Optimization of CABRI power transients with the SPARTE code and the URANIE uncertainty platform

International audienceIn a Pressurized Water Reactor (PWR), the rod ejection is a design basis accident for uncontrolled evolution of the nuclear reaction.In case of failure of a rod mechanism, the rod ejection is caused by the pressure differential between the primary loop (155 bar) and the confinement-s enclosure (atmospheric pressure).It leads to a local power transient and a fast fuel temperature increase.The power transient is limited by the reactivity feedbacks before the automatic reactor shutdown.The CABRI experimental pulsed reactor is funded by the French Nuclear Safety and Radioprotection Institute (IRSN) and is operated by CEA at the Cadarache research center.It is designed to study fuel rods behavior under Reactivity Initiated Accident (RIA) conditions.The tested fuel rod is placed at the center of the CABRI core, inside a pressurized water loop reproducing PWR conditions.CABRI is a pool type reactor, made of 1487 UO$_2$ fuel rods and controlled by 6 Hafnium control rods.A specific device allows the fast depressurization of $^3$He contained in 4 transient rods to reproduce control rods ejection conditions.Based on a BEPU approach, we developed a tool, named SPARTE, for CABRI power transients calculation.This tool is based on point kinetics, simplified thermal-hydraulics and thermal-mechanics.It computes the global behavior of the core by the calculation of a mean fuel rod. It includes models of reactivity insertion specific to the CABRI transient rods system, variable kinetics parameters and variable Doppler coefficient.This code is validated on the basis of 66 CABRI start-up power transients realized during the first quarter of 2017. One goal of the SPARTE code is to be used for the prediction of future CABRI power transients.This paper focuses on methods for optimizing a specific CABRI power transient (FWHM $\simeq$ 30 ms, Deposited energy $\simeq$ 130 $MJ$) using the target characteristics of the pulse. The selection of a method may help the experimentalists and the operation team to minimize the number of white- power transients to perform before the final test with the fuel sample. The optimization can lead to different results, that can be ranked according to their projected uncertainties. Different optimization methods are tested and compared in this paper. The Subplex method based on reiterations of the Nelder-Mead algorithm (simplex method) was selected for its high precision. Indeed, the CABRI power transients are not completely reproducible and present some uncertainties linked to the test parameters. This article focuses on the uncertainties propagation in order to identify and select the parameters that minimize the output uncertainties. The results are very satisfactory and lead to several optimized scenarios that will be tested during the next qualification test campaign

Pseudomonas aeruginosa Expresses a Functional Human Natriuretic Peptide Receptor Ortholog: Involvement in Biofilm Formation

This is the final version of the article. Available from the publisher via the DOI in this record.Considerable evidence exists that bacteria detect eukaryotic communication molecules and modify their virulence accordingly. In previous studies, it has been demonstrated that the increasingly antibiotic-resistant pathogen Pseudomonas aeruginosa can detect the human hormones brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) at micromolar concentrations. In response, the bacterium modifies its behavior to adapt to the host physiology, increasing its overall virulence. The possibility of identifying the bacterial sensor for these hormones and interfering with this sensing mechanism offers an exciting opportunity to directly affect the infection process. Here, we show that BNP and CNP strongly decrease P. aeruginosa biofilm formation. Isatin, an antagonist of human natriuretic peptide receptors (NPR), prevents this effect. Furthermore, the human NPR-C receptor agonist cANF(4-23) mimics the effects of natriuretic peptides on P. aeruginosa, while sANP, the NPR-A receptor agonist, appears to be weakly active. We show in silico that NPR-C, a preferential CNP receptor, and the P. aeruginosa protein AmiC have similar three-dimensional (3D) structures and that both CNP and isatin bind to AmiC. We demonstrate that CNP acts as an AmiC agonist, enhancing the expression of the ami operon in P. aeruginosa. Binding of CNP and NPR-C agonists to AmiC was confirmed by microscale thermophoresis. Finally, using an amiC mutant strain, we demonstrated that AmiC is essential for CNP effects on biofilm formation. In conclusion, the AmiC bacterial sensor possesses structural and pharmacological profiles similar to those of the human NPR-C receptor and appears to be a bacterial receptor for human hormones that enables P. aeruginosa to modulate biofilm expression. IMPORTANCE: The bacterium Pseudomonas aeruginosa is a highly dangerous opportunist pathogen for immunocompromised hosts, especially cystic fibrosis patients. The sites of P. aeruginosa infection are varied, with predominance in the human lung, in which bacteria are in contact with host molecular messengers such as hormones. The C-type natriuretic peptide (CNP), a hormone produced by lung cells, has been described as a bacterial virulence enhancer. In this study, we showed that the CNP hormone counteracts P. aeruginosa biofilm formation and we identified the bacterial protein AmiC as the sensor involved in the CNP effects. We showed that AmiC could bind specifically CNP. These results show for the first time that a human hormone could be sensed by bacteria through a specific protein, which is an ortholog of the human receptor NPR-C. The bacterium would be able to modify its lifestyle by favoring virulence factor production while reducing biofilm formation.We thank Magalie Barreau and Olivier Maillot for technical assistance. We thank Christine Farmer for linguistic insight for the manuscript. T. Rosay is a recipient of a doctoral fellowship from the French Ministry of Research (MRE). This work was supported by grants from the Communauté d’Agglomération d’Evreux, the Conseil Général de l’Eure, European Union (FEDER no. 31970), the French Association “Vaincre la Mucoviscidose” and the InterReg IVA PeReNE project

Different Dose-Dependent Modes of Action of C-Type Natriuretic Peptide on Pseudomonas aeruginosa Biofilm Formation.

We have previously shown that the C-type Natriuretic Peptide (CNP), a peptide produced by lungs, is able to impact Pseudomonasaeruginosa physiology. In the present work, the effect of CNP at different concentrations on P. aeruginosa biofilm formation was studied and the mechanisms of action of this human hormone on P. aeruginosa were deciphered. CNP was shown to inhibit dynamic biofilm formation in a dose-dependent manner without affecting the bacterial growth at any tested concentrations. The most effective concentrations were 1 and 0.1 µM. At 0.1 µM, the biofilm formation inhibition was fully dependent on the CNP sensor protein AmiC, whereas it was only partially AmiC-dependent at 1 µM, revealing the existence of a second AmiC-independent mode of action of CNP on P. aeruginosa. At 1 µM, CNP reduced both P. aeruginosa adhesion on glass and di-rhamnolipid production and also increased the bacterial membrane fluidity. The various effects of CNP at 1 µM and 0.1 µM on P. aeruginosa shown here should have major consequences to design drugs for biofilm treatment or prevention

Silver nanoparticle embedded copper oxide as an efficient core–shell for the catalytic reduction of 4-nitrophenol and antibacterial activity improvement

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Pseudomonas aeruginosa Biofilm Dispersion by the Human Atrial Natriuretic Peptide

This is the final version. Available on open access from Wiley via the DOI in this recordData Availability Statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.Pseudomonas aeruginosa biofilms cause chronic, antibiotic tolerant infections in wounds and lungs. Numerous recent studies demonstrate that bacteria can detect human communication compounds through specific sensor/receptor tools that modulate bacterial physiology. Consequently, interfering with these mechanisms offers an exciting opportunity to directly affect the infection process. It is shown that the human hormone Atrial Natriuretic Peptide (hANP) both prevents the formation of P. aeruginosa biofilms and strongly disperses established P. aeruginosa biofilms. This hANP action is dose-dependent with a strong effect at low nanomolar concentrations and takes effect in 30-120 min. Furthermore, although hANP has no antimicrobial effect, it acts as an antibiotic adjuvant. hANP enhances the antibiofilm action of antibiotics with diverse modes of action, allowing almost full biofilm eradication. The hANP effect requires the presence of the P. aeruginosa sensor AmiC and the AmiR antiterminator regulator, indicating a specific mode of action. These data establish the activation of the ami pathway as a potential mechanism for P. aeruginosa biofilm dispersion. hANP appears to be devoid of toxicity, does not enhance bacterial pathogenicity, and acts synergistically with antibiotics. These data show that hANP is a promising powerful antibiofilm weapon against established P. aeruginosa biofilms in chronic infections.Normandy RegionFrench Ministry of Research (MRE

Thermal-hydraulic two-phase modeling of reactivity-initiated transients with CATHARE2 – Application to SPERT-IV simulation

International audienceReactivity-Initiated Accidents (RIA) in nuclear reactor cores are very complex multiphysic transients. They consist in a very fast power excursion in the core, leading to wall temperature excursions. Many experiments have shown that the heat exchanges coefficients during fast transients differ from those in steady-states. The thermal-hydraulic phenomenology of such transients remains complex and some experimental studies allowed to better understand and quantify the heat exchanges between the wall and the fluid, for both single and two-phase flows.The current study lies in a continuous effort of developing and validating a coupled neutronic and thermal-hydraulic code for the analysis of protected and unprotected transient behavior of reactors. More specifically, this study deals with the extension of the thermal hydraulic model of the CATHARE2 code to fast transient configurations. The extended CATHARE2 model is validated against experimental results from SPERT-IV. This reactor was driven mainly by the coolant density reactivity feedback. Thanks to that, many flow regimes can be observed in the core during the transient. That allows a more accurate evaluation of the adequacy of available transient two-phase flow models and correlations. The results, that represent the state of modeling, allow concluding that introduced models in CATHARE2 are able to simulate RIA tests such as SPERT-IV involving fast transient boilin

Transient heat exchanges under fast Reactivity-Initiated Accident

International audienceHeat exchanges during fast transient are very complex phenomena. Many studies have been led in this field, trying to quantify the heat exchanges between a heating wall, under fast increasing power, and a coolant. This kind of situation is encountered for instance during RIA (Reactivity-Initiated Accidents) in nuclear reactors, whose characteristics times of wall heat flux excursion can be as low as orders of 1 ms. The CABRI reactor, an experimental pulse reactor funded by the french Institute for Radiological protection and Nuclear Safety (IRSN) and operated by CEA at the Cadarache nuclear center (France), was build in order to study and thus to better understand RIA effects on nuclear fuels. Heat exchanges characterization is definitely one of major points to tackle in the understanding and modeling of such transients, involving single and two phase flows. This paper broaches the question of single phase heat exchanges coefficients during fast transient power excursions in the CABRI reactor. The single phase pure convection is the overlap of two main mechanisms: the advection (wall axial supply in upstream cold water) and the turbulent mixing inside the boundary layer. This latter phenomenon is due to vortices in boundary layers inducing radial mixing through the velocity boundary layer. In most cases involving turbulent flows, the turbulent mixing phenomenon is preponderant. To these mechanisms is added a pure conduction heat exchange mechanism through the thermal boundary layer. Convection and conduction overlap defining a conducto-convective heat transfer coefficient, improperly only called “convection” coefficient. This paper suggests a way to model this coefficient during a CABRI-RIA transient by a non-linear superposition of transient pure conduction and convection mechanisms. Two distinct transient phases are considered; the first one presenting a wall heat flux of exponential shape followed by the second one during which the wall heat flux remains constant. The potency of this analytical model, which is implementable into computational system tools, is demonstrated

Multiphysics CATHARE2 modeling and experimental validation methodology against CABRI transients

International audienceCABRI is an experimental pulse reactor, funded by the french Institute for Radiological protection and Nuclear Safety (IRSN) and operated by CEA at the Cadarache nuclear center, France. Its aim is to study and thus to better understand RIA (Reactivity-Initiated Accident) effects on nuclear fuels. The restart of the CABRI reactor in 2015 offers the opportunity to validate tools involving multiphysic calculation schemes on reactivity insertions (RI) transients at a system scale. Physics of the in-pile CABRI tests is complex and implies various physical fields (solid and fluid thermics, thermal-hydraulics, mechanics and neutronics) and their coupled effects. The reactivity insertion in CABRI is mastered by the depressurization of a neutron absorber (3 He), contained into transient rods. The increase of the neutron flux inside the core induces the neutronic power increase inside the core and a multiphysic effect, called "TOP" effect, inside the in-core transient rods that causes an acceleration of the gas depressurization. The challenge is thus to manage the simulation of these RIA complex transients catching the governing multiphysical phenomena to be identified. In order to achieve this objective, a model for the CABRI transients and a scientific calculation tool have been developed and should be validated. This paper proposes a modeling of governing multiphysic phenomena of RIA transients in CABRI reactor based on a Quantified Phenomena Identification and Ranking Table (QPIRT). These models are introduced in the CATHARE2 tool in a dedicated version named PALANTIR and Best-Estimate simulation results are compared with experimental data obtained on CABRI commission tests: core power and 3 He pressure evolution

Nusselt correlation development in unsteady laminar gas flows for CABRI multiphysic simulations with CATHARE2

International audienceCABRI is an experimental pulse reactor, which aims at studying and thus at better understanding RIA (Reactivity Initiated Accident) effects on nuclear fuels. The restart of the CABRI reactor in 2015 offers the opportunity to validate tools involving multiphysic calculation schemes on reactivity insertions (RI) transients at a system scale. The reactivity insertion in CABRI is mastered by the depressurization of a neutron absorber (3He), contained into transient rods. This enables the realization of various types of transients. As this depressurization highly influences the reactivity insertion kinetics, it is essential to accurately simulate the 3He density evolution which depends on the heat exchanges inside the circuit. The challenge is thus to manage the simulation of the various CABRI complex transients. Previous work allowed to model with CATHARE2 the whole reactor with its specific phenomena as well as phenomena generally involved in RIA, for instance strong neutronic feedback effects, effect of the pellet-clad interaction on the gap conductance and transient heat exchanges between fuel rods and water. These studies also revealed that some CABRI transients were still difficult to model with CATHARE2 and this paper shows the necessity to catch the transient heat exchanges in the transients rods for the simulation of the power pulse in CABRI reactor. In order to achieve this objective, a correlation for the Nusselt evolution in an unsteady compressible laminar 3He flow, inside a closed tube, has been realized from numerical resolution of an analytical model and implemented in the scientific calculation tool CATHARE2. This paper describes this analytical model and its numerical resolution. After having been validated on results of the literature in steady flow inside open tube, the correlation established for the evolution of the Nusselt in a transient rods’ tube is given. Finally, Best-Estimate simulation results of CATHARE2 are compared with experimental data obtained on CABRI commission tests: core power and 3He pressure evolutio