JPH11153681A - Fuel assembly and core of reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel assembly graded in reactivity from non-adjacent cells by arranging Gd fuel rods in adjacent cells, and the core of reactor facilitating the control of reactivity characteristics and thermal characteristics by loading those fuel assemblies at the time of refueling. SOLUTION: A fuel assembly arranges in a square lattice a first group of fuel rods 10 to 5 and V containing nuclear fuel material and not containing burnable poison, a second group of Gd fuel rods G1 and G2 containing nuclear fuel material and burnable poison and one or a plurality of water rods. The core of reactor is loaded at the time of refueling with first fuel assemblies, low Gd assembly 15 having at least one set of second group Gd fuel rods G1 and G2 containing nuclear fuel material and burnable poison in adjacent cells and second fuel assemblies, high Gd fuel assembly 12 having the second group Gd fuel rods G1 and G2 in non-adjacent cells.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high burnup fuel assembly in a boiling water reactor and a reactor core of the reactor.

[0002]

2. Description of the Related Art The core of a boiling water reactor is shown in FIG.
FIG. 11 (a) shows a partially cut-out vertical sectional view and FIG.
11B is a sectional view taken along arrow B, and FIG.
As shown in a cross-sectional view taken along the arrow C, the fuel assembly 1 is formed by loading a large number of fuel assemblies 1 together with control rods (not shown). Note that this fuel assembly 1 is an example for the purpose of increasing the burnup. A large number of long fuel rods 3 and short fuel rods 4 are provided in a channel box 2 covering the periphery thereof by two large water rods. 5 and stored in a regular lattice.

The long fuel rod 3 and the large diameter water rod 5 are connected to an upper tie plate 7 through an external spring 6.
The short fuel rod 4 is fixed by the lower tie plate 8 and the lower tie plate 8, and the plurality of fuel spacers 9 appropriately maintain the mutual interval.

The long fuel rod 3 and the short fuel rod 4 are
In each case, the fuel cladding tube is filled with a large number of fuel pellets containing a nuclear fuel material such as uranium oxide. The long fuel rods 3 and the short fuel rods 4 are arranged together with the large-diameter water rods 5 in a 9 × 9 regular grid. Are arranged.

The fuel assemblies shown in the fuel rod arrangement diagram of FIG. 12A and the axial enrichment distribution and Gd concentration distribution diagram of FIG.
In 10, fuel rod numbers of each fuel rod type (ROD TYPE) are indicated by reference numerals 1 to 5, V, G1 and G2, and the large-diameter water rod 5 is indicated by W. In the core, control rods 11 are arranged at corners of the fuel assembly 10.

Here, reference numerals 1 to 5 denote long fuel rods 3 each containing a nuclear fuel substance having a different enrichment, reference numeral V denotes a short fuel rod 4 lacking an upper fuel, and reference numerals G1 and G2 denote nuclear fuel substances. And a long fuel rod 3a containing a burnable poison. Further, the fuel rods 1 to 5 and V which are different in the enrichment and contain only the nuclear fuel substance and do not contain the burnable poison are called the first group of fuel rods, and the fuel rods G1 and G2 containing the nuclear fuel substance and the burnable poison are referred to as the first group. Called two groups of fuel rods.

[0007] Further, the fuel rods in FIG.
To e and the blank portion indicate the uranium enrichment, and the magnitude of the enrichment has a relationship of a>b>c>d>e> blank portion, and X and Y in the fuel rods G1 and G2 of the second group are Shows the concentration of gadolinia, which is a burnable poison (in a normal boiling water reactor, gadolinia Gd ₂ O ₃ is used as a burnable poison, and is hereafter abbreviated as Gd). Different.

In the current operation management of a nuclear reactor, A.A.
B. In order to provide flexibility for fluctuations in the operation period, B. C. In order to make a smooth transition to the core with high fuel output, C.I. In order to improve the core characteristics by flattening the radial power distribution of the core, two types of fuel assemblies having different reactivity characteristics are adjusted according to the number of loaded bodies in each operation cycle. Also,
In order to change the reactivity characteristics of the fuel assembly, it is optimal to change only the number of Gd fuel rods and the Gd concentration while maintaining the same average enrichment of the fuel assembly.

For the Gd fuel rods 3a, which are the second group of fuel rods, two types of fuel assemblies are shown in FIGS.
13, the fuel assembly 10 of FIG. 12 has four fuel rods G1 having a high Gd concentration of X, nine fuel rods G2 having a low Gd concentration of Y, and nine Gd fuel rods. Since the total number of 3a is as small as 13 and therefore the reactivity value of Gd is low, it is generally called a low Gd fuel assembly 10.

On the other hand, the fuel assemblies shown in the fuel rod arrangement diagram of FIG. 13A and the axial enrichment distribution and the Gd concentration distribution diagram of FIG. , G
Since the number of fuel rods G1 with high d concentration is 12 and the number of fuel rods G2 with low Gd concentration is 4 and the total number of Gd fuel rods 3a is as large as 16 and the reactivity of Gd is high, a high Gd fuel assembly Called 12.

Further, as shown in FIGS. 12A and 13A, the low Gd fuel assembly 10 and the high Gd fuel assembly
The arrangement of the Gd fuel rods G1 and G2 in FIG. 12 is a non-adjacent arrangement that is not adjacent to each other. Here, each of the long fuel rods 1 to 5 in the high Gd fuel assembly 12
And the uranium enrichment a to e, blank space and Gd concentration X, Y in the short fuel rod V and the Gd fuel rods G1, G2.
Has the same specifications as the low Gd fuel assembly 10 described above.

Therefore, when comparing the infinite multiplication factor of these cross sections of the low Gd fuel assembly 10 and the high Gd fuel assembly 12 with a certain cross section, the combustion change characteristic diagram of the infinite multiplication factor shown in FIG. 14 is obtained. That is, during the period from the initial stage of combustion until the infinite multiplication factor reaches a peak, the curve 13 (solid line) of the low Gd fuel assembly 10 is more infinite than the curve 14 (dotted line) of the high Gd fuel assembly 12. It can be seen that the rate of increase of the multiplication factor is moderate, and there is a difference in the reactivity.

Accordingly, when these two types of low Gd fuel assemblies 10 and high Gd fuel assemblies 12 are loaded in the core, and the operation period is longer than the standard, the high Gd fuel assemblies 12
To increase the loading ratio. In addition, when shifting to a core having a high removal burnup, the loading ratio of the low Gd fuel assembly 10 is increased. Further, when the thermal power is improved by flattening the core radial power distribution, the high Gd fuel assembly 12 is disposed at a position where the radial power is high, and a good reactivity characteristic and good reactivity as a nuclear reactor are obtained. A core with thermal properties was realized.

[0014]

In a conventional nuclear reactor, in order to achieve good reactivity characteristics and thermal characteristics, for example, two types of low Gd fuel rods having different numbers of Gd fuel rods 3a and different Gd concentrations are used. Fuel assembly 10 and high Gd fuel assembly
Twelve had to be designed in advance. However, in the event of a sudden event such as a fluctuation in the operation period of the reactor, a fuel assembly designed in advance to have a certain reactivity will require precise analysis of the reactivity and thermal characteristics of the core. Because adjustment was difficult, it was not possible to respond quickly to obtain appropriate core characteristics, which hindered the improvement of the operating rate of nuclear power plants.

An object of the present invention is to provide a fuel assembly in which the reactivity is different from that of a non-adjacent fuel assembly by arranging Gd fuel rods adjacent to each other, and loading and reacting the fuel assemblies at the time of refueling. An object of the present invention is to provide a fuel assembly and a reactor core which are cores that facilitate adjustment of temperature characteristics and thermal characteristics.

[0016]

According to the first aspect of the present invention, there is provided a fuel assembly including a first group of fuel rods containing a nuclear fuel substance and containing no burnable poisons, a nuclear fuel substance, and a combustible fuel. In a fuel assembly in which a second group of fuel rods containing a poison and one or more water rods are arranged in a square lattice, at least one set of the second group of fuel rods containing the nuclear fuel substance and the burnable poison is provided. It is characterized by being arranged adjacently.

By arranging Gd fuel rods, which are a second group of fuel rods containing a nuclear fuel substance and a burnable poison, adjacent to each other,
The degree of freedom of fuel rod arrangement in the fuel assembly is increased. In addition, as the second group of fuel rods are densely arranged adjacent to each other, the reactivity value of the second group of fuel rods themselves decreases due to the interference effect of Gd, and combustion is delayed.

Therefore, by making Gd having a large neutron absorption cross-sectional area adjacent thereto, the neutron absorption effect can be maintained for a longer time. Therefore, merely by changing the arrangement of the second group of fuel rods, the required reactivity can be reduced. A corresponding fuel assembly is created. Further, since the reactivity value of Gd in the second group of fuel rods is reduced, Gd can be efficiently burned by lowering the Gd concentration in advance.

A fuel assembly according to a second aspect of the present invention comprises:
In claim 1, the second group of fuel rods comprises a plurality of types of fuel rod groups having different concentrations of burnable poisons.

A fuel assembly in which a Gd fuel rod, which is a second group of fuel rods containing a nuclear fuel substance and a burnable poison, is disposed adjacent to the second group of fuel rods, comprises a plurality of fuels having different burnable poison concentrations. Even in the case of the rod group, the reactivity value of the fuel rods themselves in the second group is reduced due to the interference effect of Gd, and combustion is delayed. Also, Gd in the second group of fuel rods
Therefore, Gd can be efficiently burned by lowering the Gd concentration in advance.

According to a third aspect of the present invention, there is provided a nuclear reactor core comprising: a first group of fuel rods containing a nuclear fuel substance and containing no burnable poison; a second group of fuel rods containing a nuclear fuel substance and a burnable poison; A fuel rod in which a water rod through which a coolant flows is arranged in a square lattice, and a second fuel assembly in which at least one set of the second group of fuel rods is disposed adjacent to each other. Is loaded during refueling.

A first fuel assembly in which at least one set of fuel rods of the second group is arranged adjacent to each other and a second fuel assembly in which fuel rods of the second group are arranged non-adjacently have Gd reactivity with each other. Is different from the first fuel assembly and the second fuel assembly at the time of refueling in the case where the removal burn-up increases in the core of the nuclear reactor or the reactivity is adjusted by shortening the operation period. By appropriately combining and loading, appropriate reactivity adjustment can be performed.

According to a fourth aspect of the present invention, in the nuclear reactor core according to the second aspect, the first fuel assembly and the second fuel assembly have the same number of fuel rods of the second group. Features.

At the time of refueling when the reactivity is adjusted in the core of the nuclear reactor, even if the number of fuel rods of the second group in the first and second fuel assemblies to be loaded is the same, Since at least one set of fuel rods of the second group in the fuel assembly is disposed adjacent to each other, the reactivity of the second fuel assembly with the burnable poison is different. Therefore, at the time of refueling when the reactivity is adjusted in the reactor core, the first fuel assembly containing the same number of the second group of fuel rods together with the second fuel assembly but having a different Gd reactivity. By loading the body, appropriate reactivity adjustment can be performed.

According to a fifth aspect of the present invention, in the reactor core of the third aspect, the number of fuel rods of the second group in the first fuel assembly and the number of fuel rods in the second fuel assembly are different. I do.

At the time of refueling when the reactivity is adjusted in the core of the nuclear reactor, when the concentration of the burnable poison of the fuel rods of the second group in the first and second fuel assemblies to be loaded is the same. In addition, since the numbers of the fuel rods of the second group are different from each other, the reactivity of the burnable poison differs. Therefore, at the time of refueling in the case of performing the reactivity adjustment in the core, the first fuel assembly having a different Gd reactivity by storing a different number of the second group of fuel rods together with the second fuel assembly is provided. By loading, appropriate reactivity can be adjusted.

According to a sixth aspect of the present invention, in the reactor core according to the fourth or fifth aspect, the fuel rods of the second group include a plurality of types of fuel rod groups having different concentrations of burnable poisons. Features.

At the time of refueling when the reactivity is adjusted in the core of the nuclear reactor, the number of fuel rods of the second group in the first fuel assembly and the number of fuel rods of the second group in the second fuel assembly to be loaded are the same or different. Even in this case, the reactivity differs because the concentrations of the burnable poisons are different from each other.

Therefore, at the time of refueling when the reactivity is adjusted in the reactor core, the second group of fuel rods having different concentrations of burnable poisons are housed together with the second fuel assembly.
d By loading the first fuel assemblies having different reactivity, appropriate reactivity adjustment can be performed.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to the present invention will be described with reference to the drawings. Note that the same components as those of the above-described conventional technology are denoted by the same reference numerals, and detailed description thereof will be omitted. The first embodiment is defined in claims 1 and 3 and 4.
In this regard, as shown in the fuel rod arrangement diagram of FIG. 1A and the axial enrichment distribution and Gd concentration distribution diagram of FIG. 1B, the Gd fuel assembly 15 is intended to increase the burnup. .

The Gd fuel assembly 15 includes a plurality of long fuel rods (3, 3a) 1 to 5, G1, G2, a short fuel rod (4) V lacking an upper nuclear fuel, and two thick fuel rods (3, 3a). The diameter water rods (5) W are bundled in a square lattice by a fuel spacer 9 (not shown) and fixed to an upper tie plate 7 and a lower tie plate 8 (not shown) to form a fuel rod bundle. Is covered by the channel box 2.

Here, 1 to 5 of the long fuel rods (3) and the short fuel rods (4) V are the first group of fuel rods, which represent uranium fuel rods containing uranium as a nuclear fuel substance. The enrichment ratios a to e and the size of the blank portion are as follows: a>b>c>d> e
> Blank section. The fuel rods G1 and G2 are
A group of fuel rods represents a Gd fuel rod (3a) containing uranium as a nuclear fuel substance and gadolinia (Gd ₂ O ₃ ) as a burnable poison, and Gd which is also the content of burnable poison in the Gd fuel rods G1 and G2. Is configured to be the same as X = Y.

Further, as for the Gd fuel rods G1 and G2, which are the second group of fuel rods, as shown in FIG.
In the Gd fuel assembly 15, a plurality of fuel cells are arranged adjacent to each other like a cross 16 and an L-shaped 17 surrounded by dotted lines. That is, a total of 16 second group fuel rods having the same Gd concentration
The total number of fuel rods G1 and G2 is two sets of crosses 16 (2 × 5
Book) and an L-shaped 17 (2 × 3) (claim 1).

At the time of the new operation of the nuclear reactor, a large number of new fuel assemblies are loaded in the core. However, as the combustion of the fuel progresses with the elapse of the operation time, the discharge burn-up in the core increases. Since the operating period is shortened and the core characteristics due to radial keeping and the like are reduced, it is necessary to adjust the reactivity by refueling.

At the time of adjusting the reactivity by refueling in the core, the Gd fuel assembly 15 as the first fuel assembly, the Gd fuel assembly 15 and the Gd fuel rod G
1 and G2, for example, a high Gd fuel assembly 12 shown in FIG. 13 as a second fuel assembly, and two types of fuel assemblies of the first fuel assembly and the second fuel assembly. Is loaded to form a core (claims 3 and 4).

As shown in FIG. 13, the high Gd fuel assembly 12 has a total of 16 Gd fuel assemblies 15, 12 Gd fuel rods G1, 4 G2 fuel rods and 3 Gd fuel rods (3a).
Although the number of the books is the same, they are non-adjacent to each other.

Next, the operation of the above configuration will be described. The present Gd fuel assembly 15 which is a plurality of first fuel assemblies
FIG. 2 shows a combustion change characteristic diagram of the infinite multiplication factor of FIG. 2 by comparing the infinite multiplication factor of a certain cross section with that of the high Gd fuel assembly 12 as the second fuel assembly. According to this, during the period from the initial stage of combustion to when the infinite multiplication factor reaches a peak, the Gd fuel assembly 15 has the higher Gd as shown by the curve 18 (solid line).
Compared to the curve 14 (dotted line) of the fuel assembly 12, it can be seen that the rate of increase of the infinite multiplication factor is gradual, and there is a difference in reactivity with the high Gd fuel assembly 12.

Therefore, the Gd fuel assembly 15 has the same number of Gd fuel rods G1 and G2 as those of FIG. The curve 13 indicates that the fuel assembly has a reactivity corresponding to the low Gd fuel assembly.

That is, the Gd fuel rod G which is the second group of fuel rods
By arranging the fuel rods 1 and G2 adjacent to each other, the degree of freedom in the arrangement of the fuel rods in the fuel assembly is increased, and as the Gd becomes closer and denser, the reaction effect of the fuel rods themselves of the second group by the mutual interference effect of Gd. The value can be reduced and the combustion can be delayed.

Therefore, G having a large neutron absorption cross section
Since the neutron absorption effect can be maintained longer by making d adjacent to each other, even if the number of fuel rods of the second group is the same, simply changing the arrangement of the fuel rods of the second group will provide the required reactivity. It is possible to easily produce fuel assemblies having different degrees of reactivity according to the conditions.

As a result, the specifications can be shared, the manufacturing cost of the second group of fuel rods can be reduced, and the reactivity can be adjusted due to an increase in the extraction burnup in the core and a shortened operation period. This Gd fuel assembly
According to 15, there is no need to change the number of Gd fuel rods G1, G2.

In this case, by merely changing the arrangement of the Gd fuel rods G1 and G2, for example, by arranging the cruciform 16 and the L-shaped 17 adjacent to each other, the fuel having the reactivity corresponding to the low Gd fuel assembly can be obtained. If the fuel cells are arranged in a non-adjacent manner, fuel assemblies having a reactivity corresponding to a high Gd fuel assembly can be separately formed.

As described above, in the Gd fuel assembly 15 in which the type and the number of the fuel rods of the first group and the second group are the same,
It is possible to easily obtain a reactivity corresponding to a low Gd fuel assembly or a high Gd fuel assembly. So, for example,
Even if the number of loaded low Gd fuel assemblies and high Gd fuel assemblies is changed according to a request from the reactor core, according to the previously prepared Gd fuel assemblies 15, the arrangement of the fuel rods of the second group can be changed. By doing so, it is possible to respond quickly, and the operation rate of the nuclear power plant is improved.

Since the second embodiment is a modification of the first embodiment according to claims 1 and 3 and 4, it has the same components, functions and effects as those of the first embodiment. Are omitted, and different parts will be described. As shown in the fuel rod arrangement diagram of FIG. 3A and the axial enrichment distribution and the Gd concentration distribution diagram of FIG. 3B, the Gd fuel assembly 19 is intended to increase the burnup.

Here, 1 to 5 of the long fuel rods (3) and the short fuel rods (4) V are the first group of fuel rods,
Numeral 1 and G2 denote a second group of fuel rods, which represent Gd fuel rods (3a) containing nuclear fuel material and burnable poison Gd, and having the same Gd concentration in the Gd fuel rods G1 and G2 as X = Y. Have been. As shown in FIG. 3 (a), Gd fuel rods G1 and G2, which are the second group of fuel rods, are vertically or horizontally adjacent to each other for eight of 50% of the total of 16 fuel rods. Four sets are formed as the arrangement 20 (4 × 2) (claim 1).

Further, when adjusting the reactivity by refueling in the reactor core, the G
The d fuel assembly 19 has the same number of Gd fuel assemblies 19 and Gd fuel rods G1 and G2 as shown in FIG.
A core is formed by loading the fuel assembly 12 as a second fuel assembly and loading two types of fuel assemblies, the first fuel assembly and the second fuel assembly (claims 3 and 4). .

Next, the operation of the above configuration will be described. The present Gd fuel assembly 19, which is a plurality of first fuel assemblies
FIG. 4 shows a combustion change characteristic diagram of the infinite multiplication factor of FIG. 4 comparing the infinite multiplication factor of a certain cross section by the high Gd fuel assembly 12 as the second fuel assembly. According to this, during the period from the initial stage of combustion to the peak of the infinite multiplication factor, the present Gd fuel assembly 19 has the high G shown in FIG. 13 as shown by the curve 21 (solid line).
Compared to the curve 14 (dotted line) of the d fuel assembly 12, there is almost no difference in the increase rate of the infinite multiplication factor.
It can be seen that is slightly gentler.

The Gd fuel assembly 19 is a fuel assembly in which two fuel rods of the second group are arranged adjacent to each other, and has a minimum adjacent fuel assembly which exhibits a significant difference in reactivity with other non-adjacent fuel assemblies. Degree. However, even such a difference in reactivity is effective in adjusting a small amount of reactivity in the core. It should be noted that the same effect can be obtained even when the Gd fuel rods G1 and G2 of the second group are arranged adjacent to each other even if one set of adjacent arrangements 20 is arranged vertically or horizontally.

Thus, even in the case where the removal burn-up is increased in the core or the reactivity is adjusted because the operation period is shortened, the Gd fuel rods G1 and G2 are vertically extended in the present Gd fuel assembly 19. Alternatively, a fuel assembly having a reactivity corresponding to a low-Gd fuel assembly can be obtained simply by forming the lateral adjacent arrangement 20. In addition, if a non-adjacent arrangement is used, a high G
d Fuel assemblies having a reactivity corresponding to the fuel assembly can be separately formed.

Therefore, in the Gd fuel assemblies 19 having the same type and number of fuel rods of the first and second groups, the reactivity easily corresponds to the low Gd fuel assembly or the high Gd fuel assembly. Can be. Further, even when the number of loaded low-Gd fuel assemblies and high-Gd fuel assemblies is changed due to a request from the core, quick and appropriate action can be taken.

Since the third embodiment is a modification of the first embodiment according to claims 1 and 3 and 4, it has the same components and functions as those of the first embodiment. And effects are omitted, and different parts will be described. As shown in the fuel rod arrangement diagram of FIG. 5A and the axial enrichment distribution and the Gd concentration distribution diagram of FIG. 5B, the Gd fuel assembly 22 is intended to increase the burnup.

Here, the long fuel rods (3) 1 to 5 and the short fuel rod (4) V are the first group of fuel rods,
Numeral 1 and G2 denote a second group of fuel rods, which represent Gd fuel rods (3a) containing nuclear fuel material and burnable poison Gd, and having the same Gd concentration in the Gd fuel rods G1 and G2 as X = Y. doing. Note that, as shown in FIG.
The Gd fuel rods G1 and G2, which are the fuel rods in the group, have 14 blocks of 80% or more out of a total of 16 rods.
The present invention is arranged adjacent to the book (claim 1).

Further, when adjusting the reactivity by refueling in the reactor core, the G
The d fuel assembly 22 has the same number of Gd fuel assemblies 22 and Gd fuel rods G1 and G2 as shown in FIG.
A core is formed by loading the fuel assembly 12 as a second fuel assembly and loading two types of fuel assemblies, the first fuel assembly and the second fuel assembly (claims 3 and 4). .

Next, the operation of the above configuration will be described. A comparison of the infinite multiplication factor of a cross section by a plurality of Gd fuel assemblies 22 as the first fuel assemblies and the high Gd fuel assemblies 12 as the second fuel assemblies is shown in FIG. This is shown in the characteristic diagram. According to this, during the period from the initial stage of combustion to the time when the infinite multiplication factor reaches the peak, the Gd fuel assembly 22 has the curve 14 (the dotted line) of the high Gd fuel assembly 12 as shown by the curve 24 (solid line). ), The rate of increase of the infinite multiplication factor is gradual, indicating that there is a difference in reactivity with the high Gd fuel assembly 12.

As described above, as the second group of fuel rods are adjacent to each other and densely arranged, the reactivity value of the second group of fuel rods themselves decreases due to the effect of Gd interference with the adjacent second group of fuel rods. It can be seen that the difference in reactivity becomes larger.

Thus, when the reactivity adjustment in the reactor core is performed, a large number of Gd
By simply arranging the fuel rods G1 and G2 adjacent to each other in the block shape 23, a fuel assembly having a reactivity corresponding to a low Gd fuel assembly can be obtained. In addition, if a non-adjacent arrangement is used, a high G
d Fuel assemblies having a reactivity corresponding to the fuel assembly can be separately formed.

Therefore, in the Gd fuel assemblies 22 having the same type and number of fuel rods of the first and second groups, the reactivity of the fuel rods easily corresponds to the low Gd fuel assemblies or the high Gd fuel assemblies. Can be. Further, even when the number of loaded bodies of the low Gd fuel assembly and the high Gd fuel assembly is changed due to a request from the core, it is possible to quickly and appropriately respond.

The fourth embodiment relates to claims 1 and 2, 4, and 6, and the same components and operations and effects as those of the first embodiment are omitted, and different portions are described. explain. As shown in the fuel rod arrangement diagram of FIG. 1 (a) and the axial enrichment distribution and Gd concentration distribution diagram of FIG. 1 (b), the Gd fuel assembly 25 is intended to increase the burnup.

The Gd fuel assembly 25 includes a number of long fuel rods (3, 3a) 1 to 5, G1, G2, a short fuel rod (4) V lacking an upper nuclear fuel, and two thick fuel rods (3, 3a). The diameter water rods (5) W are bundled in a square lattice by a fuel spacer 9 (not shown) and fixed to an upper tie plate 7 and a lower tie plate 8 (not shown) to form a fuel rod bundle. Is covered by the channel box 2.

Here, the long fuel rods (3) 1 to 5 and the short fuel rod (4) V are the first fuel rods containing uranium as a nuclear fuel substance.
A group of fuel rods. The fuel rods G1 and G2 are a second group of Gd fuel rods (3a) containing uranium as a nuclear fuel substance and Gd as a burnable poison.
Are different from each other, such as X> Y (claim 2).

Further, as for the Gd fuel rods G1 and G2 as the second group of fuel rods, as shown in FIG.
In the Gd fuel assembly 25, they are arranged adjacently like a cross 16 and an L-shaped 17 surrounded by a dotted line (claim 1).

At the time of new operation of the nuclear reactor, a large number of new fuel assemblies are loaded in the core. However, as the burning of the new fuel progresses as the operation time elapses, the discharge burn-up in the core increases. In addition, the operating period is shortened, and the core characteristics are deteriorated due to radial keeping and the like. Therefore, it is necessary to adjust the reactivity by refueling.

When adjusting the reactivity by refueling in the core, the Gd fuel assembly 25, which is the first fuel assembly, the Gd fuel assembly 25 and the Gd fuel rods G1,
The high Gd fuel assembly 12 having the same number of G2, for example, the high Gd fuel assembly 12 shown in FIG. 13 is used as a second fuel assembly, and two types of fuel assemblies of the first fuel assembly and the second fuel assembly are loaded. To form a core (claims 4 and 6).

As for the high Gd fuel assembly 12, as shown in FIG. 13, the Gd fuel assembly 15, the number of Gd fuel rods G1, the number of G2 fuel rods and the number of Gd fuel rods (3a) are 12 and 12, respectively. Although they are the same, they are not adjacently arranged, and the Gd concentrations in the Gd fuel rods G1 and G2 are different from each other such that X> Y.

Next, the operation of the above configuration will be described. A comparison of the infinite multiplication factor of a certain cross section by the plurality of Gd fuel assemblies 25 as the first fuel assemblies and the high Gd fuel assemblies 12 as the second fuel assemblies is shown in FIG. This is shown in the characteristic diagram. In the present Gd fuel assembly 25, since the Gd concentration of the Gd fuel rods G1 and G2, which are the second group of fuel rods, is different from X> Y, the fuel rods of the second group are arranged in a non-adjacent configuration. Then, the high Gd fuel assembly 12
Is equivalent to

However, the second group of fuel rods Gd
Fuel rods G1 and G2 are arranged adjacently like a cross 16 and an L-shaped 17. Therefore, during the period from the initial stage of combustion until the infinite multiplication factor reaches a peak, the Gd fuel assembly 25
As shown by a curve 26 (solid line), the rate of increase of the infinite multiplication factor is slower than that of the curve 14 (dotted line) of the high Gd fuel assembly 12, and the reactivity with the high Gd fuel assembly 12 It can be seen that there is a difference.

Thus, even if the second group of fuel rods has Gd
Even when the Gd concentrations of the fuel rods G1 and G2 are different from each other such that X> Y, the Gd concentration between the fuel rods of the adjacent second group and the fuel rods of the second group is made denser by the adjacent arrangement like the cross shape 16 and the L shape 17.
, The reactivity value of the second group of fuel rods themselves decreases.

Thus, even when the reactivity is adjusted in the reactor core, in the present Gd fuel assembly 25, only a large number of Gd fuel rods G1, G2 having Gd concentrations different from X> Y are arranged adjacently. Thus, a fuel assembly having a reactivity corresponding to a low Gd fuel assembly can be obtained. In addition, if the fuel assemblies are not arranged adjacent to each other, fuel assemblies having a reactivity corresponding to a high Gd fuel assembly can be separately formed.

Therefore, in the Gd fuel assemblies 25 having the same number of fuel rods of the first group and the second group but having the same number, the reactivity corresponding to the low Gd fuel assembly or the high Gd fuel assembly can be easily obtained. Can be held. Further, even when the number of loaded bodies of the low Gd fuel assembly and the high Gd fuel assembly is changed due to a request from the core, it is possible to quickly respond. Further, since the concentration of Gd can be changed according to the arrangement and the burning speed, Gd can be burned efficiently.

In the present invention, the second group of Gd fuel rods G1,
The shape for arranging G2 adjacent to each other is the cross shape 16 and L
In addition to the character shape 17, the vertical or horizontal adjacent arrangement 20 and the block shape
The same effect can be obtained by applying to all fuel assemblies having one or more sets of various arrangements such as 23 etc.

The fifth embodiment relates to claims 1 and 3, and the same components and operations and effects as those of the first embodiment are omitted, and different portions will be described. . Fig. 8 (a) is a fuel rod layout and Fig. 8 (b)
As shown in the axial enrichment distribution and the Gd concentration distribution diagram, the Gd fuel assembly 27 is intended to increase the burnup.

The Gd fuel assembly 27 includes a number of long fuel rods (3, 3a) 1 to 5, G1, G2, a short fuel rod (4) V lacking an upper nuclear fuel, and two thick fuel rods (3, 3a). The diameter water rods (5) W are bundled in a square lattice by a fuel spacer 9 (not shown) and fixed to an upper tie plate 7 and a lower tie plate 8 (not shown) to form a fuel rod bundle. Is covered by the channel box 2.

Here, the 1 to 5 of the long fuel rods (3) and the short fuel rods (4) V are the first fuel rods containing uranium as a nuclear fuel substance.
A group of fuel rods. The fuel rods G1 and G2 are a second group of Gd fuel rods (3a) containing uranium as a nuclear fuel substance and Gd as a burnable poison.
Are configured to have the same Gd concentration as X = Y.

Further, regarding the second group of fuel rods,
There are 10 Gd fuel rods G1 and 4 Gd fuel rods G2, for a total of 14 rods. Of the Gd fuel rods G1 and G2 having the same Gd concentration, 10 are 2 cross-shaped 16 (2 × 5 rods). ) (Claim 1).

At the time of new operation of the nuclear reactor, a large number of new fuel assemblies are loaded into the core. However, as the burning of the new fuel progresses as the operation time elapses, the discharge burn-up at the core increases. In addition, the operating period is shortened, and the core characteristics are deteriorated due to radial keeping and the like. Therefore, it is necessary to adjust the reactivity by refueling.

When the reactivity is adjusted by refueling in the core, the Gd fuel assembly 27, which is the first fuel assembly, the Gd fuel assembly 27 and the Gd fuel rod G
1 and G2, for example, the high-Gd fuel assembly 12 shown in FIG.
A fuel core is configured by loading two types of fuel assemblies, namely, the fuel assembly of (1) and the second fuel assembly (claims 3 and 5).

Next, the operation of the above configuration will be described. Gd fuel assemblies 27, which are a plurality of first fuel assemblies,
A comparison of the infinite multiplication factor of a certain cross section between the high Gd fuel assembly 12 and the second fuel assembly 12 is shown in the combustion change characteristic diagram of the infinite multiplication factor in FIG. In the present Gd fuel assembly 27, the Gd fuel rods G1 and G2, which are the second group of fuel rods, have the same Gd concentration of X = Y, but the second group of fuel rods are not adjacently disposed. Then, it corresponds to the high Gd fuel assembly 12. However, Gd fuel rods G1 and G2, which are the second group of fuel rods, are arranged adjacently like a cross 16.

Therefore, during the period from the beginning of combustion to the peak of the infinite multiplication factor, the present Gd fuel assembly 27 has the curve 28
As shown in (solid line), the curve of the high Gd fuel assembly 12
The rate of increase of the infinite multiplication factor is slower than 14 (dotted line)
It can be seen that there is a difference in reactivity with the high Gd fuel assembly 12. Further, in the present Gd fuel assembly 27, the rate of increase of the infinite multiplication factor shows a change similar to that of the conventional low Gd fuel assembly 10 in FIG.

Thus, the first group of Gd fuel rods G1 and G2, which are the second group of fuel rods, is different from the second fuel assembly, for example, the high Gd fuel assembly 12 described above.
According to the Gd fuel assembly 27, which is the fuel assembly of (1), it is easy to change only the arrangement of the fuel rods of the second group and to select an appropriate degree of adjacent arrangement according to the situation of the core characteristics. Reactivity adjustments can be made.

Since the sixth embodiment is a modification of the fifth embodiment according to the first and second and fifth, sixth and sixth aspects, the same components and functions as those of the fifth embodiment are described. And effects are omitted, and different parts will be described. As shown in the fuel rod arrangement diagram of FIG. 8A and the axial enrichment distribution and the Gd concentration distribution diagram of FIG. 8B, the Gd fuel assembly 29 is intended to increase the burnup.

Among the many fuel rods accommodated in the Gd fuel assembly 29, the long fuel rods 1 to 5 and the short fuel rods (4) V are the first group of fuels containing uranium as a nuclear fuel substance. The rods G1 and G2 are Gd fuel rods (3a) containing uranium as a nuclear fuel substance and Gd as a burnable poison, and a second group of fuel rods. The Gd concentration in the Gd fuel rods G1 and G2 is X> The configuration is different from Y (claim 2).

Further, regarding the second group of fuel rods,
There are 10 Gd fuel rods G1 and 4 Gd fuel rods G2, a total of 14 rods, and Gd fuel rods G1 and G2 having different Gd concentrations.
Of these, ten are arranged adjacent to two sets of crosses 16 (2 × 5) (claim 1).

At the time of the new operation of the nuclear reactor, a large number of new fuel assemblies are loaded in the core. However, as the burning of the new fuel progresses as the operation time elapses, the discharge burnup in the core increases. In addition, the operating period is shortened, and the core characteristics are deteriorated due to radial keeping and the like. Therefore, it is necessary to adjust the reactivity by refueling.

In adjusting the reactivity by refueling in the core, the Gd fuel assembly 29, which is the first fuel assembly, the Gd fuel assembly 29 and the Gd fuel rod G
1 and G2, for example, the high G shown in FIG.
d The fuel assembly 12 is used as a second fuel assembly, and two types of fuel assemblies of the first fuel assembly and the second fuel assembly are loaded to constitute a core (claims 5 and 6). .

Next, the operation of the above configuration will be described. A comparison of the infinite multiplication factor of a cross section of a plurality of Gd fuel assemblies 29 as the first fuel assemblies and the high Gd fuel assemblies 12 as the second fuel assemblies is shown in FIG. This is shown in the characteristic diagram.

In the present Gd fuel assembly 29, the Gd fuel rods G1 and G2, which are the second group of fuel rods,
If the concentrations are different from each other such that X> Y, and the fuel rods of the second group are arranged non-adjacently, they correspond to the high Gd fuel assembly 12. However, the second group Gd fuel rods G
1, G2 are arranged adjacently like a cross 16.

Therefore, during the period from the initial stage of combustion until the infinite multiplication factor reaches a peak, the present Gd fuel assembly 29 has the curve 30
As shown in (solid line), the curve of the high Gd fuel assembly 12
The rate of increase of the infinite multiplication factor is slower than 14 (dotted line)
It can be seen that there is a difference in reactivity with the high Gd fuel assembly 12.

Further, in the present Gd fuel assembly 29, the rate of increase of the infinite multiplication factor is shown by the curve 28 as shown in FIG.
12 shows the same change as in the case of the conventional low Gd fuel assembly 10 in FIG. Thus, according to the present Gd fuel assembly 29, similarly to the above-described fifth embodiment, only the arrangement of the second group of fuel rods is changed in accordance with the situation of the core characteristics to obtain an appropriate adjacent arrangement degree. By selecting, the reactivity can be easily adjusted.

In each of the above embodiments, a fuel assembly having a 9 × 9 square lattice shape for the purpose of increasing the burnup has been described as an example. However, the present invention is not limited to other irregular shapes such as a hexagonal lattice shape. The same effect can be obtained by being applied to a fuel assembly having a different shape. Further, the shapes of the second group of Gd fuel rods G1 and G2 arranged adjacent to each other are the cross shape 16 and the L shape shown in FIG.
17 and the vertical or horizontal adjacent arrangement 20 shown in FIGS.
Although the block shape 23 is taken as an example, the adjacent shape may be another shape, and is applied to all fuel assemblies having one or more sets arranged adjacently.

[0090]

According to the present invention, even if the number and concentration of Gd fuel rods in the Gd fuel assembly are the same,
By changing the arrangement of the fuel rods adjacent to each other, fuel assemblies having different reactivity values can be easily obtained, so that the types of Gd fuel assemblies can be reduced. In addition, by loading the fuel assemblies having different reactivity values into the core at the time of refueling, a smooth transition to a core having high flexibility and withdrawal burnup for fluctuations in the operation period, and flattening of radial peaking can be achieved. Good core characteristics are realized by improving the thermal characteristics and the like.

Therefore, precise adjustment for realizing good reactivity characteristics and thermal characteristics in the core during refueling can be easily performed, and appropriate measures can be taken promptly, thereby improving the operation rate of the nuclear power plant.

[Brief description of the drawings]

FIGS. 1A and 1B are fuel rod assemblies according to first and fourth embodiments of the present invention, wherein FIG. 1A is a fuel rod layout, and FIG. 1B is an axial enrichment distribution and a Gd concentration distribution.

FIG. 2 is a diagram showing a combustion change characteristic at an infinite doubling rate according to the first embodiment of the present invention.

FIG. 3 shows a fuel assembly according to a second embodiment of the present invention;
(A) is a fuel rod arrangement diagram, (b) is an axial enrichment distribution diagram and a Gd concentration distribution diagram.

FIG. 4 is a view showing a combustion change characteristic at an infinite doubling rate according to a second embodiment of the present invention.

FIG. 5 is a fuel assembly according to a third embodiment of the present invention;
(A) is a fuel rod arrangement diagram, (b) is an axial enrichment distribution diagram and a Gd concentration distribution diagram.

FIG. 6 is a combustion change characteristic diagram at an infinite doubling rate according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a combustion change characteristic at an infinite doubling rate according to a fourth embodiment of the present invention.

8 (a) is a fuel rod arrangement diagram, and FIG. 8 (b) is an axial enrichment distribution diagram and a Gd concentration distribution diagram in fuel assemblies according to fifth and sixth embodiments of the present invention.

FIG. 9 is a view showing a combustion change characteristic at an infinite doubling rate according to a fifth embodiment of the present invention.

FIG. 10 is a combustion change characteristic diagram at an infinite doubling rate according to a sixth embodiment of the present invention.

FIG. 11 is a high burn-up fuel assembly, in which (a) is a partially cutaway longitudinal sectional view, (b) is a sectional view taken along the line BB of (a),
(C) is a sectional view taken along the line CC of (a).

12 (a) is a fuel rod arrangement diagram, and FIG. 12 (b) is an axial enrichment distribution and Gd concentration distribution diagram of a conventional low Gd fuel assembly.

13 (a) is a fuel rod arrangement diagram, and FIG. 13 (b) is an axial enrichment distribution and Gd concentration distribution diagram of a conventional high Gd fuel assembly.

FIG. 14 is a combustion change characteristic diagram of a conventional Gd fuel assembly at infinite multiplication factor.

[Explanation of symbols]

1, 15, 19, 22, 25, 27, 29 ... fuel assembly, 2 ... channel box, 3 ... long fuel rod, 3a ... Gd fuel rod, 4
... short fuel rod, 5 ... large diameter water rod, 6 ... external spring, 7 ... upper tie plate, 8 ... lower tie plate, 9 ... fuel spacer, 10 ... low Gd fuel assembly, 11 ... control rod, 12 ... high Gd fuel assembly, 13 ... curved (low Gd fuel), 14 ... curved (high Gd fuel), 16 ... cross-shaped adjacent arrangement, 17 ... L-shaped adjacent arrangement, 18,21,24,26,28, 30…
Curved (adjacent), 20 ... vertical or horizontal adjacent, 23 ...
Block-shaped adjacent arrangement.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Ayumu Matsumura 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Inside the Toshiba Yokohama office

Claims (6)

[Claims] A first group of fuel rods containing a nuclear fuel substance and containing no burnable poison, a second group of fuel rods containing a nuclear fuel substance and a burnable poison, and one or more water rods are arranged in a square lattice. The fuel assembly, wherein at least one set of a second group of fuel rods containing the nuclear fuel substance and the burnable poison is arranged adjacent to each other. 2. The fuel assembly according to claim 1, wherein said second group of fuel rods comprises a plurality of types of fuel rod groups having different concentrations of burnable poisons. 3. A square grid comprising a first group of fuel rods containing a nuclear fuel substance and containing no burnable poison, a second group of fuel rods containing a nuclear fuel substance and a burnable poison, and a water rod through which a coolant flows. In the core of the nuclear reactor in which the fuel assemblies arranged in the second group are loaded, at least one set of the fuel rods of the second group is disposed adjacent to the second fuel assembly at the time of refueling. Reactor core. 4. The reactor core according to claim 2, wherein the number of fuel rods of the second group in the first fuel assembly and the number of fuel rods in the second fuel assembly are the same. 5. The nuclear reactor core according to claim 3, wherein the number of fuel rods of the second group in the first fuel assembly and the number of fuel rods in the second fuel assembly are different. 6. The reactor core according to claim 4, wherein said second group of fuel rods comprises a plurality of types of fuel rod groups having different concentrations of burnable poisons.