JPH046494A - Joining method for reactor pressure vessel and control rod drive housing - Google Patents

Abstract

PURPOSE:To improve the reliability of a welded part in the resistance to a stress and a corrosion crack without changing materials of a control rod drive mechanism (CRD) housing, a stub tube and a weld metal, by welding the CRD housing to the stub tube after cladding by welding is made on the outer peripheral surface of the joining part of the CRD housing. CONSTITUTION:A joining part by welding comprises a part 5 formed by cladding a CRD housing 1, and a part 6 welded for joining the housing 1 and a stub tube 2 together. First, the housing 1 is inserted into a pressure vessel 3 and cladding by welding is made on a part which is to be the joining part with the stub tube 2. Since the part of cladding by welding shrinks, the housing 1 is tightened in a hooping manner and changes its shape toward the inner circumference side. Accordingly, a compressive stress in the circumferential direction is generated on the inner circumferential side of the housing 1 in the vicinity of the part of cladding. After the housing 1 on which cladding is made and the stub tube 2 are positioned, subsequently, they are welded together. Since the welded part shrinks after welding, the housing 1 is pulled onto the stub tube 2 side and thus a final residual stress in the circumferential direction can be lowered.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention relates to a reactor pressure vessel and a control rod drive mechanism (C
RD) A method of welding and joining a housing via a stub tube.

(Prior art) The output of a boiling water reactor is generated by moving control rods containing neutron absorbing material in and out between fuel assemblies placed at predetermined intervals within the reactor pressure vessel. Adjusted by. The control rod moves up and down inside the control rod guide tube in the tube axis direction, and the portion that is pushed up and exits the guide tube is inserted between the fuel assemblies, absorbing neutrons and suppressing the nuclear fission reaction. The vertical movement of the control rods is performed by a control rod drive mechanism, which is housed in a cylindrical container called a control rod drive mechanism housing (CHD housing) that penetrates the bottom of the reactor pressure vessel.

The CRD housing accommodates the control rod drive mechanism and supports the guide tube, and is welded to the bottom of the reactor pressure vessel via a stub tube. 7th
The figure shows the joint structure of the CRD housing 1, stub tube 2, and reactor pressure vessel 3. CHD housing 1
is austenitic stainless steel (SUS304TP, 5tJS316T) from the viewpoint of high temperature strength and corrosion resistance.
P or modified materials thereof). Since the reactor pressure vessel 3 is made of low-alloy steel, a thin plate 4 of stainless steel is hollowed out on its inner surface in consideration of corrosion resistance. However, the lower part of the reactor pressure vessel (1, I is considered to be welded to the stub tube 2 [,, Inconel 82
is being slammed. In addition, the input tubing tube 2 has a coefficient of thermal expansion that is caused by the difference in coefficient of thermal expansion between the CRD housing, which is located between carbon steel and low-alloy steel, and the pressure vessel 3. The CRT housing 1, the stub tube 2, and the stub tube 2 are made of an alloy based on Inconel (Inconel 600), which is effective in relieving thermal stress and whose material properties are not easily changed by welding or subsequent heat treatment. Pressure vessel: 3 respectively in'' 82 and in'' connel 182 with weld metal 11. It is joined together.

(Problem to be Solved by the Invention) When Buran 1- is operated, reactor pressure vessel: 3
holds high-temperature, high-pressure water (partially steam) at 288°C and 80 atm. CRD housing] and stub tube 2
also retains similar high temperature and high sweat water.

At this time, the control rod guide tube, the control rod, and the amount of control rod
In addition to the weight of the CHD housing, the hollowing out of the pressure vessel causes high-pressure water to push out the CRU housing (1), which acts on the outside of the pressure vessel (3), and heat. Due to the expansion difference, a tensile thermal stress acts on the compression stub tube 2 in the circumferential direction of the CRD housing 1, and a similar tensile stress acts on the welded portion 6 in the circumferential direction. .

The welded portion 6 is provided 41 to withstand these loads. However, if the weld zone (heat-affected zone of the weld metal and base metal) is subjected to a load in a high-temperature, high-pressure water environment, stress corrosion cracking (S C-; C) may occur. SCC
In order to suppress the occurrence of this, it is effective to reduce the stress acting on the welded portion 6.

If SCC occurs in the weld 6 and penetrates the weld metal or stub tube 2, reactor water will flow into the reactor pressure vessel 3.
It is also expected that the water will leak outside.

Therefore, it is extremely important to realize a structure that reduces the iiJ ability to generate SCC as much as possible.

Therefore, the present invention provides a CRD housing that has a proven track record of use.
It is an object of the present invention to provide a joining structure and a joining method for a CRD housing and a reactor pressure vessel, which improve the N5CC reliability of the welded portion without changing the materials of the stub tube and the weld metal 1.

``Structure of the Invention'' (Step ``F'' for Solving Problem 1) The present invention provides a nuclear reactor pressure vessel, a control rod drive housing that penetrates the top part of the pressure vessel, and a stub inside the pressure vessel. In the method of connecting via a tube, weld build-up is applied to the outer peripheral surface of the joint of the #4 control rod drive housing,
8 (Function) According to the present invention, a compressive circumferential residual stress is generated in the CRD housing by overlay welding, and then the part is welded to the stub tube. Because of the bonding process, the circumferential residual stress generated on the inner peripheral surface of the CRL housing can be significantly reduced.
Wear.

(Example) Hereinafter, the bonding force θ and the structure of the CRD housing and stub tube according to the present invention will be explained with reference to FIGS. 1 to 8.

FIG. 1 shows a C RD housing 1 constructed according to the present invention. A longitudinal section of the joint between the stub tube 2 and the reactor pressure vessel 3 is shown. The welded joint consists of a welded part 5 for joining the CRD housing 1 to the stub knob 2.

To manufacture such a structure, as shown in Figure 2 (゛,
1 History 1] 1) Housing) J1 pressure vessel 31. : Inserting and applying weld overlay to the joint part with stub tube 2 1. FIG. 11 schematically shows the deformation state near the built-up portion Mj8 of the CRD housing 1 in this case and the vertical distribution of the circumferential residual stress σ generated in the interior m of the CRD housing 1. Since the built-up portion shrinks after welding, the first flap of the CRD housing is tightened and deformed toward the inner circumference. Therefore, compressive stress in the circumferential direction is generated in the inner circumferential curve of the CHD housing 1 near the build-up. next
After locating the RD housing 1 and the stub tube 2, they are welded together (Fig. 3). After welding, the welded part shrinks, so the CRD housing 1 is attached to the stub tube 2.
The final residual stress σ in the circumferential direction is as shown in FIG. On the other hand, in the joint manufactured by the conventional method as shown in FIG. As shown in FIG. 8, a large positive residual stress is generated on the inner circumferential surface in the circumferential direction.

The maximum positive value of the residual stress σθ in FIG. 5 is significantly lower than that in FIG. 8. This means that stress, which is one of the causes of stress corrosion cracking, is removed, and C
The SCC resistance of the RD housing 1 is greatly improved. In addition, when creating the above-mentioned joint, CHD housing 1
The weld metal 6 that joins the stub tube 2 and the stub tube 2 is directly CRD.
It must be connected to the built-up portion 5 of the CRD housing 1 without touching the housing 1. This is because if the weld metal 6 is in contact with the CHD housing 1, that portion will be pulled toward the stub tube 2 side, producing positive residual stress, as in the case of FIG.

Another embodiment is shown in FIG. 6, but unlike the example in FIG. 1, this example has a structure in which the stub tube 2 is not beveled and the built-up portion of the CRD housing 1 and the stub tube are connected directly. The weld metal for is not in contact with the CRD housing 1. In this structure as well, the action of the built-up portion is the same as in the above example, and a compressive circumferential residual stress is generated on the inner circumferential surface of the CRD housing 1. Note that it is important that the stub tube 2 has no grooves from the viewpoint of the soundness of the stub tube 2. In addition, it is expected that the efficiency of the process will be improved due to the elimination of beveling.

Although the above example has a structure in which the CRD housing 1 and the reactor pressure vessel 3 are joined via the stub tube 2, the present invention can also be applied to cases where the pressure vessel 3 and various small-diameter housings are directly welded.

〔Effect of the invention〕

According to the present invention, compressive circumferential residual stress is generated in the CRD housing in advance by overlay welding and then the stub tube is welded to the CRD housing, thereby significantly reducing the circumferential residual stress occurring on the inner circumferential surface of the CRD housing. I can do it.

Therefore, it is possible to provide a highly reliable joint structure between a CRD housing and a stub tube that reduces the stress conditions that are one of the causes of stress corrosion cracking and reduces the probability of occurrence thereof.

In addition, in a structure where the stub tube is not beveled, the CRD housing and the stub tube are welded together in the same way as in the above example, resulting in a highly reliable joint structure that reduces residual stress, but the beveling is omitted. This allows for efficient provision.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a joint structure between a CRD housing and a stub tube showing an embodiment of the present invention, and FIGS.
The figure is a longitudinal sectional view showing the sequence of assembly of the joint structure according to the present invention, Figure 4 is a schematic diagram of the circumferential residual stress distribution generated on the inner circumferential surface when welding is applied to the CRD housing, and Figure 5 is C
A schematic diagram of the circumferential residual stress distribution that occurs on the inner circumferential surface of the housing when the HD housing is welded to the stub tube after welding overlay, and FIG. 6 is another embodiment of the present invention in which the stub tube is not beveled. Fig. Y is a longitudinal sectional view showing a conventional structure. ? FIG. V is a schematic diagram of the axial distribution of circumferential residual stress on the inner circumferential surface of a stub tube of a conventional structure. 1...CRD housing 2...Stub tube 1/3...Reactor pressure vessel 4...Inner hole 5...Weld build-up 6.7 Welding department representative Patent attorney Noriyuki Chika ■ Figure Figure Figure Figure Figure Figure 5 Figure Figure Figure Figure

Claims (1)

[Claims] In a method of joining a reactor pressure vessel and a control rod drive housing that penetrates the lower part of the pressure vessel via a stub tube inside the pressure vessel, weld build-up is constructed on the outer peripheral surface of the joint of the control rod drive housing. A method of joining the reactor pressure vessel and control rod drive housing, which then welds that part to the stub tube.