H. Fillunger

Mechanical behavior of the ITER TF model coil ground insulation system after reactor irradiation

Abstract The mechanical properties of glass fiber reinforced plastics (GFRPs) suggested for the turn and ground insulation of the ITER toroidal field (TF) coils are subject to extensive investigations with respect to their design requirements at present. The insulation system used for the ITER TF model coil, manufactured by European industry, consists of a boron-free R-glass fiber reinforced tape, vacuum-pressure impregnated in a DGEBA epoxy system and partly interleaved with polyimide-foils (e.g. Kapton-H-foils). In order to assess the material performance under the actual operating conditions of ITER-FEAT, the system was irradiated in the TRIGA reactor (Vienna, Austria) to neutron fluences of 5×1021 and 1×1022 m−2 (E>0.1 MeV). The composite was screened at 77 K using static tensile, short-beam-shear (SBS) as well as double-lap-shear tests prior to and after irradiation. Furthermore, tension–tension fatigue measurements were done in order to simulate the pulsed ITER-FEAT operation. We observe that the mechanical strength and the fracture behavior of these GFRPs after irradiation are strongly influenced by the three factors: the winding direction of the tape, the quality of fabrication and the delamination process.

Dual channel cable in conduit thermohydraulics: Influence of some design parameters

In the framework of the controlled nuclear fusion by magnetic confinement programme, a particular design of a Cable-in-Conduit Conductor (CICC) is being developed, including two parallel cooling channels. The central channel is separated from the strand channel by a spiral structure whose geometry can substantially influence the overall pressure drop. The thermo-hydraulics of this so called dual channel CICC is not well known. Hence various experiments with pressurised nitrogen at room temperature, on straight and curved unit lengths from the ITER toroidal field model coil (TFMC) production, have been performed at both Ansaldo and CEA-Cadarache to characterise the friction factor of the two parallel cooling regions, in a range of representative Reynolds numbers. These experimental results are presented. It has been possible to characterise different kinds of spiral geometries used in the manufacture of the two model coils for ITER: the TFMC and the Central Solenoid Model Coil. A relative assessment of the most suitable spiral for the ITER magnets is presented. This discussion includes: (i) manufacturing aspects with the capability of the spiral to support the cabling process as a function of the geometry of the spiral and the compaction of the cable; (ii) pressure drop considerations, as a function of the spiral geometry which plays an important role in the cooling process and the required cold pump power. Conclusions and recommendations are drawn.

Calculations of pressure drop and mass flow distribution in the toroidal field model coil of the ITER project

Abstract In preparation of the ITER FEAT project, a superconducting toroidal field model coil (TFMC) including 10 parallel pancakes of between 72.2 and 82.0 m long cable-in-conduit conductor (CICC) has been built and has to be tested at FZK. A series of preliminary tests were performed at room temperature and in nitrogen at both CEA-Cadarache and Ansaldo. The tests aimed to assess the thermohydraulics of this coil and specifically to address the pressure drop and the friction factor of the dual channel CICC in a range of Reynolds numbers relevant to the TFMC. These measurements are compared with the predictions which include a hydraulic description of the joint region whose contribution to the total pressure drop is non-negligible. The mass flow distribution between the bundle region and the central channel will be calculated for the cable as well as for the joint region. Measurements on the central solenoid model coil (first layer of inner module and insert coil) in normal operating conditions with supercritical helium are presented. They are in good agreement with the calculations performed from the previously validated correlations. A description of the mass flow imbalance between the TFMC pancakes at low temperatures in helium is done. The major influence of the central spiral is confirmed, since two types of spirals have been included in the TFMC pancakes. This distribution varies as a function of the total mass flow of the analysed hydraulic circuits (TF and CS) of ITER–FEAT.

Paschen Testing on W7-X Coils and Components in the BNN Test Facility

During the fabrication of the coils for the Wendelstein 7-X experiment the need for pressure dependent high voltage testing-Paschen tests-of the coils and components arose. These tests ensure the safety of the coils in case of an emergency shutdown due to a break in the vacuum of the cryostat. For that purpose the vacuum test facility at Babcock Noell Nuclear was modified in order to perform these tests. It is now possible to test coils and their components up to 17 kV and for pressures below 1.0middot10-3 mbar. Completed coils, winding packs before insertion in the case and also several components have been tested up to now. It has been demonstrated that these Paschen tests are a powerful tool to detect insulation defects. The paper shows the effort which has been taken to set up the test facilities. It will show the preparation of the components under testing as well as present and discuss the results obtained up to now

Influence of reactor irradiation on the mechanical behavior of ITER TF coil candidate insulation systems

Extensive material tests have to be performed in order to obtain information on the radiation induced change in the mechanical behavior of insulating materials for the ITER Toroidal Field (TF) coil. The investigated insulation systems are R-glass fiber reinforced tapes, vacuum impregnated with a DGEBA epoxy resin and interleafed with Kapton H-foils. According to the actual operating conditions of ITER-FEAT, the systems were irradiated in the TRIGA reactor (Vienna, Austria) to neutron fluences of 5 × 10 21 and 1 x 10 22 m -2 (E > 0.1 MeV). Static tensile, short-beam-shear (SBS) as well as double-lap-shear (DLS) tests were carried out at 77 K prior to and after irradiation. Furthermore, results on swelling and weight loss as well as on the material properties under tension- tension fatigue loading conditions are presented.

Irradiation and mechanical testing of ITER relevant magnet insulation

In the scope of ITER Engineering Design Activities (EDA) the European Home Team performs an irradiation test program on industrially fabricated specimens of magnet insulation. At the unique test facility available at the research reactor of the Technical University of Munich, the shear compression test samples were irradiated at 5 K and tested without warming up. The samples, provided by Japanese, US and European industry, were fabricated using different types of epoxy resin, but the same boron-free glass fabrics inter-leafed with Kapton foil. The results are presented and assessed. The Munich test facility is no longer available. A complementary test program carried out at the research reactor of the Atomic Institute in Vienna will form the basis of future irradiation work. It is focused on the assessment of intrinsic material parameters and takes advantage of a new fatigue testing machine allowing operation at 77 K. Links to the Munich program were made by irradiating identical samples in both reactors (at 5 K in Munich and at ambient temperature in Vienna). Special sample geometry was developed and scaled versus standards for tensile and inter-laminar shear testing under cyclic load. Results on the static and dynamic properties are presented.

Assembly in the test facility, acceptance and first test results of the ITER TF model coil

As a joint European effort an ITER Toroidal Field Model Coil (TFMC) was manufactured in industry and has been assembled in the TOSKA test facility of the Forschungszentrum Karlsruhe. After cool down and acceptance tests of the racetrack shaped coil made of a Nb/sub 3/Sn cable in conduit conductor the first test campaign started in July 2001 reaching the design current of 80 kA within one week. This paper describes the assembly in the test facility, summarizes the acceptance tests before and after cool down, and reports on the first test results.

Innovative insulation systems for superconducting fusion magnets

Glass fibre reinforced plastics (GFRPs) are usually employed as insulating materials for the superconducting coils of large fusion magnets, e.g. of the International Thermonuclear Experimental Reactor (ITER). Both the radiation spectrum and the stresse sa t the magnet location significantly influence the mechanical behaviour of the magnet insulation and, therefore, impose high demands on the materia lp erformance. During the last few decades, advanced epoxy based GFRPs with improved mechanical properties and radiation hardness were introduced into fusion technology. More recently, cyanate ester (CE) matrix systems have become of special interest. In this paper, various magnet insulation systems containing boron-free R-glass fibre reinforcements in commercial and new epoxies as well as in pure CE and CE/epoxy blended matrix systems are presented. All systems were irradiated in a fission reactor at ambient temperature (∼340 K) to a fast neutron fluence of 1 × 10 22 m −2 (E > 0. 1M eV). The mechanical properties were assessed at 77 K in tension as well as in interlaminar shear prior to and after irradiation under static and dynamic conditions.

Resistances of electrical joints in the TF model coil of ITER: comparisons of first test results with samples results

The test of the Toroidal Field (TF) Model Coil of the International Thermonuclear Experimental Reactor (ITER) has been the opportunity to measure the DC resistances of all the joints of a real coil and to compare them to values previously measured on prototype full-size joint samples. This paper describes and discusses the different methods used for measuring all the joint resistances, and gives the results of joint resistance measurements (1-2 n/spl Omega/ range) as function of the coil current up to the maximum value of 80 kA. Comparisons with resistances measured on prototype joints in relevant field/current conditions are presented and discussed.

Neutron Decay with PERC: a Progress Report

The PERC collaboration will perform high-precision measurements of angular correlations in neutron beta decay at the beam facility MEPHISTO of the Forschungs-Neutronenquelle Heinz Maier-Leibnitz in Munich, Germany. The new beam station PERC, a clean, bright, and versatile source of neutron decay products, is designed to improve the sensitivity of neutron decay studies by one order of magnitude. The charged decay products are collected by a strong longitudinal magnetic field directly from inside a neutron guide. This combination provides the highest phase space density of decay products. A magnetic mirror serves to perform precise cuts in phase space, reducing related systematic errors. The new instrument PERC is under development by an international collaboration. The physics motivation, sensitivity, and applications of PERC as well as the status of the design and preliminary results on uncertainties in proton spectroscopy are presented in this paper.