ASME FE.1-2018 pdf – Rules for Construction of Fusion Energy Devices.
There are several methods to accomplish controlled nuclear fusion, two of which are discussed within this Draft Standard. One method is magnetic confinement, in which nuclei in a vacuum chamber are guided at high velocity by magnetic fields and heated by microwave energy and/or other means so that the high velocity of the nuclei overcomes electrostatic repulsion and fusion reactions occur. Another method, inertial confinement, uses tiny frozen pellets in a vacuum chamber; the pellets are rapidly compressed with great force by laser beams, X-ray beams, or ion beams. The beams ionize some molecules and the compression force creates a shock wave in the pellet; this overcomes electrostatic repulsion and the atoms fuse. Both magnetic confinement and inertial confinement control the fusion reaction by the amount of mass and the amount of energy input to the process, either by heating or by compression.
The tokamak, or system of magnetic confInement used in today’s experimental devices and that may be used in future power facilities, uses both resistive and superconducting magnets. The major systems that can make up the tokamak include
(a) resistive and superconducting magnets, including but not limited to the following:
(1) toroidal field (TF) coils
(2) poloidal field (PF) coils
(3) central solenoid (CS) coils
(4) correction coils (CC)
(b) vacuum vessel (VV)
(c) in-vessel coil systems
(d) in-vessel components, including blanket and divertor
(e) cryostat
(/3 VV overpressure suppression system
(g) thermal shields
Each of these major systems consists of other subsystems and components that together form a major part of the tokamak.
The tokamak has a confinement structure that also serves as a radiation-shielding barrier; the cryostat and the VV provide the vacuum boundaries. The primary purpose of the cryostat is to provide the environment for the thermal isolation of the superconducting magnets. The VV is located inside the magnet system and provides the first confinement barrier for the in- vessel radiological inventory.
The thermal shield is mounted between the VV and the superconducting magnets on the inside, and the cryostat and the magnets on the outside. All of these components are mounted inside the cryostat. Inside the VV, the internal replaceable components include blanket modules and divertor cassettes.
FAB-1210 Magnet System
The magnet system for the ITER tokamak consists of TF coils, a CS, PF coils, and, if necessary, CCs. The TF coils determine the basic toroidal segmentation of the machine and are chosen to meet the number and size requirements of access ports. A typical magnet system is shown in Figure FAB-1210-1.
The TF coil case encloses the winding pack and is the main structural component of the magnet system. The TF coil case and the winding pack are structurally linked.
The CS assembly consists of a vertical stack of winding pack modules, which is supported from the bottom of the TF coils through its preload structure. The number of CS modules is designed to satisfy the plasma-shaping requirements.
The PF coils are attached to the TF coil to allow for radial displacements. The PF coils provide suitable magnetic fields for plasma shaping and position control.
Outside the TF coils are located, if necessary, independent sets of CCs, each consisting of coils arranged around the toroidal circumference. These coils may be used to correct error fields (particularly toroidal asymmetry) arising from positioning errors in the TF coils, CS, and PF coils.
FAB-1310 FunctionaL Requirements
The vacuum vessel
(a) provides a hazardous materials confinement barrier and withstands postulated accidents without losing confinement
(b) is designed to remove the nuclear heating and maintain the surface heat flux within the allowable temperature and stress limits
(c) is designed to remove the decay heat of in-vessel components, even in conditions when the other cooling systems are not functioning
(d) provides a pressure boundary consistent with the generation and maintenance of a high-quality vacuum
(e) supports in-vessel components to specified tolerances and their loads under normal and off-normal operations
(f) together with the in-vessel components, maintains a specified toroidal electrical resistance and contributes to plasma stability by providing a conductive shell tight fitting to the plasma as far as practically feasible
(g) together with the blanket, divertor, and ancillary equipment in ports, provides adequate radiation shielding for the superconducting coils and reduces activation inside the cryostat and at connecting ducts (end parts of the port extensions) to facilitate remote handling and decommissioning.