JPS61243393A - Boiling water type 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] [Technical Field of the Invention] The present invention relates to a boiling water nuclear reactor in which the reactor internals in the reactor pressure vessel are improved, and in particular, cluster type control rods can be inserted and removed from the bottom of the reactor core. The present invention relates to a boiling point III water reactor.

[Technical background of the invention]

Generally, light water reactors operate a control rod drive mechanism to move the control rods in and out of the reactor core, thereby controlling reaction traces in the reactor core.

In a conventional boiling water reactor, a reactor core is constructed by loading a large number of four fuel assemblies into the reactor pressure vessel, while the core is composed of four adjacent fuel assemblies. A control rod, which has a cross-shaped cross section, is supported in the cross-shaped gap so as to be movable in the vertical direction, and is moved in and out of the reactor core. When withdrawing the control rod from the reactor core, the control rod is driven downward, and when it is moved to the lower limit of its stroke, it becomes fully withdrawn. Conversely, when inserting a control rod into the reactor core, the control rod is driven upward, and when it is moved to its stroke upper limit, it becomes fully inserted.

A conventional boiling water reactor has an internal structure not shown schematically in FIG. A reactor core 4 is constructed by disposing a set of fuel assemblies 3. Each of the fuel assemblies 3 is supported at its upper and lower parts by a core support plate 5 and an upper grid plate 6 attached to the core shroud 2.

On the other hand, at the bottom of the reactor pressure vessel 1, there are many control rod drive i-structure housings (hereinafter referred to as CRD housings) 7.
is installed inside this CRD housing 7. 11i
A ll rod drive mechanism 8 is provided. A control rod guide tube 9 is erected on the top of the CRD housing 7, and the top of the control rod guide tube 9 is held by the core support plate 5. A fuel support fitting 10 is fitted and supported at the top of the control rod guide tube 9, and this fuel support fitting 10 supports the lower end of each of the four fuel assemblies 3.

Further, a cross-shaped control rod 12 is detachably connected to the control rod drive mechanism 8 via a coupling mechanism 11, and the control rod 12 is guided within the control rod guide tube 9 by the drive of the control rod drive mechanism 8. At the same time, as shown in FIG. 13, the fuel assemblies 3.3 are driven up and down through the cross-shaped gaps 14 between the four fuel assemblies 3.3. In FIG. 13, the cross-sectional interior of the cruciform control rod 12 and some internal structures of the fuel assembly 3 are omitted.

A conventional cruciform control rod 12 is constructed as shown in FIG. 14, and an operating handle 16 and a speed limiter 17 are fixed to the top and bottom of a tie rod 15 having a cruciform cross section to form the skeleton of the control rod. . A sheath 18 having a deep U-shaped cross section is attached to each protruding leg of the tie rod 15, and a plurality of neutron absorption rods 19 are housed in a row within this sheath 18. A coupling socket 20 is provided at the lower end of the control rod 12, and this coupling socket 20 constitutes a coupling mechanism 11 that connects the control rod 12 to the control rod drive lateral 8. The control rod 12 has a structure that allows it to be attached to and detached from the control rod drive mechanism 8 by means of a movable handle 21.

Operation handle 16 of control rod 12 and speed limiter 17
Guide rollers 22 and 22 are respectively attached to guide the control rod 12 in vertical movement.

[Problems with background technology]

In a conventional boiling water reactor, a cross-shaped control rod 1
2 controls the reactor output by driving vertically within the gap between the four fuel assemblies 3.

If an attempt is made to increase the extraction burnup of core fuel, control rods 12 with higher reactivity will be required. However, in a nuclear reactor of the type in which the cruciform control rods 12 are inserted into the gaps between the four fuel assemblies 3.3, even if the reactivity of the control rods themselves is increased, the control rods 12 are aggregate 3
．． The control rod reaction is critical because it is placed on one side of 3.
(method of action) is uneven and stale. From this relationship,
In order to increase the intensity of control rod reactions, methods of evenly distributing neutron absorbing rods within a fuel assembly are being considered.

Theoretically, if neutron-absorbing rods with a cross section equal to the total cross-sectional area of each neutron-absorbing rod housed in a cruciform control rod are evenly distributed among four fuel assemblies, approximately 1.3 times It is known that a reactivity of 100% can be obtained, and such control rods are used as cluster-type control rods in pressurized wooden reactors. In pressurized water reactors, cluster control rods are inserted and removed from the top of the reactor core.

However, in a boiling water reactor, a steam separator and a steam dryer are installed above the reactor core. In this case, the presence of a steam separator and a steam dryer becomes an obstacle and is accompanied by technical difficulties.

Furthermore, in a boiling water reactor, steam is generated from many planes in the reactor core, and if an attempt is made to emergency insert a cluster control rod from above against the upward flow of steam, the resistance of the upward steam flow will be overcome. A downward force of just as much force is required. In addition, in the cluster type control rod, a large number of neutron absorption rods are installed vertically, and each neutron absorption rod is exposed to the rising steam flow, so there is a risk that fluid photography may occur in the steam flow.

In addition, in a boiling water reactor, the coolant is heated while passing through the core and boils, so the void ratio in the upper part of the core is high and the proportion of water as a moderator is small, so the moderating effect of fast neutrons is weak. , so the neutron flux density (hot and slow) decreases,
The power output of the reactor core is decreasing. In this state, the cluster type i! Inserting the +1111 rod further reduces the power in the upper part of the core, causing a large distortion in the power distribution of the core in its axial direction.

In order to avoid distortion of the core power distribution, it is necessary to insert cluster type control rods from below the core. However, cluster-type control rods have each neutron-absorbing rod dispersed and exposed to the outside, and are not equipped with sufficient rigidity saws like cross-shaped control rods. Low rigidity. For this reason, it is difficult to smoothly drive the cluster type control rods upward, and in particular, during emergency insertion, each neutron absorption rod of the cluster type control rods may come into contact with core components, etc., causing buckling, or It was very difficult to insert the fuel into the fuel assembly.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned circumstances, and allows the cluster-type control rods to be smoothly and smoothly inserted from below the reactor core, thereby preventing buckling or damage to the neutron absorption rods even during emergency insertion. The purpose is to provide a boiling water reactor that does not

[Summary of the invention]

In order to achieve the above-mentioned object, a boiling water nuclear reactor according to the present invention includes a reactor pressure vessel containing a reactor core, a plurality of control rod drive mechanisms attached to the bottom of the reactor pressure horn vessel, and a reactor pressure vessel containing a reactor core. , a cluster type i! that is inserted or withdrawn from below the reactor core by the control rod drive mechanism described above. 11 control rods and a guide plate to guide the movement of the cluster type control rods.
and a lower cluster guide structure capable of accommodating the cluster-type control rods, and a fuel assembly loaded in the reactor core, the fuel assembly including the clusters in the fuel bundles accommodated in the fuel channel. It is characterized in that a plurality of guide duplexes A are distributed and arranged to guide the insertion and withdrawal of the neutron absorption rod of the mold control rod.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a boiling water nuclear reactor according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing the internal structure of a boiling water reactor, and reference numeral 30 in the figure indicates the reactor pressure vessel of the boiling water reactor. A plurality of control rod drive mechanism housings (CRD housings) 31 are integrally attached to the lower mirror of the reactor pressure horn vessel 30. CRD housing 31 is a control rod drive! l! II
tI! The top of the CRD housing extends into the reactor pressure vessel 30 and has a lower cluster guide structure 33 mounted thereon. The lower cluster guide structure 33 has a rectangular tube shape, and has a cluster type control rod 3 inside.
4 can be raised and lowered freely. The cluster type control rod 34 is freely connected to the piston tube 32a on the side 32 of control rod drive #J'/11 via a coupling mechanism 35.

On the other hand, the upper part of the lower cluster guide structure 33 is supported by a core support plate 36, and its upper and lower parts are fixed. Inside the lower cluster guide structure 33, a plurality of guide plates 37 are held in a multi-stage structure at appropriate intervals in the axial direction, and the side surfaces thereof are provided with a plurality of openings 33a through which coolant (cooling water) flows. ing.

Further, a fuel assembly 39 constituting the reactor core 38 is mounted on the top of the lower cluster guide structure 33 held by the core support plate 36.
is placed. The upper ends of the fuel assemblies 39 are supported by an upper lattice plate 40 , and as a result, the plurality of fuel assemblies 39 are mounted in the reactor core within the reactor pressure vessel 30 . The fuel assembly 39 has a rectangular tube shape and has a fuel channel 41, a large number of fuel pins 42 storing nuclear fuel in the fuel channel 41, and upper and lower tie plates 43, 44 that bundle the fuel pins 42, A plurality of guide tubes (guide simple) 45 are accommodated. The guide duplex 45 is configured as an upper cluster guide structure, and as shown in FIG. 2, it is arranged in a dispersed manner between a large number of fuel bottles 42, and its lower end is expanded downward in a trumpet shape, forming a cluster type. It constitutes an insertion guide for the control rod 34. Further, a large number of fuel pins 42 are bundled by upper and lower tie plates 43, 44 to form a fuel bundle.

By the way, the cluster type control rod 34 is constructed as shown in FIGS. 3 and 4, and a plate-shaped coupling member 47 extends radially from a coupling head 46 formed integrally with the coupling mechanism 35 at the lower end. , the lower end of the neutron absorption rod 48 is held and coupled to these coupling members 47. The neutron absorption rod 48 is attached to the guide tube 45 shown in FIG.
A plurality of guide tubes are arranged in correspondence with each other, and are guided into the guide tube 45 and raised and lowered. Gaitochi 1
The top of -145 is open, and has a structure that does not impede the movement of the coolant into the guide tube 45 when the neutron absorption rod 48 is inserted or withdrawn.

Further, the guide plate 37 held by the lower cluster guide structure 33 is provided with a guide window 49 through which the cluster type control rod 34 can pass, as shown in FIG.
The cluster type control rod 33 is moved up and down by being guided by. Therefore, even if the cluster type control rods 33 are inserted or removed from the bottom of the reactor core 38, the cluster type 11J III rods 3
Each of the three neutron absorbing rods 48 is smoothly guided into the fuel assembly 39.

In addition, in FIGS. 3 and 4, the neutron absorption rod 4
Although the cluster type control rod 33 is shown in which 24 neutron absorption rods 48 are arranged, the number of neutron absorption rods 48 is not limited to 24 as long as they are arranged approximately evenly within the fuel assembly 39.

Next, a modification of the present invention will be described.

In the reactor internal structure of the boiling water reactor shown in FIG. 1, an example was shown in which one fuel assembly 39 was arranged on the top of one lower cluster guide structure 33, but as shown in FIG. In the boiling water reactor shown in the modified example, one fuel support fitting 50 is disposed on the top of one lower cluster guide structure 33A, and four fuel assemblies are placed on the fuel support fitting 50 of the bracket. 51, and as shown in FIG. 7, four fuel assemblies 51 are arranged in a set.

Channel fasteners 52 are attached to the tops of the four fuel assemblies 51 to hold the adjacent fuel assemblies 51 together, and the four fuel assemblies 51 are attached to the top of the upper grid plate 40. Arranged within a grid.

On the other hand, the fuel support fitting 50 has a block structure as shown in FIG.
A guide perforated plate 54 that guides each neutron absorption rod 48 of the rod 34
is installed. The insertion and withdrawal of the cluster type control rod 34 is guided by guide holes 55 formed in the guide porous plate 54.

As shown in FIG. 9, the four fuel assemblies 51 are disposed corresponding to one lattice of the core support plate 36, and each fuel assembly 51 is connected to a rectangular cylindrical fuel channel 56. A large number of fuel pins 42A and a plurality of guide tubes 45A are accommodated therein. Each guide tube 45Δ is arranged to be almost uniformly distributed within a fuel bundle in which fuel pins 42A of a fuel channel 56 are bundled, and each neutron absorption rod 48 of the cluster type control rod 34 is disposed within the guide tube 45A, one neutron absorbing rod 48 of the cluster type control rod 34.
Tree guided. In order to guide this cluster type control rod 34, a guide plate 37A held in a multi-stage structure by the lower cluster guide structure 33A is configured as shown in FIG.
Guide window 49A through which the cluster type control rod 34 can pass
is formed.

Therefore, the cluster type control rod 34 is connected to the multi-stage guide plate 37A of the lower cluster guide structure 33A and each fuel assembly 5.
Since the cluster-type control rods 34 are guided by guide tubes 45A housed in the reactor core, the cluster-type control rods 34 can be inserted and handled from the bottom of the reactor core.

At this time, each neutron absorption rod 48 of the cluster type control rod 34 is inserted in a substantially uniformly distributed manner between each fuel bin 42A of the fuel assembly 51, so that the reactivity of the control rod is lower than that of a conventional cruciform control rod. By increasing the burn-up of each fuel bottle 42A, the burn-up of each fuel bottle 42A can be uniformly and efficiently burned.

Moreover, since the cluster type control rods 34 are inserted from below the core 38, they are guided smoothly without going against the upward flow of steam generated within the core 38, and the occurrence of fluid vibrations can be effectively suppressed.

In addition, since the void ratio of the coolant is small in the lower part of the core, the cold IJl material actively moderates fast neutrons. Therefore, the thermal neutron density is large and the core power is large. Therefore, by inserting the control rods 34 into the core 38 from below, the core power can be controlled efficiently and the axial distortion in the power distribution of the core can be reduced.

In addition, in the embodiment of the present invention, an example was explained in which the top of the fuel assembly was held by the upper grid plate, but the fuel assembly can be inserted into the lower cluster guide structure or fuel support fitting to stand upright and stand on its own. can be done. When the fuel assembly is made to stand on its own, the presence of the upper grid plate is not necessarily required.

In addition, although FIGS. 1 and 6 illustrate an example in which the top of the lower cluster guide structure is supported by a core support plate,
The tops of the lower cluster guide structures may be bulged so that the tops of adjacent lower cluster guide structures are joined to each other, in which case the lower grid plate is not required.

Furthermore, the cluster type control rod 34 forms a recess 60 at the top of the neutron absorption rod 4B as shown in FIG. You may.

By grasping the header 61 of the neutron absorption rod 48 with the depression formed therein using a cluster control rod removing tool (not shown), it can be taken out upward.

Furthermore, the neutron-absorbing rods of the cluster-type control rods only need to contain a neutron-absorbing substance, such as boron carbide (84C) or hafnium or rare earth metals with high neutron-absorbing capacity, in the cladding tube such as a stainless steel tube or a nickel-based alloy tube. It may be a tube filled with oxide, a bare bar of hafnium, or a tube containing a silver-indium-cadmium base metal. At that time, the cluster type control rod is made by reducing the amount of neutron absorbing material contained in the top part of the neutron absorbing rod compared to the rest of the rod, or by filling the top part with a substance with a small neutron absorption capacity. Neutron absorption capacity can be reduced. 1 In one embodiment or modification of the present invention, the cluster type control rod is set so that the tip of the neutron absorption rod is located below the lower end of the guide tube when the cluster type control rod is fully drawn out as shown in FIGS. 1 and 6. However, the overall length may be determined so that the tip of the neutron absorbing rod is slightly inserted into the guide tube in the fully withdrawn state.

In that case, the lower end of the guide tube does not necessarily have to have a trumpet structure.

〔Effect of the invention〕

As described above, the boiling water reactor according to the present invention includes a lower cluster guide structure provided with a guide plate for guiding the movement of the cluster control rods in the reactor pressure vessel, and Since the fuel assembly is equipped with a guide tube that guides the insertion and withdrawal of the neutron absorption rods, cluster type control rods can be smoothly and smoothly inserted from below the reactor core. Buckling in each neutron absorption rod of the control rod! 1(i) can be effectively prevented from occurring.

Furthermore, the cluster control rods are inserted and removed from below the core and guided within guide tubes distributed within the fuel handles of the fuel assembly, making it possible to effectively control the core output. Distortion in the axial power distribution of the core power can be reduced, and each fuel can be burned effectively.

In addition, if the neutron absorption capacity of the neutron absorption rod tip of the cluster type control rod is made smaller than the neutron absorption capacity of the remaining part, the cluster type control rod can be inserted or used in the area where the neutron absorption capacity is reduced. The change in the output of the core becomes more gradual when the reactor is in the reactor, which makes it possible to make the change in the fuel output more gradual, reducing the possibility of fuel damage and maintaining the integrity of the fuel.

[Brief explanation of the drawing]

Fig. 1 is a simplified diagram of the internal structure of a boiling water nuclear reactor according to an embodiment of the present invention, Fig. 2 is a plan cross-sectional view taken along the line FIG. 4 is a plan view of the cluster control rod shown in FIG. 3, and FIG. 5 is a plan cross-sectional view taken along line V-V in FIG. 1. FIG. 6 is a diagram showing a modification of the boiling water reactor according to the present invention, and FIG. 7 is a plan cross-sectional view taken along the line ■-■ in FIG. 6. 8th
The figure is a partially cutaway perspective view showing the fuel support fittings that support four sets of fuel assemblies, Figure 9 is a plan sectional view taken along the rX-■ line in Figure 6, and Figure 10 is the same as in Figure 6. A plan cross-sectional view along the X-X line, Figure 11 shows the structure of the tip of the neutron absorption rod of the cluster control rod, Figure 1, and Figure 12 show the internal structure of a conventional boiling water reactor. . FIG. 13 is a plan view showing the arrangement of the four-dark blue fuel assembly and the cruciform control rod, and FIG. 14 is a perspective view showing the structure of the cruciform control rod. 30... Reactor vessel, 32... Control rod drive mechanism, 3
3.33A...lower cluster guide structure, 34...
Cluster type control rod, 35... Coupling mechanism, 36
...Core support plate, 37.37A...Guide plate, 38.
... Core, 39.51 ... Fuel assembly, 40 ... Upper grid plate, 41.56 ... Fuel channel, 42,4
2Δ...fuel pin, 45.45A...guide tube, 47...coupling member, 48...neutron absorption rod, 5
0...Fuel support fittings. Applicant's agent Hisashi Hatano Figure 1 Figure 2 Figure 12 Figure 14

Claims (1)

[Claims] 1. A reactor pressure vessel with a built-in reactor core, a plurality of control rod drive mechanisms attached to the bottom of the reactor pressure vessel, and a control rod drive mechanism for inserting or withdrawing from below the reactor core. A cluster-type control rod to be operated, a lower cluster guide structure provided with a guide plate for guiding the movement of the cluster-type control rod and capable of accommodating the cluster-type control rod, and a fuel assembly loaded in the reactor core. The fuel assembly is characterized in that a plurality of guide tubes for guiding the insertion and withdrawal of the neutron absorption rods of the cluster type control rods are distributed in the fuel bundle housed in the fuel channel. A boiling water reactor. 2. The lower cluster guide structure holds a plurality of guide plates in a multi-stage structure, and each guide plate is formed with a guide window through which a cluster type control rod can pass.
Boiling water reactor as described in Section. 3. Boiling water according to claim 1, wherein the cluster type control rod has a constricted portion at the top of the neutron absorption rod, and a cluster type control rod extraction head is configured at the upper end of the neutron absorption rod. type reactor. 4. The boiling water nuclear reactor according to claim 1, wherein the cluster type control rod is set such that the neutron absorption capacity of the top of the neutron absorption rod is smaller than the neutron absorption capacity of the remaining portion.