Non-linear simulation and control of xenon induced oscillations in Advanced Heavy Water Reactor

•Vectorized non-linear model of AHWR is developed and implemented using SIMULINK.•Unstable spatial modes of AHWR requiring control are reported.•Spatial stabilization of AHWR is successfully achieved.•Feedback of total power and nodal powers with RRs is sufficient for control.

The physical dimensions and the reactivity feedbacks of Advanced Heavy Water Reactor (AHWR) are such that, it is susceptible to xenon induced spatial oscillations. If these oscillations are not controlled, the power density and the rate of change of power at some locations in the reactor core may exceed their respective thermal limits, resulting into increased chances of fuel failure. Hence, it is essential to suppress xenon oscillations and achieve spatial stabilization of AHWR. Reactor core of AHWR is divided into 17 non-overlapping nodes. Non-linear model of AHWR is characterized by 90 first order differential equations. Total reactor power and 17 nodal powers are output variables. Four voltage signals to the Regulating Rods (RRs) and a feed flow rate are input variables. Applying a highly developed simulation is necessary for analysis and control of spatial oscillations developed in AHWR for safe operation. In this paper, after carrying out stability analysis, a control strategy based on feedback of total power and nodal powers in which RRs are placed is presented for spatial control of AHWR. For the same, a vectorized non-linear model of AHWR is developed and is implemented in the MatLab/Simulink environment which helps to understand the relationship between different variables of the system in a better way. With the proposed controller, non-linear model of AHWR is simulated and results are generated for different transient conditions. The behavior of delayed neutron precursor and xenon concentrations is also analyzed for each transient. From the simulation results, performance of the proposed controller is found to be satisfactory.