Modeling the nonlinear dynamic temperature and power oscillations in VVER

The nonlinear dynamic auto-oscillatory regimes of the temperature at the exit from the core and of the power of nuclear reactors are investigated and the quantitative features of the regimes are determined. A physical-mathematical model of the dynamics of a VVER-type nuclear reactor is examined, taking account of the inertial (temperature) and instantaneous (power) feedbacks in the reactor but neglecting the delayed neutrons. Analytical solutions characterizing the auto-oscillatory real-time behavior of the temperature at the exit from the core and of the reactor power are obtained. The period of these oscillations is determined. The model constructed for the dynamics of a reactor is used as a basis to simulate, using the RELAP5/Mod3.2 computer code, certain nonlinear auto-oscillatory processes occurring in the first and second loops of a nuclear power plant with a VVER-440 reactor. It is found that the oscillations of the temperature at the exit from the core and power of the nuclear reactor generate the same period for processes which were calculated.