JPS6088389A - Recirculating piping system of boiling-water type nuclear power plant - 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 The present invention relates to a piping system for a nuclear power plant, and particularly to a piping system for a PLR system, which is a system for adjusting the flow rate of coolant supplied to a reactor core in a boiling water nuclear reactor.

The PLR system piping according to the prior art is shown in FIG.
The reactor pressure vessel is shown. The recirculation system piping attached to the reactor pressure vessel 1 has the following configuration.

Bent pipe section 20, straight pipe section 21 with tee, inlet valve 5, pump 7 for forced circulation of water in reactor pressure vessel 1, motor 8 for driving pump 7, outlet valve 9, main pipe 22
, cross branch pipe (hereinafter referred to as cross) 11, header bent pipe 1
2, the reducer 13, and the riser pipe 24 are constructed as shown in FIG. 1 by butt welding.

During operation of the BWR plant, coolant in the reactor pressure vessel 1 flows through the PLR system piping. That is, the pump 7 is driven, and the coolant in the reactor pressure vessel 1 sequentially passes through the bent pipe section 20, the straight pipe section with tee 21, the inlet valve 5, the pump 7, the valve 9, and the main pipe 22. It flows into the cross 11. The flow system of the coolant is divided by the cross 11, and a part of the coolant is directly injected from the cross 11 through the reducer 13 and the liger pipe 24 into a jet pump (not shown) in the reactor pressure vessel 1. . The remaining coolant, which is the majority, is discharged from the cross 11 through the header bend pipe 12 and the riser pipe 24 into the jet pump.

Figures 2 and 3 show details of the cross section.

The flow f0 from the main pipe becomes a branched flow at a cross branching point, into flows f1 and f2 in the header curved pipe direction and a flow f3 in the reservoir direction.

The flow in the cross pipe section is as shown in Figures 4 and 5.
A flow in which the vortex core penetrates the header curved pipes on both sides (fourth
(Fig.) and a hydrodynamically unstable flow that has no vortex in the center and exhibits a very irregular flow near the reducer portion 13, and these flows alternately repeat. In other words, in the flow in the cross pipe section, vortices occur and disappear, making the flow in the pipe unstable, and the flow resistance in each direction at the branch section fluctuates, and accordingly, the flow rate distribution to each riser pipe or The pressure drop will vary over time, which may lead to variations in the output of the BWR plant.

(Objective) The object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a nuclear power plant with stable operation.

(Key Points) A feature of the present invention is that a vortex is generated inside the cross-branch pipe, which is the intersection of the main pipe, the header bend pipe, and the riser pipe.
We focused on the fact that the flow becomes unstable due to the disappearance of water, and as a means to eliminate this unstable flow, we designed the inside of the cross tube to have a structure that always maintains the flow in a hydrodynamically stable state. The present invention was developed as a result of examining the flow situation in the cross tube through visualization experiments.

(Examples and their effects) Hereinafter, one embodiment of the present invention will be described with reference to FIG.

FIG. 6 shows an overall view of a preferred embodiment of the present invention, with the PLR system piping cross pipe section removed. Components that are the same as those in the conventional example shown in FIG. 3 are designated by the same reference numerals.

This structure has a tee 31 without a cross section facing the main pipe 22.

As described above, this embodiment has a Tee structure, so that irregular flow in the reducer part is less likely to occur. That is, the Tee-shaped tube can maintain stable flow distribution in the PLR system piping. As a result, the flow resistance in each direction from the Tee branch does not change, and the flow distribution and pressure loss from each lie to the pipe are constant, and the BWR output fluctuation is
suppressed. In addition, the flow inside the reactor is stabilized, which is a favorable situation from the viewpoint of material strength.

FIG. 7 is an overall view in which the cross branch pipe is eliminated and a tee 32 is further constructed below the tee 31 in FIG. 6, and the same effects as described above are achieved in this embodiment as well.

In this embodiment, the arrangement of the reactor pressure vessel 1 and the PLR piping system is the same as that of an existing domestic plant.

FIG. 8 shows how to raise the position of the reducer 13 (lengthen the straight pipe part of the cross 33 facing the main pipe 22) so that the irregular flow in the reducer part of the conventional structure is not applied to the header curved pipe 12. FIG. 2 is a schematic diagram of a branch pipe section in which irregular flow is alleviated. In the case of this embodiment as well, effects similar to those described above are achieved.

Figure 9.10 shows the riser pipe 24 from the cross pipe section and bent pipe 12.
In order to improve unstable fluctuations in the flow caused by the generation and disappearance of vortices at the branch section where the vortex branches into the This example includes a cross 34, a branch 35, a cap 36, and a branch 37 that eliminate stagnation and improve unstable fluctuations.

FIG. 11 is a schematic diagram of a PLR system piping structure having a reducer 35 in order to throttle and stabilize the unstable flow at the cross branch. In this embodiment, the flow is also forced and suppresses flow rate fluctuations. However, the same effect as above is achieved.

(Effects of Activation) According to the present invention, the generation of vortices in the cross pipe section is prevented or stabilized, and flow rate fluctuations in the PLR system are eliminated, making it possible to operate the BWR plant stably.

[Brief explanation of drawings]

Figure 1 is a structural diagram of the conventional PLR system piping of a BWR plant, Figures 2 and 3 are structural diagrams of the cross shown in Figure 1, and Figure 4 is a structural diagram of the conventional PLR system piping of a BWR plant.
, 5 is an explanatory diagram of the flow state of the coolant at the cross portion, and FIGS. 6, 7, 8, 9, 10, and 11 are examples of the present invention. 1...Reactor pressure vessel, 7...Pump, 11...Cross, 12
...Header bent pipe, 13...Register, 22...Main pipe, 24...
Riser pipe, 31, 32...Tee 33, 34...Cross, 3
5... Branch, 36... Cap. Agent Patent Attorney Akio Takahashi Continuation of page 1 (72) Inventor Ikuo Kodama 4-6 Kanda Surugadai, Chiyoda-ku, Tokyo Hitachi, Ltd. (72) Inventor Isao Nemezawa 3-1 Saiwaimachi, Hitachi City 1
No. Hitachi Factory, Hitachi, Ltd. (72) Inventor Akimasa Izumiyama 3-1-1 Saiwai-cho, Hitachi City
No.: Hitachi Factory, Hitachi, Ltd. (72) Inventor: Koichi Suzuki 3-1-1 Saiwaimachi, Hitachi City
No. Hitachi Factory, Hitachi, Ltd. (72) Inventor Nobuo Kosugi 3-1-1 Saiwaimachi, Hitachi City
No.: Hitachi Factory, Hitachi, Ltd. (72) Inventor: Hidetoshi Takehara 3-1-1 Saiwaimachi, Hitachi City
No. Hitachi, Ltd. Hitachi Factory

Claims (4)

[Claims] 1. In the cross branch having openings on all sides, the first opening is connected to a main pipe connected to a recirculation pump outlet;
A second opening facing the opening is formed of a reducer portion whose flow passage cross-sectional area gradually decreases, and a riser pipe is formed integrally with the resistor at a portion where the flow passage cross-sectional area of the reducer portion is the minimum. , the two third and fourth openings of the cross branch to which the main pipe and the reducer are not connected,
A header bent pipe is connected to each. A BWR plant characterized by having a structure that always stabilizes flow rate distribution in a cross branch in a recirculation piping system (hereinafter referred to as a PLR piping system) of a boiling water nuclear power plant (hereinafter referred to as a BWR plant). PLR piping system. 2. 2. The PLR piping system for a BWR plant according to claim 1, wherein the cross branch part has a structure that eliminates the cross branch and always stabilizes flow rate distribution. 3. At the cross-branched part, a bulge is added to the branch part,
P of the BWR plant according to claim 1, characterized in that it has a structure that stabilizes the flow distribution of the branch part.
LR piping system. 4. Claim 1, characterized in that the cross branch part has a structure in which a reducer part provided at the second opening is provided at a position away from the cross branch part to stabilize flow distribution in the branch part. PLR piping system of BWR plant.