Platelet count, spleen length, and platelet count-to-spleen length ratio for the diagnosis of oesophageal varices in people with chronic liver disease or portal vein thrombosis

Background: Current guidelines recommend screening of people with oesophageal varices via oesophago-gastro-duodenoscopy at the time of diagnosis of hepatic cirrhosis. This requires that people repeatedly undergo unpleasant invasive procedures with their attendant risks, although half of these people have no identifiable oesophageal varices 10 years after the initial diagnosis of cirrhosis. Platelet count, spleen length, and platelet count-to-spleen length ratio are non-invasive tests proposed as triage tests for the diagnosis of oesophageal varices. Objectives: Primary objectives To determine the diagnostic accuracy of platelet count, spleen length, and platelet count-to-spleen length ratio for the diagnosis of oesophageal varices of any size in paediatric or adult patients with chronic liver disease or portal vein thrombosis, irrespective of aetiology. To investigate the accuracy of these non-invasive tests as triage or replacement of oesophago-gastro-duodenoscopy. Secondary objectives To compare the diagnostic accuracy of these same tests for the diagnosis of high-risk oesophageal varices in paediatric or adult patients with chronic liver disease or portal vein thrombosis, irrespective of aetiology. We aimed to perform pair-wise comparisons between the three index tests, while considering predefined cut-off values. We investigated sources of heterogeneity. Search methods: The Cochrane Hepato-Biliary Group Controlled Trials Register, the Cochrane Hepato-Biliary Group Diagnostic Test Accuracy Studies Register, the Cochrane Library, MEDLINE (OvidSP), Embase (OvidSP), and Science Citation Index - Expanded (Web of Science) (14 June 2016). We applied no language or document-type restrictions. Selection criteria: Studies evaluating the diagnostic accuracy of platelet count, spleen length, and platelet count-to-spleen length ratio for the diagnosis of oesophageal varices via oesophago-gastro-duodenoscopy as the reference standard in children or adults of any age with chronic liver disease or portal vein thrombosis, who did not have variceal bleeding. Data collection and analysis: Standard Cochrane methods as outlined in the Cochrane Handbook for Diagnostic Test of Accuracy Reviews. Main results: We included 71 studies, 67 of which enrolled only adults and four only children. All included studies were cross-sectional and were undertaken at a tertiary care centre. Eight studies reported study results in abstracts or letters. We considered all but one of the included studies to be at high risk of bias. We had major concerns about defining the cut-off value for the three index tests; most included studies derived the best cut-off values a posteriori, thus overestimating accuracy; 16 studies were designed to validate the 909 (n/mm3)/mm cut-off value for platelet count-to-spleen length ratio. Enrolment of participants was not consecutive in six studies and was unclear in 31 studies. Thirty-four studies assessed enrolment consecutively. Eleven studies excluded some included participants from the analyses, and in only one study, the time interval between index tests and the reference standard was longer than three months. Diagnosis of varices of any size. Platelet count showed sensitivity of 0.71 (95% confidence interval (CI) 0.63 to 0.77) and specificity of 0.80 (95% CI 0.69 to 0.88) (cut-off value of around 150,000/mm3 from 140,000 to 150,000/mm3; 10 studies, 2054 participants). When examining potential sources of heterogeneity, we found that of all predefined factors, only aetiology had a role: studies including participants with chronic hepatitis C reported different results when compared with studies including participants with mixed aetiologies (P = 0.036). Spleen length showed sensitivity of 0.85 (95% CI 0.75 to 0.91) and specificity of 0.54 (95% CI 0.46 to 0.62) (cut-off values of around 110 mm, from 110 to 112.5 mm; 13 studies, 1489 participants). Summary estimates for detection of varices of any size showed sensitivity of 0.93 (95% CI 0.83 to 0.97) and specificity of 0.84 (95% CI 0.75 0.91) in 17 studies, and 2637 participants had a cut-off value for platelet count-to-spleen length ratio of 909 (n/mm3)/mm. We found no effect of predefined sources of heterogeneity. An overall indirect comparison of the HSROCs of the three index tests showed that platelet count-to-spleen length ratio was the most accurate index test when compared with platelet count (P 909 (n/mm3)/mm, the presence of oesophageal varices of any size can be excluded and only 7% of adults with varices of any size would be missed, allowing investigators to spare the number of oesophago-gastro-duodenoscopy examinations. This test is not accurate enough for identification of oesophageal varices at high risk of bleeding that require primary prophylaxis. Future studies should assess the diagnostic accuracy of this test in specific subgroups of patients, as well as its ability to predict variceal bleeding. New non-invasive tests should be examined

Baffle jetting modelling

International audienceHorizontal flow in the lower part of the reactor pressure vessel was found responsible for the so-called baffle jets impinging in the direction almost perpendicular to the nuclear fuel rods axes. This flow may generate flow-induced vibrations of the fuel rods that can damage the rods.As opposed to the flow-induced vibrations in a purely cross-flow situation, as in the case of e.g. heat exchanger tubes, the flow direction in the bottom part of the core barrel is of a combined axial and cross flow nature. One of peculiarities of the baffle jet and fuel rods interaction is the vicinity of the solid walls of the core barrel; also, the velocity profile impacting onto the fuel rods is non-uniform.The present study aims to further investigate the nature of flow field in the geometry relevant to the baffle jetting in the pressurized water reactors (PWRs). A separate effect study is conducted in order to assess the ability of a number of turbulent models to predict the complicated flow field in the case of baffle jets. Conclusions were drawn for the models’ ability to predict both the time-average and the transient, spectral, characteristics of the flow.An experimental program PANACHET was employed in CEA, France, for the study of baffle jetting. Flow velocity was measured for the conditions mimicking the flow field in the bottom periphery part of the core barrel. The PANACHET experiments were simulated using the models validated in the separate effects study

CFD analysis and experimental validation of steady state mixed convection Sodium flow

International audienceFormation and destruction of thermal stratification can occur under certain flow conditions in the upper plenum of sodium cooled fast breeder reactors (SFR). The flow patterns in the hot sodium pool of SFR upper plenum are very complex and include zones of free and wall-bounded jets, recirculation and stagnation areas. The interaction of sodium flow and thermal stratification has been analyzed experimentally at CEA in the SUPERCAVNA facility. The facility consists of a rectangular cavity with heated side walls. The flow is driven by a wall-bounded cold jet at the bottom of the cavity. Experimental data of the temperature distribution inside the cavity are available for steady-state and transient flow conditions. In the present study, the steady state experiments are analyzed with the CEA CFD reference code TrioCFD and the commercial code FLUENT employing Reynolds Averaged Navier-Stokes (RANS) equations. The SUPERCAVNA modeling is based on preliminary separate effects’ studies of wall-bounded jets and free convection benchmark simulations for low Prandtl number fluids.It was found that a two-dimensional treatment is sufficient to reproduce correctly the measured thermal stratification for steady-state SUPERCAVNA experiments. However, it is necessary to take into account conjugated heat transfer between cavity sodium flow and side-wall heating channel. Using temperature-dependent physical properties was also found to be an important factor in simulating the experiments correctly. Applying the Boussinesq approximation to study the impact of buoyancy on the vertical flow momentum was found to be justified. Turbulence modelling is necessary for a successful simulation of the experiments. For practical reasons, the analysis was restricted to turbulence models of the k-ε family. High Re k-ε models, in either standard, realizable or RNG formulations, do not lead to significant differences in the calculated temperature fields. Non-linear eddy viscosity modelling might improve the quality of the simulation

Nozzle Geometry Effect on Stratified Layer Erosion by Vertical Turbulent Jet

International audienceKnowledge of the nuclear power plants (NPPs) containment atmosphere composition in the course of a severe accident is crucial for the effective design and positioning of the hydrogen explosion countermeasures. This composition strongly depends on containment flows which may include turbulent jet mixing in the presence of buoyancy, jet impingement onto the stratified layer, stable stratification layer erosion, steam condensation on the walls of the containment, condensation by emergency spray systems and other processes. Thus, in modeling of containment flows, it is essential to correctly predict these effects. In particular, a proper prediction of the turbulent jet behavior before it reaches the stably stratified layer is critical for the correct prediction of its mixing and impingement. Accordingly, validation study is presented for free neutral and buoyancy-affected turbulent jets, based on well-known experimental results from the literature. This study allows for the choice of a proper turbulence model to be applied for containment flow simulations. Furthermore, the jet behavior strongly depends on the issuing geometry. A comparative study of erosion process for the conditions similar to the ones of international benchmark exercise (IBE-3) is presented for different jet nozzle shapes

CFD analysis and experimental validation of mixed convection sodium flow

National audienceFormation and destruction of thermal stratification can occur under certain flow conditions in the upper plenum of sodium cooled fast breeder reactors (SFR). The flow patterns in the hot sodium pool of the upper plenum are very complex, including zones of free and wall-bounded jets, recirculation and stagnation areas. The interaction of the sodium flow and thermal stratification has been analyzed experimentally at CEA in the years 1980-1990 in the SUPERCAVNA facility. The facility consists of a rectangular cavity with temperature-controlled heated walls where the flow is driven by a wall-bounded cold jet at the bottom of the cavity. Experimental data of the temperature distribution in the cavity are available for steady-state and transient flow conditions. The experiments are analyzed with the CEA CFD reference code TrioCFD and the commercial code FLUENT by using Reynolds Averaged Navier-Stokes (RANS) equations. It is shown that a two-dimensional treatment is sufficient for the analysis of steady-state SUPERCAVNA experiments. It is necessary to take into account correctly the conjugate heat transfer between walls and cavity. Turbulence modelling with $k$-$\epsilon$ models, in either standard, realizable or RNG formulations, does not lead to significant differences in the calculated temperature fields which are in good accordance to the measurements. Different wall treatments also do not change these results. Thus, it seems that turbulence modelling is not a predominant factor in a successful simulation of the mixed convection experiments. However, using temperature-dependent physical properties is a very important factor in simulating the experiments correctly, although the Boussinesq approximation is justified. Finally, it is shown that a three-dimensional treatment is necessary for the analysis of transient experiments

Nuclear reactor containment flows - Modelling of stably stratified layer erosion by a turbulent jet

International audienceA number of international benchmarks were devoted to revealing the capability of CFD codes to predict the temporal evolution of the concentration and velocity fields of the nuclear reactor containment atmosphere in the course of severe accidents. In the most recent OECD/NEA international benchmark exercise on containment flows, a stably-stratified helium-air layer was eroded by a free turbulent jet coming from below. Velocity and helium concentration fields were measured in the course of the experiment. The results of the benchmark have shown that a correct prediction of the temporal development of the concentration field does not necessarily mean that the velocity field was resolved accurately as well. This can suggest that a wrongly predicted velocity field can compensate an erroneously modeled mass transport, still leading to a relatively correct concentration field.This work examines numerically the temporal evolution of the velocity and concentration fields for the conditions of an international benchmark exercise on containment flows performed in PANDA facility at PSI, Switzerland. A number of preliminary separate effect studies are performed on the way to choosing the final modeling scheme. It is shown that $k$-$\omega$ SST models significantly overestimate the mixing rates, whereas the standard $k$-$\epsilon$ model overestimates the spreading of the jet and its center-line velocity decay rate. A good compromise seems to be found in modification of the $C_{1 \epsilon}$ constant of the $k$-$\epsilon$ model allowing to simulate erosion of the stratified layer by round jets more reliably

Analysis of Polygonal Vortex Flows in a Cylinder with a Rotating Bottom

The present paper provides a physically sound numerical modeling of liquid flows experimentally observed inside a vertical circular cylinder with a stationary envelope, rotating bottom and open top. In these flows, the resulting vortex depth may be such that the rotating bottom disk becomes partially exposed, and rather peculiar polygon shapes appear. The parameters and features of this work are chosen based on a careful analysis of the literature. Accordingly, the cylinder inner radius is 145 mm and the initial water height is 60 mm. The experiments with bottom disk rotation frequencies of 3.0, 3.4, 4.0 and 4.6 Hz are simulated. The chosen frequency range encompasses the regions of ellipse and triangle shapes as observed in the experimental studies reported in the literature. The free surface flow is expected to be turbulent, with the Reynolds number of O(105). The Large Eddy Simulation (LES) is adopted as the numerical approach, with a localized dynamic Subgrid-Scale Stresses (SGS) model including an energy equation. Since the flow obviously requires a surface tracking or capturing method, a volume-of-fluid (VOF) approach has been chosen based on the findings, where this method provided stable shapes in the ranges of parameters found in the corresponding experiments. Expected ellipse and triangle shapes are revealed and analyzed. A detailed character of the numerical results allows for an in-depth discussion and analysis of the mechanisms and features which accompany the characteristic shapes and their alterations. As a result, a unique insight into the polygon flow structures is provided

Nuclear reactor containment flows–modelling of stratified layer erosion by a wall-deflected jet

International audienceA number of international computational benchmarks were devoted to assessing the capability ofcommercial and in-house Computational Fluid Dynamics (CFD) codes to predict transient evolution of theconcentration and velocity fields of the nuclear power plant containment atmosphere in the course of severeaccidents. In these benchmarks the velocity and concentration fields were measured during the transient.Usually, a vertically directed jet eroded an air-helium mixture stratified layer, set in the top part of theexperimental vessel, which mimics the hydrogen-air mixture in a real life nuclear power plant in the courseof a severe accident. As the jet direction can differ from vertical, the mixing process is anticipated to differfrom the one observed in the preceding benchmarks.The present study focuses on modelling a recent benchmark exercise that was organized and performed inthe MISTRA facility, CEA, Saclay. In this benchmark, a hot air jet impinges horizontally onto a cylindricalcompartment wall. After the impingement, the air flows towards and erodes a stably stratified helium-airmixture set in the top part of the MISTRA vessel.A correct prediction of the integral mixing process relies on modelling of a number of separate flowsituations, including free and buoyant horizontal jets, round jet impingement onto a cylindrical surface, jetto cylinder heat transfer, turbulent erosion in the presence of buoyancy, and more. The present studyincludes validation of the separate flow features versus experimental studies from the literature. Afterfinalizing the modeling approach based on the separate-effect numerical studies, the MISTRA benchmarkexercise is modelled and the computational and measured results are compared