Methods for qualifying the thermodynamic stability of safety valves and steam dump devices of nuclear power plants
DOI:
https://doi.org/10.15276/opu.2.72.2025.08Keywords:
qualification, passive safety system, armature, reactor, steam generator, thermodynamic stability, nuclear power plantAbstract
Analysis of known developments in reliability analysis of safety valves and steam dump devices of reactors and steam generators of nuclear power plants with VVER has recognized the need for calculation qualification of safety valves and steam dump devices under emergency conditions that are not provided for operational tests of nuclear power plants. One of such problems is determining the conditions for pulse and oscillatory thermodynamic instability of safety valves and steam dump devices under emergency conditions. The consequences of thermodynamic instability may be a violation of the performance of critical safety functions under accident management conditions. Experimental qualification of safety valves and steam dump devices under emergency conditions is not possible, therefore calculation qualification is required. The need for calculation qualification is also relevant for prospective programs for reactor operation in conditions of extended fuel campaign time, when the number of tests of passive safety systems during scheduled repairs of power units is reduced. A method for qualifying the throughflow capacity of safety valves and steam dump devices of passive safety systems of nuclear power plants under conditions of pulsed and oscillatory thermodynamic instability has been developed. A necessary condition for pulsed thermodynamic instability has been established. It is the formation of a transonic flow regime of the operating medium in the confusion zone of safety valves/steam dump devices. The consequences of pulsed thermodynamic instability are water “hummer” due to the conversion of kinetic energy of the flow into the internal energy of the water “hummer” and flow stagnation. The maximum pressure amplitude of the water “hummer” due to pulsed thermodynamic instability with complete flow stagnation has been determined. The conditions and consequences of oscillatory thermodynamic instability in subsonic flow regimes in the flow zones of safety valves/steam dump devices have been found based on the fundamental principle of thermodynamic instability of equilibrium systems. Based on the developed method for qualifying the throughflow capacity of safety valves/steam dump devices, the conditions and approaches for ensuring thermodynamic flow stability in the flow zones of safety valves/steam dump devices and preventing water “hummers” have been determined.
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