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Simulation and Analysis of the Coolant Mixing Test within the Reactor Pressure Vessel of BNPP Using ANSYS CFX 18.0

Khalvandi, Mohammad | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51908 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Ghofrani, Mohammad Bagher
  7. Abstract:
  8. Various factors, such as increasing or decreasing the heat removal from the initial circuit, or increasing the flow rate of the cooling fluid in the reactor, causes the phenomenon of the coolant mixing in the PWR reactors. In this project, the thermohydraulic test of coolant mixing has been simulated in the pressure vessel of the Bushehr nuclear reactor. In this test, the mixing of the coolant caused by the reduction of heat removal from the primary circuit by the secondary circuit is investigated. In this case, the primary circuit temperature increases in the loop where the heat removal is reduced. The most important consequence of this event is the reactivity changes at the core of the reactor due to changes in the coolant density and the presence of thermal responses, which will result in reactivity fluctuations in the reactor. The purpose of this research is calculating the distribution of coolant temperature and mixing coefficients (mixing ratio) between primary circuit loops of the reactor in the mixing test condition. For this purpose, the complete geometry of the reactor and its internal components are modeled accurately and using the CFX software, the flow equations of the reactor are solved. The equations that are solved for flow are the Reynolds Averaged Navier-Stokes equations along with the equations of the turbulence model of the two equations of SST k-ω. The reactor's mode of operation at 12% nominal power and at the beginning of the cycle with a water temperature of 270 °C, which is the same as the initial conditions for testing, is simulated as a stable state and the results have been used as a preliminary condition for simulating the coolant mixing test transiently. The calculations are carried out in two separate buoyance and non-buoyance mode, each of which consists of the calculation of a steady state and transient. By comparing the results obtained from the simulation with each other as well as with the experimental results obtained from the related test at Bushehr power plant, it is shown that the amount of coolant mixing in the mode of application of the effect of buoyancy forces is higher than that of non-buoyance and has a higher accuracy. In this study, the amount of mixing coefficients and all the thermohydraulic parameters of the cooling fluid are considered in all points of the reactor, including the core, which is very important. Also, the use of a porous media method used to generate reactor geometry in order to reduce the amount of calculation not results in a large error in simulation and is reliable
  9. Keywords:
  10. Mixing Fluids ; Pressurized Water Reactor (PWR,WWER) ; Bushehr Nuclear Power Plant ; Temperature Distribution ; Mixing Coefficients ; CFX Code ; Pressure Chamber

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