H.J. Ahn

Engineering design status of the KSTAR TF coil structure

The toroidal field (TF) magnet system of Korea Superconducting Tokamak Advanced Research (KSTAR) device consists of 16 superconducting coils enclosed in steel cases. The TF cases are wedged along the inboard straight legs to sustain in-plane centering forces. The inter-coil structures contain adjustable shear keys and conical bolts to provide pre-loading in toroidal direction and to resist in-plane and out-of-plane forces, which are the most critical loads on the TF magnet system. For effective cooling of the TF case, a pad-type cooling channel has been designed to ensure structural and thermal stability. In order to investigate the structural integrity and to increase the structural reliability of the KSTAR magnet system, structural analyses have been conducted. From the analysis results, it has been found that the TF magnet structure can safely withstand the reference scenario operations.

Engineering design status of the KSTAR central solenoid structure

The central solenoid (CS) magnet system of the Korea Superconducting Tokamak Advanced Research (KSTAR) device consists of four pairs of segmented CS coils and a CS coil structure. The maximum repulsive force between CS coils is about 12 MN. The functions of the CS structure are to apply preload on the CS coils and to support the repulsive force between CS coils during operation. The designed axial compression of 15 MN at 4.5 K will be applied partly by assembling the preload structure at room temperature with preload of about 13.4 MN and partly by the thermal contraction difference between the CS coils and the structure during cool down. Additional preload will be given by minute adjustment of wedges. The structural analysis of the CS magnet system has been performed to verify the CS structure design reliability.

Electromagnetic loads on the KSTAR magnet system

Several types of Lorenz forces and Joule heating generated in the magnet system of the Korea Superconducting Tokamak Advanced Research (KSTAR) device have been studied numerically and analytically. We have examined 225 plasma equilibrium states to calculate the maximum magnetic forces and to determine which equilibrium state(s) generate such forces. The obtained results are used as input for structural analysis. A precompression should be applied to the eight-segmented central solenoid (CS) coil assembly to prevent free motion of each coil due to attractive and repulsive forces during operation. We have also evaluated the maximum values of the vertical and lateral forces for each of the CS coils and poloidal field coils and also for the entire CS coil stack. The in-plane force due to toroidal field (TF) coil charging and the out-of-plane force due to interaction of the TF coil current with the poloidal field have been computed. The Joule heating on the TF structure due to plasma disruption has also been calculated.

Thermo-Hydraulic Performance Analysis for Conceptual Design of ITER Blanket Shield Block

Abstract Since the recommendation of blanket redesign by 2007 ITER design review, the blanket system has been developed in the framework of blanket integrated product team composed mainly of ITER organization and procuring parties. As a part of blanket conceptual design tasks, Korea domestic agency has supported the design analyses with respect to the hydraulic and thermal performance of the inboard blanket shield block. Three dimensional thermo-hydraulic and thermo-mechanical analyses of the inboard conceptual model with the poloidal cooling concept were performed. Two kinds of operation scenarios, inductive and non-inductive operations, were considered as representative loading conditions. The pressure drop, heat transfer and coolant uniformity in cooling passages were investigated in detail. The stress evaluation according to relevant code and standard was carried out and thermal bowing at flexible supports was also investigated. This paper presents the detailed analysis results, identifies issues on the conceptual configuration and makes suggestions on design improvements. In addition, this manuscript briefly describes about the complementary study such as the comparison of heat transfer coefficients calculated by empirical formula and CFD, and the effect of surface roughness inside the cooling channels.

Structural analysis of the KSTAR toroidal field magnet system

The toroidal field (TF) magnet system of Korea superconducting tokamak advanced research (KSTAR) device consists of 16 superconducting coils enclosed in the steel cases. The TF magnet structure protects the winding pack from mechanical, electrical, and thermal loads, and also supports three pairs of poloidal field (PF) coils as well as four pairs of central solenoid (CS) coils. A three-dimensional finite element (FE) model including the winding pack, insulation and filler material has been developed using solid brick elements, and a hybrid model with beam-shell elements has been also built for the verification purposes. The structural reliability of the TF magnet system is investigated by performing various analyzes such as a global/local analysis, a detailed analysis, and a fatigue evaluation. The results reveal that the maximum stress intensities of the TF magnet structure are below the allowable stress limit and its fatigue life complies with the requirements of the design criteria, so it can safely withstand the reference scenario operations. In addition, the design loads obtained from analysis results can be used for the detailed structural design of other supplementary components.

R&D Activities Regarding ITER Blanket First Wall in Korea

Abstract Korea Domestic Agency (KO-DA) was responsible for the procurement of the ITER blanket modules 1, 2, and 6 in the original procurement allocation. According to the procurement reallocation of the blanket system, Korea will procure the blanket shield block in place of the blanket first wall. Nevertheless, several R&D activities in Korea have been performed including optimization of the hot isostatic pressing (HIP) bonding process between Be/CuCrZr and CuCrZr/SS, the nondestructive test method, fabrication feasibility study, high heat flux tests, and design analysis. Especially, KO-DA participated in the qualification program for the mock-up manufacture and high heat flux tests. Several mock-ups were fabricated and tested during the qualification program. The details of the mock-up manufacture and test results are described in this paper. Also, two heat flux facilities were installed based on the graphite heating, and a new electron beam heat flux facility will be built in the near future for the enhanced heat flux mock-up test. As well, some design analysis was performed to investigate the performance of the blanket first wall against thermo-mechanical loading. In this paper, the status of the R&D activities and the results of the qualification tests for KO mock-ups are reviewed.

Design and analysis of poloidal field magnet structures for KSTAR

The poloidal field magnet system of the KSTAR consists of three pairs of coils using the cable-in-conduit conductors cooled by forced super-critical helium. The conductor of PF5 is Nb/sub 3/Sn superconductor with Incoloy 908 conduit, and that of PF6 and PF7 is NbTi superconductor with SS 316LN. The PF coils are self-supporting with regard to radial loads, and they are arranged symmetrically with respect to the equatorial plane. PF5 coil is connected to the TF coil structure at eight points by hinges, while PF6 and PF7 coils are connected at sixteen points by flexible plates to allow relative radial movements. In order to investigate the structural integrity, structural analysis has been conducted including buckling and fatigue analyses. The major design loads are dead weight, assembly loads, thermal load due to cool down, and electromagnetic loads under the critical load conditions. It is found that the PF magnet structures can safely withstand all operating conditions. In addition, AISI 316LN can be substituted for JJ1 as the material of the PF coil structures.

Design overview of the KSTAR magnet structures

The magnet structure system of the Korea Superconducting Tokamak Advanced Research (KSTAR) device consists of 16-segmented toroidal field (TF) coil structures encasing each D-shaped TF coil, a central solenoid (CS) structure surrounding 4 pairs of CS coils, modular poloidal field (PF) coil structures supporting each PF coil in 8 or 16 places, and a gravity support. The engineering design of the magnet structures has been conducted with related electromagnetic load calculations and structural analyses for various operation scenarios. A prototype TF coil structure will be fabricated to check the manufacturing feasibility. A prototype magnet supporting post has been fabricated and tested at 80 K up to 15,000 cycles of vertical load under 80 tons. In addition to the magnet structure development, winding and heat treatment of a real-sized prototype TF coil have been finished without any defect such as SAGBO. The fabrication of the coil will be completed by the middle of 2002. As an interface of the magnet system, a cryogenic facility and a current feeder system have been designed.

Structural design and analysis for the KSTAR cryostat

The KSTAR cryostat is a 8.8 m diameter vacuum vessel that provides the necessary thermal barrier between the ambient temperature test cell and the supercritical helium cooled superconducting magnet providing the base pressure of 1/spl times/10/sup -5/ torr. The cryostat is a single walled vessel consisting of central cylindrical section and two end closures, a flat base structure with external reinforcements and a dome-shaped lid structure. The base structure has 8 equally spaced support legs anchored on the concrete base. The cryostat vessel design was executed to satisfy the performance and operation requirements. The mechanical penetration components with bellows were designed to restrict the displacements of all kinds of ports due to EM loads and thermal loads within the allowable limits. The major loads considered in this paper for the design of cryostat vessel are the vacuum pressure, the dead weight of vacuum vessel, PFC, and magnet which are total about 400 tons, the electromagnetic load driven by plasma disruption, and seismic loads. Based on these loads, structural analyses were performed. It was found that the maximum stress intensity was below the allowable limit, and that the cryostat vessel had buckling safety of over 5. Based on the results, structural robustness of the cryostat vessel has been proved.

Status of Design and R&D for ITER Blanket in Korea

Abstract Since the decision of blanket redesign by 2007 ITER design review, the blanket system is being developed in the framework of Blanket Integrated Product Team (BIPT) composed mainly of ITER Organization (IO) and procuring parties. Korean Domestic Agency (KODA) is mainly contributing to the design and development of blanket Shield Block (SB). In particular, KODA is supporting the design activities including electromagnetic, thermo-hydraulic and thermo-mechanical analyses to complete the final design of blanket shield block. For the manufacturing of a blanket shield block conventional fabrication techniques based on drilling, milling and welding of stainless steel forged blocks have been adopted. As a consequence of the manufacturing feasibility study, key fabrication techniques to be verified beforehand have been identified and successfully developed in collaboration with related industries. The pre-qualification program of the fabrication and testing of Full Scale Prototype (FSP) is in progress. Until now the material development of 316L(N)-IG stainless steel forging has been successfully completed, and the fabrication of FSP is on-going. Even though the procurement of blanket First Wall (FW) was withdrawn at the 9th meeting of the ITER Management Advisory Committee, the participation of the 2nd pre-qualification program of EHF (Enhanced Heat Flux) FW small scale mock is being valid for securing core engineering technologies. At present the fabricated mock-ups are waiting for high heat flux test with the Electron Beam (EB) gun test facility being newly built in Korea. This paper provides the current status of design and relevant R&D activities of the blanket system to secure key technologies and to fulfill our promise to ITER project.