Fabrication and Repair of Ion Source Components in the 80 keV Neutral Beam Lines for DIII-D

OAK-B135 After 8 years of operation, leaks began to develop in critical components of the ion sources of the 80 keV neutral beam lines in DIII-D. Operational adjustments were made that seemed to remedy the problems, but five years later leaks began occurring again, this time with greater frequency. Failures occurred in the stainless steel bellows and molybdenum rails of the grid rail modules as well as in the Langmuir probes. Failure analyses identified several root causes of the leaks and operational adjustments were again made to mitigate the problems, but the rash of failures depleted the program's supply of spare grid rail modules and probes and removed one of the ion sources from regular operation. Fifteen years after their original fabrication, the ion source components were no longer commercially available. In 2001, a program was initiated to fabricate new grid rail modules, including new molybdenum grid rails, bellows, and stainless steel grid rail holders, as well as new Langmuir probes. In parallel, components removed from service due to leaks were to be repaired with new rails and bellows and returned to service. An overview of the root causes of the service failures is offered, details of the repair processes are described, and a summary and evaluation of the fabrication procedures for the new molybdenum rails, grid modules, and Langmuir probes are given

MUTURING ECRF TECHNOLOGY FOR PLASMA CONTROL

OAK A271 MUTURING ECRF TECHNOLOGY FOR PLASMA CONTROL. Understanding of the physics of internal transport barriers (ITBs) is being furthered by analysis and comparisons of experimental data from many different tokamaks worldwide. An international database consisting of scalar and 2-D profile data for ITB plasmas is being developed to determine the requirements for the formation and sustainment of ITBs and to perform tests of theory-based transport models in an effort to improve the predictive capability of the models. Analysis using the database indicates that: (a) the power required to form ITBs decreases with increased negative magnetic shear of the target plasma, and: (b) the E x B flow shear rate is close to the linear growth rate of the ITG modes at the time of barrier formation when compared for several fusion devices. Tests of several transport models (JETTO, Weiland model) using the 2-D profile data indicate that there is only limited agreement between the model predictions and the experimental results for the range of plasma conditions examined for the different devices (DIII-D, JET, JT-60U). Gyrokinetic stability analysis (using the GKS code) of the ITB discharges from these devices indicates that the ITG/TEM growth rates decrease with increased negative magnetic shear and that the E x B shear rate is comparable to the linear growth rates at the location of the ITB

Sub-channel CFD for nuclear fuel bundles

This paper presents a novel Computational Fluid Dynamics (CFD)-based sub-channel framework for nuclear power plants, which combines the advantageous features of modern CFD and traditional 1-D sub-channel codes. The new method is capable of producing CFD-level 3-D results with locally desirable refinement when coupled with embedded resolved models, but because a very coarse mesh is used over most part of the domain, the computing cost is typically significantly smaller than that of a conventional CFD simulation. In this new sub-channel CFD (SubChCFD), a dual-mesh system is used, comprising, (i) a filtering mesh which aligns with the mesh used in typical sub-channel codes, enabling the use of existing engineering correlations to account for integral wall friction and heat transfer effects, and (ii) a computing mesh, which provides a platform for the solution of the governing equations with turbulence modelled using a mixing-length-type model. The method has been implemented in an open-source finite volume CFD code Code_Saturne and validated initially using a 5 × 5 bare bundle case based on the OECD/NEA MATiS-H benchmarking experiment. It has been found that SubChCFD is able of satisfactorily predicting both the velocity and temperature fields. To further investigate the performance for complex flow conditions, SubChCFD was applied to two full 3-D cases. The first is a 5 × 5 rod bundle case with local blockage in one of the sub-channels, creating significant localised cross flows. The second is a two-parallel-assembly channel with different input mass flow rates at the inlet of each assembly, allowing strong inter-assembly mixing. For both cases, SubChCFD has produced results which agree well with experiments and simulations using resolved CFD. It has also been demonstrated that SubChCFD exhibits excellent flexibility in comparison with traditional sub-channel codes and that it has the potential to serve as a substitution to sub-channel codes