JPH0337157B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a beam installed in a jet pump, which is a device for supplying the necessary flow rate of coolant to the reactor core in a boiling water nuclear reactor.

A jet pump according to the prior art will be explained below with reference to the drawings. Figure 1 shows the configuration of the reactor recirculation system. In the figure, 1 indicates the reactor pressure vessel. The jet pump 2 is installed in the reactor pressure vessel 1, and together with the recirculation pump 3, is provided as a reactor recirculation system, and supplies the necessary flow rate to the reactor core 4 as the reactor output increases or decreases. 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,
As the driving fluid for the jet pump 2, it is injected from the nozzle of the jet pump 2 at high speed. The remaining coolant is sucked into the jet pump due to the low pressure created in the absorption section at the nozzle outlet by this high-speed injection, and is sent to the core lower plenum 7 after being thoroughly mixed with driving water in the jet pump.

Figure 2 shows the structure of the jet pump. In the figure, 10 is a riser elbow, 11 is a riser pipe,
12 is the transition piece, 13 is the elbow, 1
4 is a nozzle, 15 is a mixer, 16 is a diffuser, 17 is a bracket, 18 is a support, 19 is a wedge, 20 is a beam, 21 is a beam bolt,
22 is a riser place.

The riser elbow 10, the riser pipe 11, and the transition piece 12 are welded together, 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 place 22.

The most important structural and functional parts of a jet pump are the elbow 13, nozzle 14, and mixer 1.
5, especially because the inner surface of the nozzle, through which high-temperature, high-pressure water flows at high speed, wears out over time due to erosion, erosion, etc. during operation, and if the inner diameter becomes larger, the performance will decrease and there is a risk that the required core flow rate may not be obtained. It is designed to be removable and replaceable. These elbow 13, nozzle 14, and mixer 15 are each assembled integrally by welding, but the connection parts with transition piece 12 and diffuser 16 are connected by a mechanical method rather than welding so that they can be removed. There is. Details of these are shown in FIGS. 3, 4, and 5.

FIG. 3 shows an external view of the attachment portion of the transition piece 12 and the elbow 13. In the figure, 11 is a riser tube, 12 is a transition piece, 13 is an elbow, 14 is a nozzle, 15 is a mixer, 20 is a beam, 21 is a beam bolt, and 27 is a transition piece arm.

FIG. 4 shows a detailed view of the attachment of the transition piece 12 and elbow 13, similar to FIG. 3.

In the figure, 12 is a transition piece, 1
3 is an elbow, 20 is a beam, 21 is a beam bolt, 23 is a retainer, 24 is a bolt, 25 is a tensile direction of the beam 20, 26 is a tightening direction of the beam bolt 21, and 27 is a transition piece arm.

The beam 20 and beam bolt 21 are inserted into grooves provided in the transition piece arm 27. In order to press the elbow 13 to the transition piece 12, a previously prepared handler (tensioner) pulls the beam 20 in the pulling direction 25, and while the tensile force is applied to the beam 20, the beam bolt 21 is tightened. It is tightened in the direction 26. In addition, the beam bolt 21 is attached to the elbow 1
3 with bolts 24 and retainer 23.

FIG. 5 shows a mixer 15 and a differential user 16.
Installation details are shown. 15 is a mixer, and 16 is a differential user. The mixer 15 is mechanically inserted into the diffuser 16.

And removable elbow 13, nozzle 1
4. In order to prevent lateral vibration of the mixer 15 part as shown in FIG. A bracket 17, a support 18, and a wedge 19 are provided. The bracket 17 surrounds the mixer 15 in a ring shape and is fixed to the riser pipe 11 by welding, and a wedge 19 is installed in the gap between the bracket 17 and the mixer 15.
is installed to prevent lateral vibration. The wedge 19 is attached to a support 18 welded to the mixer 15 to prevent it from falling off.

As explained above, the removable elbow 1
3. The beam 20 and beam bolt 21 that tighten the nozzle 14 and mixer 15 ensure sufficient tightening force against the pressure difference between the inside of the jet pump and the reactor and the kinetic energy of the driving water inside the jet pump. Because of this, the stress is the highest in the structure, and in particular, since the beam has a bolt through hole in the center, a high peak stress occurs due to the stress concentration effect, which increases the possibility of crevice corrosion, fatigue failure, etc. have.

It is an object of the present invention to provide a jet pump beam that is unique to the jet pump inlet mixer elbow and transition piece for clamping the jet pump inlet mixer elbow and transition piece in a nuclear reactor.
By having a bolt through hole in the center of the beam, peak stress occurs, resulting in crevice corrosion and fatigue failure.We have solved this problem without reducing the tightening action exerted by the jet pump beam as much as possible when it is deflected. The objective is to improve the performance and reliability of jet pumps in nuclear reactors.

The present invention includes a bolt penetrating portion in the thickness direction at the center of the beam, and other portions whose thickness gradually decreases from the center of the beam toward both ends of the beam, and the boiling water type In a beam that tightens an inlet mixer elbow and a transition piece of a jet pump installed in a nuclear reactor, the thickness of the central part of the beam is increased to exceed the maximum thickness of the other parts. This is a jet pump beam, and this structure reduces the stress generated in the center of the beam, and the structure in which the thickness of other parts gradually decreases from the center of the beam to both ends of the beam provides sufficient deflection. It is possible to obtain a sufficient tightening effect during installation and operation, thereby solving the above-mentioned new problems specific to jet pump beams, and improving the performance and reliability of jet pumps in nuclear reactors. be.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 6 shows a plan view of the beam. In the figure, 20 is a beam, 30 is a bolt hole, and 31 is a protrusion. FIG. 7 shows a front view of a conventional beam, FIG. 8 shows a front view of a beam according to the present invention, and FIG. 9 shows a front view of a rejected beam showing an inappropriate modification. In FIGS. 7 to 9, 20 is a beam, 31 is a protrusion, 32 is a beam tightening force, and 33 is a reaction force.

The beam 20 is inserted into the groove provided in the transition piece arm 27 as previously explained in FIG. It is crimped. Therefore, as shown in FIGS. 7 to 9, an upward tightening force 32 acts on the beam 20 from the beam bolt 21, and a downward reaction force 33 acts on the beam 20 from the contact portion with the transition piece arm 27. A large bending stress will be generated. The bending stress generated in the beam is highest at the center of the upper surface of the beam, and the value is particularly high near the bolt holes due to stress concentration in the holes.

Figure 10 shows the center part of the upper surface of the beam (Figure 6-
shows the stress distribution of the cross section). As shown in FIG. 10, in the conventional type shown in FIG. 7 indicated by curve A, the stress was particularly high, and there was a high possibility that stress corrosion cracking or the like would occur. In the case of the shapes shown in Figures 8 and 9, indicated by curves B and C, by increasing the height of the center portion of the beam, the stress can be greatly reduced as shown in Figure 10, and stress corrosion cracking, etc. can be reduced. This is an improved version that reduces and improves the possibility of this occurring.

On the other hand, FIG. 11 shows the distribution of beam displacement due to the beam clamping force 32. In the figure, the vertical axis indicates the amount of upward displacement of the beam, and the horizontal axis indicates the position shown in FIG. 6 to the cross section. When tightening the beam 20, it is necessary to apply sufficient tightening force to resist the fluid force inside the jet pump, so simply turning the beam bolt will not tighten it enough, as explained in Figure 4. The beam 20 is pulled in the pulling direction 25 (upward) using a handling tool (tensioner) prepared in advance, and the beam is deformed (deflected), and the beam bolt 21 is rotated and tightened. At this time, if sufficient beam deformation (deflection) is not obtained, the beam bolts cannot be tightened sufficiently.
The required tightening force cannot be obtained.

Figure 11 shows the amount of beam displacement.Compared to the conventional type shown by curve D in Figure 7, the height of the beam is smaller in the case of the beams shown in Figures 8 and 9, shown by curves E and F. As the height increases, the rigidity increases and displacement becomes smaller. However, as shown in Figure 8, a beam in which the height of the central part of the beam is increased and the slope of the tapered parts on both sides remains unchanged has a displacement closer to that of the conventional type than a beam with a larger taper as shown in Figure 9. quantity is obtained.

From the results shown in Figures 10 and 11 above, in order to reduce the possibility of damage such as stress corrosion cracking, the following steps are required to reduce stress and to reduce changes in displacement in order to obtain the necessary tightening force. As shown in Figure 8, it can be seen that it is optimal to have a shape in which only the height of the central portion of the beam is increased.

Since the present invention is configured and operates as described above, it can produce the following effects. That is, (1) It is possible to reduce the stress generated in the beam and reduce the possibility of accidents such as stress corrosion cracking, fatigue fracture, and crevice corrosion.

(2) Sufficient displacement necessary to obtain the beam tightening effect can be secured, and sufficient tightening can be obtained during installation and operation.

(3) Through the above, the performance and reliability of the jet pump can be improved.

[Brief explanation of drawings]

Figure 1 is a block diagram of the reactor recirculation system, Figure 2 is an overall structural diagram of the jet pump, Figures 3 and 4 are detailed diagrams of the transition piece and elbow installation, and Figure 5 is the mixer and Detailed installation diagram of the differential user, Figure 6 is a plan view of the beam, Figure 7 is a
8 is a front view of the beam of the present invention; FIG. 9 is a front view of a rejected beam showing an example of inappropriate modification; FIG. 10 is a stress distribution diagram;
FIG. 11 shows a displacement distribution diagram. 12...Transition piece, 13...Inlet mixer elbow, 20...Beam.

Claims (1)

[Claims] 1 A bolt penetrating portion in the thickness direction is provided at the center of the beam, and other portions whose thickness gradually decreases from the center of the beam to both ends of the beam, and are suitable for use in boiling water reactors. A beam for tightening an inlet mixer elbow and a transition piece of a jet pump provided in a jet pump is characterized in that the thickness of the central portion of the beam is increased to a thickness exceeding the maximum thickness of the other portions. jet pump beam.