14 research outputs found
Congruent band structures in 154Gd : Configuration-dependent pairing, a double vacuum and lack of -vibrations
Recommended from our members
In-vessel phenomena -- CORA
Experiment-specific models have been employed since 1986 by Oak Ridge National Laboratory (ORNL) severe accident analysis programs for the purpose of boiling water reactor experimental planning and optimum interpretation of experimental results. The large integral tests performed to date, which start from an initial undamaged core state, have involved significantly different-from-prototypic boundary and experimental conditions because of either normal facility limitations or specific experimental constraints. These experiments (ACRR: DF-4, NRU: FLHT-6, and CORA) were designed to obtain specific phenomenological information such as the degradation and interaction of prototypic components and the effects on melt progression of control-blade materials and channel boxes. Applications of ORNL models specific to the KfK CORA-16 and CORA-17 experiments are discussed and significant findings from the experimental analyses such as the following are presented: applicability of available Zircaloy oxidation kinetics correlations; influence of cladding strain on Zircaloy oxidation; influence of spacer grids on the structural heatup; and the impact of treating the gaseous coolant as a gray interacting medium. The experiment-specific models supplement and support the systems-level accident analysis codes. They allow the analyst to accurately quantify the observed experimental phenomena and to compensate for the effect of known uncertainties. They provide a basis for the efficient development of new models for phenomena that are currently not modeled (such as material interactions). They can provide validated phenomenological models (from the results of the experiments) as candidates for incorporation in the systems-level whole-core'' codes
Recommended from our members
Optimization of transport in stellarators
Here we relate two stellarator transport optimization schemes to single particle orbits. We also show that reducing transport in the 1/..nu.. regime reduces transport over a much broader range of collisionality. 6 refs., 2 figs
Recommended from our members
Three-dimensional free boundary calculations using a spectral Green's function method
The plasma energy W/sub p/ = integral ..cap omega../sub p/(1/2B/sup 2/ + p)dV is minimized over a toroidal domain ..cap omega../sub p/ using an inverse representation for the cylindrical coordinates R = ..sigma..R/sub mn/(s)cos(mtheta - n zeta) and Z = ..sigma..Z/sub mn/(s)sin(mtheta - n zeta), where (s,theta,zeta) are radial, poloidal, and toroidal flux coordinates, respectively. The radial resolution of the MHD equations is significantly improved by separating R and Z into contributions from even and odd poloidal harmonics which are individually analytic near the magnetic axis. A free boundary equilibrium results when ..cap omega../sub p/ is varied to make the total pressure 1/2B/sup 2/ + p continuous at the plasma surface ..sigma../sub p/ and when the vacuum magnetic field B/sub ..nu../ satisfies the Neumann condition B/sub ..nu../ x d..sigma../sub p/ = 0. The vacuum field is decomposed as B/sub ..nu../ = B/sub 0/ + del Phi, where B/sub 0/ is the field arising from plasma currents and external coils and Phi is a single-valued potential necessary to satisfy B/sub ..nu../ x d..sigma../sub p/ = 0 when p not equal to 0. A Green's function method is used to obtain an integral equation over ..sigma../sub p/ for the scalar magnetic potential Phi = ..sigma..Phi/sub mn/sin(mtheta - n zeta). A linear matrix equation is solved for Phi/sub mn/ to determine 1/2 B/sub ..nu..//sup 2/ on the boundary. Real experimental conditions are simulated by keeping the external and net plasma currents constant during the iteration. Applications to l = 2 stellarator equilibria are presented
Recommended from our members
Numerical computations of transport coefficients for nonsymmetric plasmas
The linearized drift kinetic equation is solved numerically to obtain the Onsager transport matrix for a three-dimensional toroidal plasma confinement geometry. Local transport coefficients relating the cross-field fluxes to the thermodynamic forces are computed as continuous functions of the collision frequency. In particular, in the low-collision-frequency regime (..nu.. < ..omega../sub b/), the transport resulting from the nonconservation of the longitudinal adiabatic invariant J (due to particle transitions from helically trapped to toroidally trapped) is obtained. The boundary layer in velocity space resulting from these transition particles can be accurately treated using a Legendre polynomial representation for the pitch angle dependence of the distribution function. Magnetic coordinates are used so that finite-beta effects are included. The disparity in the time scales between collisionless particle orbits and collisional dynamics is treated efficiently to obtain steady-state fluxes and viscosity coefficients. This yields significant improvements in the precision and computational effort in comparison with Monte Carlo methods. The effect of a radial electric field in the ..nu.. < ..omega../sub D/ regime is studied. Applications to Advanced Transition Facility (ATF) and heliac configurations are given
Recommended from our members
Low-aspect-ratio optimization studies for ATF-II
A numerical procedure for optimizing stellarator MHD and transport properties at finite ..beta.. is described. This method is applied to finding a low-aspect-ratio ATF-II configuration. 4 refs., 6 figs