The Digital Acoustic Model of a Pressurized Water Reactor

— The digital acoustic model of a nuclear reactor (NRDAM) is represented as a self-oscillatory system belonging to a special class of nonlinear dissipative systems that can generate sustained oscillations whose parameters do not depend on the initial conditions and are only governed by the properties of the system itself. It has been found that a pressurized water reactor with coolant flowing in a turbulent mode is an open system of high complexity with a large number of components with links between them being probabilistic rather than predetermined in nature. The coolant loop components featuring negative dissipation (negative friction) are revealed. It is shown that chaotic turbulent pulsations and vortices are self-organized in these components into ordered wave oscillations, the frequency of which is determined according to the Thomson (Kelvin) formula. An electronic generator of self-oscillations with a transformer feedback used in radio engineering circuits has similar properties. A nozzle is an acoustic analog of a transformer. A negative resistance contained in nonlinear dynamic systems like a nozzle or a natural circulation loop results in that chaotic turbulent disturbances become self-organized, and self-oscillations are generated in the form of acoustic standing waves (ASW). Based on theoretical and experimental data, the certainty of the ability of a reactor together with the pipelines connected to it to simultaneously generate several ASWs—a property that has not been known previously—is confirmed. By using the NRDAM in designing and operation of nuclear power plants (NPPs), it becomes possible to reveal the sources of ASWs arising in the coolant, their occurrence conditions, and frequency. The use of the NRDAM is also necessary for determining the effect that the coolant circuit equipment geometrical parameters and layout have on the interaction of neutronic, thermal-hydraulic, and vibroacoustic processes. By applying the NRDAM, it becomes possible to optimize the engineering and design solutions in developing new-generation NPPs by eliminating the conditions causing the occurrence of undesirable self-oscillations of coolant and vibroacoustic resonances resulting from the coincidence of the ASW frequencies with the vibration frequencies of nuclear fuel and equipment in normal and emergency operation modes and also under the conditions of shock impacts and seismic loads.