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The safety analysis of an industrial installation is extensively based on modeling and simulation. However, the analysis of simulation using realistic computer codes like RELAP5/Mod3.2 will help understand thermal-hydraulic behavior of an installation during normal and accidental conditions. In a steam boiler operation, it is very important to evaluate numerous accident scenarios under real plant conditions. One of the main accidental transients is tube rupture of steam boiler. The main objective of this study consists toinvestigate the behavior of an industrial steam boiler installed in the complex of natural gas liquefaction (LNG) at Skikda in Algeria during feed water line break accident. A RELAP5 model was set up to simulate the entire system, the model represents all steam boiler components to be suitable for the analysis of the several accidents. The control and regulation systems are also considered. The model was qualified against the steam boiler data at steady-state conditions. As seen from the results, a good agreement was obtained. The transient simulation results show that the thermal-hydraulic code correctly predicts the behavior of the main steam boiler parameters and how the control system, when required, can successfully mitigate the accident.

The use of CFD for the industrial studies related to PTS, including DCC is already possible; improvements of the two-phase modeling capabilities have to be undertaken to qualify the codes for the simulation of such flows. The DCC in horizontally stratified flow regime constitutes very considerable challenge exercises for a computational fluid dynamics (CFD) simulation of the thermal hydraulics PTS phenomenon because the interplay between turbulence and interfacial heat and mass transfer problem. The main purpose of our study is to investigate numerically the DCC in horizontally stratified steam water flow in a 2D and 3D channel using TransAT CMFD code. The new methodology known as Large-Eddy & Interface (LEIS) have been implemented for treatment of turbulence combined with interface tracking ITM (level set approach). Among of the so-called ‘coarse-grained’ ITM's models, the modified original surface divergence has been chosen as well as the treatment of the turbulence by URANS and VLES. This contribution addressed on the validation of interfacial phase-change heat transfer and turbulence models with special correction of the damping function at the free surface for single and combined-effect thermal hydraulic studies for LIM and KAERI & KAIST test facilities. The LIES methodology was found to apply successfully to predict the condensing steam flow rate in the all cases of the LIM test case involving a Smooth to Wavy turbulent, concurrent stratified steam-water flow in a 2D channel. The CMFD TransAT code predicting capability is analyzed, comparing the liquid temperature and to much the velocity profile of KAERI & KAIST Countercurrent Stratified Flow (CCSF) combined-effect in 2D and 3D geometry to one predicted by analytical Biberg model. The vertical profiles of CFD local water velocity calculations have been corrected using AKN free surface damping model where the agreement with KAERI & KAIST data is sufficiently good. The KAERI & KAIST test case is actually more challenging than all low subcooling cases (COSI, TOPFLOW) where the application of the ASD model (and the other interfacial DCC models) for high subcooling (Δ T sub ∼ 70.0° K) is still questionable. A modified ASD model should be implemented, to taking into account the effect of the degree of the water subcooling through the introduction of the Jakob number.