1 Overview
The control rod guiding cylinder is one of the main components of the inner component of the nuclear island main equipment, and provides positioning and guiding for the movement of the control rod, so the manufacturing precision is very high. At present, the half-square tube and the C-shaped plate in the control rod guide cylinder assembly of the million kilowatt nuclear power plant are all vacuum electron beam welding, and the energy density is high, the heat input is highly concentrated, the heat affected zone is small, and the welding is performed by vacuum electron beam welding technology. The slit has a wide aspect ratio and a fast welding speed, which is beneficial to control the welding deformation and reduce the welding stress.
The control rod guiding cylinder assembly is located inside the reactor pressure vessel and is in a working environment of high temperature, high pressure and high radiation. The residual stress of the welding is released during long-term work, which may cause deviation of the driving line, thereby affecting the control of reactor starting, shutdown and power regulation. Great fast movement. Therefore, it is necessary to carry out in-depth research and analysis on the vacuum electron beam welding process of the control rod guiding cylinder.
2. Structure of the control rod guide cylinder
Each unit of the one-million-kilowatt pressurized water reactor nuclear power plant has 61 sets of guide cylinder assemblies mounted on the inverted pile-shaped upper stack internal components. It is designed and manufactured to meet the AFNOR and ASTM standards specified in RCCM and RCCM A1300. The common design grades are shown in Table 1.
Table 1 Control rod guide cylinder grade
The control rod guiding cylinder is first assembled and welded into a continuous guiding assembly by a double tube, a C-shaped tube, a flange plate, etc., and then the fixing plate and the fixing plate are loaded into two half-half tubes, and are formed by vacuum electron beam welding. A photo of the control rod guiding cylinder is shown in Figure 1.
Figure 1 control rod guide tube
The square tube is made by vacuum electron beam welding of two pieces of square tubes. After welding, it is necessary to ensure the requirements of penetration and control the welding deformation to a minimum. A photo of the square tube is shown in Figure 2.
Figure 2 Square tube
3. Control rod guide tube material
The materials used for the C-shaped tube and the half-square tube in the control rod guiding cylinder assembly are all Z2CN19-10 austenitic nitrogen-conducting stainless steel, and the material properties thereof should meet the requirements of RCCM M3304 and M3307, respectively.
Steel mills supplying raw materials should provide a smelting analysis report. Each batch of C-shaped tube and half-square tube should be chemically analyzed in sequence to detect the contents of C, Ni, Cr, Mo and N, especially wCo <0.10%.
The intergranular corrosion test shall be carried out on a test piece made by RCCM G2300 during the casting of raw materials or on a steel pipe of each batch. Sensitization treatment (B treatment) should be carried out before the test, heated to 670 ° C, kept for 30 min, and slowly cooled to 500 ° C and then cooled in air. The reagent used was a boiling sulfuric acid-copper sulfate solution. After the corrosion test, the sample should emit a crisp metal sound during the sound test and there is no crack or tear in the bending test.
The guide tube assembly shall be solution treated at around 1100 °C in an inert gas atmosphere, and eddy current test shall be performed after cold calibration. The mechanical properties test shall be carried out. The yield strength shall be ≥210 MPa and the tensile strength shall be ≥510 MPa.
The square tube is formed by cold working. After forming, the surface should be visually observed to ensure that there are no cracks and tears on the surface of the part; liquid surface penetration testing should also be performed, and linear display and circular display with f>2 mm are not allowed.
4. Electron beam welding of the control rod guide cylinder
At present, the welding of C-shaped tubes and semi-square tubes in the control rod guiding cylinder is generally carried out by vacuum electron beam welding. The electron beam welding process is discussed separately below.
(1) Vacuum electron beam welding of C-shaped tube The vacuum electron beam welding of the C-shaped tube does not require a beveling, the electron beam gun is placed horizontally, and the welding position is flat welding. The welding process takes place in a vacuum chamber and does not require preheating and does not require filling material. The C-tube weld is welded in two passes, and the second weld can be used to repair the weld. The structure of the C-shaped tube is shown in Figure 3, and the welding parameters are shown in Table 2.
Figure 3 C-tube welded structure
Table 2 C-tube vacuum electron beam welding parameters
For more information, please see the fourth issue of Metalworking (Hot Processing).
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