JPH1194972A - Boiling water reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve conversion ratio and burning efficiency of plutonium without lowering the critical power ratio by properly setting the pressure in the core and the ratio of boiling part area to non-boiling part area. SOLUTION: A multitude of fuel rods 10 sealed with nuclear fuel material containing plutonium are bundled, which are surrounded with a channel box 13. By arranging fuel assemblies 12 with a certain interval in a reactor pressure vessel, a core is constituted. An outer bypass part where non-boiling water flows is provided between fuel assemblies and to part or whole of the bypass part, control rods 11 with cross shape cross section movable up and down are arranged. The operating pressure of the core part is set in the range at 5 MPa or less and the ratio of boiling part area (A) in horizontal cross section in the core to the sum of non-boiling part area (B) in outer bypass part and the inside of water rods, A/B is set at 3 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiling water reactor using a plutonium-containing fuel, and more particularly to a reactor in which the pressure in the core is set low and the conversion ratio and the plutonium conversion without decreasing the critical power ratio. The present invention relates to a boiling water reactor capable of improving combustion efficiency.

[0002]

2. Description of the Related Art A conventional typical boiling water reactor using a typical fuel assembly and a cruciform control rod will be described with reference to FIG.

FIG. 10 shows the structure and arrangement of a fuel assembly and a cross control rod. As shown in FIG. 10, the fuel assembly 1 bundles a large number of fuel rods 3 in which a nuclear fuel material 6 in the form of a cylindrical pellet is sealed, and, for example, two water rods 5 through which non-boiling water flows. The surroundings are surrounded by a channel box 4, and the inside is formed as a boiling portion flow path 8.

[0004] A reactor core is formed by regularly disposing the fuel assemblies 1 at regular intervals in a reactor pressure vessel.
The mutual gap between the fuel assemblies 1 is an external bypass portion 7 through which non-boiling water flows. And the external bypass unit 7
A control rod 2 having a cross-sectional shape is disposed on one side of the control rod 2.

[0005] Most conventional boiling water reactors are operated with the core pressure set at about 7 MPa. That is, during operation of the nuclear reactor, the coolant boils in the boiling portion region 8 to generate steam, and the steam is designed so that the average volume ratio of the steam is about 40% to 50%. In this case, the ratio between the number of atoms HM of the nuclear fuel substance of the fuel and the number of hydrogen atoms H in the water as the coolant, that is, H /
HM is set in the range of 4.5 to 5.

An example in which plutonium is used as fuel in a conventional boiling water reactor is known as pluthermal, and the conversion ratio in such a reactor is about 0.6.

[0007] Further, a concept of a high conversion type reactor for increasing the conversion ratio is also known. In this high conversion type reactor, the arrangement of fuel rods is made denser to reduce the H / HM ratio. This makes it possible to increase the conversion ratio from the pull thermal.

[0008]

Problems to be solved by the present invention will be described.

First, the problem in the case of increasing the conversion ratio by using plutonium as nuclear fuel in a boiling water reactor will be described.

[0010] It is known that the use of plutonium in a nuclear reactor increases the fuel conversion ratio and contributes to the effective use of natural uranium resources. The higher the conversion ratio, the higher the amount of plutonium produced. Therefore, the higher the conversion ratio, the more natural uranium consumption can be saved. When this value exceeds 1, it is called growth. From the viewpoint of saving natural uranium resources, the higher the conversion ratio, the better. In order to increase the conversion ratio, the H / HM ratio should be reduced as much as possible so that the deceleration of fast neutrons generated by fission by hydrogen is not increased. Conventionally, as this method, a method of densely arranging fuel rods has been considered as described above.

However, in the boiling water reactor, when the fuel rods are densely arranged, there is a problem that the mass flux of the coolant increases, the heat removal efficiency decreases, and the cooling performance called a critical power ratio decreases.

Next, a description will be given of a problem in a case where plutonium is efficiently used without increasing the conversion ratio in the boiling water reactor and increasing the reactivity of the reactor core as much as possible to reduce the plutonium loading.

When plutonium is used as a fuel, its large absorption cross section causes the average energy of neutrons to be higher than that of uranium fuel, and the current fuel for boiling water reactors operated on this high energy side In this case, the deceleration becomes insufficient as compared with the case of uranium fuel, and the thermal neutron flux decreases, which is disadvantageous in reactivity.

As a remedy, there is known a method of shifting the energy to a lower energy side by using a fuel structure in which the amount of a moderator is larger than that of uranium fuel and increasing the number of water rods.

However, increasing the amount of moderator generally reduces the number of fuel rods and the area of the flow passage, and has a problem in that the limit output ratio decreases.

The present invention has been made in order to solve such a problem, and it is an object of the present invention to reduce a critical power ratio by setting a pressure in a core portion and a ratio between a boiling portion area and a non-boiling portion area. It is another object of the present invention to provide a boiling water reactor capable of improving the conversion ratio and the combustion efficiency of plutonium.

[0017]

In order to improve the conversion ratio and the combustion efficiency of plutonium without lowering the critical power ratio, the inventor of the present invention has investigated the pressure in the core and the relationship between the boiling area and the non-boiling area. Various considerations were made regarding the ratio and the like.

That is, in a boiling water reactor during power operation, a region where non-boiling water flows (a non-boiling portion), such as a bypass portion, and a region where water boils and has a constant steam void ratio (a boiling portion ( The neutron moderating capability of the reactor is governed by the average density of these water or steam. This density varies with the operating pressure.

FIG. 2 shows changes in saturated water density (solid line) and saturated steam density (dashed line) when the operating pressure is changed. In addition, in FIG.
The relative values are shown with the value of a set to 100%. This figure 2
As shown in (2), the saturated vapor density decreases uniformly with the pressure drop, while the saturated water density has the property of increasing with the pressure drop.

FIG. 3 shows the relationship between the specific volume of the saturated steam, which is the reciprocal of the saturated steam density, and the operating pressure, and FIG. 4 shows the relationship between the void fraction and the operating pressure. As shown in FIG. 3, the specific volume of the saturated steam increases due to the pressure drop,
As a result, the void fraction, which is the volume ratio of steam in the reactor pressure vessel, increases as the pressure decreases, as shown in FIG. In FIG. 4, the heat output and the coolant subcooling degree (difference from the saturation temperature) at the core inlet were made constant regardless of the pressure.

The change in the water density (moderator density) and the change in the operating pressure in the fuel assembly average are obtained by changing the ratio A: B of the area A of the boiling portion to the area B of the non-boiling portion. Can be represented by

FIG. 5 shows the relationship between the fuel assembly average water density (moderator density) and operating pressure when A: B is changed in the range of 1: 1 to 30: 1. Here, the void ratio shown in FIG. 4 is used, and the saturated water density and saturated vapor density shown in FIG. 2 are used.

In the conventional boiling water reactor, the relationship of A: B during power operation is around A / B = 2, and the average density of the fuel assemblies cancels out the density change between water and steam. No pressure effect. On the other hand, when the ratio of the area A of the boiling portion is increased and the ratio is larger than A / B = 3, the density is reduced by lowering the pressure and the ratio of the area B of the non-boiling portion is increased. In the range where / B is less than 2, the density is increased by lowering the pressure. From this, two means of increasing or decreasing the average water density from the conventional boiling water reactor according to the purpose can be selected. In the present invention, the reactor is configured as follows.

In order to reduce the water density from that of the conventional boiling water reactor for the purpose of high conversion, the pressure is reduced to A / B = 3 or more. Further, in the range of A / B = 20 or more, since the effect of water density reduction reaches a peak and a non-boiling portion is required as a control rod insertion space, a non-boiling portion is secured at a fixed rate. It is good to put
The range of / B = 20 to 30 is appropriate. Regarding the operating pressure, when A / B = 3, the density lowering effect is 5
In the case where A / B = 3 or more, it is preferable to set the pressure to 5 MPa or less.

On the other hand, when increasing the water density for the purpose of increasing the reactivity, the pressure is reduced by setting A / B to less than 2.
When A / B = 1, the density increase effect due to the pressure drop is 3MP.
Since the pressure is almost saturated at a, the operating pressure is preferably 3 MPa or more.

As described above, lowering the pressure can be used as a means for adjusting the average water density. However, as pointed out in the problem of the prior art, it is important to consider the influence on the limit output.

FIG. 6 shows the relationship between the pressure and the limit output. FIG. 6 shows the pressure change of the critical output in the power operation state of the boiling water reactor, and the critical power is 3MP.
It can be seen that the value is maximized in the range from a to 5 MPa. Therefore, from the viewpoint of the limit output, the operating pressure is 3 MPa to 5
A range up to MPa is desirable.

As for plutonium nitride, 3
It is said that a reaction with water easily occurs from a range of 00 degrees or more. On the other hand, as shown in FIG. 7, when the operating pressure is reduced, the saturation temperature is lowered. For example, at 4 MPa, the saturation temperature is 250 ° C., and there is an advantage that the reactivity of plutonium nitride can be suppressed. In the present invention, uranium is used as a base material. In this case, uranium can also be nitride.

Nitrogen naturally has several mass isotopes, and nitrogen 14 (N14), which has the largest abundance, absorbs neutrons and produces radiocarbon 14 (C14). Since this reaction increases in the thermal energy region having a large neutron absorption cross section, the reactivity decreases in thermal neutron reactors such as a light water reactor operating in the thermal energy region. To prevent this, it is necessary to concentrate N15, and to reduce the loss in reactivity to about 1% Δk or less, it is necessary to concentrate N15 to at least 99% or more.

On the other hand, in the case of high conversion, the loss in reactivity is small because the operation is not performed with heat energy. However, C14 is a nuclide whose half-life is long and its production amount should be as small as possible. Therefore, in this case as well, the smaller the concentration of N14, the better.

The form of the nuclear fuel material is not limited to the high-density nitride fuel described above. That is, the present invention is also applicable to a case where a mixed oxide (MOX) of plutonium and uranium, which does not easily react with water, is applied to a MOX fuel rod in which cylindrical mixed pellets or granular particles are encapsulated. The goal is achieved.

In order to increase the conversion ratio, H /
It is necessary to reduce the HM ratio as much as possible, and it is necessary to use a plutonium-containing fuel having an H / HM ratio of at least 1.0 or less.

The lattice arrangement is made denser to reduce the amount of coolant, and the amount of fissile material (HM) is increased to increase H / HM
In order to reduce the size, it is most advantageous in terms of geometrical shape to form a triangular lattice in which fuel rods can be densely arranged.

Since burnable poisons such as gadolinium oxide used in light water reactors absorb neutrons almost exclusively in the thermal energy region, neutron absorption in power conversion operation is small in high conversion type reactors having a small H / HM. On the other hand, a high conversion type reactor also has a neutron absorption effect at low temperatures. At low temperatures, the neutron density is much lower than during operation, so that burnable poisons hardly burn, and a small amount of about 1% can sufficiently maintain the absorption capacity during one operation period.

In the case of a high conversion furnace, the smaller the amount of water in the external bypass section, the more advantageous the conversion ratio. The upper half of the cross-shaped control rod is a water exclusion part (follower) with sufficiently small neutron absorption
By using this as an inserted state during output operation, water in the external bypass portion can be eliminated, and H / HM can be reduced. Further, by inserting a control rod as needed, a portion having a large absorption capacity can be brought into the inserted state.

Based on the above findings, the invention of claim 1
Numerous fuel rods containing nuclear fuel material containing plutonium are bundled with zero or one or more water rods through which non-boiling water flows, and the surroundings are surrounded by a channel box. A fuel core having a passage formed therein is provided, and these fuel assemblies are arranged at regular intervals in a reactor pressure vessel to constitute a core, and an external bypass portion through which non-boiling water flows between the fuel assemblies is provided. And a boiling water reactor in which a vertically or vertically movable control rod having a cross-sectional shape is arranged at a part or all of these external bypass parts, and the operating pressure of the core part is 5 M
While the ratio A / B of the area A of the boiling portion in the horizontal cross section of the core and the sum B of the areas of the non-boiling water passage portions inside the external bypass portion and the water rod is set to It is characterized by being set to three or more.

According to the present invention, the average water density can be reduced at low pressure, and the conversion ratio can be increased.

According to a second aspect of the present invention, there is provided the boiling water reactor according to the first aspect, wherein the number of heavy metal atoms HM in the fuel rods of the entire core at the time of the rated power of the reactor and the number of hydrogen atoms contained in the coolant are determined. The ratio H / HM to the number HM is set to 1.0 or less.

According to the present invention, the conversion ratio can be increased to about one.

According to a third aspect of the present invention, in the boiling water reactor according to the first aspect, plutonium and uranium contained in the fuel rods as nuclear fuel substances are present in the form of nitrogen compounds.

According to the present invention, since the weight density of plutonium can be increased, H / HM can be reduced, and the conversion ratio can be increased.

According to a fourth aspect of the present invention, there is provided the boiling water reactor according to the third aspect, wherein naturally occurring nitrogen 14 (N14) and nitrogen 1 are used as the nitrogen element for forming a nitrogen compound.
It is characterized in that those having a higher ratio of nitrogen 15 (N15) than that of 5 (N15) are concentrated and used.

According to the present invention, the amount of C14 produced can be reduced by neutron absorption of N14.

According to a fifth aspect of the present invention, in the boiling water reactor according to the second aspect, the arrangement of the fuel rods in the fuel assembly is such that the center positions of three adjacent fuel rods are vertices of an equilateral triangle. It is characterized in that the arrangement is such that a triangular lattice is formed.

According to the present invention, it is possible to reduce the amount of moderator by increasing the density of the lattice arrangement, and to increase the amount of each fissionable material to reduce H / HM.

According to a sixth aspect of the present invention, in the boiling water reactor according to the fifth aspect, the horizontal cross section of the channel box is substantially square.

According to the present invention, since the fuel rods can be arranged densely, the H / HM can be reduced and the conversion ratio can be increased.

According to a seventh aspect of the present invention, there is provided the boiling water reactor according to the second aspect, wherein gadolinium oxide is contained as a burnable poison in some or all of the fuel rods, and the nuclear fuel material in the fuel rods is provided. Characterized in that the weight ratio of the gadolinium oxide is set to 1% or less.

According to the present invention, the reactivity at the time of low-temperature stop can be reduced without impairing the reactivity at the time of operation, and the furnace shutdown margin at the time of stop can be increased to enhance safety.

According to an eighth aspect of the present invention, in the boiling water reactor according to the first aspect, the control rod is inserted from a lower part of the core, and the upper half of the control rod is made of water having a small neutron absorption capacity. It is configured as a follower to be excluded, and the lower half is made of a substance having a large neutron absorption capacity.

According to the present invention, the water density can be reduced by placing the upper part in the inserted state during operation, the conversion ratio can be increased, and the negative reactivity is applied when the inserted part is further inserted. Can be used to adjust the reactivity.

According to a ninth aspect of the present invention, a number of fuel rods in which nuclear fuel material containing plutonium is sealed and one or more water rods through which non-boiling water flows are bundled, and the periphery thereof is surrounded by a channel box. A fuel assembly having a boiling part flow path formed therein, and by arranging these fuel assemblies at regular intervals in a reactor pressure vessel to constitute a reactor core, water that does not boil between the fuel assemblies. And a control rod movable up and down in a cross-sectional shape is disposed in these external bypass sections, and the operating pressure of the core section is 3MP.
a and 5 MPa or less, while the ratio A / of the area A of the boiling portion in the horizontal cross section of the core and the sum B of the areas of the non-boiling water passages inside the external bypass portion and the water rod. B is set to 1.5 or less.

According to the present invention, the average water density can be increased, the neutron moderating effect can be enhanced, and the reactivity during operation can be increased, so that the required plutonium concentration can be reduced.

According to a tenth aspect of the present invention, in the boiling water reactor according to the ninth aspect, the number of heavy metal atoms HM in the fuel rods of the entire core at the time of the rated power of the reactor and the number of hydrogen atoms contained in the coolant are determined. The ratio H / HM to the number HM is set to 6.0 or more.

According to the present invention, since the average water density can be maximized and the reactivity during operation can be increased, the required plutonium concentration can be reduced.

According to an eleventh aspect of the present invention, in the boiling water reactor according to the tenth aspect, plutonium and uranium contained in the fuel rods as nuclear fuel substances are present in the form of nitrogen compounds, and the nitrogen compounds are formed. Naturally occurring nitrogen 14 (N14) and nitrogen 1
The method is characterized in that a substance having a higher ratio of nitrogen 15 (N15) than that of 5 (N15) is concentrated and used, and the concentration of the nitrogen 15 is set to 99% or more.

According to the present invention, a decrease in reactivity due to absorption of N14 during operation can be suppressed, and the amount of C14 generated can be reduced.

According to a twelfth aspect of the present invention, in the boiling water reactor according to any one of the first to ninth aspects, the nuclear fuel material containing plutonium encapsulated in the fuel rod is formed of cylindrical pellets or granular particles. It is a mixed oxide in a form.

According to the present invention, it is possible to use a nuclear fuel substance in a form that does not easily react with water.

According to a thirteenth aspect of the present invention, in a channel box having a square horizontal section, a large number of fuel rods in which nuclear fuel material is sealed, and the center positions of three adjacent fuel rods are vertices of an equilateral triangle. A fuel core which is housed in an arrangement forming a triangular lattice and has a boiling part flow path formed inside the channel box is provided, and these fuel assemblies are arranged at regular intervals in a reactor pressure vessel to constitute a core. In the boiling water reactor, a water exclusion rod having a small neutron absorption capacity is provided in a gap formed between a fuel rod row arranged at the outermost periphery of the channel box and an inner surface of the channel box. It is characterized by the following.

According to the present invention, H / HM can be reduced by eliminating water in the voids, and the cooling effect can be enhanced by eliminating unnecessary flow paths of the coolant.

[0062]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a boiling water reactor according to the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing a horizontal cross section of a fuel assembly suitable for a high conversion boiling water reactor.

As shown in FIG. 1, in the fuel assembly 12 of this embodiment, fuel rods 10 containing plutonium and depleted uranium as a base material are arranged in a triangular lattice,
For example, 23 or 24 pieces are arranged in the horizontal direction and 28 rows are arranged in the vertical direction, and they are bundled. The fuel rod 10 is surrounded by a channel box 13. In the gap between the inner surface of the channel box 13 and the outermost fuel rods 10 generated by the triangular lattice arrangement of the fuel rods 10, a water exclusion rod 14 containing no nuclear fuel material such as zircaloy and having a small neutron absorption capacity is provided. Are located. During the output operation, the inside of the channel box 13 becomes a boiling portion.

Projections 15 for water removal and for maintaining mutual positions with adjacent fuel assemblies are provided on the outer surface of the channel box 13 at the central position on each side. Further, a cross-shaped control rod 11 inserted from the lower part of the core is arranged so as to surround the four corners of the channel box 13.

The control rod 11 has an upper half made of zircaloy or the like and having only a water exclusion ability with a small neutron absorption ability, and a lower half made of boron carbide (B ₄ C) or the like. Neutron absorption capacity. Then, during the output operation, either the upper half or the lower half of the control rod is inserted, and when the operation is stopped, the lower half is inserted. That is, the control rod 13 is always used in the inserted state.

The water exclusion rods 14 made of Zircaloy or the like described above are arranged in gaps formed by accommodating the fuel rods 10 having a triangular arrangement in a channel box having a square horizontal section, thereby reducing the coolant flow rate. And a function of improving the cooling effect by eliminating a useless flow path of the coolant.

In this embodiment, the ratio A / B of the control rod boiling portion A and the non-boiling portion B is set to about 30,
When the core pressure during operation is 4 MPa, the H / HM is about 0.
It is 5. FIG. 8 shows a change in the conversion ratio when the operating pressure is changed. That is, FIG. 8 shows the relative change of the conversion ratio based on 7 MPa. According to FIG. 8, when the pressure is set to 4 MPa, the conversion ratio increases by about 5%, and is significantly improved by lowering the pressure. Is obtained.

As described above, according to the present embodiment, by setting the pressure to 4 MPa, a marginal output improvement effect can be obtained.
As compared with the case of Pa, the limit output can be increased by about 15%.

In this embodiment, as shown in FIG. 1, the burnable poison-containing fuel rod 16 to which gadolinium oxide having a concentration of 0.5% by weight is added as the burnable poison is moved to the outermost position in the fuel bundle. In a position not adjacent to the control rod 11, the number of required rods is arranged. Thus, the reactivity can be reduced at low temperature without loss of reactivity during output operation, and the neutron absorption capacity of the control rod 11 can be prevented from being impaired.

In this embodiment, a mixture of a plutonium oxide and a uranium oxide can be used as the fuel pellets contained in the fuel rod 10.
Plutonium nitride and uranium nitride can also be applied. In the case of using a nitride, the density of heavy metals is about 1.4 times that of the oxide, so that the H / HM ratio can be further reduced and the conversion ratio can be increased. In this case, if a nitrogen-enriched nitrogen is used,
The formation of C14 can be suppressed.

In the present embodiment, the operating pressure is set to 4 MPa as described above, but the present invention is not limited to this.
The effect is almost the same even if the operation is performed within the range of 5 MPa or less.

FIG. 9 shows the structure of a fuel assembly according to another embodiment of the present invention. The fuel assembly according to this embodiment is suitable for increasing the water density in a boiling water reactor using plutonium for the purpose of increasing the reactivity.

That is, as shown in FIG. 9, the fuel assembly 20 includes a fuel rod 21 containing plutonium therein, a small-diameter water rod 24 having substantially the same diameter as the fuel rod 21, and
A large diameter water rod 25 having a larger diameter than this is arranged in a 10 × 10 matrix in a rectangular lattice and bundled.

A part of the fuel rod is a fuel rod 26 containing a burnable poison, to which a burnable poison such as gadolinium oxide is added.
It has been. The concentration of this burnable poison is 1% by weight or more. The water rod 25 having a large diameter is, for example, 2
The small number of water rods 24 are arranged near the center of the book and the fuel bundle, for example, six small diameter water rods 24 are arranged in the periphery thereof.

The periphery of these fuel bundles is surrounded by a square channel box 22, and the inside of the channel box 22 becomes a boiling portion during output operation. A cross-shaped control rod 23 is arranged in an external gap on one side of the channel box 22. In the embodiment shown in FIG. 9, the control rod 23 is made of a substance having a large neutron absorption capacity using boron carbide (B ₄ C) or hafnium (Hf), like the conventional control rod. .

In this embodiment, the plutonium pellet is a nitride, and the nitrogen content of N15 is 99.9.
%. By setting it to 99.9%, the absorption of N14 in the thermal region can be almost ignored, which is effective in increasing the reactivity and has the advantage that C14 is hardly generated.

In this embodiment, the ratio A / B between the control rod boiling portion A and the non-boiling portion B is about 1.5, and H / HM is about 6 at a pressure of 4 MPa. As described above, by setting the average coolant density higher than that of the conventional boiling water reactor, the reactivity can be increased as compared with the case of the conventional H / HM of 5, thereby increasing the average fissile property of the aggregate. The plutonium ratio can be reduced.

When the water rods 24 and 25 were increased more than shown and the H / HM was set to a range larger than 6, the effect of increasing the reactivity was obtained, but the effect leveled off. Therefore, about 6 is appropriate as H / HM.

As described above, by replacing a part of the fuel rod with the water rod and disposing it near the center of the fuel bundle, the neutron deceleration near the center can be improved, and the reactivity at the time of output can be improved. become able to.

On the other hand, the fuel rods 21 are reduced by the number of water rods, the heat transfer area is reduced, and the limit output is reduced. Instead, the operating pressure is set to 4 MPa and the limit output is increased by about 15%. The overall marginal power can be increased.

In the embodiment shown in FIG. 9, the fuel rods are replaced with water rods. However, the number of water rods is reduced to about two as in the conventional boiling water reactor, and the fuel rods are made thinner. The same effect can be obtained even in the moving method. Further, it is possible to simultaneously employ a method of increasing the number of water rods and a method of making fuel rods thinner. The same effect can be obtained by increasing the width of the external gap.

Also in this embodiment, the operating pressure is set to 4MP.
a, but of course the pressure is 3MPa to 5MPa
The effects are almost the same in the following ranges. Although the depleted uranium is used as the base material, the above effects can be obtained in the same manner even when natural uranium is used.

Further, the burnable poison-bearing fuel rods 16 are arranged on the periphery of the bundle of fuel rods 21, but they can be dispersedly arranged inside the fuel bundle as needed. In this case, 1
Although the absorption effect per book is reduced, there is an advantage that the arrangement position is less restricted and a larger number can be arranged.

[0084]

As described in detail in the above embodiment, according to the present invention, the core pressure during operation of a boiling water reactor and the ratio of a boiling portion and a non-boiling portion are set in appropriate ranges. As a result, excellent effects such as improvement of the conversion ratio or the combustion efficiency of plutonium, and the core reactivity can be achieved without lowering the critical power ratio.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of a boiling water reactor according to one embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating the concept of the present invention and showing the relationship between water or steam density and core pressure.

FIG. 3 is a characteristic diagram illustrating a concept of the present invention and showing a relationship between a steam specific volume and a core pressure.

FIG. 4 is a characteristic diagram illustrating a concept of the present invention and showing a relationship between a void fraction and a core pressure.

FIG. 5 is a characteristic diagram illustrating the concept of the present invention and showing the relationship between moderator average density and core pressure.

FIG. 6 is a characteristic diagram illustrating the concept of the present invention and showing a relationship between a critical power and a core pressure.

FIG. 7 is a characteristic diagram for explaining the concept of the present invention and showing a relationship between a saturation temperature and a core pressure.

FIG. 8 is an explanatory diagram showing an effect of the embodiment, and is a characteristic diagram showing a relationship between a conversion ratio and a core pressure.

FIG. 9 is a plan view showing a configuration of a boiling water reactor according to another embodiment of the present invention.

FIG. 10 is a plan view showing a configuration of a conventional boiling water reactor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Fuel rod 11 Control rod 12 Fuel assembly 13 Channel box 14 Water exclusion rod 15 Projection 16 Fuel rod containing burnable poison 20 Fuel assembly 21 Fuel rod 22 Channel box 23 Control rod 24 Small diameter water rod 25 Large diameter water rod 26 Fuel rod with burnable poison

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G21C 3/62 G21C 3/30 T 7/00 GDB GDBW 7/10 7/10 H

Claims (13)

[Claims] 1. A method in which a number of fuel rods in which nuclear fuel material containing plutonium is sealed and zero or more water rods through which non-boiling water flows are bundled, and the periphery thereof is surrounded by a channel box. A fuel core having a boiling part flow path formed therein is provided, and these fuel assemblies are arranged at regular intervals in a reactor pressure vessel to constitute a core, and non-boiling water flows between the fuel assemblies. A boiling water reactor in which an external bypass portion is provided and control rods movable up and down in a cross-sectional shape are arranged at some or all of the external bypass portion, and the operating pressure of the core portion is 5 MPa or less. While the ratio of the area A of the boiling portion in the horizontal cross section of the core to the sum B of the areas of the non-boiling water passage portion inside the external bypass portion and the water rod is set. A boiling water reactor wherein A / B is set to 3 or more. 2. The boiling water reactor according to claim 1, wherein the number of heavy metal atoms HM in the fuel rods of the entire core and the number of hydrogen atoms H contained in the coolant at the time of the rated power of the reactor.
A boiling water reactor, wherein the ratio H / HM to M is set to 1.0 or less. 3. The boiling water reactor according to claim 1, wherein plutonium and uranium contained in the fuel rods as nuclear fuel substances are present in the form of nitrogen compounds. 4. The boiling water reactor according to claim 3, wherein the nitrogen element for forming the nitrogen compound is nitrogen 15 which is higher than the ratio of naturally existing nitrogen 14 to nitrogen 15.
A boiling water reactor characterized in that a reactor having a high ratio of the above is concentrated and used. 5. The boiling water reactor according to claim 2, wherein the arrangement of the fuel rods in the fuel assembly forms a triangular lattice in which the center positions of three adjacent fuel rods are the vertices of an equilateral triangle. A boiling water reactor characterized by being arranged in an arrangement. 6. The boiling water reactor according to claim 5, wherein the horizontal cross section of the channel box is substantially square. 7. The boiling water reactor according to claim 2, wherein gadolinium oxide is contained as a burnable poison in some or all of the fuel rods, and the gadolinium oxide reacts with nuclear fuel material in the fuel rods. A boiling water reactor having a weight ratio of 1% or less. 8. The boiling water reactor according to claim 1, wherein the control rod is inserted from a lower part of the reactor core, and an upper half of the control rod is configured as a follower having a small neutron absorption capacity and excluding water. The boiling water reactor is characterized in that the lower half is made of a substance having a high neutron absorption capacity. 9. A fuel cell in which a plurality of fuel rods in which nuclear fuel material containing plutonium is sealed and one or more water rods through which non-boiling water flows are bundled, and the periphery thereof is surrounded by a channel box to boil the inside. An external bypass section in which a fuel core having a partial flow path is formed, and the fuel assemblies are arranged at regular intervals in a reactor pressure vessel to form a core, and water not boiling between the fuel assemblies flows. And a control rod movable up and down in a cross-sectional shape in the external bypass portion, wherein the operating pressure of the core portion is 3 MPa or more and 5 MPa
The ratio A / B of the area A of the boiling portion in the horizontal cross section of the core and the sum B of the areas of the non-boiling water passage portions inside the external bypass portion and the water rod is set to be 1 in the following range. A boiling water reactor characterized by having a setting of not more than .5. 10. The boiling water reactor according to claim 9, wherein the number of heavy metal atoms HM in the fuel rods of the whole core and the number of hydrogen atoms H contained in the coolant at the time of the rated power of the reactor.
A boiling water reactor, wherein the ratio H / HM to M is set to 6.0 or more. 11. The boiling water reactor according to claim 10, wherein plutonium and uranium contained in the fuel rods as nuclear fuel substances are present in the form of nitrogen compounds, and the nitrogen element for forming the nitrogen compounds is used. In the method, a substance having a higher ratio of nitrogen 15 than that of naturally occurring nitrogen 14 and nitrogen 15 is concentrated and used.
5. A boiling water reactor, wherein the concentration of No. 5 is set to 99% or more. 12. The boiling water reactor according to claim 1, wherein the nuclear fuel material containing plutonium enclosed in the fuel rod is in the form of mixed pellets or granular particles. A boiling water reactor characterized by being a substance. 13. A large number of fuel rods filled with nuclear fuel material are formed in a channel box having a square horizontal section into a triangular lattice in which the center positions of three adjacent fuel rods are vertices of an equilateral triangle. A fuel assembly having a boiling portion flow path formed inside the channel box,
In a boiling water reactor in which a core is formed by disposing these fuel assemblies at regular intervals in a reactor pressure vessel, a fuel rod array disposed on the outermost periphery of the channel box, and an inner surface of the channel box. A boiling water reactor characterized in that a water exclusion rod having a small neutron absorption capacity is provided in a gap formed between the two.