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Passive autocatalytic recombiners (PARs) are being used in most modern nuclear power plants (NPPs) for mitigating the hydrogen risk both in normal and accidental scenarios. Development of a systematic model of PARs based on computational fluid dynamics (CFD) is the subject of this paper. 2D simulations of AREVA (a nuclear technology company) recombiner have been performed to validate PARs data and then the developed methodology has been applied to a Chashma NPP-II (C-2) recombiners to assess their performance. Two cases have been discussed; one with constant velocity at inlet and other one is devoted to the startup response of the PAR. Within the recombiner, the hydrogen and oxygen recombine on catalytic plates surface by an exothermic reaction to produce steam. Reaction heat is dissipated among the plates, surroundings and air inside the PAR. Flow inside the PAR will continue downwards until the gas absorbs enough heat to become lighter in weight than the gas outside the PAR. In addition, hydrogen accumulation in containment dome of a C-2 has been modeled and the results have been compared with methods for estimation of leakages and consequences of releases (melcor) code results. Without PARs, hydrogen got buildup within the containment dome, but when PARs are activated, hydrogen concentration first started to rise until the recombination reaction activated at about ∼2% hydrogen concentration. The comparison shows that the results obtained by the model agree well with the melcor results.

Purpose – The purpose of this paper is to present a numerical solution for the problem of steady laminar flow and heat transfer characteristics of viscous incompressible fluid. Design/methodology/approach – For this purpose a two dimensional code has been developed to simulate the natural convection heat transfer along a vertical cylinder, for four different geometries: from vertical cylinder in infinite medium; from a vertical flat plate in an infinite medium; from an open assembly of a finite vertical cylinder; and from an open rectangular pitch assembly of cylinders. Findings – The effects of various parameters of interest have been discussed through simulations. The Nusselt numbers of constant wall temperature and constant heat flux cylinders calculated numerically and compared with Lee et al. and Heckel et al., respectively, and are found within reasonable agreement. For large radius, a vertical cylinder has been treated as a vertical flat plate, so that the curvature effects become negligible. For the case of vertical flat plate, Nusselt number has been compared with analytical relation for the local Nusselt number given by Jaluria. Practical implications – The natural convection has been studied for four different geometries: the flow regime in all the case studies has been assumed to be Laminar. Originality/value – Computer code developed for current study can be applied to many other geometries to simulate natural convection heat transfer. [ABSTRACT FROM AUTHOR]

This research presents a numerical study of deposition efficiency and decontamination factor of the radioactive nuclide in steam generator tubes of a typical 325 MWel pressurized water reactor (PWR). To find out the deposition of aerosol, the discrete phase model (DPM) has been used. The flow has been characterized as compressible, adiabatic, turbulent and wall-bounded. When steam generator tube gets ruptured, the radioactive nuclides can escape from primary side and create a radioactive field on the secondary side. This can be harmful at the personnel working at the plant. Therefore, in order to ensure the safety of the plant and personnel, it is important to study the particles deposition on the wall of steam generator tubes. In the present study, a computational fluid dynamics (CFD) methodology has been first developed and validated with the published results. After methodology validation, it has been applied to the U-tube of a typical PWR steam generator. It has been observed that due to the action of centrifugal force near the bent, the velocity magnitude is high toward the inner wall and the flow separates at the bent entrance. Furthermore, the flow inside the tube is rotational with vortices throughout the domain due to the presence of the bent. Finally, the deposition efficiency and decontamination factor have been calculated and it has been observed that both increase with the increase in particle size due to inertial effects.