The nuclear reactor coolant surge lines are installed in the reactor building to connect the pressurizer and hot section of RCL (Reactor Coolant Loop). After being adjusted through heating or spraying, the pressure in the pressurizer is transmitted to the main loop through the surge lines so as to maintain stable working pressure inside the main loop. The weld of surge line is required to have in-service inspection. According to the requirements for the inner diameter counter bore indicated in surge line groove machining drawings, the design standard states that “if the weld is subject to service inspection, the length of the counter bore shall be 2Tmin for pipe and Tmin for components and fittings. After the surge lines of XXX project arrived on site, it was found that the back wall thickness of internal boring exceeded tolerance by analyzing the minimum wall thickness in the boring processing area of the surge lines. In order to solve the problem of back wall thickness of these borings less than the designed wall thickness, this paper carries out specific analysis and gives solutions. As for the problem of out-of-tolerance of minimum wall thickness in the boring processing area inside the grooves in the middle section of surge lines; it is recommended to modify the diameter of supposed internal boring of the groove to 367.0.00mm to satisfy the requirement of minimum wall thickness. As for the out-of-tolerance of minimum wall thickness in the boring processing area on the inner wall of groove of the connection-line nozzle in both hot section of main pipe of surge lines and in the pressurizer, it is recommended to modify the angle of inner boring of groove of surge lines. Specific solutions include:
Solution 1:
Modify the internal groove form from being perpendicular to the end face as shown in the design drawing to being 0°–4° included angle between the internal boring face and the end face.
Solution 2:
Correct the inner diameter of pipe section S001F to the designed inner diameter, in order to satisfy the requirement of processing inner diameter and minimum wall thickness. Analyze and calculate the wall thickness based on the corrected inner diameter to obtain the data of wall thickness on the equipment interface end of the surge lines after groove preparation.
Solution 1 and Solution 2 were used simultaneously, which is to modify the groove design on the one hand and ask the manufacturer to correct the inner diameter on the other hand so as to meet the design scope. By applying the above-mentioned combined solutions, we have solved the out-of-tolerance of wall thickness of surge lines. At present, the groove processing technology of surge lines has been approved by Administration and the installation has already been completed on the whole, which testifies to been a successful practice.
