JPH01196596A - Connection part of control rod driving mechanism housing and reactor pressure vessel - Google Patents

Abstract

PURPOSE:To lower the generation of a stress corrosion crack, by welding the peripheral surface of a CRD (control rod driving mechanism) housing to a cylindrical seat while allowing force to act on the welded part of the CRD housing and the upper end of a stub tube. CONSTITUTION:A stub tube 2 is brought into contact with the through-hole 9 provided to the inner surface of the bottom plate of a pressure vessel and the welded parts 4, 5 of the inner and outer peripheries of the lower end of the stub tube 2 are subjected to fillet welding. A cylindrical seat 8 is brought into contact with the outer surface of the bottom plate of the pressure vessel 1 at the position of the through-hole 9 and the ridge 8a thereof is subjected to fillet welding on both sides thereof. A CRD housing 3 is inserted through the stub tube 2, the through-hole 9 and the cylindrical seat 8 and welded to the upper end of the stub tube 2. The under surface of the cylindrical seat 8 is welded to the CRD housing 3 while the upward force acting on the welded part of the CRD housing 3 and the upper end of the stub tube 2 and the force having equal magnitude in the opposite direction are allowed to act on the CRD housing at the operation time of a nuclear reactor. By this method, the stress corrosion crack-resistant reliability of the welded part is markedly enhanced.

Description

Detailed Description of the Invention [Object of the Invention (Industrial Application Field) The present invention provides a control rod drive mechanism housing for a boiling water nuclear reactor (
This relates to the joint between the CRD housing (hereinafter referred to as the CRD housing) and the reactor pressure vessel (hereinafter referred to as the pressure vessel).

(Prior art) The output of a boiling water reactor is generated by inserting and removing control rods containing neutron absorbers between fuel assemblies that are regularly arranged at predetermined intervals within a pressure vessel. adjust. The control rod is moved up and down in the axial direction within the control rod guide tube, and the portion that is pushed up and protrudes from the control rod guide tube is inserted between the fuel assemblies, absorbs neutrons, and controls the nuclear fission reaction. It is something. The vertical movement of the control rod is performed by a CHD, and this CRD is a cylindrical CHD that penetrates the bottom of the pressure vessel.
contained within the housing. The CHD housing supports the control rod guide tube and also supports the control rod drive mechanism (
It houses the CHD (hereinafter referred to as CHD) and is welded to the bottom of the pressure vessel via a stub tube.

FIG. 8 shows a joint between a conventional CHD housing and a pressure vessel. In this figure, the lower end of a stub tube 2 is welded to the inner surface of the bottom plate of a pressure vessel 1 at its inner and outer circumferences. In addition, the stub tube 2 has a CHD
A housing 3 is inserted, and the upper end of the stub tube 2 is welded to the CHD housing 3. In addition, 4 in the figure
．． 5.6 each shows a welded part.

In the above joint structure, the CRD housing 3 is made of austenitic stainless steel (SUS304 TP, 5US316TP, or an improved material thereof) from the viewpoint of high temperature strength and corrosion resistance. The pressure vessel 1 is made of low-alloy steel, and its inner surface is lined with a thin stainless steel plate 7 for corrosion resistance. In order to improve welding and joining with the stub tube 2 on the inner bottom surface of the pressure vessel 1, buttering of Inconel 182 is applied to the lining.

In addition, the stub tube 2 has a coefficient of thermal expansion between that of austenitic stainless steel and low alloy steel, and is effective in alleviating thermal stress between the CRD housing 3 and the pressure vessel 1, and its properties hardly change due to welding heat treatment. It is made of a material such as a nickel-based alloy such as Inconel 600.

The welded parts 4 (inner periphery of the stub tube), 5 (outer periphery of the stub tube), and 6 (upper end of the stub tube) between the CHD housing 3 and the stub tube 2, and between the stub tube 2 and the pressure vessel 1 are made of Inconel 82 and Inconel, respectively. 1
82.

(Problems to be Solved by the Invention) In a boiling water nuclear reactor equipped with a joint having the above configuration, during operation, the coolant in the pressure vessel is high-temperature, high-pressure water at 288° C. and 80 atm. At this time, the weight of the control rod guide tube, the control rod, the CHD (none of which is shown), and the CHD housing 3 acts on the welded portion 6 between the CRD housing 3 and the stub tube 2 . In addition, the CRD housing 3 that penetrates the bottom plate of the pressure vessel 1 and protrudes outside the vessel,
The force of the high-temperature, high-pressure water that tries to push it out of the pressure vessel 1 also acts.

Of course, the welded portion 6 is designed to be able to resist each of the above-mentioned forces, but since it is in a corrosive environment of high-temperature, high-pressure water, there is a risk of stress corrosion cracking (hereinafter referred to as SCC) occurring. At present, not everything has been elucidated regarding the SCC resistance reliability of the welded portion 6, and many studies are being conducted to elucidate it.

If SCC occurs in the weld 6 and penetrates the weld, reactor water will leak from the pressure vessel 1, causing a serious accident.

Maintaining the health of nuclear reactors is socially important. Therefore, it is extremely important to prevent SCC from occurring in the welded portion.

The present invention has been made based on the above-mentioned circumstances, and the present invention improves the SCC resistance reliability of the welded part while keeping the materials of the CRD housing and stub tube the same as those of the conventional ones.
The purpose is to provide a joint between the RD housing and the pressure vessel.

[Structure of the Invention] (Means for Solving the Problems) The joint portion between the CRD housing and the pressure vessel of the present invention includes a control rod drive mechanism housing that penetrates the bottom plate of the reactor pressure vessel, and a control rod drive mechanism housing that penetrates the bottom plate of the reactor pressure vessel, and the control rod on the inner surface of the bottom plate. The reactor pressure vessel of the control rod drive mechanism housing includes a stub tube that is provided surrounding the drive mechanism housing and is welded to the inner surface of the bottom plate at the lower end and to the peripheral surface of the control rod drive mechanism at the upper end. When a cylindrical seat welded to the outer surface of the bottom plate is engaged with the part that hangs outward, and the control rod drive mechanism housing and the stub tube are restrained in the axial direction, the control rod drive mechanism housing and the stub tube are connected to each other during reactor operation. The control rod drive mechanism housing surface is welded to the lower surface of the cylindrical seat while applying a force opposite to and equal in magnitude to the upward force applied to the welded portion with the upper end of the stub tube.

(Function) At the joint between the CRD housing of the present invention and the pressure vessel having the above configuration, a force of the same magnitude and in a direction opposite to the upward force that acts on the weld between the CRD housing and the upper end of the stub tube during reactor operation is applied. Since the CHD housing surface and the cylindrical seat are welded together while acting, the above-mentioned upward force during reactor operation is eliminated. Therefore, the load conditions that would cause SCC to occur in the welded portion in the pressure vessel are removed, the risk of SCC occurring is greatly reduced, and there is no risk of reactor water leakage or other troubles that could lead to accidents for personnel.

(Embodiment) FIG. 1, in which the same parts as in FIG. 8 are denoted by the same reference numerals, is a longitudinal cross-sectional view of one embodiment of the present invention. In this figure, a cylindrical seat 8 made of the same material is engaged with the portion of the stub tube 3 that protrudes outside the pressure vessel 1. The surface of this cylindrical seat 8 facing the outer surface of the bottom plate of the pressure vessel 1 is a concave curved surface matching the curvature of the outer surface of the bottom plate.
is provided. The cylindrical seat 8 is welded to the outer surface of the bottom plate of the pressure vessel 1 by welding portions 10.11 on both the inner and outer sides of the protrusion 8a. Also, CHD housing 3
is welded to the lower end of the cylindrical seat 8 at a welded portion 12.

The joint portion having the above structure is constructed in accordance with the procedure described below with reference to FIGS. 2 to 4. That is, as shown in FIG. 2, first, the stub tube 2 is brought into contact with the position of the through hole 9 on the inner surface of the bottom plate of the pressure vessel 1, and the welded portion 4 on the inner and outer periphery of the lower end of the stub tube 2 is inserted.
．． As shown in FIG. 3, the cylindrical seat 8 is brought into contact with the through hole 9 on the outer surface of the bottom plate of the pressure vessel 1.
This constitutes a welded portion 10.11 on both sides of the protrusion 8a. Further, as shown in FIG. 4, the CHD housing 3 is inserted into the stub tube 2, the through hole 9, and the cylindrical seat 8, and the position of the CRD housing 3 is determined accurately.

The CHD housing 3 and the upper end of the stub tube 2 are welded together. Finally, while applying the downward force P to the CHD housing 3, a welding portion 12 is formed between the lower surface of the cylindrical seat 8 and the CHD housing. Note that R in the figure indicates a welding rod.

The force P to be applied when constructing the joint of the present invention as described above is determined as follows.

First, as shown in FIG. 5, the length between the inlet of the stub tube 2 and the outlet of the cylindrical seat 8 of the CRD housing 3 is fl, and the cross-sectional area of the CHD housing 3 is A. Also, the distance from the upper end of the stub tube 2 to the lower end of the cylindrical seat 8 is h, the dimension of the shortest part of the stub tube 2 in the axial direction is h, the dimension of the longest part of the cylindrical seat 8 in the axial direction is h3, and the distance between the shortest part and the longest part of the stub tube 2 is h3. Let the distance between the parts be h2.

When the reactor is in operation, if there is no restraint, the portion of length ρ and the portion of length h are given by the following formula d
12. Shows the thermal expansion of dh.

dQ=αC・ΔT−Q Town・1・・Town・・・・
(1) dh=(C5(hi+h2)+αa-h2)・
ΔT ・・・・・・・・・・・・・・・・・・(2) Here,
ΔT indicates the temperature difference between the reactor's shutdown state and operating state. Further, αC1αS and αa respectively indicate the coefficient of thermal expansion of the material of the CRD housing 3, the material of the stub tube 2, and the material of the reactor pressure vessel 1.

However, in reality, the CRD housing 3 is
and 12, and the rigidity of the stub tube 2 is greater than that of the CHD housing 3, so the amount by which the CRD housing 3 can expand and contract is approximately equal to dh. As a result, a compressive force P given by the following equation acts on a portion of the length Q of the CRD housing 3.

P=AXEX (d Q-d h)/ (fl+α Q
)................................................................... (3) where E is the Young's modulus of the CHD housing material. This force P acts upward on the weld 6.

Therefore, after welding and joining the CHD housing 3 and the stub tube 2, the CHD housing 3 is
By welding (welding part 12) to the lower end of cylindrical seat 8, the force acting on welding part 6 during reactor operation can be reduced to O. In addition, pressure, control rods, CRD housing 3,
The downward force based on the weight of the guide tube and the like is supported by the welded portion 12 on the outside of the pressure vessel 1.

As a result, the load condition, which is one of the conditions for the occurrence of SCC in the welded portion 6 in the pressure vessel 1, where the occurrence of SCC can cause a serious accident, can be removed, and the risk of occurrence of SCC can be significantly reduced.

Therefore, the reliability of the joint between the CHD housing and the pressure vessel can be improved.

FIG. 7, in which the same parts as in FIG. 1 are given the same reference numerals, shows another embodiment of the present invention. In this embodiment, the present invention is applied to an existing nuclear reactor, and one cylindrical seat is divided into two pieces 13a, 13a in a plane including the axis as shown in FIG. It is said to be 13. This 2
The divided piece 13a of the divided cylindrical seat 13 is engaged with the CHD housing 3 hanging outside the pressure vessel 1, and after welding between the divided pieces, it is welded to the bottom plate of the pressure vessel 1 (welded part 11).
While applying the force P to the RD housing, the CRD
The housing 3 and the lower surface of the two-part cylindrical seat 13 are welded together (welded portion 12). In this way, the cylindrical seat, through which the CHD housing 3 passes, can be welded to the bottom plate of the pressure vessel of an existing nuclear reactor. It goes without saying that this embodiment also provides the same functions and effects as those of the embodiment described above.

[Effects of the Invention] As is clear from the above, at the joint between the control rod drive mechanism housing and the reactor pressure vessel of the present invention, all the downward force acting on the control rod drive mechanism housing is directed outside the pressure vessel. This acts on the welded portion between the housing and the cylindrical seat joined to the bottom plate of the pressure vessel, and the load on the welded portion between the housing and the stub tube inside the pressure vessel is significantly reduced. Therefore, no force is applied to the welds inside the pressure vessel during reactor operation, and as mentioned above, load conditions such as various dead weights, which are one of the conditions for SCC occurrence, are eliminated, and the welds SCC resistance of
Reliability is significantly improved, and the cause of serious accidents can be eliminated, which is extremely beneficial for maintaining the integrity of the nuclear reactor.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of one embodiment of the present invention, FIGS. 2 to 4 are longitudinal sectional views showing the order of construction of the embodiment, and FIG. 5 is necessary for explaining the operation of the embodiment. 6 is a perspective view of the main parts of another embodiment of the present invention, FIG. 7 is a longitudinal sectional view of the other embodiment, and FIG. 8 is a diagram of a conventional joint. FIG.

Claims (1)

[Claims] a control rod drive mechanism housing that penetrates the bottom plate of the reactor pressure vessel; and a control rod drive mechanism housing provided on the inner surface of the bottom plate surrounding the control rod drive mechanism housing, and welded to the inner surface of the bottom plate at a lower end and to the peripheral surface of the control rod drive mechanism at an upper end. A cylindrical seat welded to the outer surface of the bottom plate is engaged with a portion of the control rod drive mechanism housing that hangs outside the reactor pressure vessel, and the control rod drive mechanism housing and the When the stub tube is restrained in the axial direction, while applying a force equal in magnitude and opposite to the upward force that acts on the weld between the control rod drive mechanism housing and the upper end of the stub tube during reactor operation, A joint portion between a control rod drive mechanism housing and a reactor pressure vessel, characterized in that a peripheral surface of the control rod drive mechanism housing is welded to a lower surface of the cylindrical seat.