Abstract
The drop time of the control rod plays an important role in judging whether a nuclear reactor can be safely shut down in an emergency condition and has become one of the most important parameters for the safety analysis of nuclear power plants. Exact assessment of the drop time is greatly dependent on the forces acting on the control rod. In this research, a three-dimensional numerical simulation of the control rod in a low-temperature heating reactor was established based on 6DOF (6 degrees of freedom) model using dynamic meshing technology, and it was used to analyze the control rod dropping experiment. The behavior of dropping the control rod was obtained, including the velocity, the displacement, and the pressure distribution on the control rod guide tube. The comparison between the simulation and the experiment results indicated that the simulation was capable of simulating the dropping characteristic of the control rod. Some important parameters can be calculated, such as the time of control rod dropping process and the maximum impact force. Based on this, useful information could be provided for the design of control rod driveline structure.
Highlights
The reactor control rod assembly is generally set up with a star frame and several control rods
The displacement-time curve and velocity-time curve in the process of rod dropping were measured by a highspeed camera, whereas the pressure-time curve of the guide tube was measured by using pressure sensors
This section intends to verify the correctness of the simulation results by comparing the speedtime curve and displacement curve of the control rods
Summary
The reactor control rod assembly is generally set up with a star frame and several control rods. The control rod drive mechanism is required to move slowly under normal working conditions to ensure the safety of the reactor; in the case of an accident, the driving mechanism can be automatically detached so that the control rod assembly can be quickly inserted into the core under the gravity. If the control rod drops too slowly or the control rod assembly corresponding to the component with the highest reactivity yield fails to act during the emergency shutdown, a set of serious accidents can be generated. Under the first and second working conditions of the reactor, the drop time according to the safety standards of the control rods is less than 3.5 s (Yoon et al, 2009). In some nuclear power plant designs, the time of dropping to falling of the control rod into the inlet of the guide tube buffer section is within 2 s
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