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• The FDRs air cooling system based on the air forced circulation produced by seventeen fans in a complex system of series-parallel channels formed by air supply and return pipes, vertical modules and chimneys has been developed and studied. • The essential non-uniformity of air flow distribution in parallel channels, which considerably increases the cooling time, is observed when performing the numerical analysis of the FDR cooling system. • The problem with equalization of flow rates could be formulated as the problem on providing an equal flow rate for each module from a certain group, which has a common intake, by individually selecting the hydraulic resistance for the diaphragms installed in the modules. • The thermohydraulic simulation of the FDR modules cooldown, with the diaphragms introduced into the cooling system, has verified that it is possible to decrease the temperature of the resistive elements to their initial 40⁰C within required 3–4 h. Starting in 2010, work is being underway at NIIEFA on developing the air-cooling system for Fast Discharge Resistors (FDR). The first attempts have been unsuccessful. The free-convective cooling method taken as the basis, though being simple and appealing, could not ensure complete cooling of all modules within the required 3–4 h. The reason was that the obtained distribution of the air flow over separate resistive modules composing the parallel cooling branches was strongly nonuniform. Repeated attempts to equalize the air flows (increase in the flow-through section of supply/return air ducts, division of the single cooling circuit into groups of separate circuits) were unsuccessful: the cooling time was decreased, but the required 3–4 h were not attained. The presented work continues the previously performed analyses of the versions of the cooling system for the FDRs. This paper presents the results of the analysis of the forced cooling of the resistors by fans installed in the inlet section of the air duct. The possibilities are studied to ensure equal flow rates in parallel modules of the hydraulic circuit. The method has been developed for equalizing the flow rates in the modules and selection of relevant hydraulic characteristics of diaphragms, making it possible to attain the specified time for cooling of FDR resistive elements. [ABSTRACT FROM AUTHOR]

Abstract In tokamaks, residual gases and especially water vapors adsorbed in shell pores are removed by baking the vacuum vessel (VV) and in-vessel elements to a temperature not lower than 200 °С. The combined method for VV baking is proposed for the KTM tokamak, namely, baking by ohmic heaters to heat the outer shell of the vacuum vessel (the main method) and by eddy currents induced, mainly, in the inner shell by the central solenoid (CS) (additional induction method). To realize the proposed method the authors have developed the baking system consisting of active heaters arranged on the VV outer shell and an AC source supplying the central solenoid initiating eddy currents in the shell of the VV inner cylinder. The process of the KTM VV baking was numerically simulated by the numerical simulator developed by the authors. As a result, (a) the baking scenario has been defined, which satisfies the requirements both for the process duration and for the temperature non-uniformity; (b) the requirements have been formulated for the induction heating source and power supply source of the outer heaters. [ABSTRACT FROM AUTHOR]

For effective vacuum leak testing all cooling circuits serving the ITER vessel and in-vessel components shall be drained and dried so that after this procedure taking less than 100 h the purge gas passing through a component has water content less than 100 ppm. This process is four-stage, with the first stage using a short blast of compressed nitrogen to blow most of water in the coolant channels out of the circuit. This process is hindered by volumes which trap water due to gravity. To remove the trapped water, it is necessary, first, to heat up the structure by hot and compressed nitrogen, and then water is evaporated by depressurized nitrogen. The cooling system of the ITER Diagnostic Equatorial Port Plugs is of a complicated hydraulic configuration. The system branching might make difficult removal of water from the piping in the scheduled draining mode. The authors have proposed the KORSAR computation code to simulate draining of the GEPP cooling circuit. The numerical simulation performed has made it possible to describe the process dynamics during draining of the entire GEPP cooling circuit and to define the process time, amount and location of residual water and evolution of two-phase flow regime. [ABSTRACT FROM AUTHOR]

The superconducting magnets of the ITER are capable of accumulating up to 50 GJ. In case of coil quench the energy stored in the coils must be extracted rapidly. The problem can be solved by the Fast Discharge Resistors (FDR) under development at the Efremov Institute. The fast discharge of the coils results in practically adiabatic heating of the resistive elements up to 250 °C. The resistors should be cooled to their initial temperature within a reasonable time (4–6 h). With this in mind, the authors have designed the cooling system based on natural air circulation. When performing the numerical analysis of the cooling process, the authors have faced the problem of the essential non-uniformity of air flow distribution in parallel channels, which considerably increases the cooling time. Thus, while the cooling time does not exceed 3 h for a single FDR module, it exceeds 10 h for several modules. The numerical studies performed over the last few years have allowed the authors to propose a number of measures to optimize the air cooling system so as to mitigate the negative effect of the air flow non-uniformity in the FDR cooling system. [ABSTRACT FROM AUTHOR]

The First Mirror (M1), as part of the ITER core CXRS diagnostics, is responsible for acquisition and transportation of the optical signal from the plasma to the corresponding spectrometer. The M1 is the most vulnerable component of this system working in severe conditions caused by its location in the direct view of the plasma. Based on the numerical analysis an optimized arrangement of baffles was found for the optical channel. It is shown that such measures like the deeper M1 positioning in the shielding, duct configuration and baffles implementation made it possible to reduce heat loads on the M1 by a factor of about 10 2 –10 3 . [ABSTRACT FROM AUTHOR]

Abstract: The key role in direct measurement of the ITER fusion power is assigned to the neutron diagnostic system for measurement of total neutron flux of the D–D and D–T fusion reaction with the help of a neutron flux monitor located under the divertor dome. High plasma heat loads in this position implies stringent requirements for the detector design and its cooling system to ensure the required temperature operation regime of the neutron detector. The paper describes the neutron flux monitor design developed in close collaboration with IO ITER diagnostic division. Two numerical models (hydraulic and thermal) built up to simulate the water flow in the cooling system and the temperature state of detector components are also presented and discussed. The numerical investigations carried out on the developed models have shown that only good thermal contact between the shell of the detector blocks and water-cooled casing of the monitor (fit, brazing) will provide the required temperature operation regimes of the most temperature-sensitive IFC electrodes. The obtained high temperature of the detector supports makes necessary an auxiliary direct cooling of the supports or their redesign so as to provide their higher thermal conductivity. [Copyright &y& Elsevier]

Abstract: The ITER superconducting magnets will store up to 50GJ of magnetic energy per operation cycle. In case of coil quench the energy stored in the coils must be extracted rapidly with a time constant from 7.5 to 14s. It will be achieved by fast discharge resistors (FDR) normally bridged by circuit breakers and inserted in series with the superconducting coils. The fast discharge of the coils results practically in adiabatic heating of the resistive elements up to 200–300°C. The resistors need to be cooled to the initial temperature over 6–8h. Natural air circulation is proposed as a cooling method. In order to simulate the temperature response of the resistors to energy released in the resistive plates and to demonstrate their cooling capability within the required time by natural air circulation the numerical model of the resistor cooling circuit has been developed. As the calculations have shown, the developed FDR cooling system based on cooling by natural air circulation is capable of providing the required temperature operation regime of FDRs, but the supply channels are to be optimized so that the cooling time does not exceed the permissible one. [Copyright &y& Elsevier]

The ITER magnet system will operate in extremely severe conditions, which impose high requirements for mechanical and dielectric strength of the electrical insulation of the superconductive coils. Only monolithic structure obtained during the VPI procedure is capable to provide the required mechanical and dielectric strength for electrical insulation. To provide the qualitative insulation, a temperature non-uniformity of the electrical insulation should be kept within the range of [−5, +5 °C] and [−0, +20 °C] during filling with epoxy compound and its curing, respectively. The PF1 coil is about 150 t in weight and consists of materials with different thermal conductivity. Besides, a complicated geometry of the coil adds complexity to VPI. Since the VPI is usually a long-term and irreversible process (within pot life of compound), the whole process should be controllable. The paper describes the developed calculation model of the ITER PF1 coil and presents the results of numerical simulation of this model at VPI of electrical insulation. The completed VPI of the ITER PF1 coil has verified the proposed method for coil heating and proved an acceptable agreement between the calculated and measured temperature distributions throughout the VPI procedure. [ABSTRACT FROM AUTHOR]

Abstract: The ITER core charge exchange recombination spectroscopy (core CXRS) is a diagnostic system designed to collect the light emitted from interaction of the Diagnostic Neutral Beam (DNB) with the core plasma and guides it via a mirror labyrinth through the Upper Port Plug toward a fiber bundle, which then transmits the light to a set of spectrometers for spectral analysis. The first mirror (M1), being the most important part of the optical system which defines workability of the entire CXRS, works in direct view of the plasma. The latter strongly impacts the mirror causing its surface erosion and deposition with degradation of the optical capability. The fast shutter (FS) is supposed to play the main role in reducing the time of the first mirror exposition to the plasma. The performed work is focused on the detailed thermal and hydraulic analyses of the main components of the M1 protecting device (blades, arms and actuator) and its cooling and pneumatic systems. The performed analysis confirms, in general, the workability of the helium-operated shutter and verifies the pneumatic actuation concept proposed for the M1 protecting device. [Copyright &y& Elsevier]

The generic upper port plug (GUPP) structure in ITER is a 6 m long metal box which deploys diagnostic components into the vacuum vessel. This structure is commonly used for all the diagnostic upper ports. The final design of the GUPP structure, which has successfully passed the final design review in 2013, is described here. The diagnostic port plug is cantilevered to the vacuum vessel with a heavy payload at the front, so called the diagnostic first wall (DFW) and the diagnostic shield module (DSM). Most of electromagnetic (EM) load (∼80%) occurs in DFW/DSM. Therefore, the mounting design to transfer the EM load from DFW/DSM to the GUPP structure is challenging, which should also comply with thermal expansion and tolerance for assembly and manufacturing. Another key design parameter to be considered is the gap between the port plug and the vacuum vessel port. The gap should be large enough to accommodate the remote handling of the heavy port plug (max. 25 t), the structural deflection due to external loads and machine assembly tolerance. At the same time, the gap should be minimized to stop the neutron streaming according to the ALARA (as low as reasonably achievable) principle. With these design constraints, the GUPP structure should also provide space for diagnostic integration as much as possible. This requirement has led to the single wall structure having the gun-drilled water channels inside the structure. Furthermore, intensive efforts have been made on the manufacturing study including material selection, manufacturing codes and French regulation related to nuclear equipment and safety. All these main design and manufacturing aspects are discussed in this paper, including requirements, interfaces, loads and structural assessment and maintenance. [ABSTRACT FROM AUTHOR]

Abstract: The first mirror (M1) as an important part of the CXRS diagnostic system is responsible for acquisition and transportation of the optical signal of required quality from the ITER plasma to detectors. At the same time, the M1 is the most vulnerable component of this system working in drastic and severe conditions caused by its location in the direct view of the plasma. To minimize impurities deposition and guarantee the required lifetime for M1 its temperature shall be maintained within the operational range of 350±50°C. The computation of M1 of the reference CXRS design demonstrates that, firstly, helium is the best candidate among the analyzed gases (He, N2, Ar) to be used as a coolant to maintain the M1 temperature in the required operational range of 350±50°C giving the highest heat transfer coefficient and the lowest hydraulic losses at moderate flow rates (v gas =40–60m/s) and, secondly, optimization of the cooling channels configuration together with an increase in the gas velocity and/or with heat transfer intensifiers makes it possible to provide the required M1 temperature conditions. [Copyright &y& Elsevier]