M. Huguet

Eddy Currents, Electromagnetic Forces and Related Mechanical Effects in the NET Plasma Facing Components

The plasma facing components (PFCs) of a magnetic confinement fusion reactor are located in a region where the magnetic fields are very large and strongly varying during normal or abnormal transients. These variations induce high eddy currents in the passive metallic structures, and, related to these, large forces and energy dissipation. Therefore, it is essential to perform a detailed analysis of the electromagnetic response of the PFCs to an extremely demanding condition such as a plasma disruption. First objectives of this analysis are to: - determine the currents distribution in order to select a proper geometry to mitigate their effects; - evaluate the forces in order to choose the thicknesses and the reinforcement adequate to cope with them; - to investigate mechanical effects and define the requirements for the supporting structure.

Tests on the Hypervapotron Cooling Technique for Divertor Application

Basic tests on the hypervapotron cooling technique have been performed by the NET Team and the ENE A and SIET laboratories using a high power direct electrical heating system. The scope of the tests was to better understand the hypervapotron effect and to estimate the influence of the main hydraulic parameters on the heat transfer and on the critical heat flux. The main results are here presented.

THE DIVERTOR SYSTEM FOR NET

A double null divertor system is foreseen for NET. It is divided into 64 remote maintainable segments which consist of target plates designed to sustain the thermal and mechanical loads from the plasma, and their supporting and cooling system. This paper describes the present divertor design and the basic technological R&D which has been launched to demonstrate its basic feasibility.

Manufacture of Full Scale Models of the ITER Toroidal Field Coil Cases

The EFDA Close Support Unit (CSU) has initiated a technological development task to manufacture three full scale models of the austenitic steel cases of the ITER Toroidal Field (TF) coils. The main goals are to verify the feasibility of such a thick construction, assess the achievable material properties, and develop the manufacturing processes and quality control procedures. A first model (called Model 1), reproducing the geometry of the inner curved region of the TF coil, has been manufactured with thick forgings. A second model (Model 2), representing the geometry of one outer intercoil structure, has been produced by casting. A third model of the inner straight leg is being manufactured. The work has included a large campaign of development and qualification of welding processes and inspection procedures for thick case sections. Numerical models for the prediction of the geometrical deformations and residual stresses due to the welding have been developed. The goal of this task is the assessment of the manufacturing and quality procedures for the production of the ITER TF coil cases.

DOSES TO THE PUBLIC DUE TO ACCIDENTAL TRITIUM RELEASES

New computer models, taking into account the complex behaviour of tritium deposition on plants and soil, conversion of HT to HTO in the air-plant-soil system and the subsequent reemission of HTO to the atmosphere, have been used to calculate the doses to a most exposed individual of the public (MEI) following accidental tritium releases. An early dose (effective dose equivalent (EDE) due to inhalation and skin absorption for 50-year dose commitment from 7-days exposure) of 0.5 mSv per g tritium released in HTO form for a MEI has been derived. That value, however, is uncertain by about a factor of 2 (up and down). Although HT compared to HTO is considerably less radiotoxic early and chronic doses due to HT releases differ only by factors of about 10 to 500 in the vicinity of the plant (<10 km), basically depending on meteorological conditions.

Technological Aspects of the Fabrication Control and Testing of a Representative First Wall Panel for NET

Two large size mock-up panels have been manufactured within a comprehensive ENEA-Ansaldo development program for the NET first wall. The panels, manufactured according to the fully brazed solution, will be part of a thermal cycling campaign to be started at ISPRA by the end of the year. The paper describes all the steps followed for the manufacturing and the non destructive examination, together with the analytical work.

Predesign and Feasibility Studies of the NET Shielding Blanket Segments

This paper summarizes the main conclusions of a study contracted by the NET Team to the CEA, with Framatome as subcontractor, to perform predesign and feasibility studies of the NET shielding blanket segments. A first phase of the study has been devoted to a comparative assessment of candidate blanket concepts, according to a list of criteria including the main design features, the operating performances and the relevant manufacturing process. A second phase of the study is currently in progress, with the dual objective of producing a detailed design of the selected concept for the updated NET configuration, and proposing a development programme for the qualification of the specific manufacturing methods and the verification of the target performances.

Design and Performance of Mechanically Attached Low Z Armour Tiles for the NET Integrated FW

The thermomechanical performance of radiatively and conductively cooled armour variants has been comparatively evaluated via parametric 2-D transient elastic F.E. calculations, and the design of a remotely maintainable radiatively cooled carbon based armour compatible with the reference NET integrated FW developed. The scope of the paper covers the comparative thermomechanical analysis, the detailed design of the armour scheme, RH features and maintenance procedure. An evaluation of the erosion of carbon based FW armour operating in the different temperature ranges is also reported.

Forepumping Concept for NET Torus Exhaust

The multiple functions of the NET Torus Exhaust Forepumping System require a concept comprising both mechanical and cryotransfer pumping trains. The mechanical train will be used for initial stages of pump-down (from atmospheric pressure to approx. 10−2 mbar), and will back the turbomolecular pumps during torus conditioning and later stages of pump down. The installed capacity of the system is determined primarily by the helium glow discharge duty. Test results from a series connected pair of oscillating scroll pumps provide the basis for determining the configuration of the pumping train. Compound cryopumps (CCPs) pump the helium from the torus during burn and dwell by cryosorption on solid sorbent or cryotrapping in an argon frost layer. The latter calls for a dedicated process to separate the argon, which contains a small fraction of (activated) 41Ar, from the torus exhaust gas. This step, and the separation of helium ash will be carried out in successive stages of a cryotransfer pump subsystem (CTPS). The argon separated in the CTPS will be recycled to the CCPs as cryotrapping agent. A small fraction of this stream will be bled off and sent to the fuel clean-up system, to limit the build-up of impurities in the recycled argon. The DT, along with residual impurities trapped in the following stage will be forwarded to the fuel clean-up loop. The helium will be pumped through by the mechanical pumping installation. Process parameters and system components and configuration are described in the paper, along with strategy for limiting tritium inventory to acceptable levels and design measures to ensure adequate decay of 41Ar before argon is forwarded to unshielded process systems.

Effects of Runaway Electrons Energy Deposition on Plasma Facing Components

Results of preliminary analyses of the impact of runaway electrons mainly with energies of 100 and 300 MeV and an incidence angle of 1° on various first wall and divertor materials with respect to volumetric energy deposition, thermal response and, partly, mechanical effects are presented. Tentative indications on thresholds of incident energy density are given on the basis of a simple criterion of assumed allowable maximum metal temperature or in one divertor case on the basis of some more detailed thermomechanical considerations.