The Numerical Simulation Of Cooling Methods For CRDM On The Nuclear Power Plant

The control rod assembly is driven by the control rod drive mechanism (CRDM). At least one of the coil assemblies is energized to form the internal heat source during different operation modes. Obviously, it can lead the coil to exceed the permitted temperature if lacking suitable cooling measures. In order to ascertain the reliability of the CRDMs during operation,the maximum temperature of the coil in CRDMs is strictly required below the permitted value.Based on the layout of the CRDMs in a traditional pressurized water nuclear power plant,the CFD numerical simulation techniques are used in the studies on the flow field and temperature distribution within CRDMs and neighboring zones. Through the studies and analysis, the feasibility of natural circulation cooling mode is investigated. Furthermore, the researches of the influences of such factors are also performed on the temperature distribution profiles as the containment temperature, the length of spindle sleeve, the length of outer hood and CRDM upper cover.Firstly, the Pro/E software is used to establish a 3D geometric model containing the CRDMs on the top of the pressure vessel with the surrounding air basin; Secondly, the computational region is meshed with ICEM; a CFD software, Fluent, is applied to solve the flow field and temperature distribution of the CRDMs and related region. The strategy in this work is first to identify the position of the highest temperature through the 3D numerical simulation and the heat transfer coefficient on the wall of the identified CRDM as well.Afterwards, the 2-D geometric model is setted up for accurate simulation analysis. In the end,the feasibility of the natural circulation cooling mode is evaluated with the highest temperature of the coil.Through the calculation and analysis,it can be found that when the CRDM group is in the running state and the ambient temperature in containment does not exceed 70 ?,The highest temperature of the coils do not exceed 320 ?, which is lower than the coil limit value of 350°?. so we can judge that the CRDMs and the coils can be cooled effectively only by natural convection of air. In addition, the article also explore on influence of the air natural convection cooling effect by the CRDM Structure, such as the length of the upper cover, the length of the spindle sleeve of driving rod, The air gap between the coil and the shell. At last proper advice is given for the the design for the CRDM structure.