JPS608594A - Distributing pipe of recirculating piping for nuclear reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to recirculation piping for boiling water nuclear power plants, and in particular, measures against stress corrosion cracking, inspection performance, installation performance, and limited space during modification. This invention relates to a piping structure suitable for dealing with.

[Background of the invention]

Conventional recirculation piping will be explained below with reference to FIGS. 1 and 2.

FIG. 1 shows an elevational view of the piping system, and FIG. 2 shows a plan view of FIG. 1.

In Figure 1, 1 is a reactor pressure vessel (hereinafter abbreviated as RPV), 2 is a main pipe that connects directly to the RPVI and is composed of straight pipes, elbows, and tees, and 3 is a pump for forced circulation of coolant. and a motor, 4 is a main pipe that guides the coolant pressurized by the pump 3 to the RPV, 5 is a cross for branching from the main pipe 4, 6 is a distribution pipe that is distributed from the main pipe 4 and the cross 5, and 7 is a A reducer 8 attached to the top of the cross 5 guides the coolant from the distribution pipe 6 to the RPVI (representing a riser pipe).

The distribution pipe 6 has a structure that requires a nozzle 9 in order to branch to the riser pipe 8.

Further, the riser pipe 8 and the main pipe 2.4 are made of a welded structure composed of straight pipes and joints of standard dimensions and structure. 1o
indicates the inlet/outlet valve of Bomb 3.

FIG. 2 shows the planar configuration of FIG. 1.

The recirculation piping for a boiling water nuclear power plant consists of the main piping 2 and 4, the pump 3, etc. as shown in the figure, in view of connection with the rLPV 1, ease of installation, and ease of assembly.

The conventional technology has the following drawbacks due to the structure and configuration described above.

(1) From the perspective of SCC in domestic and overseas plants, standard dimensions and
It is a welded structure that uses O1-made pipes and fittings, and has a structure with extremely high SCC potential. Moreover, since -SU8304 is used, there is a concern that the occurrence of SCC caused by the high tensile residual stress in the weld and the combination of three conditions of material and environment is extremely high.

(2) As a measure against SCCO during operation, the adoption of low-carbon stainless steel is being promoted, and as a result, the timber sill 1 is being replaced at every periodic inspection. In this case, unlike the installation space at the time of construction, it is necessary to carry the replacement material for the piping into a very narrow and limited space due to the layout and setting of other equipment and equipment, and the installation Because it is necessary to reduce work under high radiation conditions as much as possible, it is necessary to simplify piping routes and improve installation ease as much as possible.
It is essential.

In particular, in the distribution pipe 6, at the welded part between the cap 11 and the distribution pipe 6 in FIG. Due to the occurrence of SCC, in addition to changing the material of the replacement pipe, it is necessary to consider a method and structure for replacing only the end of the distribution pipe. When considering the structure, it is desirable to be able to improve the structure without changing the existing mounting position as much as possible from the perspective of stress analysis, etc.

[Purpose of the invention]

The purpose of the present invention is to improve the reliability of the piping system and improve the workability of the piping system in order to eliminate the drawbacks of the prior art described above. It is about providing.

[Summary of the invention]

The feature of the present invention is that 8CC resistant material is used to prevent 8CC of pipe welds in existing plants in distribution piping, and as a countermeasure against SCC that occurs only in the end caps of distribution piping in existing plants. Consider the following points: High frequency bending, hot bending. The piping structure has pipes bent by cold bending or the like.

(1) Ensuring smooth flow of internal fluid and proper circulation of coolant into the RPV.

+2) Reduced welded parts to eliminate SCC potential.

(3) Reduction of radiation exposure of workers due to the above.

(4) Improved installation efficiency by taking into account the usability of existing space [Embodiments of the invention] An embodiment of the present invention is shown in FIGS. 3 to 6.

FIG. 3 shows an elevational view of a distribution piping structure according to the invention. 5
, 6, 7.8 indicate the cross, distribution pipe, reducer, and riser pipe described in the prior art. 121d, a reducer for mating with a conventional distribution pipe 6; 13, a three-dimensional bent pipe according to the invention;

FIG. 4 shows a plan view of FIG. 3. As shown in Figure 4, it is necessary to equalize the maintenance space by making the distance L of the riser pipe 8 from the center of the RPV as uniform as possible. When remodeling, it is necessary to place it as much as possible within the space at the time of installation. For this reason, although the details will be described later, a three-dimensional bent pipe 13 is required.

FIG. 5 shows details of the three-dimensional bent pipe 13. In order to deal with the distribution pipe 6 which has a radius of large curvature, JIS and A
It is necessary to engage the riser pipe 8 by using a reducer 12 or the like specified in the NSI standard or the like. For this reason, the length Ll from the center of the adjacent riser pipe 8 in the distribution pipe 6 (a distance greater than the outer diameter of the distribution pipe 6 from the center of the welded part of the nozzle holder provided in the distribution pipe for SCC countermeasures) is required. The reducer 12 is directly attached to a distribution pipe that has a (preferable in terms of processing residual stress caused by welding)

By installing this reducer 12, there will be a difference in the radius of curvature of the distribution pipe 6, and in order to install it straight on the small diameter side of the reducer 12 without changing the position of the riser pipe, it is necessary to It is necessary to have a two-dimensional bending radius R2. Furthermore, on the side that interfaces with the riser pipe 8. S
As a countermeasure against CC, by reducing the number of weld lines as much as possible.
In order to eliminate the potential for SCC generation, it is necessary to have a two-dimensional bending radius. Moreover, in the bent portion on the riser pipe 8 side, an angle α is formed in order to geometrically balance the positions of the reducer 12 and the riser pipe 8. As described above, improving the piping structure without changing the connection position of the riser pipe 8 inevitably requires three-dimensional bending. Hereinafter, the three-dimensional bent pipe 13 will be explained based on the symbols shown in FIG. A reducer 12 is attached facing the center of the large radius of curvature of the distribution pipe 6 and having the above-mentioned dimension L1 and linear length L2. Since it is welded to the reducer 12, the position of the parallel straight pipe part LH (straight pipe part for securing grip margin for bending described later and ultrasonic flaw detection during operation), and the position of the riser pipe 8. This is a three-dimensional bent pipe 13 consisting of a bending radius R2 for not changing the bending radius R2, a bending radius Rs on the side that engages with the straight pipe portion L4 and the riser pipe, and an angle α that interfaces with the riser pipe 8.

FIG. 6 shows details of the shape of the side that interfaces with the riser pipe 8 explained in FIG. 5. In the figure, −L4 is a parallel straight pipe section L< that is designed to match the height of the reducer section 7 and to be welded to the riser pipe 8, considering the inspectionability of the entire distribution pipe.
It has a structure with (a gripping margin or pushing margin for bending, which will be described later, and a straight pipe portion to ensure sonic flaw detection during M-rolling).

I will now explain the process of bending.

(1) Bending method: High frequency bending, hot bending, or cold bending.

(2) Bending conditions: In the case of high-frequency bending and hot bending, a bending condition of around 1000'c is preferable in terms of bending workability. Further, in cold bending, room temperature or extremely low temperature is preferable.

(3) Bending procedure; a. In the case of high-frequency bending, a master pipe is used that has gripping and pushing allowances at each bending end depending on the capabilities of the processing machine, taking into account thinning of the bending part in advance, and the high-frequency bending part is cooled by water cooling or air cooling. by.

In addition, in the case of hot or cold bending, Depending on the mold according to the specified bending radius Shall be molded.

mouth. After bending, residual stress due to bending Solution heat treatment to reduce force shall be applied.

From the viewpoint of manufacturing a three-dimensional bent pipe using the above-mentioned bending procedure, there is no particular problem with the existing bending techniques in satisfying the specifications stipulated in domestic and international standards and standards.

〔Effect of the invention〕

According to the present invention, the cap structure at the end of the distribution pipe of the conventional structure can be made into a three-dimensional bent pipe, so that the following effects can be obtained.

(1) Since it is possible to smooth out the turbulent flow rate distribution of the coolant flowing inside the pipe in the case of a cap structure,
The distribution capacity of coolant circulated within the RPV is equalized. This can contribute to improving the circulation capacity of the coolant, which in turn contributes to improving the output and reliability of the plant.

(2)'! ! In addition, when considering SCC countermeasures at the welds between caps and distribution pipes, rather than cases of SCC occurrence in overseas plants, local piping replacement is possible.
The responsiveness of CC countermeasure methods increases.

(3) Since there are two fewer weld lines compared to the conventional structure (cap structure), it is possible to shorten the installation process and reduce radiation exposure for workers when replacing piping.

(4) It can contribute to improving the reliability of the plant by reducing the SCC generation potential.

An example of application of the distribution pipe structure of the present invention is shown in FIG.

This structure shows the integration of the riser pipe 8, the three-dimensionally bent pipe 13, and the reducer 12. Further, in this structure, even if the structure is constructed with a welded structure such as an elbow and a straight pipe, or if it is constructed with a structure in which the bending radius and bending angle are changed, these are also considered to be part of the present invention.

[Brief explanation of drawings]

1 and 2 are a front view and a plan view of a recirculation pipe with a conventional structure, FIGS. 3 and 4 are a front view and a plan view of a distribution pipe according to the present invention, and FIG. 5 is an A of FIG. Detailed view of the part,
FIG. 6 is a view taken along arrow B in FIG. 5, and FIG. 7 is a diagram illustrating an example of application of the present invention. 1...RPV. 2... Main piping, 3... Pump and motor, 4... Main piping, 5... Cross, 6...
Distribution pipe・7...reducer, 8...riser pipe, 9
... Nozzle stand 10 ... Pump and motor inlet/outlet valve,
11...Cap, 12...Reducer, 13...
・Three-dimensional bent pipe ・14...Bent pipe. -601-

Claims (1)

[Claims] 1. Reactor recirculation piping in a boiling water nuclear power plant has a straight pipe section at one end for attaching to the end of the distribution pipe and a part that connects with the riser pipe, and the middle part of each of the pipes perpendicular to the straight pipe is horizontal. A distribution pipe for nuclear reactor recirculation piping, characterized in that it has a three-dimensional bend consisting of a bent pipe section bent by high frequency, hot, cold bending, etc. so that it is two-dimensional in the vertical direction. cormorant