It is known that the typical six equation two-fluid model of the two-phase flow possesses complex characteristics, exhibits unbounded instabilities in the short-wavelength limit and constitutes an ill-posed initial value problem Among the suggestions to overcome these difficulties, one model for the virtual mass force terms were studied here, because the virtual mass represents real physical effects to accomplish the dissipation for numerical stability It was found that the virtual mass has a profound effect upon the mathematical characteristic and numerical stability Here a quantitative bound on the coefficient of the virtual mass terms was suggested for mathematical hyperbolicity and numerical stability It was concluded that the finite difference scheme with the virtual mass model is restricted only by the convective stability conditions with the above suggested value

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The effect of virtual mass on the characteristics and the numerical stability in two-phase flow

The High-Performance Light Water Reactor (HPLWR) is the European version of the Supercritical-pressure Water Cooled Reactor (SCWR). Light water reactors at supercritical pressure, being currently under design, are the new generation of nuclear reactors. The present article is a thermal–hydraulic analysis of the HPLWR fuel assembly cluster. The existing thermal hydraulic codes are not capable of analyzing and designing the HPLWR fuel assembly. It is necessary to introduce a new thermal–hydraulic code that can incorporate the parameters and specifications of the HPLWR fuel assembly. The governing equations include energy, mass and momentum equations beside thermal–hydraulic equations are solved numerically using the finite volume (upwind) method. The recent thermal–hydraulic code will be coupled with netronic code to yield a complete analysis of the HPLWR fuel assembly cluster.

Thermal–hydraulic analysis of HPLWR fuel assembly cluster

In this study the thermal-hydraulic analysis of the SCWR reactor with a new geometric design is discussed. In the new design, coolant and moderator circuits are separated and nanofluid has been used as coolant of the reactor core. In the performed sub-channel analysis, the conservation equations of mass, momentum and energy are solved numerically. Since in the new geometry the coolant and moderator circuits are separated, compared to previous plans, using the nanofluids with higher mass fraction of nanoparticles is applicable. In this article, the thermal-hydraulic analysis is performed for various mass fractions of Al2O3 nanoparticle and moderator velocities. Calculations show that the core outlet temperature grows up with increasing nanoparticle mass fraction. As it was expected, by increasing the nanoparticle mass fraction the core pressure drop will be raised, but in the proposed design this pressure drop is much lower.

Thermal-hydraulic analysis of a novel design super critical water reactor with Al2O3 nanofluid as a coolant

PWR accident conditions and analysis methods have been reviewed. Limitations of the simplified method with respect to analysis of these accident conditions are drawn and two transients ( loss of coolant flow, seized rotor) identified as candidates for analysis by this method. These transients have been examined in detail by this one-stage approach (the simplified method). It is concluded that the steady state one-stage simplified method can be applied to the above two transient conditions.

Transient thermal analysis of PWR’s by a single-pass procedure using a simplified nodal layout

The comparison of available data with analytical predictions has been illustrated in this report. Since few data on the cross flow are available, a study of parameters in the transverse momentum equation was performed to assess the sensitivity of results to their assumed values. It is confirmed that effects of these parameters on the overall results are not significant under PWR operating conditions. Data on subchannel properties of quality and mass flux were also assessed. From the data comparisons, it is evident that COBRA can successfully predict the PWR normal operating conditions but cannot predict the trend under bulk quality conditions (X sub e >0.02).

N. Todreas

Papers

The comparison of available data on PWR assembly thermal behavior with analytical predictions. Topical report (final)