No abstract

In this study, RELAP5’s capability to simulate thermal stratification under different conditions is assessed. In nuclear power plants (NPPs), thermal stratification can occur in the following locations: pressurizer, piping systems such as hot legs, cold legs, surge lines, and cooling tanks if available. In general, thermal stratification in a horizontal pipe could not be simulated by RELAP5 due to the inherent one-dimensional setting. Moreover, RELAP5 failed to simulate turbulent penetration which was often a pre-requisite prior to thermal stratification in a pipe. This type of situation could arise in connection between hot leg and surge line, spray lines, feed water lines, etc. It is recommended that for this type of problem CFD be used. In the literature, it was found that RELAP5 was capable of simulating thermal stratification in a pool or a tank-like component if multiple channels and crossflow junctions were used. However, due to uncertainties associated with the input model, the current RELAP5 model failed to reproduce experimental data and therefore further investigation would be required to identify the sources of error.

No abstract

\bfA \bfb \bfs \bft \bfr \bfa \bfc \bft. This paper presents an isogeometric (IGA) solver for steady-state incompressible magnetohydrodynamics (MHD). MHD is the study of the behavior of electrically conducting fluids and can be viewed mathematically as a coupled system: the Navier-Stokes equations (for the fluid) and a reduced form of Maxwell's equations (for the electromagnetic field). A key feature of MHD flow is the potential development of very strong shear, usually in proximity to walls. This results in two correlated demands on numerical simulation: the need to represent the geometry and the near-wall shear accurately. In addition, for both the Navier-Stokes and the Maxwell's equations, appropriate discretizations are required for the problem to be well-posed. IGA analysis is a variant of the conventional finite element (FE) method, but utilizing the underlying approximations commonly used in computer-aided design (CAD) to represent geometry, basis functions, and test functions. As a result, IGA can represent curved shapes such as circles and conic sections exactly using Bsplines and nonuniform rational B-splines (NURBS). Furthermore, IGA can obtain much improved accuracy in the computed solution, for a given number of degrees of freedom, due to its inherent smoothness and higher continuity of basis functions when compared with standard FE and finite volume (FV) methods. To address the issue of well-posedness, a set of stable IGA discretizations for the Navier-Stokes and Maxwell's equations is developed and incorporated into the IGA solver. A detailed convergence study is carried out to verify the convergence, accuracy, and performance of the IGA scheme for certain benchmark cases. \bfK \bfe \bfy \bfw \bfo \bfr \bfd \bfs. isogeometric, incompressible, steady-state, MHD \bfA \bfM \bfS \bfs \bfu \bfb \bfj \bfe \bfc \bft \bfc \bfl \bfa \bfs \bfs \bfi fi\bfc \bfa \bft \bfi \bfo \bfn \bfs. 76W05, 65N30