JP3115392B2 - Fuel assembly for boiling water reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a boiling water reactor (BW).
The present invention relates to a fuel assembly for R), and particularly to a fuel assembly suitable for achieving improved fuel economy by increasing burnup when there is a restriction on the maximum uranium enrichment that can be applied.

[0002]

2. Description of the Related Art In recent years, in light water reactors, improvement of fuel economy and reduction of waste amount (reduction of the number of taken out fuel bodies) have become important issues. In order to improve the fuel economy and reduce the number of fuel assemblies to be taken out, it is effective to increase the take-up burnup of the fuel assembly (to increase the burnup).

[0003] In order to increase the discharge burnup of the fuel assemblies, it is necessary to increase the uranium-235 ratio of the uranium pellets of the new fuel assemblies loaded in the core, that is, to increase the average uranium enrichment of the new fuel assemblies. is necessary.

However, when the burnup is increased in this way, first, fuel assemblies having greatly different burnups are adjacent to each other in the reactor, that is, fuel assemblies having greatly different reactivity and generated output. Since the bodies are present next to each other, the aggregate power difference, that is, the power peaking coefficient in the core radial direction increases. Next, if the uranium enrichment is increased to increase the burnup, the excess reactivity at the beginning of the cycle is suppressed, and the concentration of burnable poisons (Gd, etc.) must be increased and the number of burnable poisons must be increased. The output peaking in the body, that is, the local peaking coefficient increases.

When the burnup is increased as described above, the radial output peaking coefficient and the local peaking coefficient increase, so that the maximum linear power density (MLHG), which is a thermal limitation condition of the fuel, is obtained.
R, Maximam Linear Heat Generation Ratio) and the critical output ratio (MCPR, Minimum CriticalRatio) become severe. In order to keep the maximum linear power density etc. small, the boiling water reactor controls the uranium enrichment distribution of the fuel assemblies. General methods for controlling the uranium enrichment distribution include, for example, those shown in FIG. 6 of JP-A-1-178893, FIGS. 5 and 6 of JP-B-64-28587, and JP-A-63-271192. Publication Number 9
As shown in FIG. 1 and FIG. 1 of JP-A-63-31195, the outermost layer of a fuel assembly, in which neutron deceleration is relatively likely to occur and the output is likely to increase even with the same uranium enrichment, particularly its corners There is a method of lowering the enrichment of the nearby fuel rods.

In addition, fuel rods to which gadolinia (burnable poison) is added in order to suppress excessive reactivity at the beginning of the cycle have a thermal conductivity of several% compared to fuel rods containing only uranium.
become worse. Therefore, even if the output is the same, the fuel rod center temperature becomes high, which is not preferable for safety. Therefore, the uranium enrichment is lowered.

On the other hand, in the current production technology, there is a restriction that the maximum uranium enrichment applicable to the fuel assembly is 5.0 wt%, and it is very difficult to control the uranium enrichment distribution of the fuel assembly. ing. As a conventional technique for increasing the burnup when there is a restriction on the applicable maximum uranium enrichment, there is JP-A-64-28587 described above. In this prior art, in order to lower the enrichment of the outermost layer of the fuel assembly and increase the average enrichment of the fuel assembly, the uranium enrichment of the gadolinia-containing fuel rod is determined by the uranium enrichment used in the fuel assembly. And the effective fuel length of the fuel rod containing gadolinia is shortened to suppress an increase in internal pressure due to an increase in output caused by maximizing uranium enrichment.

[0008]

However, first of all,
When a conventional technique other than JP-A-64-28587 is applied to a technique for increasing uranium enrichment and achieving high burnup, the fact that enrichment of a fuel rod containing gadolinia cannot be increased directly affects the average enrichment, There is a problem that it is difficult to increase the burnup.

In the prior art described in Japanese Patent Application Laid-Open No. 64-28587, the uranium enrichment of a gadolinia-containing fuel rod is made the highest enrichment, at the expense of shortening the active fuel length. In addition to the above, there are problems in design such as the inability to use fuel rods having the specifications described above, and a problem that the fuel loading amount is reduced. In addition, since a rise in the center temperature of the fuel rod containing gadolinia having poor thermal conductivity cannot be prevented, there is a problem that the thermal limit value cannot be cleared.

[0010] It is an object of the present invention to increase the average uranium enrichment and increase the burnup without causing a problem in the fuel rods to which the burnable poison is added when the maximum uranium enrichment is restricted. Further, it is an object of the present invention to provide a boiling water reactor fuel assembly that can satisfy thermal limits such as the maximum linear power density.

[0011]

Means for Solving the Problems] To achieve the above object, the present invention may have a plurality of fuel rods and water rods, the double
The number of fuel rods includes fuel rods containing burnable poisons,
Fuel rods containing toxic poisons have the same concentration of flammable poisons.
In the boiling water reactor fuel assembly, the fuel rods
The fuel rods having an arrangement of 10 rows and 10 columns or more and excluding 4 to 12 fuel rods and fuel rods containing burnable poisons at the four corners of the fuel assembly are ２ or more of the active fuel length. The uranium enrichment in the region is uniformly the highest value in the fuel assembly, the uranium enrichment of the other fuel rods is lower than this, and all the fuel rods facing the water rod are flammable.
A fuel rod containing a poison, wherein at least 1/2 of the total number of fuel rods containing the burnable poison faces the water rod.

Preferably, the maximum uranium enrichment is
Ru der between 5.0wt% and 4.9wt%.

In one embodiment, the average uranium enrichment of the twelve fuel rods at the four corners of the fuel assembly is between 0.80 and 0.86 of the maximum uranium enrichment, Concentrations of 5.0 wt% and 4.9 wt%
%, The average uranium enrichment of the twelve fuel rods at the four corners of the fuel assembly is between 3.9 wt% and 4.3 wt%.

In another embodiment, the fuel assembly 4
The average uranium enrichment of the four fuel rods located at the four corners of the twelve fuel rods at the corners is between the maximum uranium enrichment of 0.70 and 0.76, Uranium enrichment of 5.0 wt% and 4.9 wt%
%, The average uranium enrichment of the four fuel rods located at the four corners of the fuel assembly itself is 3.
It is between 4 wt% and 3.8 wt%.

In another embodiment, the average uranium enrichment of the fuel rod containing the burnable poison is between 0.84 and 0.96 of the maximum uranium enrichment, and the maximum uranium enrichment is 5. If it is between 0 wt% and 4.9 wt%,
The average uranium enrichment of the fuel rod containing the burnable poison is 4.
It is between 1 wt% and 4.8 wt%.

[0016]

In a fuel assembly having a fuel rod arrangement of 10 rows and 10 columns or more, if at least 1/2 of the total number of fuel rods containing burnable poisons is arranged around the water rod, the fuel rods around the water rod will Almost all become burnable poisoned fuel rods. Therefore, in the present invention, by adopting the above configuration,
The uranium enrichment of the fuel rods excluding the fuel rods at the corners, excluding 4 to 12 fuel rods, the fuel rods around the water rod, and the fuel rods containing burnable poisons, becomes the highest value in the fuel assembly uniformly, and When a restriction is imposed on the enrichment, it is possible to increase the uranium enrichment on the average of the fuel assembly while clearing a thermal limit value such as the maximum linear output density, thereby achieving high burnup.

In addition, by uniformly setting the uranium enrichment in the region equal to or more than two-thirds of the active fuel length to the highest value, the low enrichment at the upper end and lower end of the active fuel length with a large amount of neutron leakage is obtained. , Particularly natural uranium, can be loaded, thereby efficiently burning the fuel and increasing the burnup.

The average uranium enrichment of four fuel rods, one at each corner of the fuel assembly, is 0.70 of the maximum uranium enrichment.
Or 0.76, or the average uranium enrichment of the twelve fuel rods at the four corners of the fuel assembly is 0.80 to 0.86 of the maximum uranium enrichment.
By satisfying the thermal limit values such as the linear power density in consideration of the neutron moderating effect at the periphery of the fuel assembly, especially at the corners, the output peaking is set at another position. It can be equivalent to a fuel rod containing only certain uranium.

By configuring the average uranium enrichment of the fuel rod containing the burnable poison to be between the maximum uranium enrichment of 0.84 and 0.96, the local peaking of the fuel rod containing the burnable poison can be achieved. At the end of the first cycle in which the burnable poison is burned out, it can be made several percent or more smaller than the local peaking of the other fuel rods, so that the fuel to which the burnable poison has poor thermal conductivity of the fuel rod is added. The rods can be at the same rod center temperature as normal uranium fuel rod output without other burnable poisons.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a view showing a fuel assembly according to a first embodiment of the present invention. In this first embodiment, the fuel rods
They are arranged in rows and 10 columns. In this embodiment, the maximum uranium enrichment of the fuel assembly 10 is 5.0 wt%.

In FIG. 1, a fuel assembly 10 according to this embodiment is shown.
Has a plurality of fuel rods 20, 21, 22, 23 and four water rods 30, and these fuel rods 20 to 23 and water rod 30 are arranged in a channel box 31. Among these fuel rods, the fuel rods 21 and 22 are twelve fuel rods at the four corners of the fuel assembly 10, and the fuel rod 23 is a fuel rod containing a burnable poison (Gd or the like). Reference numeral 20 denotes another fuel rod. Fuel rod 20
Is 5.0 wt%, that is, the highest uranium enrichment, and the enrichment of the fuel rod 22 located at the fourth corner itself is 3.6 wt%, and the enrichment of the fuel rod 21 adjacent to the fuel rod 22 is Is 4.30% by weight. The concentration of the fuel rod 23 containing the burnable poison is 4.45 wt%. The total number of fuel rods 23 is 20, of which 1 /
Two or more twelve rods are arranged facing the water rod 30.

Further, in the fuel rods 20 to 23, the enrichment of the area of 21/24 (= 7/8) excluding the natural uranium disposed in the upper area of 2/24 and the lower area of 1/24 of the fuel effective portion. The degree is uniform.

In this embodiment, when the maximum uranium enrichment (hereinafter, referred to as the maximum uranium enrichment) applicable to the fuel assembly is restricted, the average uranium is satisfied while satisfying the thermal limit values such as the linear power density. The above configuration is employed to increase the enrichment and achieve a high burnup. The reason is as follows.

First, when there is a restriction on the maximum uranium enrichment, in order to increase the average uranium enrichment of the fuel assembly as much as possible and to increase the burnup, as many fuel rods as possible have the maximum uranium enrichment. desirable.

However, in order to satisfy the thermal limit values such as the linear power density, neutron deceleration is relatively likely to occur, and the uranium enrichment in the periphery of the fuel assembly where the output tends to increase even with the same uranium enrichment is required. Need to lower the degree.

In the periphery of the fuel assembly, neutron deceleration is likely to occur at the fuel rods at the four corners (three at each corner), especially at the corners themselves (one at each corner). For this reason, the uranium enrichment may be lowered particularly with these 4 to 12 fuel rods.

Further, neutron deceleration is relatively likely to occur around the water rod, and the output tends to increase even with the same uranium enrichment. Therefore, some measure to reduce the output is necessary.

On the other hand, in the fuel rods to which a burnable poison (Gd or the like) is added in order to suppress the excessive reactivity at the beginning of the cycle, the thermal conductivity of the fuel rods is several% worse than the fuel rods containing only uranium. For this reason, even if the output is the same, the fuel rod center temperature becomes high, which is not preferable for safety. Therefore, it is necessary to lower the uranium enrichment.

Therefore, in order to increase the average uranium enrichment of the fuel assembly as much as possible and to achieve high burnup, (1) the fuel rods on the outer periphery of the fuel assembly, especially 4 to 12 fuel rods at the four corners Rods (3 corners each) (2) Fuel rods around water rods (3) Uranium enrichment of fuel rods excluding fuel rods containing burnable poisons is defined as the maximum uranium enrichment, and uranium of other fuel rods What is necessary is just to make a concentration degree smaller than this.

Further, when the fuel rod containing the burnable poison is disposed at the outermost periphery, particularly at the outermost periphery facing the control rod, the neutron spectrum becomes hard by the action of the burnable poison. Since the reactivity value of the control rod as the material becomes small and the furnace stop margin at the time of cold shutdown becomes strict, it is not preferable to dispose the control rod at the outermost peripheral part, especially at the outermost peripheral part facing the control rod.

On the other hand, Gd, which is often used as a burnable poison, plays a role as a burnable poison because its energy absorption value rapidly increases with decreasing energy in the thermal neutron energy region and the reactivity value increases. Easier,
Controlling the same reactivity has the effect of reducing the concentration of burnable poison or reducing the number of fuel rods containing burnable poison.

Further, as described above, the fuel rods containing burnable poison must have a low uranium enrichment from the viewpoint of fuel heat conduction. In this manner, the fuel rods containing burnable poison are disposed around the water rod. Then, while keeping the output peaking at a position where the output tends to be relatively large,
There is an effect that the average uranium enrichment of the fuel assembly can be increased.

That is, according to the study by the present inventors,
Uranium enrichment of fuel rods excluding 4 to 12 fuel rods at the corners of (1), fuel rods around water rods of (2) and fuel rods containing burnable poisons of (3) Is uniformly set to the highest value in the fuel assembly, the uranium enrichment of the other fuel rods is made smaller than this, and the fuel rods containing burnable poisons are arranged as the fuel rods around the water rod in the above (2). This means that when restrictions are imposed on the maximum uranium enrichment, it is possible to increase the average uranium enrichment of the fuel assembly and achieve high burnup while clearing thermal limits such as the maximum linear power density. It became clear that there was.

When the burn-up is increased, the number of burnable poison-containing fuel rods in the fuel assembly increases, and it is better to arrange as many burnable poison-containing fuel rods as possible around the water rod. The effect of increasing the average uranium enrichment is large. In a fuel assembly having 10 or more rows of fuel rods, if as many as possible burnable poisoned fuel rods are arranged around the water rod, the number of burnable poisoned fuel rods is １ ／ of the total number of burnable poisoned fuel rods. That is all.

For the above reasons, in the present embodiment, at least one half of the fuel rods 23 containing the burnable poison is disposed around the water rod 30 and the fuel rods 12 are disposed at the four corners of the fuel assembly 10.
Fuel rods 21 and 22 and fuel rods 23 containing burnable poisons
Is defined as the maximum uranium enrichment of 5.0 wt%, and when the maximum uranium enrichment is restricted by this, thermal limits such as the maximum linear power density are cleared. While increasing the average uranium enrichment of the fuel assembly, high burnup can be achieved.

In order to flatten the power distribution, there is a method of changing the uranium enrichment in the axial direction of the core, that is, lowering the uranium enrichment in the lower part of the core and increasing the upper part of the core. In some cases, it is necessary to have the highest uranium enrichment in the upper part of the core and the lowest uranium enrichment in the lower part of the core. In this case, the average burnup of the fuel assembly is in a downward direction, which is meaningless in terms of increasing the burnup. That is, from the viewpoint of increasing the burnup, it is desirable that the burnup be uniform in the core axis direction.

On the other hand, considering the neutron leakage of the nuclear reactor, it is more efficient to make the upper and lower ends of the active fuel length low enrichment, especially natural uranium. That is, regarding the leakage of neutrons, the void ratio is high and the neutron diffusion distance is large at the upper end, so that about 5/24 is natural uranium at the maximum, and the void rate is low and the neutron diffusion distance is small at the lower end, so that the maximum is 3/24. The efficiency is better if the degree is made of natural uranium.
For this reason, the upper end of the active fuel length to the area of 5/24 and the lower end
From the viewpoint of high burnup, it is necessary to uniformly set the uranium enrichment in the remaining region to the highest value in the fuel assembly with reference to the remaining 2/3 region excluding the 3/24 region. Will be appropriate.

In this embodiment, as described above, the uranium enrichment is uniform in the area of 7/8 of the active fuel length, whereby the fuel can be burned efficiently and the high burnup can be achieved. .

Next, it has been described that neutron deceleration is relatively likely to occur in the periphery of the fuel assembly and output is likely to be produced even with the same uranium enrichment. This effect is at the four corners of the fuel assembly. This is remarkable in 12 fuel rods (three in each corner), especially one in each corner, for a total of four.
In consideration of this neutron moderating effect, in order to satisfy the thermal limit values such as the linear power density and to make the output peaking equal to that of a fuel rod containing only uranium at another position, each of the fuel assemblies One of the corners, a total of four uranium enrichments may be configured to be between 0.70 and 0.76 of the maximum uranium enrichment, or twelve at the four corners of the fuel assembly. It is necessary to configure the fuel rod so that the average uranium enrichment is between 0.80 and 0.86 of the maximum uranium enrichment.

Generally, the local peaking in the fuel assembly is maximized at the time of the initial combustion, that is, at the time when the burnup is 0 GWd / t. At this time, the local peaking is maximized in the fuel rods 22 located at the four corners. Therefore, in the present embodiment, the enrichment of the four fuel rods 22 at the corners is set to 3.6 wt% in order to keep local peaking small. At this time, the average uranium enrichment of the four fuel rods 22 at the corners is 0.72 of the highest uranium enrichment.

Further, the enrichment of the four corners is 3.60.
The enrichment of each of the two fuel rods 21 adjacent to the wt% fuel rod 22 was 4.30 wt%. At this time, the average uranium enrichment of the twelve fuel rods 21 and 22 at the four corners is 4.07 wt%, which is 0.81 of the highest uranium enrichment.

Further, in a fuel rod to which a burnable poison (Gd or the like) is added, as described above, the thermal conductivity of the fuel rod is several percent.
For safety reasons, in order to maintain the same fuel rod center temperature as the normal uranium fuel rod output that does not contain other burnable poisons, local peaking of fuel rods containing burnable poisons will cause burnable poison burnout. At the end of one cycle, it is effective to reduce the local peaking of other fuel rods by several percent or more. For this reason,
It is preferable that the average uranium enrichment of the fuel rod containing the burnable poison be between 0.84 and 0.96 of the maximum uranium enrichment.

In the present embodiment, the average uranium enrichment of the fuel rod containing the burnable poison was 4.45 wt%. At this time,
The enrichment of the fuel rod 23 containing the burnable poison is 0.89 of the maximum uranium enrichment.

In a current fuel manufacturing plant, the uranium enrichment that can be handled under various conditions is 5%, and the maximum uranium enrichment from 4.9 wt% to 5.0 w
Therefore, in this embodiment, 1% of the four corners is used.
2 fuel rods, 2 other fuel rods containing burnable poisons
With the enrichment of 0 being the maximum uranium enrichment of 5.0 wt%, the average uranium enrichment of the fuel assembly 10 can be increased to 4.75 wt%.

FIG. 2 shows a fuel assembly 1 according to the first embodiment.
The local peaking distribution of 0 is shown.

FIG. 2A shows a local peaking distribution at the beginning of the first cycle, that is, at a burnup of 0.0 GWd / t. From this figure, it can be seen that the local peaking is largest at the corner. However, the peaking is suppressed to about 1.5, and this value is in an acceptable range from the viewpoint of thermal limitations such as linear power density.

FIG. 2B shows the distribution of local peaking at the end of the first cycle, that is, at a burnup of 13.2 GWd / t. The maximum value of the local peaking of the fuel rod containing the burnable poison is 1.006, which is smaller than the maximum value 1.125 of the local peaking of the other fuel rods.

Therefore, according to the present embodiment, when the maximum uranium enrichment applicable to the fuel assembly is restricted,
The fuel assembly average uranium enrichment can be increased while satisfying the thermal limit values such as the linear power density, and the fuel economy can be improved by increasing the burnup.

Next, an embodiment will be described below in which the condition of the fuel manufacturing plant changes in the future and the maximum uranium enrichment that can be handled becomes 6.0 wt% or 7.0 wt%.

FIG. 3 is a view showing a second embodiment according to the present invention, which is an embodiment when the maximum uranium enrichment is 6.0 wt% in the fuel assembly 11 having the fuel rod arrangement of 10 rows and 10 columns. is there.

The enrichment of the four fuel rods 221 at the corners was 4.30 wt%. At this time, the average uranium enrichment of the four fuel rods 221 at the corners is 0.72, which is the highest uranium enrichment.

The enrichment of each of the four corners is 4.3.
Two fuel rods 21 each adjacent to 0 wt% fuel rod 221
The concentration of 1 was 5.20 wt%. At this time, the average uranium enrichment of the twelve fuel rods 211 and 221 at the four corners is 4.90 wt%, which is 0.82 of the highest uranium enrichment.

The arrangement of the fuel rods 231 containing burnable poisons is as follows:
This is the same as the first embodiment, and 12 or more of 1/2 of the total 20 are adjacent to the water rod. The concentration of 231 containing the burnable poison was 5.4 wt%. At this time, the enrichment of the fuel rod 231 containing the burnable poison is 0.9 of the maximum enrichment.

In the present embodiment, the enrichment of the fuel rods 201 other than the twelve fuel rods at the four corners and the fuel rods containing burnable poisons is set to the maximum uranium enrichment of 6.0 wt%, and the average of the fuel assemblies 11 is set. Uranium enrichment can be increased to 5.71 wt%.

FIG. 4 shows a third embodiment according to the present invention.
This is an example when the maximum uranium enrichment is 7.0 wt% in the fuel assembly 12 having the fuel rod arrangement of 10 rows and 10 columns.

The enrichment of the four fuel rods 222 at the corner was 5.10 wt%. At this time, the average uranium concentration of the four fuel rods 222 at the corners is 0.73, which is the highest uranium enrichment.

The enrichment of each of the four corners is 5.1.
Each two fuel rods 21 adjacent to the 0 wt% fuel rod 222
The concentration of No. 2 was set to 6.15 wt%. At this time, the average uranium enrichment of the twelve fuel rods 212 and 222 at the four corners is 5.80 wt%, which is the maximum uranium enrichment of 0.83.

The arrangement of the fuel rods 232 containing burnable poisons
This is the same as the first embodiment, and 12 or more of 1/2 of the total 20 are adjacent to the water rod. The concentration of the fuel rod 232 containing the burnable poison was 6.30 wt%. At this time, the concentration of 232 containing the burnable poison is 0.9 of the maximum concentration.

In this embodiment, the enrichment of the fuel rods 202 other than the twelve fuel rods at the four corners and the fuel rods containing burnable poisons is set to the maximum uranium enrichment of 7.0 wt%, and the average of the fuel assemblies 12 is set. Uranium enrichment can be increased to 6.68 wt%.

FIG. 5 is a sectional view of a fuel assembly showing a fourth embodiment according to the present invention. In the first to third embodiments, the fuel rods are arranged in a fuel assembly having 10 rows and 10 columns. In this embodiment, the highest uranium is used in the fuel assemblies 13 having 11 rows and 11 columns. 5.0 W concentration
This is an example in which t% is set.

The enrichment of the fuel rod 223 in the corner portion, the enrichment of the fuel rod 213 adjacent to the fuel rod, and the enrichment of the fuel rod 233 containing burnable poisons are as in the case of the first embodiment shown in FIG. Is the same as

In this embodiment, the fuel assembly 13 has two water rods 30A at the center. There are a total of 24 fuel rods 233 containing burnable poison in the fuel assembly 13.
Half or more of them, that is, 18 fuel rods 233 are arranged so as to face the water rod 30A.

In this embodiment, the enrichment of the twelve fuel rods at the four corners and the fuel rods 203 other than the fuel rods containing burnable poisons is set to the maximum uranium enrichment of 5.0 wt%, and the average of the fuel assemblies 13 is determined. Uranium enrichment can be increased to 4.77 wt%.

FIG. 6 shows a modification of the fourth embodiment.
In the fuel assembly 13A of this modification, in the fuel assembly 13 shown in FIG. 5, the fuel rods adjacent to the fuel rods 223 at the corners are replaced with the fuel rods 20 having the maximum uranium enrichment of 5.0 wt%.
3 is replaced. When the fuel rod arrangement is 11 rows and 11 columns, the thermal burden on one fuel rod is reduced, so that the enrichment of the fuel rod adjacent to the fuel rod 223 at the corner can be prevented from being reduced. Assuming that the enrichment of the four fuel rods at the corners and the fuel rods 203 other than the fuel rods containing burnable poisons is the maximum uranium enrichment of 5.0 wt%, the average uranium enrichment of the fuel assembly 13A is 4.82 w.
t%, and higher burnup can be achieved.

[0065]

As described above, according to the present invention,
When there is a restriction on the maximum uranium enrichment applicable to the fuel assembly, while satisfying thermal limits such as linear power density,
Fuel economy can be improved by increasing the burnup.

[Brief description of the drawings]

FIG. 1 is a horizontal sectional view of a fuel assembly according to a first embodiment of the present invention and a view showing a configuration of a fuel rod thereof.

FIG. 2 is a local peaking distribution diagram of the fuel assembly shown in FIG.

FIG. 3 is a horizontal sectional view of a fuel assembly according to a second embodiment of the present invention and a view showing a configuration of a fuel rod thereof.

FIG. 4 is a horizontal sectional view of a fuel assembly according to a third embodiment of the present invention and a view showing a configuration of a fuel rod thereof.

FIG. 5 is a horizontal sectional view of a fuel assembly according to a fourth embodiment of the present invention and a view showing a configuration of a fuel rod thereof.

FIG. 6 is a horizontal sectional view of a fuel assembly as a modification of the fourth embodiment shown in FIG. 5, and a diagram showing a configuration of a fuel rod thereof.

[Explanation of symbols]

10; 11; 12; 13 Fuel assembly 20; 201; 202; 203 Highest enriched fuel rods 21,22; 211,221; 212,222; 21
3,223 Low enriched fuel rod 23; 231; 232; 233 Fuel rod with gadolinia 30; 30A Water rod

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-149588 (JP, A) JP-A-1-188993 (JP, A) JP-A-2-249995 (JP, A) JP-A-3-3 179293 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G21C 3/30

Claims (8)

(57) [Claims] [Claim 1] have a plurality of fuel rods and water rods, wherein the plurality
Fuel rods contain fuel rods containing burnable poisons
The fuel rods containing the poison have the same concentration of the burnable poison. In the boiling water reactor fuel assembly, the arrangement of the fuel rods is 10 rows or more and 10 columns or more . Except for the fuel rods containing 4 to 12 fuel rods and burnable poisons at the four corners, the fuel rods have a uniform uranium enrichment in a region more than 2/3 of the active fuel length. The highest value, the uranium enrichment of the other fuel rods is lower, and all fuel rods facing the water rod are
A fuel assembly for a boiling water reactor, comprising: a fuel rod containing the burnable poison , wherein at least 1/2 of the total number of the fuel rods containing the burnable poison faces the water rod. body. 2. The boiling water reactor according to claim 1, wherein said maximum uranium enrichment is between 5.0 wt% and 4.9 wt%. Fuel assembly. 3. A fuel assembly for a boiling water reactor according to claim 1, wherein said fuel assembly is provided at four corners of said fuel assembly.
The fuel assembly for a boiling water reactor, wherein the average uranium enrichment of the fuel rods is between the maximum uranium enrichment of 0.80 and 0.86. 4. The fuel assembly for a boiling water reactor according to claim 3 , wherein the maximum uranium enrichment is between 5.0 wt% and 4.9 wt%, and at the four corners of the fuel assembly. The average uranium enrichment of some 12 fuel rods is 3.9w
A fuel assembly for a boiling water reactor, wherein the fuel assembly is between t% and 4.3 wt%. 5. A fuel assembly for a boiling water reactor according to claim 1, wherein said fuel assembly is provided at four corners of said fuel assembly.
4 located at the 4th corner of the fuel rods
The fuel assembly for a boiling water reactor, wherein the average uranium enrichment of the fuel rods is between the maximum uranium enrichment of 0.70 and 0.76. 6. The fuel assembly for a boiling water reactor according to claim 5 , wherein the maximum uranium enrichment is between 5.0 wt% and 4.9 wt%, and the four corners of the fuel assembly are themselves. The fuel assembly for a boiling water reactor, wherein the average uranium enrichment of the four fuel rods located in the range of 3.4 to 3.8 wt% is between 3.4 wt% and 3.8 wt%. 7. The fuel assembly for a boiling water reactor according to claim 1, wherein the average uranium enrichment of the fuel rod containing the burnable poison is 0.84 to 0.96 of the maximum uranium enrichment.
A fuel assembly for a boiling water reactor. 8. The fuel assembly for a boiling water reactor according to claim 7 , wherein said maximum uranium enrichment is between 5.0 wt% and 4.9 wt%, and wherein said fuel rod contains said burnable poison. A fuel assembly for a boiling water reactor, wherein the average uranium enrichment is between 4.1 wt% and 4.8 wt%.