CATHARE simulation results of the natural circulation characterisation test of the PKL test facility

Salah, Anis Bousbia Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.5

In the past, several experimental investigations aiming at characterizing the natural circulation (NC) behavior in test facilities were carried out. They showed a variety of flow patterns characterized by an inverted U-shape of the NC flow curve versus primary mass inventory. On the other hand, attempts to reproduce such curves using thermal-hydraulic system codes, showed 10-30% differences between the measured and calculated NC mass flow rate. Actually, the used computer codes are generally based upon nodalization using single U-tube representation. Such model may not allow getting accurate simulation of most of the NC phenomena occurring during such tests (like flow redistribution and flow reversal in some SG U-tubes). Simulations based on multi-U-tubes model, showed better agreement with the overall behavior, but remain unable to predict NC phenomena taking place in the steam generator (SG) during the experiment. In the current study, the CATHARE code is considered in order to assess a NC characterization test performed in the four loops PKL facility. For this purpose, four different SG nodalizations including, single and multi-U-tubes, 1D and 3D SG inlet/outlet zones are considered. In general, it is shown that the 1D and 3D models exhibit similar prediction results up to a certain point of the rising part of the inverted U-shape of the NC flow curve. After that, the results bifurcate with, on the one hand, a tendency of the 1D models to over-predict the measured NC mass flow rate and on the other hand, a tendency of the 3D models to under-predict the NC flow rate.

Assessment of CATHARE code against DEC-A upper head SBLOCA experiments

Bousbia Salah Anis 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.3

Design Extension Conditions (DEC)-A assessments of the operating nuclear power plants are generally considered for the purpose of getting additional safety demonstrations of their capability to undergo conditions that are generally more severe than DBAs by features implemented in the design and accident management measures. The pursued methodology is generally based upon Best Estimate approaches aiming at verifying that the safety limits in terms of integrity of the barriers against eventual large or early releases of radioactive material are fulfilled. These aspects are nowadays being experimentally and analytically addressed within the OECD/NEA experimental projects like the ATLAS and PKL series where a set of DEC-A experiments are considered. In this paper, experiments related to SBLOCA at the vessel upper head of the pressurized vessel of ATLAS and PKL are analytically assessed using the CATHARE code. These experiments includes issues related to common cause failure of the safety injection system and operator actions for preventing core excessive overheating. It is shown that, on the one hand, the safety features embedded in the design together with the operator actions are capable to prevent the progression towards a severe accident state and on the other hand, the code prediction capabilities for such scenario are generally good but still to be enhanced.

Unsteady Single-Phase Natural Circulation Flow Mixing Prediction Using CATHARE Three-Dimensional Capabilities

Anis Bousbia Salah,Jacques Vlassenbroeck 한국원자력학회 2017 Nuclear Engineering and Technology Vol.49 No.3

Coolant mixing under natural circulation flow regime constitutes a key parameter that mayplay a role in the course of an accidental transient in a nuclear pressurized water reactor. This issue has motivated some experimental investigations carried out within the OECD/NEA PKL projects. The aim was to assess the coolant mixing phenomenon in the reactorpressure vessel downcomer and the core lower plenum under several asymmetric steadyand unsteady flow conditions, and to provide experimental data for code validations. Formerstudies addressed the mixing phenomenon using, on the one hand, one-dimensionalcomputational approaches with cross flows that are not fully validated under transientconditions and, on the other hand, expensive computational fluid dynamic tools thatare not always justified for large-scale macroscopic phenomena. In the current framework,an unsteady coolant mixing experiment carried out in the Rossendorf coolant mixingtest facility is simulated using the three-dimensional porous media capabilities ofthe thermalehydraulic system CATHARE code. The current study allows highlighting thecurrent capabilities of these codes and their suitability for reproducing the main phenomenaoccurring during asymmetric transient natural circulation mixing conditions.

STATE OF THE ART IN USING BEST ESTIMATECALCULATION TOOLS IN NUCLEAR TECHNOLOGY

FRANCESCO D'AURIA, ANIS BOUSBIA-SALAH, ALESSANDRO PETRUZZI, ALESSANDRO DEL NEVO 한국원자력학회 2006 Nuclear Engineering and Technology Vol.38 No.1

Numerical modeling of two parallel tunnels interaction using three-dimensional Finite Elements Method

Nawel, Bousbia,Salah, Messast Techno-Press 2015 Geomechanics & engineering Vol.9 No.6

Due to the extension of communication ways (metro, highways, railways), hence, to improve traffic flow imposes often the difficult crossing that generally drive to the construction of underground works (tunnel, water conveyance tunnel...) plays a major role in the redevelopment of urban areas. This study is focused on the assessment of the interaction response of parallel tunnels, so this study uses the results from the simulation of two tunnels to illustrate a few observations that may aid in practical designs. In this article, simultaneous drilling of highway's twin tunnels is simulated by means of Finite Element Method (FEM) implemented in Plaxis program. So the treated subject appears in a setting of geotechnical where one can be to construct several tunnels sometimes in a ground of weak mechanical characteristics. The objective of this study is to simulate numerically the interaction effects caused by construction of two parallels tunnels. This is an important factor in the study of the total answer of the problem interaction between parallels underground works. The importance of the effects transmitted is function of several parameters as the type of the works, and the mechanical characteristics (tunnel size, depth, and the relative position between two tunnels, lining thickness...). This article describes numerical analyses of two parallels tunnels interaction. This study will be applied to a real case of a section tunnel T4 of the highway East-West (Algeria); the study presented below comprises a series of numerical simulations of two tunnels using the computer program Plaxis which is used in the analyses is based on Finite Element Method.

Comparative study of CFD and 3D thermal-hydraulic system codes in predicting natural convection and thermal stratification phenomena in an experimental facility

Graževičius Audrius,Bousbia-Salah Anis 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.4

Natural circulation phenomena have been nowadays largely revisited aiming to investigate the performances of passive safety systems in carrying-out heat removal under accidental conditions. For this purpose, assessment studies using CFD (Computational Fluid Dynamics) and also 3D thermal-hydraulic system codes are considered at different levels of the design and safety demonstration issues. However, these tools have not being extensively validated for specific natural circulation flow regimes involving flow mixing, temperature stratification, flow recirculation and instabilities. In the present study, an experimental test case based on a small-scale pool test rig experiment performed by Korea Atomic Energy Research Institute, is considered for code-to-code and code-toexperimental data comparison. The test simulation is carried out using the FLUENT and the 3D thermal-hydraulic system CATHARE-2 codes. The objective is to evaluate and compare their prediction capabilities with respect to the test conditions of the experiment. It was observed that, notwithstanding their numerical and modelling differences, similar agreement results are obtained. Nevertheless, additional investigations efforts are still needed for a better representation of the considered phenomena.

STATE OF THE ART IN USING BEST ESTIMATE CALCULATION TOOLS IN NUCLEAR TECHNOLOGY

D'AURIA FRANCESCO,ANIS BOUSBIA-SALAH,PETRUZZI ALESSANDRO,NEVO ALESSANDRO DEL Korean Nuclear Society 2006 Nuclear Engineering and Technology Vol.38 No.1

System thermal-hydraulic codes have been used in the past decades in the areas of design, operation, licensing and safety of Nuclear Power Plants (NPPs). The development and validation of these codes have reached a high degree of maturity, through the consideration of huge experiments and advanced numerical models. Nowadays, the analyses are based upon realistic approaches rather than the conservative evaluation models. However the applications of these computational tools require preliminary qualification issues. Although huge amounts of financial and human resources have been invested for the development and improvement of codes, the calculation results are still affected by errors. In the sophisticated nuclear technology, design and safety of NPP, these errors must be quantified. An overview of the state of the art of the current thermal-hydraulic system code is developed and the need of uncertainty analysis in code calculations is emphasized. Several sources of uncertainty have been classified and commented, and typical applications of such methods are shown.