KR20180092857A - Fuel assembly, core design method and fuel assembly design method of light-water reactor - Google Patents

Abstract

Provided is a method of designing a fuel assembly for a light-water reactor, when it is assumed that the number of fuel rods (11, 12) included in a fuel assembly (10) is N, the number of the fuel rods (12) containing a combustible poisonous substance contained in the nuclear fuel rods sealed with a nuclear fuel material including combustible poison is n, an average mass ratio of the combustible poison in the nuclear fuel material is p, and the average uranium 235 is e, which includes: a core determination data accumulation step of accumulating core determination data indicating whether each combination of a plurality of p·n / N and e is established as a core by an analysis or an experiment; a core decision formula determination step of determining whether the combination of p·n / N and e is established as a core on the basis of the core determination data; and a core determination step of determining whether the configuration of a temporarily set fuel assembly is established as a core on the basis of the decision formula.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a fuel assembly for a light-water reactor, a method of designing a light-reactor core, and a fuel assembly design method for a light-

An embodiment of the present invention relates to a fuel assembly for a light-water reactor, a method for designing a light-reactor core, and a method for designing a fuel assembly for a light-water reactor.

Generally, in a core of a fuel assembly for a light-water reactor and a light-water reactor, the fuel is designed so that the surplus reactivity is zero at the end of cycle (EOC) of one operation cycle, and the reactor is operated.

In the boiling water reactor (BWR), the concentration adjustment is performed so that the neutron absorbing ability of a combustible poison such as gadolinium oxide (gadolinia) disappears from the EOC. In the case of the BWR plant's first cycle core, the initial load core, deliberately burns off some fraction of the fuel's flammable toxicant while supplementing the lack of surplus response with the remaining fuel, Some examples improve the thermal properties.

In the PWR, concentration adjustment is performed so that the boric acid concentration in the chemical shim is zero at EOC. The degree of concentration of the fissile material is adjusted according to the target blowout degree (here, achieved combustion and synergy), and unnecessarily high concentration is not used.

When the fuel is recycled, the fuel for the light-water reactor and the fuel used in the core of the light-water reactor are removed from the core and then reprocessed. By reprocessing, uranium isotopes and plutonium isotopes are extracted for reuse, and minor actinides are discarded as high level radioactive waste. Because minor actinides have a high degree of toxicity, in particular the harmful minor actinides are separated by a reprocessing process called group separation. The separated minor actinides are converted to noxious nuclides by burning in a high speed furnace, or by irradiating the accelerator with a minor actinide, in addition to MOX (Mixed Oxcide) fuel. In this way, so-called separation conversion is considered.

Japanese Patent Application Laid-Open No. 62-106391 (hereinafter referred to as Patent Document 1) and Japanese Patent Laid-Open Publication No. 2008-145286 (hereinafter referred to as Patent Document 2) have.

If an on-through cycle is used without fuel recycling, final disposal will be done with the spent fuel being used. In the ounce through cycle, since the same process as the separation conversion described above is not performed, the harmfulness of the minor actinide is not reduced.

On the other hand, by using uranium fuel intentionally highly enriched, it is possible to reduce the amount of minor actinide produced. This is because the ratio of the fission reaction by the uranium 235 is increased by using the uranium fuel having a high enrichment ratio of uranium 235, and the rate of the absorption reaction by the uranium 238 is decreased, so that the amount of the minor actinide is reduced. However, by increasing the enrichment degree of uranium 235, the surplus reactivity is increased, and the surplus reactivity exceeds the reactivity value by the reactivity control device such as the control rod, and the reaction degree control becomes difficult.

Surplus reactivity when uranium enrichment is increased can be suppressed by using combustible toxicants. The use of flammable toxicants is also effective for fuel assemblies with enhanced uranium enrichment to reduce the hazard of minor actinides. However, it is necessary to carry out many complex calculations in order to determine the concentration or the number of combustible poisons, so that no effective design has been made so far.

An embodiment of the present invention has been made to solve the above-described problems, and an object of the present invention is to reduce the degree of surplus reactivity when a uranium enrichment degree is increased in a light-water reactor.

According to one embodiment of the present invention, there is provided a method of designing a fuel assembly for a light-water reactor, wherein the fuel assembly for a light-water reactor has a plurality of parallel fuel rods, Wherein the fuel rod has a cladding tube and a nuclear fuel material based on uranium dioxide which is enclosed within the cladding tube and contains at least a portion of enriched uranium, wherein at least some of the nuclear fuel material comprises combustible poisons Wherein the number of fuel rods contained in the fuel assembly is N (where N is an integer of 2 or more), the number of fuel rods containing a combustible poison in which the fuel material containing the combustible poison contained in the fuel rods is enclosed is n (n (Mass%) of the combustible poison in the nuclear fuel material is p, and an average mass ratio (Mass%) of the average uranium 235 over the total number of the fuel assemblies is expressed by e, the combination of each of the plurality of p · n / N and e is determined as the core A determination step of determining whether or not a combination of p · n / N and e is established as a core based on the core determination data; And a core part determination step of determining whether or not the configuration of the fuel assembly temporarily set as a core is established based on the determination formula.

According to an embodiment of the present invention, there is provided a method of designing a light-water reactor core, wherein the light-water reactor core has a plurality of fuel assemblies, and the fuel assemblies are disposed adjacent to each other in a direction perpendicular to the longitudinal direction And a fuel assembly for the light-water reactor has a plurality of parallel fuel rods, and the fuel rods are arranged in a direction perpendicular to the longitudinal direction Wherein the fuel rod has a cladding tube and a fuel material based on uranium dioxide which is enclosed within the cladding tube and contains at least a portion of enriched uranium, wherein at least some of the fuel material comprises combustible poisons, The design method is characterized in that at least a part of the plurality of fuel assemblies The number of fuel rods contained in the fuel assemblies is N (N is an integer of 2 or more), the number of fuel rods containing combustible poisons enclosing the nuclear fuel material containing combustible poison in the fuel rods is n (% By mass) of the combustible poison in the nuclear fuel material is p, and the concentration (mass%) of the average uranium 235 over the total number of the fuel assemblies is e, N / N and N based on the core determination data, and a core decision data accumulating step of accumulating core determination data indicating whether or not each combination of p, n, e is determined as a core, and a determination step of determining, based on the determination formula, whether or not the configuration of the fuel assembly temporarily set as a core The core part is determined for determining whether the characterized in that it comprises a step.

According to an embodiment of the present invention, there is provided a fuel assembly for a light water reactor, in which a plurality of fuel rods extending in parallel to each other in the longitudinal direction are arranged in parallel with each other at a distance in a direction perpendicular to the longitudinal direction, Wherein each of the fuel rods of the nuclear fuel material has a longitudinally extending cladding tube and at least a portion of uranium dioxide-enriched fuel material encapsulated within the cladding tube and containing at least a portion of the enriched uranium, Wherein N is an integer greater than or equal to 1 but less than N, and the number of fuel rods included in the fuel assembly is N (N is an integer of 2 or more), the number of fuel rods enclosing the fuel material containing combustible poison in the fuel rod is n ), An average mass ratio (mass%) of the combustible poisonous substance in the nuclear fuel material is p, and a total number of the fuel assemblies Wherein the relationship of 0.57e-1.8 < p n / N < 0.57e-0.8 is satisfied when the concentration (mass%) of the uranium enumerated 235 is e.

According to the embodiments of the present invention, it is possible to reduce the degree of surplus reactivity when the uranium enrichment degree is increased in the light-water reactor.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan sectional view showing one control rod in a boiling water reactor core according to one embodiment of the present invention, four fuel assemblies surrounding it, and the periphery thereof; Fig.
FIG. 2 is a detailed view of an example of the internal configuration of a fuel assembly in a boiling water reactor core according to an embodiment of the present invention, and is a schematic view of a part II of FIG. 1;
Fig. 3 is a view showing in detail an example different from that of Fig. 2 of the internal structure of a fuel assembly in a boiling water reactor core according to an embodiment of the present invention, and is a schematic view of part II of Fig.
4 is a plan sectional view showing the structure of a fuel rod constituting a fuel assembly for boiling water type fuel according to an embodiment of the present invention.
5 is a graph showing the results of calculation and calculation of the formation and non-formation of the core for various combinations of the combustible toxic substance average mass ratio and the uranium enrichment degree in a fuel assembly for a boiling water reactor according to an embodiment of the present invention Yes.
6 is a graph showing an example of an analysis result of the relationship between cycle combustion and surplus reactivity when the fuel assembly within the optimum range of the combustible poison average mass ratio in Fig. 5 is burned in the boiling water reactor.
7 is a graph schematically showing a change in the aggregate infinite increase rate when the uranium enrichment degree is increased in the design of the fuel assembly according to the embodiment of the present invention.
8 is a graph schematically showing a change in the number of fuel rods containing a combustible poison corresponding to a change in reactivity of a combustible poison in the design of a fuel assembly according to an embodiment of the present invention.
9 is a flowchart showing a procedure of a method for designing a fuel assembly according to an embodiment of the present invention.
10 is a graph showing the control rod response of the top 10 control rods having a high reactivity value in a control cell in a general boiling water reactor core.

Hereinafter, a method for designing a fuel assembly for a light-water reactor, a light-water reactor core and a light-water reactor according to an embodiment of the present invention will be described with reference to the drawings. Herein, mainly for a boiling water reactor is described as an example, but it is also applicable to a pressurized water reactor.

1 is a plan sectional view showing one control rod in a boiling water reactor core according to one embodiment of the present invention, four fuel assemblies surrounding it, and the periphery thereof. 1, the detailed structure of each fuel assembly is not shown. Fig. 2 is a detailed diagram of an internal configuration of a fuel assembly in a boiling water reactor core according to an embodiment of the present invention, and is a detailed schematic diagram of part II of Fig. 1; Fig. Fig. 3 is a detailed schematic view of an internal structure of a fuel assembly in a boiling water reactor core according to an embodiment of the present invention, which is different from Fig. 2 and is a detailed view of part II of Fig. 4 is a plan sectional view showing the structure of a fuel rod constituting a fuel assembly for boiling water type fuel according to an embodiment of the present invention.

In the boiling water reactor core, hundreds of fuel assemblies 10 are arranged in a square lattice shape in a horizontal plane. Regarding the degree of enrichment of uranium, the average of the aggregate in the conventional uranium fuel assemblies is, for example, 3.8%. For example, in Japan, facilities related to conventional conventional uranium fuel assemblies are designed on the premise that uranium concentration is less than 5.0%. On the other hand, in the fuel assembly 10 for a light-water reactor in the present embodiment, it is higher than that of the conventional uranium fuel assembly and is, for example, 5.0%. Hereinafter, the degree of enrichment of uranium is shown as an example of 5.0%, but it is not limited thereto. As will be described later, if the effect can be obtained, the concentration may be more than 5.0% or the concentration may be less than 5.0%.

In each fuel assembly 10, fuel rods 11 and 12 extending in parallel to each other in the vertical direction are arranged in a square lattice shape (an array of longitudinal and transverse 9 × 9 in the example shown in FIGS. 2 and 3) . A vertical outer periphery of the fuel assembly 10 is surrounded by a channel box 13 having a substantially rectangular tube shape extending in the vertical direction. Two water rods 14 (indicated by &quot; W &quot; in Figs. 2 and 3) are arranged at the center of the fuel assembly 10. The water rod 14 is a tubular structure in which water flows. In the example shown in Figs. 2 and 3, the water rod 14 is two circular tubes, but may be one, three or more, or may have a square tube shape or the like.

Each of the fuel rods 11 and 12 includes a tube-shaped cladding tube 20 extending in the vertical direction and a fuel material 21 enclosed in the cladding tube 20. The nuclear fuel material 21 contains uranium oxide containing enriched uranium and is usually formed into a cylindrical pellet so that a plurality of pellets are laminated in the axial direction in the cladding tube 20. [ The fuel rod 12 is a fuel rod containing a combustible poison (indicated by "G" in FIGS. 2 and 3) and the fuel material 21 in the fuel rod 12 contains a combustible poison (eg, gadolinia) . The fuel rod 11 is a fuel rod (indicated by "R" in FIGS. 2 and 3) that does not include a combustible poison, and the fuel material 21 in the fuel rod 11 does not contain a combustible poison.

Control of the reactivity of the BWR using a control cell core is considered. This is a core design in which the number of unit grids for inserting control rods in normal operation is small. Control rods used for output control during normal operation are surrounded by four fuel assemblies to form control cells. Specifically, in a control cell, control rods 30 (reaction control devices) each having a cross-sectional shape of a cross section and extending vertically are arranged at the center of the 2 × 2 array of fuel assemblies 10 adjacent to each other, Respectively. At the time of normal operation of the reactor, the outside of the channel box 13 is filled with light water. The control rod 30 is configured such that the water in the outside of the channel box 13 is vertically inserted and extracted to control the reactor output.

A local output area monitor (LPRM) 31, which is a nuclear instrumentation device, is disposed outside the channel box 13 at a diagonal position from the center of the control rod 30.

In general, the thermal conductivity of combustible poisons such as gadolinia is lower than the thermal conductivity of uranium oxide. The enrichment degree of the uranium 235 in the fuel material 21 in the fuel rod 12 containing the combustible poison is lower than the highest value of the enrichment degree of the uranium 235 in the fuel material 21 contained in the fuel assembly 10 . With this configuration, the heat output of the fuel rod 12 containing the combustible poison can be prevented from becoming larger than the heat output of the other fuel rods, and the overheat of the fuel rod 12 containing the combustible poison can be prevented.

It may be designed not to dispose the fuel rod 12 containing the combustible poison in a place adjacent to the control rod 30 in the fuel assembly 10 as shown in Fig. 2 and Fig. With this configuration, since the rate at which the control rod 30 absorbs the thermal neutrons that are likely to contribute to the fission reaction is not lowered, the core configuration can be realized without lowering the reactivity value of the control rod 30. [

2 and 3, it is desirable to design the fuel assembly 10 so as not to dispose the fuel rod 12 containing the combustible poison in a place adjacent to the nuclear instrumentation device 31 . With this configuration, it is possible to realize the core configuration without lowering the accuracy of the nuclear instrumentation apparatus 31.

2 and 3, in the fuel assembly 10, with respect to the fuel rod 12 containing at least one combustible poison, the fuel rod 12 is arranged in the arrangement direction of the square-shaped fuel rod arrangement At least one of the four surfaces corresponding to the fuel rods 11 and 12 may not be adjacent to the other fuel rods 11 and 12. [ That is, the fuel rod 12 containing at least one combustible poison is disposed at a position adjacent to the channel box 13 at the position adjacent to the water rod 14 or the outermost periphery of the aggregate, for example. With this configuration, the thermal neutrons, which are liable to cause an absorption reaction by the combustible poison, collide with the combustible poison much, and the proportion of the neutrons absorbed by the combustible poison is increased. As a result, the value of the reactivity of the flammable poison increases, thereby greatly suppressing the surplus reactivity.

2 and 3, in the fuel assembly 10, the fuel rods 12 containing at least a part of the combustible poison may be disposed adjacent to each other. As the fuel rods 12 containing the combustible poison are adjacent to each other, the number of the combustible poison of the adjacent surface colliding with the thermal neutron decreases. Therefore, the rate at which the combustible poison is burned is slowed, and the reactivity of the combustible poison is more sustained than when the fuel rods 12 containing the combustible poison are not adjacent to each other.

FIG. 5 is a graph showing the results obtained by analytical calculation of the formation and non-formation of the core for various combinations of the combustible toxicant average mass ratio and the uranium enrichment degree in the fuel assembly for a boiling water reactor according to the embodiment of the present invention. . Here, the average mass ratio of the combustible poison is represented by the ratio of the number of fuel rods containing the combustible poison p × combustible poison. Further, the ratio of the number of fuel rods containing combustible poisons is represented by the number n of fuel rods containing combustible poisons / the total number N of fuel rods of the fuel rods. Therefore, the average mass ratio of combustible poisons is represented by p · n / N.

In the nuclear characteristic evaluation analysis of Fig. 5, a configuration similar to that of the fuel assembly shown in Figs. 2 and 3 is assumed. Here, assuming that homogeneous fuel assemblies are arranged endlessly in the horizontal direction in an infinite manner, it is possible to determine whether the core is formed or not. The flammable poison was gadolinium.

In the nuclear characteristic evaluation analysis of Fig. 5, the fuel rod arrangement in the fuel assembly was set to 9 x 9. However, if the hydrogen-uranium ratio of the fuel assembly is the same, the same result as in Fig. 5 is obtained irrespective of the number of fuel rods in the fuel assembly, because the influence of the nuclear characteristic (neutron spectrum) do. For example, even in the case of a 10 × 10 array or an 11 × 11 array, substantially the same result as in FIG. 5 is obtained.

In the example of Fig. 2, the number n of fuel rods 12 containing combustible poisons is 24, and the total number N of fuel rods of the fuel assembly is 74. In the example of Fig. 3, n = 36 and N = 74.

The uranium enrichment degree is called e. At this time, for various combinations of the combustible toxicant average mass ratio (p · n / N) and the uranium enrichment degree e, whether or not the core was established was determined by analysis. As a result, as shown in Fig. 5, two straight lines could be obtained as a boundary condition of whether or not the core was established. That is, the range in which the average mass ratio (p · n / N) of the combustible toxicant is larger than (0.57e-1.8) and smaller than (0.57e-0.8) is the optimum ratio of the addition of the combustible poison. That is, the judgment formula (1) expressing the requirement for establishing the core in this case,

0.57e-1.8 < p? N / N < 0.57e-0.8 (1)

.

Therefore, the design of the actual fuel assembly can be performed using the determination formula (1).

In addition, for the design of different fuel assemblies of various conditions, it is necessary for the various combinations of the uranium enrichment degree e and a sufficient number of the combustible poison average mass ratio (p · n / N) It is possible to accumulate data by obtaining by analysis whether or not the core is established and to obtain a graph corresponding to Fig. 5 under the condition. Based on the graph, another judgment formula corresponding to the judgment formula (1) in the condition can be obtained.

In general, the form of the following expression (2) is considered appropriate.

a1 · e-b <p · n / N <a2 · e-c (2)

However, a1, a2, b, and c are positive integers, and a1? A2.

Although the above formulas (1) and (2) are linear expressions, in addition to the linear expressions, there may be quadratic expressions and various expressions.

6 is a graph showing an example of the analysis result of the relationship between cycle combustion and surplus reactivity when the fuel assembly within the optimum range of the combustible poison average mass ratio in Fig. 5 is combusted in the boiling water reactor. 7 is a graph schematically showing a change in the aggregate infinite increase rate when the uranium enrichment degree is increased in the design of the fuel assembly according to the embodiment of the present invention. 8 is a graph schematically showing a change in the number of fuel rods containing a combustible poison corresponding to a change in reactivity of a combustible poison in the design of a fuel assembly according to an embodiment of the present invention. In Figs. 7 and 8, although straight lines are shown together, these are schematically shown and can not always be said to be straight lines.

Here, FIG. 10 is a graph showing the values of the control rod reactivity of the control rods of the upper 10 control rods having a high reactivity value in the control cell core of a typical typical BWR. As shown in FIG. 10, the value of the control rod response value of this control cell is a value slightly exceeding 0.1%? K at maximum. In the case of the control boiler water reactor (ABWR), the maximum number of control cells is 29, so that the surplus reactivity that can be controlled in the control cell is at most 3% Δk.

By designing the combination of the average mass ratio (p 占 / / N) of the combustible poisonous substance of the fuel assembly 10 and the uranium enrichment degree e to be in a range satisfying the formula (1) or (2) As can be seen, the surplus reactivity during the reactor operating cycle can be designed to be 0-3.0%? K, which is controllable by the control rod. This is because the amount of reaction change? S (? E) when the uranium enrichment degree e shown in FIG. 7 is changed to (e +? E) is larger than the number n of the fuel rods in the fuel rod containing the combustible poison shown in FIG. (DELTA S (DELTA Gd)) as an absorbing material which is changed into the absorbency. That is, by changing the total amount of combustible poison by ΔGd, the change Δe of the uranium enrichment degree e can be compensated.

Next, a method of designing the fuel assembly for a light-water reactor using the above-described examination results will be described with reference to Fig. Fig. 9 is a flowchart showing a procedure of a method for designing a fuel assembly according to an embodiment of the present invention.

First, assuming the configuration of the fuel assembly for the light water reactor to be within a predetermined range, the various factors of the combination of the average mass ratio (p · n / N) of the combustible poison and the uranium enrichment degree "e" And accumulates the core part determination data as shown in Fig. 5 (step S10).

Next, on the basis of the core part determination data obtained in step S10, it is determined whether or not the core mass (p · n / N) of the combustible poison mass ratio p · n / The judgment formula is determined (step S11).

Next, the combination of the average mass ratio (p 占 / / N) of the combustible poisonous substance of the fuel assembly for the light-water reactor and the uranium enrichment degree e is specifically assumed (step S12) (Step S13).

When the result of the step S13 is the core non-establishment (No), the combination of the combustible poison mass average ratio (p 占 / / N) and the uranium enrichment degree e is changed and steps S12 and S13 are performed again. When the result of the step S13 is the core establishment (Yes), the fuel assembly is determined as the design of the fuel assembly by the combination of the combustible poison average mass ratio p · n / N at that time and the uranium enrichment degree e (step S14) .

According to the above-described designing method, it is possible to reduce the surplus reactivity when the uranium enrichment degree is increased in the light-water reactor. In addition, by determining the core form part formulas in advance, it is possible to easily identify the parts of the core in the case of changing various parameters in the design of the specific fuel assemblies, to speed up the design work and to save labor (labor saving) .

In this embodiment, the combustible poison added to the nuclear fuel material is preferably a compound containing gadolinium, a compound containing erbium, or a compound containing boron.

In addition, when the combustible poison added to the fuel material is inert, it is preferable that the maximum mass ratio is less than 20% by mass. This is because if the mass fraction of gadolinia is 20 mass% or more, the mixture of gadolinia and uranium oxide becomes hard to generate solid solution.

As the flammable poison in the embodiment described herein, it is preferable to use gadolinium which has been subjected to concentration of gadolinium of an odd mass number (for example, 155 or 157). As a result, the absorption cross-sectional area of gadolinium is increased, so that the effect of reducing the addition amount of the flammable poison can be obtained.

Further, by loading the fuel assembly into the light water reactor core including the control cell, it is possible to suppress the change range of the reaction degree due to the operation of the control rod and to make it easy to satisfy the thermal soundness of the fuel assembly in the light water reactor core Effect can be obtained.

While the present invention has been described in detail with reference to certain embodiments thereof, these embodiments are provided by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, alterations, and combinations can be made without departing from the gist of the invention. These embodiments and their modifications fall within the scope of the invention as defined in the claims, as well as the scope of the invention.

10 ... Fuel assembly, 11, 12 ... Fuel rod, 13 ... Channel box, 14 ... Water Rod, 20 ... Clogs, 21 ... Nuclear fuel material, 30 ... Control rod (reactivity control device), 31 ... Nuclear instrumentation system (local output area monitor, LPRM)

Claims (16)

A method of designing a fuel assembly for a light water reactor,
Wherein the fuel assembly for a light-water reactor has a plurality of parallel fuel rods,
Wherein the fuel rods are arranged at a distance from each other in a direction perpendicular to the longitudinal direction,
Wherein the fuel rod has a cladding tube and a nuclear fuel material mainly composed of uranium dioxide which is enclosed in the cladding tube and contains at least a part of enriched uranium,
Wherein at least some of the fuel material comprises combustible poisons,
In this design method,
The number of fuel rods included in the fuel assembly is N (N is an integer of 2 or more), and the number of fuel rods containing combustible poisons enclosing the fuel material containing the combustible poison in the fuel rods is n (n is 1 or more but less than N (Mass%) of the combustible poison in the nuclear fuel material is p, and the concentration (mass%) of the average uranium 235 over the total number of the fuel assemblies is e,
A core determination data accumulating step for accumulating core determination data indicating whether or not each combination of p, n, and N and e is satisfied as a core;
A core determining equation determining step of determining a determining formula for determining whether or not a combination of p · n / N and e is established as a core on the basis of the core determination data,
And determining whether or not the configuration of the fuel assembly temporarily set as a core is established based on the judgment formula. The method according to claim 1,
And e is 5% or more. The method according to claim 1,
The determination equation is based on the assumption that the positive constants a1, a2, b, and c (where a1 &amp;ge; a2)
a1 · eb <p · n / N <a2 · ec. 3. The method of claim 2,
The determination equation is based on the assumption that the positive constants a1, a2, b, and c (where a1 &amp;ge; a2)
a1 · eb <p · n / N <a2 · ec. 5. The method of claim 4,
Wherein the constants a1 and a2 are 0.57, the constant b is 1.8, and the constant c is 0.8. The method according to claim 1,
Wherein the uranium enrichment degree of uranium (235) in the nuclear fuel material including the combustible poison is lower than a maximum value of uranium (235) enrichment degree of nuclear fuel material contained in the fuel assembly. The method according to claim 1,
In the fuel assembly, the fuel rods are arranged in a square lattice,
Wherein the fuel rods containing at least one combustible poison are not adjacent to the other fuel rods on at least one of the four planes corresponding to the arrangement direction of the tetragonal grid. The method according to claim 1,
In the fuel assembly, the fuel rods are arranged in a square lattice,
Wherein at least one fuel rod containing the combustible poison is adjacent to a fuel rod containing the combustible poison at least one of four sides corresponding to the arrangement direction of the tetragonal fuel rod arrangement Way. The method according to claim 1,
Wherein the combustible poison added to the nuclear fuel material is a compound containing gadolinium or a compound containing erbium or a compound containing boron. The method according to claim 1,
Characterized in that the combustible poison added to the nuclear fuel material is gadolinia and the maximum mass ratio thereof is less than 20 mass%. The method according to claim 1,
Wherein the combustible poison added to the nuclear fuel material is gadolinium-containing compound, and the gadolinium of odd mass number is concentrated more than natural gadolinium. As a design method of light water reactor core,
Wherein the light water reactor core has a plurality of fuel assemblies,
Wherein the fuel assemblies are arranged in a tetragonal lattice shape adjacent to each other with an aggregate gap therebetween in a direction perpendicular to the longitudinal direction,
A plurality of reaction degree control devices are disposed in the gaps between the assemblies,
Wherein the fuel assembly for a light-water reactor has a plurality of parallel fuel rods,
Wherein the fuel rods are arranged at a distance from each other in a direction perpendicular to the longitudinal direction,
Wherein the fuel rod has a cladding tube and a fuel material that is enclosed within the cladding tube and contains at least a portion of uranium dioxide-enriched nuclear fuel material,
Wherein at least some of the fuel material comprises combustible poisons,
(N is an integer of 2 or more) of the fuel bundles contained in the fuel assembly, and the fuel material including the combustible poison in the fuel rod is supplied to the fuel assemblies of at least some of the plurality of fuel assemblies (N is an integer of 1 or more but smaller than N), the average mass ratio (mass%) of the combustible poison in the nuclear fuel material is p, the average uranium (Mass%) of 235 is defined as e, a core determination that accumulates core determination data indicating whether or not each combination of p, n / N, and e constitutes a core by analysis or experiment A data accumulating step,
A core determining equation determining step of determining a determining formula for determining whether or not a combination of p · n / N and e is established as a core on the basis of the core determination data,
And a core part determining step of determining, based on the determination formula, whether or not the configuration of the fuel assembly temporarily set up is a core. 13. The method of claim 12,
Wherein the fuel rod containing the combustible poison is disposed at a position not adjacent to the reactivity control device among the fuel assemblies. 13. The method of claim 12,
Wherein the light water reactor core further comprises a nuclear instrumentation unit and the nuclear instrumentation unit is disposed in the gaps between the collective bodies where the reactivity control unit is disposed and the fuel rod containing the combustible poison And is disposed at a position not adjacent to the nuclear instrumentation apparatus. 13. The method of claim 12,
Wherein a part of the fuel assemblies of the plurality of fuel assemblies constitutes a control cell surrounding the reactivity control device adjacent to the reactivity control device,
The core matter determining step may include determining the fuel part of the reactor core based on the determination formula determined in the core decision making step with respect to the configuration of the fuel assembly temporarily set in the fuel assembly constituting the control cell A method of designing a light water reactor core. Wherein a plurality of fuel rods extending in parallel to each other in the longitudinal direction are arranged in parallel and spaced apart from each other in a direction perpendicular to the longitudinal direction to be bundled,
Wherein each of the plurality of fuel rods comprises:
A cladding tube extending in the longitudinal direction,
A fuel material containing uranium dioxide as a main component, which is enclosed in the cladding tube and contains at least a part of enriched uranium,
Wherein at least some of the fuel material comprises combustible poisons,
(N is an integer of 2 or more), the number of fuel rods enclosing the fuel material including combustible poison in the fuel rod is n (n is an integer of 1 or more and smaller than N), the number of fuel rods contained in the fuel assembly is N (% By mass) of the combustible poisonous substance in the fuel material is represented by p, and the concentration (mass%) of the average uranium 235 over the total number of the fuel assemblies is represented by e,
0.57e-1.8 <p · n / N <0.57e-0.8
Of the total amount of the fuel.

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