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AbstractThis 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 UO2fuel 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−1up 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.

AbstractThis 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.

AbstractThis paper presents 2D(r,$\it \theta $θ) simulations of the HBC-4 power-to-melt experiment performed with the fuel performance code ALCYONE. The HBC-4 experiment is one of the two test cases selected for the simulation exercise on past fuel melting experiments of the Power to Melt and Maneuverability (P2M) project. The ramp terminal level (RTL) at peak power node (PPN) has been estimated at 66 kW·m−1by gamma scanning and 70 kW·m−1based on online measurements of thermal fluxes. The fuel burnup at PPN was close to 60 GWd/tU−1. The cladding failed during the short holding time at a RTL of 40 s. Fuel melting took place at the pellet center, and in particular, in front of clad cracks.In this paper, simulations of the HBC-4 power-to-melt experiment are performed using an updated version of the 2D(r,$\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.

AbstractTo 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].

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.

This paper discusses the algorithmic formulation of chemoplastic models with internal couplings. Developed within the framework of closed reactive porous continua, chemoplasticity allows for the introduction of the kinetics of a chemical reaction directly at the macro-level of material description. The resulting couplings (chemoelastic, chemoplastic) slightly complicate the integration of stresses at the material level, leading to chemoplastic hardening1pt/softening. In this paper, the numerical integration of stresses for this type of constitutive laws with chemomechanical (internal) couplings is presented. Based on the definition of return mapping algorithms for standard plasticity, a closest-point projection algorithm is developed, which preserves the quadratic rate of convergence of the Newton–Raphson iterative scheme. Examples are presented with an increasing degree of complexity: perfectly plastic behaviour with chemical hardening for concrete at early ages, coupled creep-plastic behaviour, plastic behaviour with combined viscoplastic hardening1pt/softening for concrete in high-rate dynamics. Copyright © 2000 John Wiley & Sons, Ltd.

Background: Dual therapy with ranitidine bismuth citrate plus clarithromycin twice daily for 14 days is an effective regimen for eradicating Helicobacter pylori infection.

Background: Dual therapy with ranitidine bismuth citrate plus clarithromycin twice daily for 14 days is an effective regimen for eradicating Helicobacter pylori infection.

The aim of this study was to identify and eradicate H. pyloriinfection in patients with haemophilia. Patients were screened for IgG antibodies against H. pylori; active infection was determined using a 13C‐urea breath test and infected patients were given combination therapy with antibiotics to eradicate infection. Seventy‐eight of 219 (36%) patients with haemophilia were found to have an elevated serum antibody titre against H. pylori; of 36 antibody‐positive patients with confirmatory testing, 14 were found to have active H. pyloriinfection. H. pyloriinfection was successfully eradicated in every infectedpatient using acombination of ranitidine plus two antibiotics (usually amoxycillin and metronidazole). It is concluded that eradication of H. pyloriinfection is likely to be a cost‐effective screening strategy in patients with haemophilia, to prevent complications of peptic ulcer disease.