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ã€Keywords】 temperature bypass; valve; numerical simulation; flow resistance characteristics.
ã€Abstract】Split forging technology is applied in the manufacture of the globe valve used in the bypass temperature measurement of the reactor coolant system(RCS) in some nuclear power plants.This technology,however,leads to the leakage risk at the lips weld on The connecting point between the deck and body of the valve.Thus,using the integrated-casting valve instead is necessary and moreover,this type of valve should satisfy the requirement of flow resistance characteristic.This work focuses on the analysis for the flow resistance characteristic Of the integrated-casting valve based on the numerical CFX simulation. The result shows that the requirement of the flow resistance characteristic of this valve type can be satisfied for the bypass temperature measurement.
ã€Key words】 Resistance temperature detector by pass manifold system;Valves;Numerical simulation;Flow resistance characteristics
0 Introduction Domestic in-service nuclear power plants completed and put into commercial operation in recent years, dozens of safety level 1 manual shut-off valves for the reactor coolant system (referred to as the main system) temperature bypass, The structure of Figure 1) is a threaded connection between the valve body and the valve cover. Feedback from Fuqing No. 1 and No. 2 nuclear power plant operation experience showed that the multiple manual shut-off valves of this type all experienced lip welding failure during the hot test stage, which resulted in the leakage of coolant at the place, and the repairs were performed by grinding. After such defects are dealt with, a small number of valves still have the phenomenon of leakage failure of the lip welding.
The safety level 1 manual shut-off valve of the temperature measurement bypass of the main system is used as the primary pressure bearing boundary. If uncontrollable lip welding leakage occurs during the operation of the unit, the unrecognizable leak rate of the primary circuit may exceed the standard and the temperature measurement bypass may not be available. The resulting nuclear safety risks affect the safety and economy of nuclear power plants. In order to avoid the leakage of the lip welding during the operation of this kind of valve and improve the reliability and safety stability of the unit, according to the requirement of the nuclear power plant, this type of manual shut-off valve is replaced.
The new cut-off valve must satisfy the characteristic requirements of the temperature shut-off safety level 1 manual shut-off valve of the main system of the in-service nuclear power plant, and it must also meet the flow resistance requirements of the temperature measurement bypass system. Therefore, this paper will use CFD modeling analysis to analyze the adaptability of the replacement valves used in the flow resistance requirements of the temperature measurement bypass system.
1 Alternative valve characteristics require in-service nuclear power plant main system temperature measurement bypass safety Class 1 manual shut-off valve equipment selection principles are as follows:
1) The new valve meets the technical specifications in the equipment specification in order to meet the main system safety and functional requirements;
2) The new valve should be in the structure to avoid leakage of the lip welding, and there is good feedback on the operation.
3) The flow resistance of the new valve is low enough to meet the coolant transmission time requirement in the temperature measurement bypass of the main circuit;
4) The size, weight, and center of gravity of the new valve should be similar to those of the original valve to ensure that the installation space and mechanical evaluation requirements are met.
According to the investigation of valve selection, the manual valve of RAMA produced by VELAN in France can meet the temperature measurement bypass of the main system. The manual valve of the valve body adopts integrated forging, and does not require lip welding. The size, weight, and center of gravity should be similar to those of the original valve. Claim.
2 Valve flow resistance analysis The manual shut-off valve on the temperature measuring bypass is used as the main partial resistance, and its resistance coefficient is clearly defined in the equipment specification. After replacing the main system temperature measurement bypass valve, the resistance coefficient of the new valve should still meet the relevant requirements in the equipment specification.
2.1 Control equation 2.2 Geometric model RAMA manual shut-off valve structure shown in Figure 1, under normal circumstances, the valve valve and valve seat separation, the valve is fully open. Therefore, the geometric modeling object is the internal flow path of the valve in the fully open state of the valve. This selected the use of commercial modeling software UG on the three-dimensional modeling of the internal flow path of the valve after the RAMA manual shut-off valve is fully opened.
The internal diameter of the inlet and outlet of the stop valve is 40mm. After the valve is fully opened, the top of the valve plug is 13.39mm away from the valve seat. The other parameters of the valve are shown in Fig. 2. The dimensions of the valve in the figure are in mm.
2.3 Meshing The fluidic channel was meshed using the grid division software ICEM. The number of grids was 139925.
2.4 Boundary Conditions The grid was imported into the commercial fluid calculation software CFX to set the boundary conditions. The valve inlet pressure was 15.5 MPa, the outlet flow rate was 25 m/s, and the tube wall roughness was 6.3 μm.
2.5 Numerical simulation results The distribution of the flow field in the valve is shown in the figure below. It can be seen from the figure that the flow field in the valve is unevenly distributed and there are vortex phenomenon in some areas. In the valve flow resistance calculation, the pressure at the valve outlet is the average pressure. After measurement, the average pressure at the outlet of the valve was 14.6 MPa.
3 Results and Discussion 4 Conclusions The manual shut-off valve of the main system temperature bypass is used as the primary pressure bearing boundary. If uncontrollable lip welding leakage occurs during the operation of the unit, it may lead to unrecognizable leakage rate of the primary circuit. In order to avoid leakage of the lip welding during the operation of this type of valve, the nuclear power plant replaced the split valve with the RAMA manual integrated globe valve produced by VELAN. Then, in order to determine the resistance characteristics of the integrated valve, the CFD method was used to analyze the resistance characteristics of the valve. After analysis and confirmation, the equivalent length L/D of the new valve is 282.3, and the temperature bypass valve L/D?燮 340 requirements.
ã€references】
[1] Study on reform of temperature bypass valve of Fuqing No. 1 unit [J]. Science and Technology Vision, 2016, 13:1-2.
[2] Numerical Heat Transfer [M]. Xi'an: Xi'an Jiaotong University Press, 2001.
Numerical Simulation Analysis of Resistance Characteristics of Temperature Bypass Valve in Nuclear Power Plant
ã€Abstract】According to the operational feedback of in-service nuclear power plants in China, if the valve body cover of the primary system temperature measurement bypass safety level 1 manual cut-off valve is split forged, the lip welding at the connection between the valve body and the valve cover will leak. Or there is a risk of leakage, so the body valve cover integral casting shut-off valve should be used instead. In order to determine whether the resistance characteristics of the integrated casting valve can meet the resistance requirements of the system, CFD software CFX was used to numerically simulate the flow resistance characteristics of the integrated valve and analyze the adaptability of the replacement valve to the flow resistance requirements of the temperature measurement bypass system. Sex. The analysis results show that the flow resistance of the integrated valve can meet the requirements of the temperature measurement bypass system.