JPS6359039B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a jet pump for supplying the required coolant flow rate to a reactor core, particularly in boiling water nuclear reactors.

Jet pumps in boiling water reactors are installed in the reactor recirculation system. The reactor recirculation system is shown in Figure 1, and a jet pump 2 installed in the reactor pressure vessel 1 constitutes the reactor recirculation system together with a recirculation pump 3 to respond to changes in reactor power. The required amount of coolant is supplied to the core 4. A part of the coolant 5 circulating in the reactor core 4 is taken out to the outside of the reactor pressure vessel 1, and after being pressurized by the recirculation pump 3, it is pumped out from the nozzle of the jet pump 2 at high speed as the driving fluid for the jet pump 2. Injected. The remaining coolant is sucked into the jet pump as indicated by the bold arrow A due to the pressure drop in the absorption section at the nozzle outlet due to this high-speed jet. After the coolant is sufficiently mixed with the driving fluid in the jet pump 2, it is sent to the lower core plenum 7.

The structure of a conventional jet pump is shown in FIG.
In the figure, 10 is a riser elbow, 11 is a riser pipe, 12 is a transition piece, 13 is an elbow, 14 is a nozzle, 15 is a mixer, 16 is a diffuser, 17 is a bracket, 18 is a support, 1
9 is a wedge, 20 is a beam, 21 is a mounting bolt, and 22 is a riser brace.

The riser elbow 10, the riser pipe 11, and the transition piece 12 are substantially integrally formed by welding, and the end of the riser elbow 10 is fixed to the reactor pressure vessel by welding. Further, in order to prevent the riser pipe 11 from vibrating in the lateral direction, it is fixed to the pressure vessel by a riser brace 22.

In a jet pump, the most important structurally and functionally are the elbow 13, nozzle 14, and mixer 1.
5, the inner diameter of the nozzle through which high-temperature, high-pressure fluid flows at high speed wears out over time due to erosion and corrosion during operation, causing the inner diameter to increase, resulting in a decrease in performance and the inability to obtain the required core flow rate. Since there is a risk that the product may become damaged, it is designed to be able to be removed and replaced. That is, the elbow 13, the nozzle 14, and the mixer 15 are each substantially integrally assembled by welding, but the transition piece 12 and the differential user 16 are not welded but mechanically assembled so that they can be removed from their joints. connected in a specific manner. Details of these attachment parts are shown in FIGS. 3, 4 and 5.

First, the attachment portion between the transition piece 12 and the elbow 13 is shown in FIGS. 3 and 4, and in these figures, 12 is the transition piece;
13 is an elbow, 20 is a beam, 21 is a mounting bolt, 23 is a retainer, 24 is a bolt, 27 is a transition piece arm, arrow B is the pulling direction of the beam 20, and arrow C is the tightening direction of the mounting bolt 21. . Transition piece arms 27 are arranged opposite both sides of the elbow 13 and are welded to the transition piece 12. Grooves 27A are formed on opposite sides of the transition piece arm (hereinafter referred to as arm) 27.
is formed. The beam 20 is a mountain-shaped plate with a screw hole formed in the center thereof passing through the beam in the vertical direction, both ends of which are inserted into the grooves 27A of the arm, and the mounting bolts 21 are screwed into the screw holes. and move the elbow 13 to the transition piece 12.
In order to press the beam 20, the beam 20 is pulled in the direction of the arrow B using a handling tool (tensioner) prepared in advance, and the mounting bolt 21 is tightened in the direction of the arrow C while the tensile force is applied to the beam 20. Also, the mounting bolt 21 is attached to the elbow 13.
It is attached by the retainer 23 and bolts 24 in a pressed state.

FIG. 5 shows the installation details of the mixer 15 and the differential user 16. 15 is a mixer, 16 is a differential user, and mixer 15 is mechanical (spill type).
It is inserted into the differential user 16.

Returning to FIG. 2, the bracket 17, support 18,
A wedge 19 is provided, and a bracket 17
is welded and fixed to the riser pipe 11 so as to surround the mixer 15 in a league shape, and a wedge 19 is driven into the gap between the bracket 17 and the mixer 15 to prevent lateral vibration. The wedge 19 is attached to a support 18 welded to the mixer 15 to prevent it from falling off.

By the way, in the jet pump described above, the removable elbow 13, the nozzle 14, the beam 20 that tightens the mixer 15, and the mounting bolts 21 are operated by the pressure difference between the inside of the jet pump and the reactor, and the kinetic energy of the driving fluid inside the jet pump. It is necessary to ensure sufficient tightening force against this, resulting in the highest structural stress, and since it has threaded parts, the stress is particularly high at the bottom of each screw, which is a disadvantage that tends to cause fatigue failure, crevice corrosion, etc. have. In the event that the beam 20 or the mounting bolts 21 are damaged, the elbow 13,
The welded assembly of the nozzle 14 and mixer 15 was scattered,
There is also the possibility that other structures inside the reactor pressure vessel, which is the heart of a nuclear power plant, may be damaged. The jet pump is the most important equipment located at the heart of the surrounding nuclear power plant, and improving the above-mentioned shortcomings and problems is extremely important from the perspective of plant reliability and safety. That's true.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned drawbacks of the prior art and to provide a jet pump in which the beam and mounting bolts are free from damage.

In the jet pump according to the present invention, a beam having a protrusion integrally formed at the lower center thereof that presses the top of the elbow is inserted into a groove of a transition piece arm arranged oppositely, with both ends of the beam engaged. At least one end of the beam is brought into contact with one end of a mounting bolt screwed into a screw hole of the transition piece arm, and the elbow is pressed against the elbow by threading the mounting bolt.

Hereinafter, the present invention will be explained in detail based on the drawings. Components that are the same as those of the conventional example are indicated by the same reference numerals. FIGS. 6 and 7 are a partially external perspective view and a partially sectional view showing a preferred embodiment of the present invention. In these figures, the main components relevant to the invention are transition piece arm 2.
7, transition arm bolt (hereinafter referred to as attachment bolt) 28, beam 29, and elbow 13.

The transition piece arm 27 has grooves 27A formed on opposing sides as in the conventional case, and both ends of the beam 29 can be inserted and removed freely, but there are screw holes 27B penetrating the grooves 27A on both sides.
are formed respectively. A mounting bolt 28 is screwed into this screw hole 27B so that it can move forward and backward. The beam 29 is a trapezoidal plate with both ends protruding, and a cylindrical protrusion 29A is integrally formed at the lower center thereof. The protrusion 29A is inserted into a recess provided at the top of the elbow in the shape of a pin.

Therefore, by rotating and threading the mounting bolt 28, the lower end of the mounting bolt 28 presses both ends of the beam 29, and as a result, the projection 29A of the beam 29 presses the top of the elbow. The retainer 23 and the bolt 24 are used to attach the protrusion 29A, and the keeper 30 is used to prevent the mounting bolt 28 from rotating. As a result of this action, it not only satisfies the original performance of a jet pump, but also eliminates problems such as fatigue failure and crevice corrosion that occur due to the threaded portion being formed in the part of the beam where the stress is highest. The beam will be highly reliable. Furthermore, since the beam does not require screwing in mounting bolts, a shape that can avoid stress concentration can be selected. On the other hand, the transition piece arm is made of molybdenum-containing stainless steel, which is strong in strength and resistant to crevice corrosion, and is very suitable for preventing crevice corrosion, which is a problem in bolt structures. In addition, since the mounting bolt is screwed into the transition piece arm, the load on the mounting bolt is reduced to half of the conventional one due to the lever principle, making it easy to reduce the stress added to the mounting bolt, reducing fatigue failure and crevice corrosion. It can be made stronger against

Regarding the removability of the beam and elbow,
It is as good as before. That is, by loosening the mounting bolts and rotating the beam parallel to the transition piece arm, the beam and elbow can be removed upward. Assembly can be done by reversing this procedure.

Another embodiment of the invention is shown in FIG. That is, in this case, the mounting bolt 28 is attached only to one side of the transition piece arm 27, and the upper surface of the groove 27A of the transition piece arm 27 on the other side where the mounting bolt 28 is not attached.
The ends of the beams 29 are in direct contact. In this case as well, the tightening load applied to the mounting bolt 28 is half of the conventional one, and the same effect as in the previous embodiment is achieved.

As described above, according to the present invention, there is no risk that the beam and the mounting bolts will be damaged during operation.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a recirculation system in a boiling water reactor, Figure 2 is an overall structural diagram of a conventional jet pump, and Figures 3 and 4 are the installation of the transition piece and elbow shown in Figure 2. FIG. 5 is a structural diagram of the attachment portion of the mixer and differential user shown in FIG. Fig. 8 is a structural diagram of a transition piece and an elbow attachment part according to another embodiment of the present invention. 1... Reactor pressure vessel, 2... Jet pump, 13... Elbow, 14... Nozzle, 27...
Transition piece arm, 28... Transition bolt, 29... Beam.

Claims (1)

[Claims] 1. An elbow that makes a U-turn in the flow of coolant and connects it to the nozzle, an arm that is fixedly placed opposite to both sides of the elbow and has grooves formed at positions facing each other, and a groove at both ends of the arm. a beam that is engaged with the upper part of the elbow and straddles the upper part of the elbow;
In a jet pump installed in a reactor pressure vessel, the arm has a pressing means for pressing the top of the elbow at the lower center of the beam, and has a threaded hole penetrating the groove formed in the upper end of at least one side; A beam integrally formed with a protrusion in the lower center portion that presses the top of the elbow, and a bolt that is screwed into the screw hole and has one end abutted against the end of the beam, and the bolt is screwed. A jet pump characterized in that the beam protrusion presses the top of the elbow.