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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: 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]