JP3514869B2 - Fuel assemblies for boiling water reactors - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly for a boiling water reactor, which is particularly suitable for increasing burnup.

[0002]

2. Description of the Related Art In recent years, for the purpose of improving fuel economy and reducing the number of spent fuel assemblies, a higher burnup is being made to increase the energy that can be taken out from one fuel assembly. An example of a high burnup fuel assembly used in a boiling water reactor will be described with reference to FIG.

In FIG. 12, a fuel assembly 1 is composed of 74 fuel rods 2 and 3 formed by filling a fuel cladding tube with fuel pellets obtained by sintering oxides of enriched uranium, and two large diameter waters. The rods 6 are arranged in a lattice of 9 rows and 9 columns and fixed to the upper tie plate 4 and the lower tie plate 5 to form a fuel bundle, and the fuel bundle is surrounded by a channel box 7. A spacer 8 keeps the flow distance between the fuel rods 2 and 3 and the water rod 6 by a spacer 8.

The 74 fuel rods 2 and 3 further include 66 long fuel rods 2 in which the fuel rods have a normal fuel rod active length filled with fuel pellets, and the fuel rod active lengths. Is composed of eight short fuel rods 3, which is about ⅔ of the long fuel rods.

Further, in some fuel rods, fuel pellets obtained by mixing and sintering oxides of enriched uranium and oxides of gadolinium (gadolinia), which is a burnable poison, in order to control the excess reactivity within an appropriate range. Is filled.

The short fuel rod 3 expands the coolant passage above the fuel assembly to reduce the pressure loss and improve the stability of the core. At the same time, in the upper part of the core where a peak of neutron flux occurs when the reactor is shut down, an increase in the amount of cooling material causes an excessive deceleration state of neutrons, increasing the reactor shutdown margin.

Here, when the reactor is shut down, all the control rods are inserted into the core and are in a subcritical state. However, even if one control rod is not inserted, it is required to be subcritical. The subcriticality when the control rod with the highest reactivity value is not inserted is called the reactor shutdown margin.

By the way, the high burnup fuel assembly shown in FIG. 12 is designed to be suitable for the takeout burnup of 40 to 50 GWd / t. The problem that the stop margin is reduced occurs.
This is because if the uranium enrichment is increased to increase the take-out burnup, the difference in reactivity between when the reactor is operating and when it is shut down increases, and the effective multiplication factor when the reactor shuts down increases.

As described above, the short fuel rod 3 used in the fuel assembly shown in FIG. 12 has the function of improving the reactor shutdown margin. This action is more effectively exhibited by devising the arrangement of the short fuel rods 3 within the cross section of the fuel assembly. As a means for solving the problem of reducing the reactor shutdown margin by utilizing this point, a technique of arranging the short fuel rods 3 at the four outermost corners of the fuel bundle is disclosed in, for example, JP-A-59-137.
It is disclosed in Japanese Patent No. 886.

Further, JP-A-64-23195 and JP-A-64-23195
No. 5-232273 discloses the arrangement of various short fuel rods for improving the reactor shutdown margin, and some of the short fuel rods are arranged at the outermost periphery of the fuel bundle or at a position adjacent to the water rod. Has been done.

[0011]

A conventional example of a fuel assembly in which short fuel rods are arranged at the outermost periphery of a fuel bundle will be described with reference to FIG. As shown in FIG. 13 (a), this conventional example has two water rods 6 in the channel box 7 as in FIG.
And 74 fuel rods are arranged in a square lattice of 9 rows and 9 columns, and four short fuel rods A out of eight short fuel rods 3 are arranged on the outermost periphery of the fuel assembly. ing.

Each long fuel rod 2 is provided with a natural uranium region at the lower end corresponding to 1/24 of the total length and the upper end corresponding to 2/24 of the total length, so that neutrons leak from above and below the core. To improve fuel economy. The uranium enrichment of each fuel rod is large in the order of a>b> c, and 16 long fuel rods indicated by G contain gadolinia with a concentration of 4.0% as a burnable poison.

However, when the short fuel rods are arranged at the outermost circumference of the fuel bundle, a new problem arises that the output peaking increases especially when the reactor is shut down. In the fuel assembly shown in FIG. 13, the power peaking in the cross section above the upper end of the short fuel rod is 1.38 when the reactor is operating, but becomes 1.51 when the reactor is stopped. Here, the output peaking when the reactor is shut down should be sufficiently low in order to prevent the output from rising due to the reactivity added when the control rod inserted when the reactor shuts down should it fall. This is very important.

In the conventional example shown in FIG. 13, the output peaking becomes excessively large especially when the reactor is shut down. The shortest fuel rods A arranged at the outermost circumference are adjacent to the outermost circumference. This is because the change in output of the long fuel rods B of the book is large.

That is, in the long fuel rod B on the outermost periphery and adjacent to the short fuel rod A, a large amount of cooling water is filled in the region where the fuel rod is absent, especially when the reactor is shut down, and this is the channel. In combination with the cooling water outside the box 7, neutron moderation is promoted, and this action increases the output of the adjacent fuel rods.

On the other hand, when the reactor is in operation, the cooling water flowing in the region where the fuel rods are absent contains many steam voids, and the density of the water is relatively low. It does not overpower the long fuel rods.

In FIG. 14, a short fuel rod D is attached to a water rod 6
A conventional example in which the reactor shutdown margin is improved by arranging it adjacent to the above is shown. However, unlike the fuel assemblies shown in FIGS. 12 and 13, the fuel assemblies are water rods 6 and fuel rods arranged in a square lattice of 10 rows and 10 columns in the channel box 7.

In this example, 8 of 14 short fuel rods are evenly arranged in the second layer from the outermost periphery of the fuel bundle, and 6 short fuel rods are arranged adjacent to the water rod. Has significantly improved the shutdown margin. Natural uranium regions are provided at the upper and lower ends of each long fuel rod 2, and the uranium enrichment of each fuel rod increases in the order of d>e> f. Contains gadolinia at a concentration of 4.5%.

However, even when the short fuel rod D is adjacent to the water rod, the neutron moderating effect of the short fuel rod D and the water rod causes the
In particular, the output of the long fuel rod E adjacent to the two short fuel rods D increases. As a result, in the conventional example shown in FIG.
The power peaking in the cross section above the upper end of the short fuel rod is 1.28 when the reactor is operating, but becomes 1.51 when the reactor is shut down.

By the way, the means for suppressing the output of the long fuel rods B adjacent to the short fuel rods A arranged on the outermost periphery and the long fuel rods E adjacent to the short fuel rods D adjacent to the water rods 6 are suppressed. For this purpose, it is conceivable to reduce the uranium enrichment of the long fuel rod B or the long fuel rod E itself, or to add the burnable poison to the long combustion rod B or the long fuel rod E itself.

However, when the uranium enrichment is lowered, the average uranium enrichment of the fuel assembly is lowered, and it becomes impossible to achieve a sufficiently high burnup. Further, when a burnable poison is contained, the following problems occur.

That is, the fuel rod containing the burnable poison has a lower thermal conductivity than the fuel rod containing only enriched uranium and tends to increase the temperature of the fuel rod, so that the uranium enrichment is sufficiently low. There is a need. As a result, the average enrichment of the fuel assembly is also lowered, and there is a problem that high burnup cannot be achieved.

Further, in the case of the long fuel rod B arranged at the outermost periphery of the fuel bundle, the burnable poison which is a neutron absorbing substance approaches the control rod which is also a neutron absorbing substance so that the neutron absorbing action is performed. Are canceled out, and as a result, the reactivity control capability of the control rod is reduced, so that there is a problem that the ability to shut down the reactor is reduced.

The present invention has been made in order to solve the above-mentioned problems, and enhances the average uranium enrichment of the fuel assembly to increase the burnup without increasing the output peaking and the safety of the reactor. It is an object of the present invention to provide a fuel assembly for a boiling water reactor capable of achieving the above.

[0025]

In a first fuel assembly according to the present invention, a plurality of fuel rods filled with a large number of fuel pellets in a channel box and at least one water rod are formed in a square lattice. In a boiling water nuclear reactor fuel assembly in which the fuel bundles are arranged in a linear fashion, the fuel rods are long fuel rods having a long effective length filled with fuel pellets, and the fuel rods are longer than the long fuel rods. The fuel assembly comprises a short fuel rod having a short effective length, and at least one short fuel rod A and a long fuel rod B adjacent to the short fuel rod A are arranged at the outermost periphery of the channel of the fuel assembly. At least one long fuel rod C is arranged adjacent to the long fuel rod B, and the long fuel rod C is filled in at least most of the upper portion of the effective length of the short fuel rod A. The pellets contain flammable poisons And wherein the Rukoto.

In the first aspect of the invention, preferably, the long fuel rods C are arranged in the second layer from the outermost periphery of the fuel assembly. In this case, the fissile material of the nuclear fuel material contained in at least a part of the fuel pellets filled in the long fuel rods C arranged at positions other than the four corners of the second layer from the outermost periphery of the fuel bundle. It is desirable that the concentration be the maximum concentration of the fissile material concentration of the nuclear fuel material used in the fuel assembly.

In the second fuel assembly according to the present invention, a plurality of fuel rods filled with a large number of fuel pellets in the channel box and at least one water rod are arranged in a square lattice to form a fuel bundle. In the boiling water reactor fuel assembly described above, the fuel rod is composed of a long fuel rod having a long effective length filled with fuel pellets and a short fuel rod having an effective length shorter than that of the long fuel rod. , At least 1
A plurality of short fuel rods D are arranged adjacent to the water rods, further adjacent to the long fuel rods E adjacent to the short fuel rods D, and arranged at a position adjacent to the water rods or the short fuel rods D. In the at least one long fuel rod F thus prepared, at least most of the fuel pellets above the upper end of the effective length of the short fuel rod D are filled with a burnable poison.

[0028]

The long fuel rods E are adjacent to at least two short fuel rods D, or at least 1
The present invention is even more effective when it is adjacent to one short fuel rod D and at least one water rod. Furthermore, the fuel assembly of the first invention and the fuel assembly of the second invention can be used together.

[0030]

The neutron absorbing action of the burnable poison is more remarkable as the amount of the coolant also serving as the moderator is large and the neutron moderating action is large. Therefore, the neutron absorbing effect of the burnable poison contained in the long fuel rod C and the long fuel rod F is greater when the reactor is shut down, where the moderator density is higher than when the reactor is operating.

As a result, by making the long fuel rods B and E adjacent to the long fuel rods C and F containing the burnable poison, the long fuel rods E and E can be disposed particularly at the time of reactor shutdown. Since the outputs of the long fuel rods B and the long fuel rods E can be suppressed, the output peaking when the reactor is stopped can be reduced.

Further, when the long fuel rods C containing burnable poisons are arranged at positions other than the four corners of the second layer from the outermost periphery of the fuel assembly, the uranium enrichment of these fuel rods is set to the fuel assembly. The output does not become excessive even at the highest concentration used in the body. Therefore, the average enrichment of the fuel assembly can be increased without causing an excessive increase in the fuel rod temperature, so that a higher burnup can be achieved.

Further, the neutron absorption effect of the burnable poison is greater when the reactor is shut down than when the reactor is in operation, and the effect is more remarkable when it is arranged adjacent to the water rod or the short fuel rod D having many moderators. Is. Therefore, when the long fuel rod F containing the burnable poison at least in the upper part is arranged adjacent to the water rod or the short fuel rod D to form the fuel assembly, the reactor shutdown margin can be improved.

On the other hand, a long fuel rod F containing burnable poisons
Is arranged at a position not adjacent to the water rod and the short fuel rod D, the output does not become excessive even if the uranium enrichment of these fuel rods is set as the maximum enrichment used in the fuel assembly. Therefore, the average enrichment of the fuel assembly can be increased without causing an excessive increase in the fuel rod temperature, so that a higher burnup can be achieved.

[0035]

【Example】

(First Embodiment) A first embodiment of the fuel assembly according to the present invention will be described with reference to FIGS. Similar to the conventional example shown in FIG. 13, the fuel assembly of this embodiment has 74 fuel rods and two large diameter water rods 6 arranged in a square lattice of 9 rows and 9 columns, and the upper and lower end portions thereof are arranged. The upper tie plate and the lower tie plate are bundled to form a fuel bundle, and the fuel bundle is surrounded by the channel box 7 to form a fuel assembly.

In FIG. 1 (a), out of the eight short fuel rods marked with an X inside the circle, four short fuel rods are four at the four corners of the second layer from the outermost periphery of the fuel bundle. The short fuel rod A is arranged at the center of each outermost side of the fuel bundle.

The structure of the fuel assembly of this embodiment is the same as that of the conventional example shown in FIG. 13, and the fuel rod containing burnable poisons (in FIG. 1 (a), circled with a circle (G)) is used. Only the arrangement is different. That is, eight burnable poison-containing fuel rods C are located on the outermost periphery of the fuel channel and adjacent to eight short fuel rods A that are adjacent to the short fuel rod A, and are arranged in the second layer from the outermost periphery of the fuel channel. Has been done.

This arrangement of the fuel rods C containing burnable poisons reduces the output of the long fuel rods B especially when the reactor is shut down. As a result, in comparison with the conventional example of FIG. 13 in which the average enrichment of the assembly is the same, the power peaking in the cross section above the upper end of the short fuel rod A is 1.
36, a slight improvement, but 1.41 when the reactor was shut down
It could be reduced by 0.1.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIG. When the reactor is shut down, a peak of the neutron flux occurs at a site that is ¼ to ⅓ of the total length down from the upper end, that is, a site above the upper end of the short fuel rod. It suffices if the long fuel rod C contains a burnable poison at this portion in the axial direction.

In the second embodiment of the present invention shown in FIG. 2, eight long fuel rods each having a G inside the circle in FIG. 2 (a) contain gadolinia over the entire length except the upper and lower ends. However, the eight long fuel rods C with T in the circles contain gadolinia only above the upper ends of the short fuel rods A.

In addition, four long fuel rods marked with P in the circle and four short fuel rods marked with + in the circle arranged at the four corners of the second layer from the outermost periphery of the fuel bundle Indicates that gadolinia is contained only in the lower part than the upper end of the short fuel rod in which a circle is marked with a cross.

Here, the uranium enrichment a'of the short fuel rod with + in the circle is a> a ', which is slightly lower than that of the first embodiment using the highest enrichment. . this is,
Since the output of the fuel rod is relatively high at this position, it is necessary to mitigate the temperature rise due to the decrease in thermal conductivity due to the inclusion of gadolinia, and the enrichment of uranium has been lowered in advance.

In this embodiment, the output peaking of the four outermost corners of the fuel bundle and adjacent fuel rods is lower than the upper ends of the short fuel rods by the gadolinia of the short fuel rods marked with + in the circle. In, it is sufficiently suppressed.

In this embodiment, the average enrichment of the fuel assembly is lower than that of the first embodiment, but the uranium enrichments of the four outermost corners of the fuel bundle and the fuel rods adjacent to them are It is also possible to make the average enrichment of the fuel assembly the same as in the first embodiment by making it slightly higher than in the first embodiment.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. In this embodiment, all the eight short fuel rods A marked with a circle in the circle are arranged at the outermost periphery of the fuel bundle, and are adjacent to these eight short fuel rods A at the outermost periphery of the fuel bundle. Adjacent to the twelve long fuel rods B, twelve long fuel rods C containing burnable poisons are arranged in the second layer from the outer circumference of the fuel bundle. These twelve long fuel rods C suppress the output of the long fuel rods B especially when the reactor is shut down to reduce the output peaking.

In the present embodiment, the uranium enrichment of the long fuel rod C marked with G in the circle is the highest enrichment in the fuel assembly, but the uranium enrichment in the four corners of the second layer from the outermost periphery of the fuel bundle. The uranium enrichment of the long fuel rods with L in the circles arranged is the second enrichment in the fuel assembly.

(Fourth Embodiment) A fourth embodiment of the present invention will be described with reference to FIG. In this embodiment, all the eight short fuel rods A are arranged at the outermost circumference of the fuel bundle including the four corners, and these eight short fuel rods A are at the outermost circumference of the fuel bundle.
Adjacent to the 16 long fuel rods B adjacent to each other, 12 long fuel rods C containing burnable poisons are arranged in the second layer from the outermost periphery of the fuel bundle. Since the operation and effect of this embodiment are the same as those of the third embodiment, the description thereof will be omitted.

(Fifth Embodiment) A fifth embodiment of the present invention will be described with reference to FIG. In the present embodiment, all eight short fuel rods D marked with “×” are arranged adjacent to the water rods. Long fuel rods E and E ′ are arranged adjacent to the two short fuel rods D, and adjacent to the two long fuel rods E, there are four fuel rods including a burnable poison with a G inside the circle. Long fuel rod F
Is arranged at a position that is not adjacent to the short fuel rod D or the water rod 6. With these four long fuel rods F, the output of the long fuel rods E is suppressed especially when the reactor is shut down to reduce the output peaking.

In this embodiment, in the long fuel rod E adjacent to the two short fuel rods D, the output peaking at the time of reactor shutdown is most likely to increase, but the long fuel rod E adjacent to one short fuel rod D is most likely to increase. Power peaking also increases at fuel rod E '. Therefore, the long fuel rod F'containing the burnable poison
By arranging F and F as in this embodiment, it is possible to sufficiently reduce the output peaking at the time of reactor shutdown.

(Sixth Embodiment) A sixth embodiment of the present invention will be described with reference to FIG. The arrangement of the short fuel rods in this embodiment is the same as that of the fifth embodiment, but a long fuel containing a burnable poison adjacent to a long fuel rod E ′ adjacent to a short fuel rod D adjacent to a water rod is included. The rod F ″ is adjacent to the water rod. By thus placing the burnable poison-bearing fuel rod adjacent to the water rod, the reactor shutdown margin is improved.

However, at this position, as with the fuel rods with burnable poisons arranged in the four corners of the second layer from the outermost periphery of the assembly, the output is relatively high, so the uranium enrichment is reduced to reduce the thermal conductivity. The temperature rise due to the decrease of

(Seventh Embodiment) A seventh embodiment of the present invention will be described with reference to FIG. This embodiment is different from the first to sixth embodiments in that ten short fuel rods each having a cross inside a circle are arranged. Of these, eight are arranged in the second layer from the outermost periphery of the fuel bundle, and two are arranged adjacent to the water rod 6. Adjacent to the four long fuel rods E adjacent to the two short fuel rods D adjacent to the water rod 6, four long fuel rods F containing burnable poisons are arranged. With these four long fuel rods F, the output of the long fuel rods E is suppressed particularly when the reactor is stopped, and the output peaking is reduced.

(Eighth Embodiment) An eighth embodiment of the present invention will be described with reference to FIG. In this embodiment, a rectangular cylindrical water rod 6'occupying a cross-sectional area corresponding to nine fuel rods, 64 long fuel rods and 8 short fuel rods are arranged in a square lattice.

In this embodiment, of the eight short fuel rods,
Four are arranged on the outermost periphery of the fuel bundle and four are arranged adjacent to the water rod. At the outermost periphery of the fuel bundle, these 4
Adjacent to the eight long fuel rods B adjacent to the one short fuel rod A, eight long fuel rods C containing burnable poisons are arranged in the second layer from the outermost periphery of the assembly.

Furthermore, 4 adjacent to the water rod 6 '
8 adjacent to the short fuel rod D of the book and the water rod 6 '
Adjacent to the long fuel rods E, four long fuel rods F containing burnable poisons are arranged. It should be noted that the long fuel rod C containing the burnable poison disposed in the second layer from the outermost periphery of the fuel bundle
Is also adjacent to the long fuel rod E arranged adjacent to the water rod 6, and the output thereof is also reduced.

(Ninth Embodiment) A ninth embodiment of the present invention will be described with reference to FIG. This embodiment corresponds to the second conventional example shown in FIG. 14, in which fuel rods are arranged in 10 rows and 10 columns, and two water rods 6 are arranged in the central portion of the fuel assembly. , A long box of 78 fuel rods and a short tube of 14 fuel rods are bound in a square lattice and surrounded by a channel box 7.

In this embodiment, the reactor shutdown margin is improved by arranging six short fuel rods D adjacent to the water rods 6, and the long fuel rods D adjacent to two long fuel rods D are arranged. Adjacent to the fuel rod E, four long fuel rods F containing a burnable poison are arranged.

As a result, the output peaking of the present embodiment in the cross section above the upper end of the short fuel rod is 1.29 when the reactor is operating, which is almost the same as that of the conventional example shown in FIG. 14, but 1.41 when the reactor is stopped. It is improved by 0.1 compared to the conventional example.

(Tenth Embodiment) A tenth embodiment of the present invention will be described with reference to FIG. In this embodiment, the fuel rods are arranged in 10 rows and 10 columns as in the ninth embodiment, but two of 14 short fuel rods are arranged adjacent to the water rod 6, The books are arranged at the outermost periphery of the fuel bundle, and the four are arranged at the four corners of the second layer from the outermost periphery of the fuel bundle.

Adjacent to the eight long fuel rods B, which are on the outermost periphery of the fuel bundle and adjacent to the eight short fuel rods A, are burnable poisons in the second layer from the outermost periphery of the fuel bundle. Eight long fuel rods C to be contained are arranged. Also, the water rod 6
The four long fuel rods F containing the burnable poison are arranged adjacent to the four long fuel rods E adjacent to the two short fuel rods D arranged adjacent to each other. . Since the operation and effect of this embodiment are the same as those of the ninth embodiment, the description thereof will be omitted.

(Eleventh Embodiment) An eleventh embodiment of the present invention will be described with reference to FIG. In this embodiment, a large water rod 6 ″ occupying a cross-sectional area of 12 fuel rods, 76 long fuel rods and 12 short fuel rods are arranged in a square lattice shape. 8 out of 12 short fuel rods are arranged at the outermost periphery of the fuel bundle, and 4 are arranged adjacent to the water rod 6 ″.

Adjacent to the 16 long fuel rods B that are on the outermost periphery of the fuel bundle and adjacent to the 8 short fuel rods A, 16 long fuel rods C containing burnable poisons are the fuel bundles. Is arranged on the second layer from the outermost periphery. Further, four long fuel rods F containing burnable poisons are arranged adjacent to eight long fuel rods E adjacent to four short fuel rods D adjacent to the water rod. Since the operation and effect of this embodiment are the same as those of the ninth embodiment, the description thereof will be omitted.

[0063]

EFFECTS OF THE INVENTION According to the present invention, the local power peaking during reactor shutdown is sufficiently reduced without increasing the local power peaking during reactor operation, and the average uranium enrichment of the fuel assembly is significantly increased. Therefore, it is possible to realize a high burnup while sufficiently securing the thermal margin during reactor operation and the fuel integrity at the time of a control rod drop accident.

As a result, the uranium resource can be efficiently used, so that the fuel economy is improved and the number of spent fuel assemblies can be reduced, so that the burden on the storage facility and the reprocessing facility is greatly reduced. It becomes possible to do.

[Brief description of drawings]

FIG. 1A is a cross-sectional view showing a first embodiment of a fuel assembly according to the present invention, and FIG. 1B is a bar diagram for explaining the concentration distribution of fuel rods in FIG. 1A.

2A is a cross-sectional view showing a second embodiment of the fuel assembly according to the present invention, and FIG. 2B is a bar diagram for explaining the concentration distribution of the fuel rods in FIG. 2A.

FIG. 3 is a transverse cross-sectional view showing a third embodiment of the fuel assembly according to the present invention.

FIG. 4 is a cross-sectional view showing a fourth embodiment of the fuel assembly according to the present invention.

FIG. 5 is a transverse sectional view showing a fifth embodiment of the fuel assembly according to the present invention.

FIG. 6 is a cross sectional view showing a sixth embodiment of the fuel assembly according to the present invention.

FIG. 7 is a cross sectional view showing a seventh embodiment of the fuel assembly according to the present invention.

FIG. 8 is a transverse sectional view showing an eighth embodiment of the fuel assembly according to the present invention.

9A is a transverse sectional view showing a ninth embodiment of the fuel assembly according to the present invention, and FIG. 9B is a bar diagram for explaining the concentration distribution of the fuel rod in FIG.

FIG. 10 is a cross sectional view showing a tenth embodiment of the fuel assembly according to the present invention.

FIG. 11 is a transverse sectional view showing an eleventh embodiment of the fuel assembly according to the present invention.

12 (a) is an elevation view showing a fuel assembly in which conventional fuel rods are arranged in 9 rows and 9 columns, FIG. 12 (b) is a sectional view taken along the line BB of FIG. 12 (a), and FIG. (A) CC sectional view taken on the arrow.

13A is a cross-sectional view showing a fuel assembly in which conventional fuel rods are arranged in 9 rows and 9 columns, and FIG. 13B is a bar line for explaining the concentration distribution of the fuel rods in FIG. 13A. Fig.

FIG. 14A is a cross-sectional view showing a fuel assembly in which conventional fuel rods are arranged in 10 rows and 10 columns, and FIG. 14B is a bar line for explaining the concentration distribution of the fuel rods in FIG. 14A. Fig.

[Explanation of symbols]

1 ... Fuel assembly, 2 ... Long fuel rod, 3 ... Short fuel rod, 4
... Upper tie plate, 5 ... Lower tie plate, 6 ... Large diameter water rod, 7 ... Channel box, 8 ... Spacer, A ... Outermost peripheral short fuel rod, B ... Long fuel rod, C ... Long fuel burnable poison Fuel rods, D ... Short fuel rods, E ... Long fuel rods.

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-6-281769 (JP, A) JP-A-63-234192 (JP, A) JP-A-6-102384 (JP, A) JP-A-7- 92210 (JP, A) JP-A-7-151883 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G21C 3/328 G21C 3/326

Claims (5)

(57) [Claims] 1. A fuel for a boiling water reactor in which a fuel bundle is configured by arranging a plurality of fuel rods filled with a large number of fuel pellets in a channel box and at least one water rod in a square lattice shape. In the assembly, the fuel rods are composed of long fuel rods having a long effective length filled with fuel pellets and short fuel rods having an effective length shorter than that of the long fuel rods. At least one short fuel rod A, a long fuel rod B is arranged adjacent to the short fuel rod A, and at least one long fuel rod C is arranged adjacent to the long fuel rod B. The boiling water reactor is characterized in that at least most of the long fuel rods C above the upper end of the effective length of the short fuel rods A are filled with combustible poisons in the fuel pellets. Fuel assembly. 2. The fuel assembly for a boiling water reactor according to claim 1, wherein the long fuel rods C are arranged in the second layer from the outermost periphery of the fuel bundle. 3. The nuclear fuel material contained in at least a part of the fuel pellets filled in the long fuel rods C arranged at positions other than the four corners of the second layer from the outermost periphery of the fuel bundle. The fuel assembly for a boiling water reactor according to claim 2, wherein the fissile material concentration is the maximum concentration of the fissile material concentrations of the nuclear fuel material used in the fuel assembly. 4. A boiling water reactor in which a fuel bundle is configured by arranging a plurality of fuel rods filled with a large number of fuel pellets in a channel box and at least one water rod in a square lattice pattern. In the fuel assembly, the fuel rod comprises a long fuel rod having a long effective length filled with fuel pellets and a short fuel rod having an effective length shorter than that of the long fuel rod, and at least one short fuel rod. D is disposed adjacent to the water rod, further adjacent to the long fuel rod E adjacent to the short fuel rod D, and the water rod.
Or filling in single elongated fuel rods F even least <br/> without being located adjacent to the short fuel rods D, the upper end of the effective length of at least the length fuel rods D the majority of the upper A fuel assembly for a boiling water reactor, characterized in that the fuel pellets contained therein contain a burnable poison. 5. The long fuel rods E are adjacent to at least two of the short fuel rods D or at least one of the short fuel rods D and at least one of the water rods. The fuel assembly for a boiling water reactor according to claim 4.