JPS5866895A - Bwr 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 (1) Technical field of the invention The present invention relates to boiling water nuclear reactors, and in particular to the structure of control rods. (2) Prior art See Figures 1 to 5. and explain.

In the figure, 1 is a reactor pressure vessel, which is constructed to withstand a reactor pressure of about 7 N/32.

A reactor core 2 is housed in the reactor pressure vessel 1, and coolant (light water) flows into the core 2 from below, boils due to the heat generated by the nuclear reaction of the fuel, and becomes a two-phase flow of water and steam. It is then sent to the upper part of the reactor core 2.

This two-phase flow of water and steam is separated into water and steam by a steam/water separator 3.

Moisture is removed from the separated steam by a steam dryer 4, and the steam is sent to a turbine (not shown) K via a main steam pipe 5.

The separated fine wood is sent to the lower part of the reactor pressure spring 1 along with the water supplied from the water supply sparger 6, and flows into the reactor core 2 from below.

As shown in FIGS. 2 and 3, the reactor core 2 has four fuel assemblies 9 loaded around control rods 8 having a cross-shaped cross section to form a unit grid 10. , this unit cell 1
0... are arranged in a grid pattern as shown in FIG. In addition, in Fig. 3, each square represents one unit cell 10..., and the O cross inside 0 represents the control rod 8...
・Indicates.

The fuel assembly 9... constitutes a fuel bundle by arranging fuel rods (not shown) containing fuel pellets in a lattice of 8 rows and 8 columns, and this fuel bundle is connected to a channel with a substantially square cross section. It is surrounded by a box, and the coolant flows upward through this channel.

The coolant (light water) flowing inside this fuel assembly 9 acts as a coolant to remove the heat generated in the fuel rods, and also acts as a moderator to moderate fast neutrons generated in the nuclear fission reaction into thermal neutrons. .

Reactor water (light water) also exists in the gaps between the nine fuel assemblies 9, and this reactor water acts as a moderator.

The control rod 8 has four radially protruding blades 11 formed by forming stainless steel thin plates into a U-shape.
/
Z x... is accommodated. The neutron absorbing material 13, for example, powder of boron carbide B4C, is filled in the inside of the f-inte, -fll-, and is configured to absorb neutrons.

Incidentally, the above-mentioned elements 4 and 12 serve to prevent the diffusion of radioactive substances generated by the absorption of neutrons by the neutron absorbing material 13.

Also, below the core 2 are control rod guide tubes J4-...
are provided, and control rod drive mechanisms 15 are connected to the lower ends of these control rod guide tubes 14. The control rods 8... are connected to the control rod guide tubes 14...
The control rod drive mechanism 15 is guided up and down by the control rod drive mechanism 15, and is inserted between the fuel assemblies 9 in the core 2.
Or be pulled out.

When the control rods 8 are inserted, they absorb neutrons in the reactor core 2, control the reactivity of the reactor core 2, and control the output. In addition, in the boiling water y# reactor, the flow rate of the coolant flowing through the reactor core 2 is changed, and the ratio of steam and water of the coolant flowing inside the fuel assembly 9 is 0, i.e.? The output can also be controlled by changing the id ratio, increasing the amount of water present in the core 2, adjusting the water-to-fuel ratio, and controlling the moderation effect of neutrons.

The control rods 8 are safety rods that are completely pulled out when the reactor is in operation and inserted into the core only when the reactor is stopped.
It is inserted during operation and is divided into adjustment rods that control the reactivity of the reactor core 2. Normally, about 20 control rods 8 out of all the control rods 8 are used as adjustment rods. Ru. In addition, FIG. 3 shows a control rod 8 used as an adjustment rod.
Control rod 8, which shows the O value arrangement pattern and is circled in the figure...
indicates a rod used as an adjustment rod.

(3) Problems with the Prior Art Conventionally, control rods filled with neutron-absorbing substances are inserted into the reactor core to absorb neutrons and control the output of the reactor core. For this reason, the neutrons absorbed by the control rods are completely wasted, resulting in a problem that is less economical. That is,
The neutrons produced by the nuclear fission reaction must be used effectively to generate the next nuclear fission reaction, and the efficiency with which these neutrons are used is called neutron economy.

By increasing this neutron economy, it is possible to efficiently burn and use fuel, but as mentioned above, the neutrons absorbed by the control rods are completely wasted, and the neutron economy is 90(4) Purpose of the Invention The purpose of the present invention is to reduce wastefully absorbed neutrons, improve neutron economy, and increase fuel usage efficiency. Corner.

(5) Invention O configuration If a neutron non-absorbing substance is filled inside the invention
A control rod is used which has a neutron non-absorbing part with this property to prevent water inside the reactor pressure vessel, that is, reactor water, from entering into the reactor pressure vessel.

By inserting this control rod into the reactor core, the reactor water in the reactor core is removed by that amount, the water-to-fuel ratio of the reactor core is changed, the output is controlled, and the control rod acts as a control rod.

Since this control rod does not absorb neutrons, neutrons are not absorbed in vain, improving neutron economy.

(6) The first embodiment of the invention will be described with reference to FIGS. 6 to 13 (Hata) to (d).

In the figure, 101 is the reactor pressure vessel, which weighs approximately 70 kg.
It is constructed to withstand a furnace pressure of /al.

A reactor core 102 is housed within this reactor pressure vessel 101, and coolant (light water) flows into this reactor core 102 from below, boils due to the heat generated by the nuclear reaction of the fuel, and is divided into water and steam.
It becomes a phase flow and is sent above the core 1aX.

The two-phase flow of water and steam (B) is separated into water and steam by a steam/water separator 103.

Moisture is removed by a separated steam dryer 104 and sent to a turbine (not shown) K via a main steam pipe 105.
Sent.

The separated water is sent to the lower part of the multiple reactor pressure vessel 101 together with the water supplied from the water supply tank A-jar 10g, and flows into the reactor core 102 from below again.

As shown in FIGS. 2 and 3, the reactor core 102 is constructed by loading four fuel assemblies 109 around the peripheries of control rods 10, 8, each having a cross-shaped cross section. . is constructed by arranging a large number of unit cells 110 . In addition, each square in Fig. 3 indicates one unit cell 110-, and the cross in the square indicates the control rod 108°.e The above fuel assembly J09-... A fuel bundle is constructed by accommodating nine fuel rods (not shown) arranged in a grid of 8 rows and 8 columns, and this fuel bundle is surrounded by channels and boxes with a substantially square cross section. Kfi moves upward within the channel.

The coolant (light water) flowing within this fuel assembly JO#-... acts as a coolant to remove the heat generated in the fuel rods, and also as a moderator to reduce the fast neutrons generated in the nuclear fission reaction into thermal neutrons. act.

Reactor water (light water) also exists in Sekiken between the fuel assemblies xoe..., and this reactor water acts as a moderator.

(9) The control rod guide tube 111 is located below the core 101t).
... are provided, and these lll111 rods inner tubes 111
A control rod drive mechanism 112... is connected to the bottom 114 of the control rod XOS... The control rod XOS... is guided by the control rod guide tube 111...K to the control rod drive mechanism 112...
... is driven up and down by the fuel assembly 109 in the reactor core 102, or is pulled out.

The control rods 108... are completely pulled out when the reactor is operating, and the safety rods 108*... are inserted into the reactor core 102 only when the reactor is stopped, and the safety rods 108*... are inserted into the reactor core 102 when the reactor is in operation.
It is divided into a control aS108b... which controls the reactivity of 2. In addition, FIG. 8 shows the arrangement pattern of the adjustment rods 108b..., and the control rods circled in the figure are the adjustment rods! I stick 1
011b-...

The control rods 10g, which are used as the safety rods 108b, are formed by forming a thin stainless steel plate into a U-shape and protruding radially, as shown in Figure @9.
It has blades 113..., and these blades 1
13...A pressure-resistant tube made of stainless steel tubes inside?
It accommodates Izunchi, -bu 114, and so on. These four tubes 114 are filled with a neutron absorbing material such as boron carbide B4C over the entire length.
filled with powder.

Further, the total length L of the control rod used when the baton xosb is closed is longer than the height of the reactor core 102. As shown in FIG. 10, the adjustment rod 108b... has its end 9, for example, a part of the upper end, which is connected to the neutron absorbing section 108b.
151, and the other part is the neutron non-absorbing part 1.
15b.

As shown in FIG. 11, the neutron absorbing portion 115a has a neutron absorbing material 111 such as boron monocarbide filled in a neutron absorbing material 116, as in the conventional case.

Further, in the neutron non-absorbing portion 115b, as shown in FIG. 12, hollow tubes 119...
is accommodated. Both ends of this hollow tube 11m are sealed, giving it watertightness to prevent reactor water from entering inside, and pressure resistance to prevent it from being crushed by reactor pressure. . And this hollow tube 11
#... is filled with a gas cape that does not absorb neutrons. The blade 11 of this adjustment rod 108b...
8..., hollow tube 119... The cape is made of a material that does not absorb neutrons, such as a zirconium alloy.

The length Ll of the neutron absorbing portion 1151 is set to 20 to 50 − of the total length L of the adjustment rod 108b, and the length of the neutron non-absorbing portion 116bO is set to 20 to 50 − of the total length L of the adjustment rod 108b.
is set approximately equal to the height of

Next, the operation of this first embodiment will be explained.

First, when starting the reactor, the safety rod 108b...
All are pulled out from the reactor core 102.

Then, insert the adjustment rod 108b into the core 102,
The reactivity of the reactor core 102 is controlled. In this case, the adjustment rod 10
As shown in FIG. 13(,), 8b... is in a state where its neutron non-absorbing part 115b... is inserted into the core 102, and the neutron absorbing part 1#a m-... is in a state of protruding above the core 102. Make it so that

Then, this adjustment rod 108b...neutron non-absorbing portion 1
11b-... is inserted into the core 101,
O water in the core 102 is removed by that amount, and the core XOZ
The water-to-fuel ratio changes. Therefore, the moderation effect of fast neutrons changes, and the core xoxo reactivity can be controlled. In the case of Jin, the number of fast neutrons in the reactor core 102 increases by the amount that the water-to-fuel ratio decreases, and these fast neutrons are absorbed by the uranium-238 in the fuel.
8 is converted into the nuclear fuel material glu)=umzse.

Therefore, these fast neutrons contribute to the production of PULL)=RAM 239, are not wasted, and the neutron economy improves.

This improves fuel usage efficiency and improves economic efficiency.

In addition, in this first embodiment, the company training baton I OIl b -・
Since the blades 118 and the hollow tubes 119 are made of a zirconium alloy that absorbs few neutrons, the absorption of neutrons is extremely small, improving neutron economy.

In addition, when stopping the reactor, the safety rod 108 &...
· is fully inserted into the reactor core 192, and the adjustment rod 108b
. . as shown in FIGS. 13~) and positioning the neutron absorbing portion 115a above the reactor core 102, the reactivity of the reactor core 10'2 can be sufficiently reduced in pressure. That is, since such adjustment rods f08b... control the reactivity by excluding reactor water from the neutron non-absorbing portions 115b, the reactivity control effect is smaller than that of conventional control rods. However, as in this first embodiment, a neutron absorbing section 1151 is formed in the upper part, and this neutron absorbing section 1151 is
If they are located in the core 102 as shown in FIG. 3(b), neutrons are absorbed by the neutron absorbing portion 1151 of the core, so that the reactivity suppressing effect of the adjustment rods 108b can be increased.

In addition, the id ratio in the fuel assembly 109... is the core 10.
2, the moderation effect of fast neutrons is small in the upper part of the reactor core 102, so there are many fast neutrons in the upper part of the reactor core 101, and the uranium-238 becomes plutonium-119VC.
There is a high rate of alteration, and a large amount of plutonium-239 is produced in the upper part of the reactor core 101, resulting in a high degree of reactivity. Therefore, the neutron absorption part 1 of this adjustment rod 101b...
By locating 15 m above the core 1071, the reactivity suppressing effect can be maximized.

Also, as shown in Fig. 13 (c) K: this adjustment rod J O8
b... by moving up and down and changing the length of the neutron non-absorbing part 115b inserted into the core 101, the reactivity of the core 102 can be finely adjusted, increasing the degree of freedom in reactivity adjustment. increases.

When the adjustment rod 1011b is pulled out, it is pulled out at the trench where the neutron absorbing portion 115 island is pulled out from the core 102, as shown in FIG. 13(d).

(7) # of inventions! A second embodiment will be explained with reference to FIG. It is a sectional view of the neutron non-absorption part of the control rod used as this 14th weight adjustment rod.

In this second embodiment, the control rod blade 118'...
This blade 11 has a pressure-resistant structure that can withstand the reactor pressure and a watertight structure that prevents reactor water from entering the inside.
8'...9 blades 1 without housing a hollow tube inside.
18'... The entire inside is made hollow and filled with a gas etc. that absorbs little neutrons.

In addition, this 21ii1! This embodiment has the same structure as the 1st embodiment described above except for the above points.

And this? In the second embodiment, the volume inside the blades 118' is large and the amount of reactor water removed is large, so the reactivity control effect is large.

(8) Third embodiment of the invention This will be explained with reference to FIG. 15. This FIG. 15 is a plan view of a part of the reactor core.

In this third embodiment, all the control rods in the unit cell 110 are closed with the safety rods 108a, and control rods filled with a neutron absorbing material over the entire length are used as in the conventional case.

Then, the adjustment rod 1 (#b...
The adjustment rods 108b, .

Since the third embodiment has sufficient stop margin, there is no need to provide a neutron absorbing section at the upper end of the adjustment rod 108b as in the first embodiment.

(9) Other Modifications In each of the above embodiments, the non-neutron-absorbing part of the control rod was filled with a gas that absorbs only a small amount of neutrons. However, if a pressure-resistant hollow tube is housed within the blade, the blade itself does not need to have a pressure-resistant structure.

αQ Effects of the Invention The present invention uses a control rod having a neutron non-absorbing part filled with a substance with low neutron absorbing property, so by inserting this control rod, reactor water is removed and the water-to-fuel ratio of the reactor core is increased. can control the reactivity of the reactor core. Since this control rod does not absorb neutrons, the water-to-fuel ratio decreases due to the insertion of this control rod, and the increased fast neutrons are captured by uranium-238 in the fuel and absorbed. (pul) which is nuclear fuel material
Converting to Ni-239 improves neutron economy,
The effects are great, such as the ability to burn fuel efficiently and improve economic efficiency.

[Brief explanation of the drawing]

Figures 1 to 5 show conventional examples, where Figure 1 is a schematic block diagram of a nuclear reactor, Figure 2 is a plan view of a part of the core, Figure 3 is a schematic plan view of the core, and Figure 4 is a schematic diagram of the reactor. The figure is a perspective view of the control rod, and FIG. 5 is a sectional view taken along the line v-■ in FIG. 4. 6 to 13 (d) show the tIX1 embodiment of the present invention, FIG. 6 is a schematic configuration diagram of a nuclear reactor, FIG. 7 is a plan view showing a part of the reactor core, and FIG. The figure is a schematic plan view of the reactor core, Figure 9 is a perspective view of a control rod used as a safety rod, Figure 10 is a side view of a control rod used as an adjustment rod, and Figure 11 is the same as Figure 10. A cross-sectional view along the line XI-XI, Figure 12 is the 10th
The cross-sectional views along the cutting line in the figure, FIGS. 13(-) to (d), are schematic diagrams for explaining the action of the p4 straightening rod. FIG. 14 is a sectional view of the adjustment rod of the second embodiment. Tuna 15 figure is the third
FIG. 3 is a plan view showing a part of the reactor core of the embodiment. 101... Nuclear reactor pressure vessel, 102. ...Reactor core, 1
0 B-...Control rod, 104t a = Safety rod, Itl
llb...Adjustment rod, 109-...Fuel assembly, 116
...-Izunchi, -P, 111...Neutron collecting substance, 118...Blade%11B'...Blade, 1
1#...Hollow tube O Applicant's agent Takehiko Suzue Figure 1 Figure 3 Figure 5 Figure 6 Figure 12 Figure 13 (b-3

Claims (5)

[Claims] (1) The large number of fuel assemblies that make up the reactor core, and the fact that a substance that does not absorb neutrons is inserted between these fuel assemblies and is filled with the material that does not absorb neutrons. 1. A boiling water nuclear reactor comprising: 9 control rods having neutron non-absorbing parts. (2) The boiling water reactor described in Patent No. 1, wherein the neutron non-absorbing portion has a hollow interior, and the interior thereof is filled with a gas that does not absorb neutrons. (3) The boiling water nuclear reactor according to claim 1, wherein the control rod has an end portion filled with a κ neutron absorbing material to form a good neutron absorbing portion. (4) The boiling water nuclear reactor according to claim 1, wherein the control rod is made of a zirconium alloy. (5) The above-mentioned claim is characterized in that the control rod is arranged at a position where it is used as an adjustment rod, and control rods at other positions are filled with a neutron-absorbing material over their entire length. Boiling water reactor according to paragraph 1.