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The effects of nanoprecipitations on the mechanical properties of Al-Zn-Mg-Cu alloys after GBF (gas bubbling filtration) and EMS (electromagnetic stirring) casting were investigated. Dendritic cell structures were formed after GBF processing, while globular dendritic structures were nucleated after EMS processing. Equiaxed cell sizes were smaller in the EMS-processed specimens compared to the GBF-processed specimens, confirmed by EBSD (electron backscatter diffraction) analysis. Nanoprecipitations of η′ phases inside of dendrites were observed by TEM (transmission electron microscope), and other Fe-bearing compounds were located in the dendritic boundaries. The yield strength of the T4 and T6 heat-treated specimens was close to 400 MPa and 500 MPa, respectively. Fractographic analysis was performed to investigate the effect of precipitations on tensile fracture.

This paper proposes a nonlinear model for more accurate and efficient dynamic analysis of a rotating cantilever beam with elastic deformation. The proposed nonlinear model is described by partial integro-differential equations with non-Cartesian deformation variables, i.e., the stretch, chordwise and flapwise deformations. After the equations of motion are discretized by using the mode superposition method, dynamic responses are computed by applying the Newmark time integration method to the discretized equations. To show the accuracy and efficiency of the proposed model, convergence characteristics and dynamic responses for the present model are compared with those for previous models. This study shows that the proposed model not only yields good accuracy and efficiency in terms of computation, but also overcomes the limitations of a previous conventional nonlinear model expressed by Cartesian variables.

SMART is a small sized integral type pressurized water reactor and its design minimizes the potential for an occurrence of transients and accidents. To achieve these purposes, engineered safety features enhance the accident resistance. A large volume of semi-passive pressurizer can accommodate a wide range of pressure transients. Low core power density increases the thermal margin, and negative fuel and moderator temperature coefficients yield beneficial effects on a core self-stabilization, and limit the reactor power during accidents. Considering the enhanced engineered safety features and design characteristics, anticipated transient without scram scenarios are adopted to evaluate the strength of the SMART design. The peak pressure does not exceed 116% of the nominal pressure and the fuel can maintain its integrity for the transient. The intrinsic SMART design characteristics having passive safety features and a large primary coolant inventory can maintain a stable condition safely although the reactor protection and diverse protection systems are not available for the anticipated transient without scram transients.

CUPID-SG (CUPID code for Steam Generators) is a computer code for analyzing two-phase flows and heat transfer in PWR steam generators. It was derived from CUPID (Component Unstructured Program for Interfacial Dynamics), which is a component-scale thermo-hydraulic analysis code developed at KAERI (Korea Atomic Energy Research Institute). CUPID-SG shares the code structure with CUPID, which adopts two-fluid, three-field conservation equations, and semi-implicit numerical algorithms. CUPID-SG supports unstructured meshes to handle complex geometries, and adopts constitutive models of two-fluid model based system analysis codes for two-phase boiling flows. FRIGG tests are the benchmark in confirming the correct implementation of the transport models and the applicability of CUPID-SG to two-phase flows over heated tube bundles. A comparison with the FRIGG experiments showed that the constitutive models are properly implemented, and that CUPID-SG is capable of analyzing vertical two-phase boiling flows over tube bundles typically appearing in steam generators.

The CUPID code has been developed at KAERI for a transient, three-dimensional analysis of a two-phase flow in light water nuclear reactor components. It can provide both a component-scale and a CFD-scale simulation by using a porous media or an open media model for a two-phase flow. In this paper, recent advances in the CUPID code are presented in three sections. First, the domain decomposition parallel method implemented in the CUPID code is described with the parallel efficiency test for multiple processors. Then, the coupling of CUPID-MARS via heat structure is introduced, where CUPID has been coupled with a system-scale thermal-hydraulics code, MARS, through the heat structure. The coupled code has been applied to a multi-scale thermal-hydraulic analysis of a pool mixing test. Finally, CUPID-SG is developed for analyzing two-phase flows in PWR steam generators. Physical models and validation results of CUPID-SG are discussed.

A heat transfer test facility, SPHINX, which uses carbon dioxide as a medium at supercritical pressures, has been built at KAERI. A series of experiments are under way for various geometries including tubes of several diameters and narrow annulus passages of a concentric and eccentric layout. The experiments aim to collect heat transfer data and to provide an empirical heat transfer correlation required for a SCWR design. In this paper the test results for tubes of 4.4 mm and 9.0 mm IDs, and a concentric annular passage (ϕ8 mm × ϕ10 mm × L1800 mm) are presented for certain combinations of the heat fluxes and mass fluxes. The heat transfer coefficients produced in the tests were compared with those from the existing heat transfer correlations with different media. A new correlation was introduced for the experiment data presented in this paper.