in future exposure assessments. [ABSTRACT FROM AUTHOR]

This paper presents simulations of the VERDON 1 and RT6 tests (temperature increase up to fuel-clad melting, oxidizing and/or reducing conditions within the furnace) performed with high burnup UO 2 fuel (i.e., up to 72 GWd/tU) and considering a coupling between irradiated fuel thermochemistry and a fission gas release model. The thermochemical calculations rely on the Thermodynamics of Advanced Fuels - International Database (TAF-ID) for the description of the phases likely to form from the 15 fission product considered in the fuel (Ba, Ce, Cs, I, La, Mo, Nd, Np, Pd, Rh, Ru, Sr, Tc, Te, Zr) and on the OpenCalphad solver for the minimization of the Gibbs energy of the system. The gas release model describes a diffusion process for the gases within equivalent spherical grains. It accounts for the gases formed by reaction between the fission products as well as the chemically inert noble gases. The progressive fission product depletion of the fuel due to their release in gas form closes the coupling. The impact of the fission product release kinetics on the thermochemical equilibria within the fuel is then studied by coupling the thermochemical calculations with a gas diffusion model. The coupled simulations led to a very good agreement with the release kinetics of various fission products (I, Te, Cs, Mo, Ba). The released fractions of the low-/non-volatile fission products and of uranium, plutonium are also well reproduced. The observed differences in the fuel-clad melting temperatures in the two tests (2200 °C during RT6 and 2600 °C during VERDON 1) are however not reproduced by the simulations. [ABSTRACT FROM AUTHOR]

In this paper, a novel approach where irradiated fuel thermochemistry and gas release are coupled is presented in details and illustrated by the simulations of some tests of the VERCORS program characterized by increasing temperatures and varying gas composition in the furnace (oxidizing or reducing conditions). At each step of the tests, the oxidation/reduction of the nuclear fuel and the fission product chemical speciation are precisely assessed thanks to a thermochemical equilibrium calculation relying on the OpenCalphad thermochemical solver and on a built-in thermochemical database derived from the SGTE database and completed by a solid solution model for the U-O-fission product system. Fission product releases are estimated from the chemically reactive gases that form in the fuel (according to the thermochemical calculation) and from a gas diffusion model based on the equivalent sphere model. The gas diffusion model takes into account not only the noble gases available in the fuel prior to the test but also the chemically reactive gases that form during the test. It is shown that the proposed coupled approach provides a consistent estimation of fission product release (I, Te, Cs, Mo, Ba) during the VERCORS tests in spite of the simple gas diffusion mechanism considered in the simulations (no distinction between the fission products). The proposed coupled approach is used to test some thermochemical hypotheses to improve the calculated release of some fission products (Ba, Mo). [ABSTRACT FROM AUTHOR]

Abstract: This paper presents 2D(r, θ) plane strain and 3D simulations of PCI during base irradiation and ramp tests. Inverse analysis is used to estimate the evolution of friction at the pellet–clad interface with burnup. The number of radial cracks that form during power ramp tests in seventeen UO2-Zy4 rodlets with burnups in the range 20–60GWd/tU is the main parameter on which inverse analysis is based. It is shown that the sole evolution of the friction coefficient with burnup is sufficient to capture the radial crack pattern of the rodlets after power ramping. A simple relation between the friction coefficient and the burnup variation after initial pellet–clad contact is thus proposed and used in 3D simulations of PCI. The delayed gap closing at mid-pellet level with respect to inter-pellet level leads to an axial variation of the friction coefficient, with maximum values near the pellet ends. The consequences in terms of PCI failure propensity are then discussed. [Copyright &y& Elsevier]

• Development of a phase-field model for a two-phase multicomponent system • Coupling of the phase-field model with the TAF-ID • Derivation of a partitioned fixed-point numerical solving • Simulation of incipient fuel melting and oxygen transport in nuclear fuel In this paper, a phase-field model is developed for a two phase compositional (multicomponent) system and combined with the thermodynamic description provided by a CALPHAD database. The model is applied to a uranium-oxygen binary system within a solid/liquid mixture to simulate incipient melting and oxygen transport (oxygen-uranium inter-diffusion and Soret effect) in the fuel with thermodynamic properties coming from the Thermodynamics for Advanced Fuels-International Database (TAF-ID). The interface with the TAF-ID required the coupling of the phase-field model with the OpenCalphad thermochemical solver. This coupling led to the development of a partitioned scheme that is solved at each time step with a fixed-point algorithm. To analyze the response of and to parameterize the phase-field model, two 1D demonstration problems from the open literature have been considered and solved using a finite-difference scheme. The first problem deals with oxygen transport in UO 2.005 fuel under an imposed parabolic temperature profile below liquidus. The second one describes the incipient melting and oxygen transport in oxidized fuel under an increasing temperature profile. Oxygen thermal diffusion is considered both in the solid and liquid phases. All the results presented in this paper are in good agreement with those already published but are here performed considering a direct coupling with the TAF-ID database. They demonstrate the thermodynamic consistency of the phase-field model as well as its capability to simulate incipient melting and oxygen transport in the fuel with advanced thermodynamics databases. [ABSTRACT FROM AUTHOR]

Abstract: This study is concerned with the modelling of fuel behaviour and of pellet–cladding interaction (PCI). A new fuel software (PLEIADES) is currently co-developed by the Atomic Energy Commission (CEA) and Electricité de France (EDF). This software includes a multi-dimensional FE program (ALCYONE) devoted to Pressure Water Reactors (PWR) fuel rods. PCI studies are mainly undertaken with the 3D model of ALCYONE. The objectives of this work are twofold: first, to propose a constitutive model for the fuel pellet which accounts for the stress relaxation of the material resulting from cracking and creep, second, to estimate the impact of the pellet cracking on PCI. In this paper, a mathematical formulation which couples a viscoplastic law for creep with a multi-surface plastic softening law for cracking is detailed, leading a two inelastic strains model. Mesh dependency is overcome thanks to a material parameter related to the finite element size. The 3D calculations of PCI presented in this paper show that the considered modelling of fuel cracking is consistent with the experimental knowledge available on crack development under irradiation. A parametric study is then presented which leads to the conclusion that the tangential stresses at the pellet cladding interface and hence the risk of PCI failure are significantly reduced when the fuel tensile strength is divided by two. [Copyright &y& Elsevier]

Abstract: This study is concerned with structural integrity assessment of Pressure Water Reactor''s (PWR) fuel rods under pellet–cladding interaction (PCI) loading condition. An important experimental and research cooperative program between EDF, AREVA-NP and the Atomic Energy Commission CEA is achieved in order to get a better understanding of the mechanisms possibly leading to PCI failure, as well as to qualify a PCI resistant rod design. The objectives of this work are: first, to improve the understanding of the pellet mechanical properties impact on cladding local loading with 3D simulations results, and second, to propose a new phenomenological rupture criterion for a better assessment of the failure risk. In this study fuel behaviour modelling under nominal and transient loading conditions is achieved with a multi-dimensional simulation tool called ALCYONE, included in the new fuel software PLEIADES currently co-developed by the CEA and EDF. Cladding loading due to mechanical interaction during power transient stage is first analysed through pellet–cladding interfacial stresses computed in the 3D simulation. Then, a 2D model is proposed in order to establish a correlation between interfacial loading and stress concentration in the cladding. In order to assess the failure risk under PCI a phenomenological criterion based on the membrane circumferential stress in the cladding and shear stresses at pellet–cladding interface is proposed. To compute the shear loading at pellet–cladding interface a new parameter (called W rθ ) is introduced. Based on 3D calculations of PCI, it is shown in this paper that pellet fracture properties can have a significant effect on PCI loading. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental study of gas diffusion in binary mixtures of hydrogen–nitrogen and xenon–nitrogen through cement pastes (CEM I and CEM V) of different water/cement ratios (0.35 and 0.45). First, the impact of water saturation on gas diffusion is investigated by performing tests on samples pre-conditioned in specific atmospheric conditions (dry, 55, 70, 82, 93 and 100% RH) by means of saline solutions. The comparison of the results obtained for the CEM I and the CEM V samples (w/c ratio of 0.45) demonstrate the importance of pore size distribution/connectivity on gas diffusion. Second, diffusion tests at different total pressures and using two different mixtures (hydrogen–nitrogen, xenon–nitrogen) are performed to study the nature of gas diffusion in cement paste. Results demonstrate that gas diffusion in cement paste is controlled by Knudsen and ordinary diffusion at pressures greater than 100 kPa and mainly by Knudsen diffusion at pressures less than 100 kPa. [Copyright &y& Elsevier]

Abstract: This paper presents theoretical work aiming at studying the behaviour of leached bituminized waste materials and the development of a saline solution-filled pore structure (called permeable layer) in the material. In Part I of this paper, the constitutive model COLONBO which describes mathematically the evolution of the pore structure, the water uptake, the salt and RN release of leached bituminized waste is presented. By the introduction of adequate simplifications, an analytical solution of the problem is obtained which gives the main relations between measurable leaching indicators (water uptake, soluble salt release, porosity profiles and apparent thickness of the permeable layer) and material (soluble salt content, bituminized waste density) or environmental parameters (chemical activity of water in the leachant). In the companion paper (Part II), the validity of these relations is investigated experimentally. [Copyright &y& Elsevier]

Abstract: This paper presents experimental work aiming at studying the behaviour of leached bituminized waste materials and the development of a saline solution-filled pore structure (called permeable layer) in the materials. Standard leach tests are performed on two synthetic BW materials containing different soluble salt contents and leached by solutions of varying chemical activities. The water uptake and the sodium nitrate leach rates are measured continuously during the tests. Porosity profiles are obtained from ESEM image analyses performed on the same BW samples leached during periods of varying durations. These experimental results provide a precise description of the internal structure of BW materials during leaching. The impact of the leaching duration, of the soluble salt content, and of the chemical activity of water in the leachant on the overall behaviour of leached BW materials is by this way assessed and compared to the theoretical trends presented in Part I of this paper. [Copyright &y& Elsevier]

Abstract: This paper presents experimental results obtained on cement paste samples (water/cement ratio of 0.4) subjected to a low-concentration (15 mmol/l) external sulfate attack during several weeks. Chemical and microstructural analyses include the continuous monitoring of calcium loss and sulfate consumption within the cement paste, periodic layer by layer X-ray diffraction (XRD)/energy-dispersive spectrometer (EDS) analyses of the solid constituents of the cement matrix (ettringite, portlandite, gypsum) within the calcium-depleted part of the samples. Scanning electron microscopy (SEM) and visual observations are used to follow the crack pattern evolution during the external sulfate attack. The relation between the size of the specimen and crack initiation/development is investigated experimentally by performing tests on samples with different thickness/diameter ratios. [Copyright &y& Elsevier]

Simple, inexpensive methods of sampling from allergen reservoirs are necessary for large-scale studies or low-cost householder-operated allergen measurement.We tested two commercial devices: the Indoor Biotechnologies Mitest Dust Collector and the Dräger Bio-Check Allergen Control; two devices of our own design: the Electrostatic Cloth Sampler (ECS) and the Press Tape Sampler (PTS); and a Vacuum Sampler as used in many allergen studies (our Reference Method). Devices were used to collect dust mite allergen samples from 16 domestic carpets. Results were examined for correlations between the sampling methods.With mite allergen concentration expressed asμg/g, the Mitest, the ECS and the PTS correlated with the Reference Method but not with each other. When mite allergen concentration was expressed asμg/m2 the Mitest and the ECS correlated with the Reference Method but the PTS did not. In the high allergen conditions of this study, the Dräger Bio-Check did not relate to any methods.The Mitest Dust Collector, the ECS and the PTS show performance consistent with the Reference Method. Many techniques can be used to collect dust mite allergen samples. More investigation is needed to prove any method as superior for estimating allergen exposure. [ABSTRACT FROM AUTHOR]

Prototype nasal filters were developed to collect inhaled pollen. This study evaluated the efficacy of the filters for prevention of rhinitis symptoms during acute outdoor pollen exposure.A randomized double-blind design was used. Subjects (n = 46) with a history of autumn exacerbation of rhinitis and positive skin test to ragweed, Bermuda and/or Bahia grass wore either active or placebo nasal filters for 2 h in autumn in a park containing these species. Major and Total Symptoms scores were recorded at 0, 30, 60, 90 and 120 min.Subjects wearing active nasal filters had significantly reduced scores, at all time-points compared with placebo group (allP < 0.05). Of 14 individual symptoms measured, seven were significantly reduced (number of sneezes, runny nose, itchy nose, sniffles, itchy throat; itchy eyes and watery eyes) and another three showed a trend towards lower severity. The nasal filters also enabled the resolution of existing symptoms. Maximal difference in symptoms was seen immediately after subjects had spent 20 min sitting beside a large patch of ragweed.This is the first clinical trial of a nasal filter. The results suggest it has potential for enhancing rhinitis management during acute allergen exposure. [ABSTRACT FROM AUTHOR]

This paper presents experimental results concerning the behaviour of ordinary, high-strength and high-performance concretes under constant mechanical loading and increasing temperatures up to near 300 °C. Heat was applied at a rate of 0.1 °C/min such that successive constant temperature levels were reached and maintained sufficiently to ensure internal temperature stabilisation. The analysis of experimental measures focuses on the so-called transient thermal creep, obtained during the transient thermal loading stages. To study the importance of changes in the internal properties, especially those related to free and bound water, some specimens were submitted to a second heating cycle. Test results confirm the existence of transient thermal strains during first heating, and its occurrence during the second cycle only when the maximum temperature of the first cycle was exceeded even if the specimen had spent a recovery period at ambient temperature. The transient thermal creep values were estimated for different temperature levels, above 105 °C, and they were inversely proportional to the water/cement ratio. [ABSTRACT FROM AUTHOR]

This paper is concerned with the evolution of the microstructure of cementitious materials subjected to high temperatures and subsequent resaturation in the particular context of long-term storage of radioactive wastes, where diffusive and convective properties are of primary importance. Experimental results obtained by mercury intrusion porosimetry (MIP) are presented concerning the evolution of the pore network of ordinary portland cement (OPC) paste heated at temperatures varying between 80 and 300 °C. The consequences of heating on the macroscopic properties of cement paste are evaluated by measures of the residual gas permeabilities, elastic moduli and Poisson''s ratio, obtained by nondestructive methods. Resaturation by direct water absorption and water vapour sorption are used to estimate the reversibility of dehydration. The results provide some evidence of the self-healing capacity of resaturated cement paste after heating at temperatures up to 300 °C. [Copyright &y& Elsevier]

Background:Histamine H2-receptor antagonists are available over the counter for the treatment of heartburn. Aim:To compare the effects of low doses of ranitidine and famotidine on intragastric acidity in a three-way crossover study. Methods:Healthy subjects (12 male, 12 female) were dosed on three occasions with single oral doses of placebo, ranitidine, 75 mg, and famotidine, 10 mg, 1 h after lunch. The pH of gastric aspirates was then measured for 20 h. Subjects ate standard meals and snacks. Analysis of variance was used to determine the statistical significance of differences in acidity (mmol/L) during the day (12.30–22.30 hours) and night (22.30–08.30 hours). Results:Ranitidine and famotidine were superior (P < 0.05) to placebo in decreasing acidity for daytime and night-time intervals. There were no significant differences in mean gastric acidity between ranitidine and famotidine during the daytime (11.37 mmol/L vs. 13.42 mmol/L, respectively) and night-time (23.57 mmol/L vs. 24.74 mmol/L, respectively). Intragastric acidity after ranitidine was significantly lower than that after famotidine in the first 2.5-h period following dosing (4.32 mmol/L vs. 9.28 mmol/L; P < 0.05). Conclusions:Lunchtime doses of ranitidine and famotidine decreased acidity during day- and night-time periods. The effect of ranitidine was significantly greater for the first 2.5 h after dosing. [ABSTRACT FROM AUTHOR]

• Coupling between ALCYONE fuel performance code and OpenCalphad thermochemical code. • 3.5D challenging simulation of a complete rodlet during a power transient. • Reduction of the equilibrium calculation time by defining a good initial estimate of stable phases. In this paper, a robust, accurate and efficient coupling between the PLEIADES/ALCYONE 2.1 fuel performance code and the OpenCalphad thermo-chemical solver is presented. A challenging 3.5D simulation of a power ramp, consisting of the 3D simulations of all the fuel pellets within a complete rodlet, serves as a base case to illustrate the difficulty inherent to extensive thermochemical equilibrium calculations (more than 1.5 million in this example) within fuel performance simulations, related both to the wide temperature and pressure range encountered in irradiated nuclear fuels. In the first part of this paper, a detailed analysis of the main quantities of interest (i.e. temperature, hydrostatic pressure, fission products concentration) is provided to illustrate the couplings at hand during a power ramp and, above all, to demonstrate the good agreement of the results with those already published in the literature and with available measurements of xenon, cæsium and iodine releases. In the core of this paper, several numerical strategies are proposed to reduce the overall time spent in the thermochemical solver by defining at each node and for each time step a good initial estimate of the set of stable phases that are likely to form. The first one, referred to as the spatial strategy, relies on an intelligent reorganization of the mesh nodes as a function of temperature or hydrostatic pressure with an appropriate initialization of the thermochemical equilibrium calculation at a node by the phase composition calculated at the node with the closest thermo-mechanical conditions. The second strategy, referred to as the hybrid strategy, combines the spatial strategy during the power transient (where large power variations take place at each time step) with an initialization of the nodal equilibria from the solution obtained at the previous time step in case of small power variations. The 3.5D simulation has been run several times in order to assess and compare the spatial and hybrid strategies. The simulations show that the spatial strategy is the most efficient. It leads to an overall increase of the calculation time related to the incorporation of thermochemistry in the 3.5D fuel performance simulation of less than 2.25%, showing the feasibility of large thermal-chemical–mechanical simulations within the PLEIADES/ALCYONE 2.1 fuel performance code. Finally, as a first step towards more complicated simulations (i.e. including a greater number of phases and/or performed with a finer spatial discretization), a primitive parallelization algorithm based on a multiprocess approach is proposed. Combined with the most efficient spatial strategy, it leads to a substantial reduction of the extra (real) calculation time related to thermochemistry which become less than 0.65% of the total computation time when the thermochemical equilibrium calculations are distributed over 4 cores. [ABSTRACT FROM AUTHOR]

The aim of this contribution is to deeply introduce the ALCYONE Fuel Performance Code. ALCYONE is being implemented within the PLEIADES numerical framework and is dedicated to the multiphysics behavior of fuel rods in pressurized water reactors (PWRs). It has been a joint development between CEA, EDF and Framatome since 2005 and has been used since then for numerous studies covering normal, off-normal and accidental conditions. However, a detailed description of ALCYONE's physical and numerical foundations has never been published. In this sense, this paper is intended to be the reference presentation paper for ALCYONE. On the first hand, it provides a comprehensive description of the modeling features and associated multiphysics and multiscale computational schemes. On the other hand, focuses are made on advanced modeling features showing enhanced capabilities of simulation of ALCYONE. • Detailed description of ALCYONE, the PLEIADES PWR Fuel Performance Code. • ALCYONE's physical models and numerical features are presented. • ALCYONE's simulations cover normal, off-normal, and accidental conditions. • Verification, validation and uncertainty quantification process is discussed. • Insights on some advanced modeling capabilities and numerical coupling schemes. [ABSTRACT FROM AUTHOR]

To refine knowledge about pressurized water reactor fuel melting, the Power to Melt and Maneuverability (P2M) project in the Framework for Irradiation Experiments II (FIDES-II) managed by the Nuclear Energy Agency of the Organisation for Economic Co-operation and Development aims to perform two irradiation tests to reach fuel centerline partial melting using instrumented experimental fuel rodlets irradiated in a pressurized water capsule (PWC) of the Belgian Reactor 2 (BR2) [Studiecentrum voor Kernenergie (SCK CEN), Belgium]. Prior to these experiments, two preliminary tests will be performed in the PWC for qualification purpose toward safety. The experimental rodlets will be instrumented with a fuel centerline thermocouple in the lower part of the fuel and a pressure sensor (PS) in the upper part. An objective of the P2M experiments is to determine the amount of fission gas released from the fuel thanks to the PS measurement. The plenum pressure evolution is known from the measurement, and knowledge of the gas plenum temperature is required to determine the amount of fission gas released from the fuel to the plenum. The gas plenum temperature will depend on natural convection of the PWC coolant, and no temperature measurement will be possible within this gap during the test. This paper describes the setting up of a model of the BR2 PWC equipped with the P2M rodlets based on the coupled NEPTUNE_CFD (multiphase fluid calculation code) and SYRTHES (solid thermal module) simulation tools. Simulations performed thanks to this model allow assessment of the thermal-hydraulic (TH) behavior of the pressurized water in the capsule and the thermal behavior of the rodlet, in particular, regarding the temperature of the gas located in the plenum. For consistency of the results, computations presented in this paper were performed using a single and consistent set of TH models. A mesh sensitivity analysis was carried out for all the studied cases. Simulation results related to the water capsule behavior were found to be in good agreement with the available experimental data. The gas plenum temperature results obtained from this study will be used to assess the fission gas release during the test from the plenum pressure measurements. Overall experimental validation of fission gas release during the test will be possible after the transient test in BR2 based on the postirradiation examination program foreseen on the rodlets at the LECA-STAR facility [Commissariat à l'énergie atomique et aux énergies alternatives (CEA) Cadarache, France]. [ABSTRACT FROM AUTHOR]

This paper focuses on the PLEIADES fuel performance software environment and its application to the modeling of pellet-cladding interaction (PCI). The PLEIADES platform has been under development for 10 yr; a unified software environment, including the multidimensional finite element solver CAST3M, has been used to develop eight computation schemes now under operation. Among the latter, the ALCYONE application is devoted to pressurized water reactor fuel rod behavior. This application provides a three-dimensional (3-D) model for a detailed analysis of fuel element behavior and enables validation through comparing simulation and postirradiation examination results (cladding residual diameter and ridges, dishing filling, pellet cracking, etc.). These last years the 3-D computation scheme of the ALCYONE application has been enriched with a complete set of physical models to take into account thermomechanical and chemical-physical behavior of the fuel element under irradiation. These models have been validated through the ALCYONE application on a large experimental database composed of approximately 400 study cases. The strong point of the ALCYONE application concerns the local approach of stress-corrosion-cracking rupture under PCI, which can be computed with the 3-D finite element solver. Further developments for PCI modeling in the PLEIADES platform are devoted to a new mesh refinement method for assessing stress-and-strain concentration (multigrid technique) and a new component for assessing fission product chemical recombination. [ABSTRACT FROM AUTHOR]

Background: Measurement of exposure to the dust mite allergen Der p 1 is important in asthma research and is potentially useful in managing asthma. As no single measure can capture all characteristics of an exposure, it is important to recognize differences in the available methods of measuring exposure to Der p 1. Methods: Fourteen bedrooms and living rooms were sampled using four methods for 1 week. Airborne allergen was sampled by static Institute of Occupational Medicine samplers. Settling dust was collected on Petri dishes and an adhesive–membrane system (A-book). Vacuumed reservoir dust samples were collected from floors at the end of 1 week. Der p 1 was measured in all samples by enzyme-linked immunosorbent assay, except A-books, in which it was measured by Halogen immunoassay. Results: All four methods intercorrelated moderately (r range = 0.40–0.64, P = 0.04), except between allergen in reservoir dust (as μ g/m2 and μ g/g dust) and settling dust by Petri dishes (P = 0.2). Reservoir allergen, expressed as μ g/m2 , did not correlate with any measure, except reservoir allergen expressed as μ g/g (r = 0.39, P = 0.04). No differences in these associations occurred between bedrooms and living rooms. Conclusions: While the four methods examined correlated moderately, all have practical advantages and difficulties. No method can be considered as ideal for measuring individual exposure. For practicality, use of vacuum cleaner and Petri dish methods are recommended. [ABSTRACT FROM AUTHOR]

During irradiation in a nuclear reactor, the UO2 fuel and the Zr cladding come into contact due to fuel thermal expansion and cladding creep. The inner surface of the Zr cladding in contact with the UO2 fuel therefore oxidizes. This paper analyzes the microstructure of zirconia formed at the Zr cladding/UO2 interface in two samples with different burnups. It seems that the zirconia develops 'normally' until it comes into contact with the fuel. The development of internal zirconia is, however, constrained mechanically by the contact of the UO2 fuel. Four different zones can be distinguished in the zirconia layer of each sample. In the medium-burnup sample (37 GWd/tU), the zirconia in the first zone in contact with the cladding exhibits the same kind of microstructure as 'ordinary' zirconium oxide formed on the cladding outer surface, which is characterized by columnar and equiaxed grains. Thereafter, two intermediate zones can be observed: a first composed of very small equiaxed grains and a second with a mixture of intermediate and large grains. In the high-burnup sample (61 GWd/tU), zirconia presents a wavy interface with some circumvolutions. The ZrO2 in contact with the fuel is more developed in this case than in the medium-burnup sample, but it shows the same microstructure. [ABSTRACT FROM AUTHOR]

• Fission products implanted in zirconia layer at the fuel-cladding interface. • Morphology of the fission product agglomerates. • Chemical analysis of fission product agglomerates. • Fission products distribution within zirconia layer at the fuel-cladding interface. During irradiation in light water reactors, numerous fission products are produced by the fission reactions. At the periphery of the fuel, these elements implant by recoil in the cladding inner oxide layer (zirconia) located at the fuel-cladding interface. In the present study, two irradiated UO 2 fuel rods with different burnups (37.3 and 61.4 GWd/tU) have been analyzed. The coupling of FIB-SEM tomography and S/TEM-EDS chemical analyses allowed 3D analysis of the distribution, sizes, shape and chemical composition of the bubbles and precipitates of fission products in zirconia. The fission product structure, observed in the two samples was quite similar. A complex morphology of the fission product agglomerates have been highlighted. They are organized in three parts: the bubble (Xe), the deposit (Cs, I) and the metallic precipitates (Mo, Tc, Ru, Rh, Pd, Sn). Tellurium is partly found with the deposit, but also with the metallic precipitates. Different kind of bubbles have been observed, classified by size, potentially linked to different steps of growth. In particular, Xe form bubbles arranged in three populations: sub and/or nanobubbles within the grains and along the grain boundaries (< 1 nm), larger bubbles (a few nanometers to a few tens of nanometers) anchored to the metallic precipitates, and finally, much larger bubbles (several tens to several hundreds of nanometers), which are part of more complex systems, and are also stuck to metallic precipitates. [ABSTRACT FROM AUTHOR]

• Mechanical characterization of the fuel-cladding interface by nanoindentation. • Hardness and Young's modulus measurements in the fuel-cladding interface. • SEM characterization of grain size and shape in the fuel-cladding interface. • Correlation between microstructure, phases and mechanical properties. During irradiation in a nuclear reactor, the fuel swelling and the cladding creep are at the origin of the contact between the fuel and the cladding, which in turn leads to the initiation of Zr oxidation by the UO 2 fuel. In high burnup fuels, the zirconia layer formed at the Fuel Cladding Interface (FCI) presents numerous circumvolutions and a heterogeneous microstructure within its thickness. In this paper, nanoindentation measurements are carried out in the fuel-cladding interface of a PWR fuel rod irradiated up to a high burnup of 61 GWd/tU. The measured hardnesses and Young's moduli of the internal zirconia layer are compared to reference measurements obtained on a non-irradiated sample of commercial Y-TZP. The study of the evolution of mechanical properties across the zirconia layer led to the identification of four distinct zones related to the zirconia microstructure (phase, grain size, porosity and fission product recoil). Close to the cladding, the zirconia hardness H Zr O 2 tends toward the zirconium hardness H Zr. Then, the zirconia hardness increases significantly with the grain size, until reaching a plateau at the middle of the zirconia layer, where the maximum hardness is obtained. Following the same trend, the elastic modulus progressively increases in the zirconia layer and reaches a plateau near the fuel High Burnup Structure. [ABSTRACT FROM AUTHOR]

Abstract: The behavior of advanced cladding materials under challenging conditions needs to be fully characterized, understood and modeled. This paper assesses the current predictability of fuel performance codes under loadings expected from pellet–clad mechanical interactions. A set of scenarios experimentally characterized within the SCIP project, were chosen so that a variety of materials and ramp power sequences could be examined. Four codes have been used in this study: ALCYONE V1.1, FALCON-PSI, FRAPCON-3 v3.3 and STAV7.3. Their predictions have been compared to data in terms of cladding oxidation, diameters and elongation. Predictability of clad oxidation was certainly scattered and while some codes showed reasonable accuracy, other results were notably deviated. As for diameters, most of the codes were capable of qualitatively capturing the axial profile, and showed consistency between diameters and hoop stress and strain predictions. Elongation estimates were generally poor, and were rather far from measurements in most cases (even the trends observed just vaguely followed by the codes). The results reported have been discussed in the light of the set of individual hypotheses and approximations made by modelers and codes regarding both boundary conditions (i.e., power histories, inlet coolant temperature, refabrication, etc.) and fuel and clad characterization (i.e., densification, rim porosity, materials properties, etc.). Additionally, code-to-code comparisons of some key variables (i.e., fuel temperature, contact pressure, hoop and axial stresses, etc.) highlighted systematic tendencies of the codes and supported the observations made. [Copyright &y& Elsevier]

The problem of porous media submitted to high temperature is of high interest. In this paper, we propose to approach the phenomena taking place in a heated medium using the nonsaturated reactive porous media theory. We describe the material microstructure with a porosymmetric curve taking into account the effects of dehydration put in evidence by experimental studies. This paper focuses on an application of a simplified version of the model to an axisymmetrical structure under thermal load. A quasi-analytical model under simplified hypothesis is established. The various steps of calculation are detailed. Results of finite volumes calculi are then presented, showing the fields evolution. [Copyright &y& Elsevier]

Summary Background : The eradication of Helicobacter pylori decreases the antisecretory activity of omeprazole and lansoprazole. Rabeprazole is a potent proton pump inhibitor that may not be affected as greatly by H. pylori status. Aim : To compare the effect of H. pylori eradication on intragastric acidity and plasma gastrin during dosing with lansoprazole, omeprazole, rabeprazole and placebo. Methods : Twenty-four healthy H. pylori -infected volunteers were studied on day 7 of dosing with placebo, lansoprazole 30 mg, omeprazole 20 mg and rabeprazole 20 mg, before and at least 5 weeks after H. pylori eradication. On each occasion, the 24-h intragastric acidity was measured by gastric aspiration. Plasma gastrin concentrations were measured hourly from 08.00 to 13.00 h. Results : Sixteen subjects completed the study. For all three drugs and placebo, H. pylori eradication increased intragastric acidity, particularly nocturnal acidity, and decreased plasma gastrin. There were no differences between the three drugs with respect to 24-h acidity, percentage of time pH > 4 or 5-h plasma gastrin, either before or after H. pylori eradication. Before eradication, the percentage nocturnal time at pH > 3 was significantly greater during rabeprazole than during lanso-prazole dosing. Conclusions : The increase in intragastric acidity seen after H. pylori eradication during dosing with proton pump inhibitors is a drug–class effect, particularly affecting nocturnal acid control. This is related to increased spontaneous intragastric acidity after H. pylori eradication. [ABSTRACT FROM AUTHOR]

The investigation on the behaviour of nuclear fuels under thermal loads representative of RIA (Reactivity Initiated Accident) conditions in nuclear reactors is a significant challenge. In this work we introduce a new concept of a laboratory experiment relying on high power lasers to reproduce the temperature gradients experienced by nuclear fuel pellets during such events. The concept is experimentally demonstrated on UO 2 samples, supported with numerical simulations to estimate the temperature gradients within the samples. This is a first step in the perspective of applying the technique on irradiated fuels. [ABSTRACT FROM AUTHOR]