JPS62266492A - 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 [Objective of the Invention] (Industrial Application Field) The present invention improves the mounting structure of a flow skirt housed in a reactor pressure vessel (RPV) such as a pressurized water reactor (PWR). Regarding nuclear reactors.

(Prior Art) Generally, a pressurized water nuclear reactor is constructed as shown in FIG. (not shown) is loaded, and a core shroud (not shown) surrounds the fuel assembly.

The coolant flows in from the coolant inlet nozzle 3, flows down between the wall of the reactor pressure vessel 1 and the core barrel 2, is reversed and TRed at the lower part of the reactor pressure vessel 1, and heads toward the reactor core. In the reactor core, nuclear reaction heat is removed and guided through the coolant outlet nozzle 4 to an evaporation generator (not shown), where heat is exchanged and steam is generated.
Drives a turbine etc.

On the other hand, the nuclear reaction in the reactor core is controlled by inserting and withdrawing a control rod cluster (not shown) from within the control rod guide assembly 6 installed in the upper core structure 5 above the reactor pressure vessel 1. , their insertion and withdrawal are performed by the control rod drive mechanism 7.

Further, a flow skirt 8 is attached to the lower part of the reactor pressure vessel 1 to uniformly distribute the coolant flowing down into the reactor. As shown in FIG. 9, this flow skirt 8 has a cylindrical body 9 with a large number of distribution holes 1 for distribution of the flow.
It consists of a 0. Further, a reinforcing ring 11 is welded and fixed to the inner surface of the cylindrical body 9.

When attaching the flow skirt 8 to the reactor pressure vessel 1, since the flow skirt is made of stainless steel and the reactor pressure vessel is made of low-alloy steel, there is a difference in linear expansion coefficient between the two, so it is necessary to It is necessary to take into account that thermal stress will occur during the process. In other words, yen? An elongated notch 12 in the axial direction is provided at the lower end of 1li9, and a narrow tongue portion formed between the notches 12 is welded to the reactor pressure vessel 1.

The above-mentioned thermal stress is reduced by the mounting method provided with such a notch 12.

Furthermore, since the reactor pressure vessel 1 and the flow skirt 8 are made of different materials, direct welding is not preferable, and as shown in FIG. This is a structure in which the skirt 8 is welded.

(Problems to be Solved by the Invention) In the above-described mounting structure for the flow skirt 8, the flow skirt 8 absorbs the difference in thermal expansion during reactor operation and is attached in a deformed state, so that stress is constantly applied to the flow skirt 8. It is configured as follows.

Furthermore, the flow skirt 8 is used in a harsh environment where the coolant flowing down between the reactor pressure vessel 1 and the core barrel 2 collides with each other, and as a result, it is subject to severe stress and may be damaged. . That is, the flow skirt 8 is subjected to severe stress due to the load generated by the difference in thermal expansion with the reactor pressure vessel 1 and the load generated by fluid vibration, and there is a risk that damage may occur due to this stress.

If the flow skirt 8 is damaged, not only will the ability to distribute the coolant flow to the core be lost, but also mechanical damage caused by interference with other equipment due to phenomena such as the flow skirt 8 floating up. In particular, interference with the lower core support plate 14 that supports the core causes an adverse effect on core characteristics. Therefore, if the flow scars 1 and 8 are damaged, they must be replaced or repaired.

However, the replacement of flow skirt 8 and the relocation work are
This is extremely difficult because it is carried out in a highly radioactive environment. That is, since the flow skirt 8 is located at the lower part of the reactor pressure vessel 1, the flow skirt 8 is first
It is necessary to remove all reactor internals from inside the reactor pressure vessel 1 except for the following.

After removing the reactor internals, it is necessary to install a working platform 15 inside the reactor, as shown in FIG. 11, thereby reducing the radiation exposure of the working U4. After that, a worker descends into the reactor and repairs the damaged area or cuts the welded part of the reactor pressure vessel 1 and flow skirt 8, thereby removing the old flow skirt 8 and installing a new flow skirt 8. Replace by welding.

On the other hand, the reactor pressure vessel 1 is periodically inspected using techniques such as ultrasonic flaw detection. Although this inspection is performed by removing all removable reactor internals, the flow scars 1 and 8 themselves cannot be removed, so the inspection is performed with them still attached. Therefore, inspection of the flow skirt 8 was extremely difficult and troublesome compared to other devices.

The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a nuclear reactor with an improved flow skirt mounting structure that allows the flow skirt to be replaced by remote control.

[Structure of the invention]

(Means for Solving the Problems) A nuclear reactor according to the present invention introduces a coolant from a coolant inlet nozzle provided in a reactor pressure vessel, and supplies the introduced coolant from the lower part of the reactor pressure vessel to the reactor. In a nuclear reactor in which a flow skirt placed at the bottom of the reactor pressure vessel distributes and guides the coolant into the reactor core, and the heated coolant is led out from a coolant outlet nozzle, a spring is attached to the outer surface of the flow skirt, and the spring is attached to the outer surface of the flow skirt. The flow skirt is engaged with the mounting seat formed at the bottom of the reactor pressure vessel by an elastic force, and the flow skirt is attached to the mounting seat by the difference in thermal expansion that occurs between the flow skirt and the reactor pressure vessel, which are made of different materials. It is pressed and fixed in a removable manner.

(Function) In the nuclear reactor according to the present invention, the spring attached to the outer surface of the flow skirt elastically engages with the mounting seat formed at the bottom of the reactor pressure vessel. On the other hand, at room temperature, floating is prevented and bonding occurs.

That is, when the flow skirt is suspended within the reactor pressure vessel, the spring comes into contact with the mounting seat and is elastically engaged with the mounting seat due to the spring action generated therebetween. In addition, by forcibly disengaging the spring from the mounting seat,
The spring is free from the mounting seat, and by lifting the flow skirt, it can be removed from the mounting seat and removed from the reactor pressure vessel.

In addition, the difference in thermal expansion between the flow skirt and the reactor pressure vessel is such that in high temperature conditions, the flow skirt thermally expands and is pressed and fixed against the inner surface of the mounting seat of the reactor pressure vessel, and receives a reaction force from this mounting seat. . As a result, the flow skirt is firmly connected to the mounting seat under pressure, and together with the spring action of the spring, the flow skirt and the reactor pressure vessel are integrated.

Further, even if the flow skirt heat-shrinks and separates from the reactor pressure vessel when the temperature returns to room temperature, the spring maintains elastic engagement with the mounting seat and is retained. The flow skirt can be removed from the reactor pressure vessel by releasing the elastic hold provided by the spring.

(Example) An example of the nuclear reactor according to the present invention will be described below with reference to FIGS. 1 to 7.
This will be explained with reference to the figures.

In FIG. 1, reference numeral 20 indicates a reactor pressure vessel of a pressurized water reactor, and a cylindrical core barrel 22 is supported on an inner periphery 7 flange portion 21 of this reactor pressure vessel 20. As shown in FIG. A lower core support plate 23 is fixed to the lower end of the core barrel 22, and a fuel assembly (not shown) constituting the core 24 is attached to the lower core support plate 23. Covered by a core shroud (not shown). Also,
The lower part of the fuel assembly is supported by the lower core support plate 23, and the upper end is fixed by being pressed from above by the upper core structure 25. The inside of the reactor pressure vessel 20 is cold together with the reactor internals! Contains II materials.

This coolant flows into the reactor pressure vessel 20 from a coolant inlet nozzle 26 provided at the top of the reactor pressure vessel 20, and flows downward through the annular space between the reactor pressure vessel 20 wall and the core barrel 22. Flow down.

At the lower part of the reactor pressure vessel 20, the coolant is turned 180 degrees to become an upward flow and guided toward the reactor core 24.

As the coolant passes through the fuel assembly in the core, it absorbs the heat of the nuclear reaction i? Yes, it gets heated. The heated coolant reaches the region of the upper core structure 25 and coolant outlet nozzle 2
7 and is led to a steam generator (not shown) via piping.

In a steam generator, heat is removed from the coolant and steam is generated.
Drives turbines and more. The coolant from which heat has been removed is −
The coolant is then pressurized by a coolant bomb (not shown), flows into the reactor pressure vessel 20 again, passes between the wall of the reactor pressure vessel 20 and the core barrel 22, and is guided below the reactor core.

On the other hand, a control rod guide assembly 28 is installed above the reactor core, and a control rod cluster (not shown) guided by this control rod guide assembly 28 is inserted into and withdrawn from the reactor core by a control rod drive mechanism 29. control the reactor core reaction. Control rod drive mechanism 29 is installed above control rod guide assembly 28 .

Furthermore, a flow skirt 30 is attached to the lower part of the reactor pressure vessel 20 to uniformly distribute the coolant flowing down into the reactor. The flow skirt 30 has a structure that allows it to be attached and removed by remote control from the reactor pressure vessel 20 when an abnormality is discovered during a normal inspection or the like.

As shown in FIG. 2, the flow skirt 30 includes a cylindrical body 32 in which a large number of distribution holes 31 having a flow distribution function are formed, and a cylindrical body 32 in order to reinforce this circle f[32, as in the conventional case. A reinforcing ring 33 attached to the inner surface and a mounting spring 34 for attaching to the reactor pressure vessel 20
Equipped with.

The lower part of the cylinder I432 is thinner than the upper part, and
Long sides 35 and short legs 36 having different axial lengths are provided alternately in the circumferential direction by cutouts provided at the lower part. The lower end of the short leg 36 is located above the mounting seat 37 formed with a thick wall on the lower inner surface of the reactor pressure vessel 20, and does not come into contact with the mounting seat 37.

The long side 35 has an engagement protrusion 39 at its lower end that engages with an engagement recess 38 formed on the inner surface of the mounting seat 37. As shown in the figure, the engaging protrusion 39 is tapered so that it becomes thinner toward the lower end, and its outer surface is curved in an arc shape and is processed to the extent that it does not come into contact with the mounting seat 37 at room temperature. (See Figure 5).

Since the flow skirt 30 and the reactor pressure vessel 20 are made of different materials having different coefficients of linear expansion as described above, the flow skirt 30 expands relatively during operation due to the difference in thermal expansion. Therefore, as shown in FIG. 5, the relationship between the long WJ 35 with a gap and the mounting seat 37 is as follows.
During high temperature operation, as shown in FIG. 6, the flow skirt 30 expands and contacts the mounting seat 37 in a pressed state, and the reaction force from the mounting seat 37 fixes the entire flow skirt 30. There is.

Further, the spring 34 contacts and engages the mounting seat 37 at room temperature, and is attached to the long side 35 so as to protrude outward from the long side 35. For example, as shown in FIG. 3, the spring 34 is fixed by fastening an arc-shaped mounting plate 40 on the upper (base) part of the spring 34 to the outer surface of the long side 35 with a fixing device such as a bolt or a nut 41. As shown in FIG. 7, the mounting plate 40 is integrated with a curvature similar to that of the flow skirt 30, and is fixed to the long side 35 at four locations on the left, right, top, and bottom of the mounting plate 40.

Further, the spring 34 is made of a material with good spring characteristics, such as Inconel X750. and,
As shown in FIG. 3, when it is attached to the mounting seat 37, it is always in contact with the mounting seat 37 due to elastic deformation and receives a reaction force from the mounting seat 37. The contact portion with the mounting seat 37, ie, the lower end of the spring 34, is a curved surface having the same curvature as the mounting seat 37.

Furthermore, the spring 34 has an engaging protrusion 42 protruding from its lower end that engages with the engaging recess 38 of the mounting seat 37 to prevent the flow skirt 30 from floating. As shown in the figure, the engagement protrusion 42 is tapered toward the lower end (thus gradually becoming thinner) to enable smooth engagement with the engagement recess 38. has a release operation (V projection 43 protruding) for forcibly deforming the spring 34 inward and releasing the engagement protrusion 42 from the engagement recess 38 of the mounting seat 37. .

Next, the replacement work of the flow skirt 3O having the above-mentioned h configuration will be explained.

First, the upper core structure 25, the two control rod drive grooves, other upper reactor internals, and the reactor internals such as the core barrel 22 are removed. This removal can be easily carried out by lifting the reactor pressure vessel 20 from above using a crane or the like. The removed nuclear reactor internals are temporarily placed on a special bit.

Next, a jig (
(not shown) is suspended from the top of the reactor pressure vessel 20. When the jig presses the release operation protrusion 43 inward by hanging it down, this causes the engagement protrusion 4 at the lower end of the spring 34 to
2 releases the engagement with the mounting seat 37. After release, it is enough to just lift it up, so the jig itself has no tjl.
Needless to say, a W-lifting rock groove is provided.

To install the flow skirt 30, the procedure for removing it may be reversed. That is, flow skirt 3
In this case, the spring 34 moves inward along the inner surface of the mounting seat 37 by the weight of the device itself without having to press the release projection 43 inward. , mounted in place.

The long legs 35 are engaged and fixed to the mounting seat 37 by the spring force of the spring 34 in a normal temperature state, and thermally expand in a high temperature state, and are fixed to the mounting seat 37. The reaction force of the lower part of the flow skirt 30 accompanying this is utilized.

In this way, by making it possible to remove all the internal reactor structures in the reactor pressure vessel, including the flow skirt 30, the inside of the reactor pressure vessel can be easily inspected, and the reliability of the inspection itself is improved. Not only this, but also the reliability of the device is improved accordingly.

〔Effect of the invention〕

According to the present invention, the spring attached to the outer surface of the flow skirt is elastically engaged with the mounting seat formed at the lower part of the reactor pressure vessel, and the flow skirt is made of different materials. By pressing the lower end of the flow skirt against the mounting seat due to the difference in thermal expansion between the skirt and the reactor pressure vessel, the flow skirt can be detachably fixed, making it extremely easy to attach the flow skirt to the reactor pressure vessel. It can be attached and detached.

In other words, in the unlikely event that the flow skirt is damaged,
The flow skirt can be installed and removed by remote control. At room temperature, the spring engages with the mounting seat, ensuring a stable installation without lifting up. Also, when the temperature increases due to operation, the flow skirt is removed due to the difference in thermal expansion. is rigidly connected to the reactor pressure vessel.

Therefore, when repairing or replacing the flow skirt, there is no need for workers to directly enter the furnace, reducing exposure to radiation and allowing the work to be carried out safely.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of an embodiment of the nuclear reactor according to the present invention, FIG. 2 is a perspective view of a flow skirt used in the reactor, and FIG. 3 is a line I-I in FIG. 2. Sectional view along 4th
The figure is a cross-sectional view taken along the line ■-■ in Figure 2, Figure 5 is a cross-sectional view showing the positions of the long legs and the mounting seat at room temperature, and Figure 6 is a cross-sectional view showing the positions of the long legs and the mounting seat at high temperatures. FIG. 7 is a perspective view of the spring, FIG. 8 is a longitudinal cross-sectional view of a conventional pressurized water reactor, and FIG. A cross-sectional view of the flow skirt used,
FIG. 10 is a cross-sectional view of a main part showing the attachment structure between the flow skirt and the reactor pressure vessel, and FIG. 11 is a longitudinal cross-sectional view showing an overview of the flow skirt when it is replaced. 1... Reactor pressure vessel, 2... Core barrel, 3...
・Coolant inlet nozzle, 4...Coolant outlet nozzle, 5・
・・Upper core structure, 6・Control rod guide assembly, 7・
...Control rod drive mechanism, 8...Flow skirt, 9...
・For cylinder, 10...Distribution hole, 11...Ring, 12
... Notch, 13... Mounting seat, 14... Lower core support plate, 15... Working platform, 20...
Reactor pressure vessel, 22... Core barrel, 23... Lower core support plate, 24... Reactor core, 25... Upper core structure, 26... Coolant inlet nozzle, 27... - Coolant Outlet nozzle, 28... Control guide assembly, 29...
Control rod drive fI1 mechanism, 30...Flow skirt, 31
...Distribution hole, 32...Cylindrical body, 33...Ring,
34... Spring, 35... Long leg, 36...
Short leg, 37... Mounting seat, 38... Engagement recess, 39
...Engagement protrusion, 40...Mounting plate, 41...Bolt, nut, 42...Engagement protrusion, 43...Release operation protrusion. Applicant's agent Hatano Docking l Figure $2 Figure 3 Figure if

Claims (1)

[Claims] 1. Coolant is introduced from a coolant inlet nozzle provided in the reactor pressure vessel, and the introduced coolant is passed from the lower part of the reactor pressure vessel to a flow skirt arranged in the lower part of the reactor pressure vessel. In a nuclear reactor in which the coolant after heating is distributed and guided through the reactor core and is led out from a coolant outlet nozzle, a spring is attached to the outer surface of the flow skirt, and this spring is formed at the lower part of the reactor pressure vessel. The flow skirt is removably fixed by resiliently engaging the mounting seat and pressing the flow skirt against the mounting seat due to the difference in thermal expansion that occurs between the flow skirt and the reactor pressure vessel, which are made of different materials. A nuclear reactor characterized by: 2. The flow skirt has a lower wall thickness thinner than an upper wall, and a notch formed in the circumferential direction in the lower part to form long legs and short legs having different axial lengths, 2. The nuclear reactor according to claim 1, wherein the lower end of the long leg is provided with an engaging protrusion that projects into an engaging recess formed on the inner surface of the mounting seat. 3. The spring has an engaging protrusion protruding from the lower end that engages with the engaging recess formed on the inner surface of the mounting seat, and a release operation protrusion that releases the engaging protrusion from the engaging recess protruding from the middle part. A nuclear reactor according to claim 1 or 2. 4. The nuclear reactor according to claim 3, wherein the spring is attached to the outer surface of the long leg. 5. The engagement projections formed on the long legs and springs are
The nuclear reactor according to claims 2 to 4, wherein the reactor is tapered so that it becomes thinner toward the lower end.