JPH0636049B2 - Fuel assembly for boiling water reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a fuel assembly for a boiling water reactor, which is particularly suitable for high burnup long-term cycle operation.

(Prior Art) Generally, the enrichment of fuel assemblies and the distribution of burnable poisons are determined by the following procedure.

That is, when the operating period and the average extraction burnup are given for the replacement fuel, the number of fuel replacements and the required average enrichment are known, and when this enrichment is determined, the initial excess reactivity of the core is set to an appropriate value. , And determine the number and concentration of combustible poisons that flatten the combustion change. Next, the number of fuel rod enrichment types and the fuel rod arrangement are determined so that the aggregate local output peaking coefficient is equal to or less than a certain value.

By the way, in the conventional design method, in designing this fuel, the burnable poisons are arranged avoiding the peripheral position of the assembly, and in order to avoid the interference of the absorption reaction between the burnable poisons as much as possible, the burnable poisons are not adjacent to each other. It was

FIG. 5 shows an example of the fuel enrichment and the arrangement of burnable poisons designed on the premise of a certain operating period and a certain burn-up degree in this method. The square in FIG. 5 indicates the fuel rod position, and e
_{1, e 2, e 3,} e 4, e 5 shows the fuel rods not containing burnable poison, indicating that the higher the uranium 235 enrichment numbers less. Further, G indicates the position of the fuel rod containing burnable poison, and 20 rods are used in total. FIG. 6 shows an example of the combustion change of the local output peaking coefficient due to this fuel.

(Problems of the prior art) Generally, when designing a high burnup fuel core by increasing the enrichment, the number of combustible poisons necessary for suppressing the initial excess reactivity increases and the high enrichment increases. As the neutron absorption of uranium 235 increases with the increase in the number of uranium compounds, the reactivity value per burnable poison gradually decreases, and the number of burnable poisons required rapidly increases. In particular,
In the high burnup region, a large number are required as shown in FIG. In this case, the following problems occur.

, The number of combustible poisons cannot be increased.

In the case of 9 × 9 fuel with a large diameter water rod in the center, 20 burnable poisons are the limit and cannot be further exceeded by a method that is not arranged in the periphery of the assembly and not adjacent to each other. Therefore, in some cases, an appropriate initial excess reactivity cannot be obtained, and it is necessary to satisfy the reactor shutdown margin by unavoidably burning the burnable poison at the end of the operation cycle. in this case,
Take-out burnup decreases and economic efficiency deteriorates.

, The number of enrichment types increases.

Since the burnable poison having a low output is present in most of the central part of the assembly, the local output in the peripheral part becomes relatively large. Therefore, it is necessary to reduce the degree of enrichment in the vicinity and to increase the number of types, which complicates the fuel manufacturing process.

, The maximum enrichment is high.

As a result of increasing the number of types of enrichment as described above, the maximum enrichment becomes high, and it becomes necessary to tighten the criticality safety control during fuel production.

(Problems to be Solved by the Invention) The present invention has been made to solve the problems in the case of using a fuel assembly using a large diameter water rod with a high extraction burnup as described above, Maximum degree of enrichment is achieved by adopting the arrangement of burnable poison-bearing fuel rods, which allows flexibility in the placement of burnable poison-bearing fuel rods and enables a low local output peaking coefficient even when a small number of enrichments are used. The present invention aims to provide a fuel assembly for a reactor capable of reducing the fuel consumption, suppressing the excess reactivity of the core, impairing the fuel economy, and having an appropriate fuel design even with a high burnup. Is.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention has a square lattice-shaped fuel rod array, and has a round or square shape at the center position of the fuel rod array. In the fuel assembly for a boiling water nuclear reactor, which is configured by arranging one or more water rods of the above and surrounding the outer circumference of these arrays with a channel box, a fuel rod using a burnable poison is used for the fuel assembly of the fuel assembly. It is placed in a part of the peripheral position adjacent to the four channels and the position adjacent to the water rod, and the burnable poison concentration in the position adjacent to the channel is set to be higher than the burnable poison concentration in the position adjacent to the water rod by 30% or more. , Of the fuel rods that do not use the burnable poison located in the periphery of the assembly, are located adjacent to the burnable poison in the periphery of the assembly and at the four corner positions. And yet not and part length rods with the enrichment of the fuel rods that are not adjacent to the same or higher enrichment and the average enrichment of the enrichment of the assembly is characterized in.

(Operation) Next, the basic idea of the present invention will be described.

In order to solve the above-mentioned problems regarding the decrease in reactivity per burnable poison at a high burnup and a high degree of enrichment, the inventors of the present invention have conducted two-dimensional diffusion combustion for fuel design of which accuracy has been confirmed. The following facts were found by investigating the fuel rod position where the local power peaking coefficient was suppressed using the calculation code and the reactivity per burnable poison was increased. This point will be described with reference to FIGS. 3 and 4.

(1) First fuel rod position in the fuel assembly shown in FIG. 3a
Row (x ₁ , x ₂ , x ₃ , x ₄ , x ₅ ), second row (x ₆ ,
_{x 7, x 8, x 9} ), third column _{(x 10, x 11, x} 12) in the case of arranging the burnable poison, reactivity at the time of unburned per one burnable poison-containing fuel rods (negative It is found that the absolute value of) is large in the order of the first column> third column> second column, and the reactivity of the first column is about 40% larger than that of the second column as shown in FIG. 3b. It was

(2) As shown in FIG. 4, by sufficiently lowering the enrichment at the four corner positions x ₁ in FIG. 3a and by making the enrichment of the burnable poison-bearing fuel rod the same as the enrichment. To
Even if the enrichment used in the fuel assembly is two types, e ₁ and e ₂ , it is possible to sufficiently suppress the local output peaking coefficient over the entire combustion period. As a result, it has been found that the fuel can be designed even when the number of enrichment types is two or three.

(8) Regarding the position of the burnable poison, the burnup rate of the burnable poison at the position of the first row is different when the reactivity decrease rate of the burnable poison is different between the first row and the third row and the concentration is the same. Is about 30% faster than the position in the third row. Therefore this 2
In order to eliminate the reactivity of the burnable poison at one position at the same time, it was found that the concentration of the burnable poison at the position in the first row should be increased by about 30% of the position in the third row. .

(Example) The Example of this invention is described with reference to drawings.

An embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 (a) is a fuel rod arrangement view of a fuel assembly which is an embodiment of the present invention, and FIG. 2 is a transverse sectional view of the fuel assembly shown in FIG. 1 (a). As shown in FIG. 2, in the fuel assembly of the present invention, the fuel rods 1 are arranged in a square lattice in 9 rows and 9 columns, and a large diameter water rod having a diameter that fits in the region of 9 fuel rods in the center thereof. 2 are arranged, they are bundled, and the circumference is surrounded by the channel box 3. The control rod is constructed by arranging neutron absorbing rods 5 inside a cross-shaped control rod sheath 4, and when the control rod is inserted, it is arranged close to the fuel assembly as shown in FIG.

The fuel rod arrangement of this fuel assembly is as shown in FIG. 1 (a). Of these, the fuel rods designated by e ₁ and e ₂ and p do not contain burnable poisons, and the fuel e ₂ is 4 of the fuel assembly.
It is placed only in the corner position. G ₁ and G ₂ are fuels containing burnable poisons, G ₁ is arranged in a peripheral position adjacent to e ₂ , and G ₂ is arranged in a position adjacent to the water rod 2. FIG. 1 (b) is the axial enrichment distribution of each fuel rod shown in FIG. 1 (a). e ₁ Fuel uranium 235 enrichment e _{11 in} the central part from the lower 2/24 position to the 22/24 position of the effective part e ₁₁ is 7.2 w / o and the upper 2/24 and lower 1/24 natural uranium A considerable enrichment e _N is used.
e ₂ uranium 235 enrichment e _{21 in} the central part from the lower 2/24 position to the 22/24 position of the effective part of the fuel is 5.4 w / o, and the upper 2/24 and lower 1/24 are natural uranium. A considerable enrichment e _N is used. p fuel is a partial length fuel with the length of 9/24 at the upper end missing, and the uranium 235 enrichment ep at the center of the effective region from the position of 2/24 to 15/24 is 5.4 w / o, and the lower end 1/24 uses the enrichment e _N equivalent to natural uranium.

The uranium 235 enrichment concentration e _G1 of the central portion of the effective portion of the G ₁ fuel from the lower 2/24 position to the 22/24 position is 5.4 w / o, and the gadolinia concentration g ₁ which is a combustible poison is 1
It is 0.5w / o. The upper end 2/24 and the lower end 1/24 are enriched in natural uranium, e _N , and do not contain burnable poisons. The uranium 235 enrichment e _G2 of the central part of the effective part of G ₂ from the lower 2/24 position to the 22/24 position is 5.
4 w / o, and the concentration g _{2 of} gadolinia, which is a burnable poison, is 8.0 w / o. Upper end 2/24 and lower end 1 /
No. 24 uses enrichment e _N equivalent to natural uranium, and does not contain combustible poisons.

When such a fuel rod enrichment is used, the enrichment of the fuel assembly is about 5.7 w / o on average.

Next, the operation of this embodiment will be described.

The fuel of this example is a fuel designed for the purpose of high burnup and long-term operation cycle, and has the following characteristics.

That is, the fuel change (a) in the local output peaking coefficient of the fuel of this embodiment is about the same as that of the conventional example (b) as shown in FIG. Also, as shown in FIG. 8, G ₁ , G
The local output peaking coefficient of ₂ shows almost the same combustion change, and the toxic reactivity of the burnable poisons of G ₁ and G ₂ disappears at about the same time. Further, as shown in FIG. 9, the combustion change (c) of the excess reactivity of the core of the present example shows a flatter characteristic over the operating period than the conventional example (d), and the cycle burnup also extends. Further, the uranium blankets on the upper and lower ends of the fuel reduce neutron leakage in the vertical direction as compared with the conventional example.

As is clear from the above description, the effects of this embodiment are listed below.

(1) The local output peaking coefficient can be equal to or lower than that of the conventional array method, even though the concentration type is simplified to two.

(2) The fuel production process is simplified by simplifying the two enrichment types.

(3) By increasing the number of fuel rods with the highest enrichment with two enrichment types, the value of the highest enrichment can be reduced compared to the conventional method, and the criticality control during fuel production etc. becomes easier.

(4) By adopting the partial length fuel, the pressure loss of the assembly can be reduced and the control characteristics of the core are improved.

(5) By using natural uranium blankets for the upper and lower ends of the fuel, neutron leakage in the vertical direction of the core can be reduced,
Fuel economy can be improved.

FIGS. 10 (a) and 10 (b) are for explaining the second embodiment of the present invention. FIG. 10 (a) is the fuel rod layout drawing and FIG. 10 (b) is the same drawing (a). FIG. 6 is an axial enrichment distribution map for the indicated fuel rods. In this embodiment, the concentration types are e ₁ (5.2w / o) and e ₂ (6.2w / o).
o) and e ₃ (6.6 w / o), as shown in FIG. 11, the combustion change (e) of the local output peaking coefficient during unburning in this embodiment is the same as in the first embodiment. That combustion change of the example (f)
It has been improved. Further, in this embodiment, the maximum enrichment can be made lower than that in the first embodiment, which facilitates the criticality control during fuel production.

FIGS. 12 (a) and 12 (b) are for explaining the third embodiment of the present invention. FIG. 12 (a) is its fuel rod arrangement drawing, and FIG. 12 (b) is shown in FIG. 12 (a). FIG. 6 is an axial enrichment distribution map for the indicated fuel rods. In this embodiment, 12 fuel rods containing burnable poison are provided at the outermost circumference.
The four rods are arranged adjacent to the water rod and the water rods are adjacent to each other, and two types of enrichment types can be used as in the first embodiment, and the local output can be further reduced from that of the first embodiment.

FIGS. 13 (a) and 13 (b) are for explaining a fourth embodiment of the present invention, and are a fuel rod arrangement diagram and a fuel rod axial enrichment distribution diagram, respectively. In this embodiment, four fuel rods containing combustible poisons are arranged at the outermost periphery and 12 fuel rods are arranged at positions adjacent to the water rod, respectively, so that the fuel rods are constituted by three kinds of enrichment. In this embodiment, the number of fuel rods containing burnable poisons on the outermost periphery is reduced as compared with the first embodiment. Therefore, the interference between the burnable poison and the absorption of the control rod is reduced, and the control rod value is increased as compared with the first embodiment.

FIGS. 14 (a) and 14 (b) are for explaining the fifth embodiment of the present invention and are a fuel rod arrangement diagram and a fuel rod axial enrichment distribution diagram, respectively. This embodiment shows a design example in the case of lower burnup than the first embodiment. When the burnup is low, the number of burnable poison-bearing fuel rods can be reduced, so it is possible to design the burnable poison-bearing fuel rods to be arranged only on the outermost periphery.

FIGS. 15 (a) and 15 (b) are for explaining the sixth embodiment of the present invention, and are a fuel rod arrangement diagram and a fuel rod axial enrichment distribution diagram, respectively. This embodiment shows a design example in the case of lower burnup than the first embodiment. When the burnup is low, the number of burnable poison-containing fuel rods can be reduced, so that it is possible to design the fuel rods to be arranged only at the water rod peripheral position.

A seventh embodiment is shown in FIG. 16 and FIG. In this embodiment, the case is shown in which a fuel assembly having a round water rod 8 equivalent to 2 rows and 2 columns is applied to 8 rows and 8 columns fuel as shown in FIG. Figure 17 (a) and (b)
Shows the fuel rod arrangement and the axial enrichment distribution map of the fuel rods in this case.

An eighth embodiment is shown in FIG. 18 and FIG. In this embodiment, a case is shown in which the present invention is applied to a fuel assembly having round water rods 9 of 9 rows and 9 columns and having a center offset of 2 rows and 2 columns as shown in FIG. Fig. 19
(a) and (b) show the fuel rod arrangement and axial enrichment distribution map of the fuel rod in this case.

A ninth embodiment is shown in FIGS. 20 and 21. This embodiment shows a case where the fuel assembly has a round water rod 10 corresponding to 4 rows and 4 columns in a 10 rows and 10 columns fuel as shown in FIG. Figure 21 (a) and
(b) shows the fuel rod arrangement and the axial enrichment distribution map of the fuel rod in this case.

22 and 23 show a tenth embodiment. This embodiment shows a case where the present invention is applied to a fuel assembly having square water rods 11 corresponding to 3 rows and 3 columns in 9 rows and 9 columns fuel as shown in FIG. 23 (a) and 23 (b) show the fuel rod arrangement and the axial enrichment distribution map of the fuel rods in this case.

An eleventh embodiment is shown in FIGS. 24 and 25. This embodiment is applied to a fuel assembly having a round water rod 12 corresponding to 3 rows and 3 columns and four water rods 13 corresponding to 1 row and 1 column in a 9-row 9-column fuel as shown in FIG. The case is shown. Figure 25 (a) and (b)
Shows the fuel rod arrangement and the axial enrichment distribution map of the fuel rods in this case.

[Effects of the Invention] As described above, according to the fuel assembly for a nuclear reactor of the present invention, the following excellent effects are exhibited.

That is, by optimizing the arrangement of the fuel rods containing burnable poisons, the local output peaking coefficient of the assembly can be sufficiently suppressed even if a small number of enrichments are used. At the same time, it is possible to reduce the number of fuel rods containing burnable poisons necessary for obtaining an appropriate excess reactivity. By reducing the type of enrichment, the maximum enrichment can be lowered and the criticality control during fuel production becomes easier. By optimizing the concentration of the burnable poison by the position of the fuel rods containing burnable poison, the reactivity change due to the combustion of the assembly can be controlled appropriately, and the burn of burnable poison at the end of the operating cycle can be controlled. You can reduce the rest and increase fuel economy. By lowering the concentration of fuel rods containing burnable poison, the local output peaking coefficient of the fuel rod containing burnable poison can be suppressed even after the burnable poison has burned, and the fuel temperature can be kept below the limit value. As a result, the health of the fuel can be increased. By adopting the partial length fuel, the pressure loss of the assembly can be reduced and the control characteristics of the core are improved. By adopting natural uranium blankets for the upper and lower ends of the fuel, it is possible to reduce neutron leakage in the vertical direction of the core and improve fuel economy.

[Brief description of drawings]

1 (a) and 1 (b) are a fuel rod arrangement diagram and an axial enrichment distribution diagram of the fuel rod of the first embodiment of the present invention, respectively, and FIG. 2 is a 9 × 9 column to which the present invention is applied. ， Cross section of large diameter water rod fuel, Fig.3 (a) and (b) show the fuel rod position in the fuel assembly, and the relationship between the fuel rod position and the reactivity value of burnable poisoned fuel FIG. 4, FIG. 4 is a conceptual diagram of fuel rod arrangement according to the present invention, FIG. 5 is a conceptual diagram of conventional fuel rod arrangement, FIG. 6 is a diagram showing local output peaking coefficient combustion change of conventional fuel, and FIG. The figure compares the local output peaking coefficient combustion change of the present invention and the conventional fuel, FIG. 8 shows the local output peaking coefficient combustion change of the fuel containing burnable poison of the present invention, and FIG. 9 shows the present invention. Figure 10: Changes in surplus reactivity months of the core loaded with fuel
(a) and (b) are a fuel rod arrangement diagram and a fuel rod axial enrichment distribution diagram, respectively, of the second embodiment of the present invention, and FIG. 11 is a local view of the second and first embodiments. Figures comparing the output peaking coefficient combustion changes, Figures 12 (a) and (b) are the fuel rod arrangement diagram and the axial enrichment distribution diagram of the fuel rod of the third embodiment of the present invention, respectively. a) and (b) are the fuel rod arrangement diagram and the axial enrichment distribution diagram of the fuel rod of the fourth embodiment of the present invention, and FIGS. 14 (a) and (b) are the fifth embodiment of the present invention, respectively. The fuel rod arrangement diagram and the fuel rod axial enrichment distribution diagram of the embodiment are shown in FIGS. 15 (a) and 15 (b), respectively, and the fuel rod arrangement diagram and the fuel rod axial enrichment of the sixth embodiment of the present invention are shown. FIG. 16, FIG. 16, FIG. 17 (a) and FIG. 17 (b) are a conceptual diagram of the fuel rod arrangement of the seventh embodiment of the present invention, a fuel rod arrangement diagram and an axial enrichment distribution of the fuel rods, respectively. , FIG. 18, the first
19 (a) and (b) are a conceptual view of the fuel rod arrangement, a fuel rod arrangement diagram, and an axial enrichment distribution diagram of the fuel rod of the eighth embodiment of the present invention, FIG. 20, FIG. a) and (b) are a conceptual view of the fuel rod arrangement of the ninth embodiment of the present invention, a fuel rod arrangement diagram and a fuel rod axial enrichment distribution diagram, FIG. 22,
23 (a) and 23 (b) are a conceptual view of the fuel rod arrangement of the tenth embodiment of the present invention, a fuel rod arrangement diagram and an axial enrichment distribution diagram of the fuel rods, FIGS. 24 and 25, respectively. (a) And (b) is the conceptual diagram of the fuel rod arrangement | positioning of the 11th Example of this invention, a fuel rod arrangement | positioning diagram, and the axial enrichment distribution map of a fuel rod, respectively. 1 …… Fuel rod 2 …… Water rod 3 …… Channel box 4 …… Control rod sheath 5 …… Control rod poison tube 6 …… Fuel pellet 7 …… Fuel cladding 8 …… 8 rows and 8 columns Fuel water Rod 9 …… 9 row 9 column Fuel center offset water rod 10 …… 10 row 10 column fuel water rod 11 …… 9 row 9 column fuel square water rod 12 …… 9 row 9 column fuel diameter Water rod 13 …… 9th row and 9th column Fuel water rod

Claims (5)

[Claims] 1. A fuel cell array having a square lattice shape, wherein one or more round or square water rods are arranged at the central position of the fuel rod array, and the outer circumference of these arrays is surrounded by a channel box. In the fuel assembly for a boiling water reactor configured, a fuel rod using a burnable poison is arranged at a part of a peripheral position adjacent to the four channels of the fuel assembly and a position adjacent to the water rod, The burnable poison concentration in the position adjacent to the channel is set to be 30% or more higher than the burnable poison concentration in the position adjacent to the water rod, and the fuel rods around the assembly that do not use the burnable poison are placed around the fuel rod. The concentration of the fuel rods adjacent to the burnable poison rod in the position and not arranged in the four peripheral corner positions and not adjacent to the partial length fuel rods. Average enrichment equal to or higher enrichment and boiling water reactor fuel assembly, characterized by the. 2. A fuel rod using a burnable poison is low uranium.
A boiling water reactor fuel assembly according to claim 1, characterized in that a concentration of 235 is used. 3. The upper part 1/3 to 1/2 of the effective portion of the fuel rod.
The fuel assembly for a boiling water reactor according to claim 1, characterized in that four or eight partial length fuel rods lacking in are used at positions other than the peripheral position of the fuel. 4. The upper part 1/3 to 1/2 of the effective portion of the fuel rod.
The fuel assembly for a boiling water reactor according to claim 5, wherein a combustible poison is not used for the four or eight partial length fuel rods lacking. 5. A natural uranium or lower uranium 235 enriched fuel is used in the upper 1/24 to 3/24 and lower 1/24 to 2/24 portions of the fuel rod. A fuel assembly for a boiling water reactor according to claim 1.