JP2000019280A - Core of light water cooling reactor and operation method of the reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the coolant void coefficient negative, increase the conversion ratio and simultaneously flatten the power distribution without much reducing the core height in a core densified for raising the conversion ratio and a core minor actinide is loaded. SOLUTION: A fuel assembly enriched in plutonium and adjacently arranged in a tight-pitch grid is provided. This fuel assembly is constituted of normal fuel assembly formed by bundling normal fuel rods loading core fuel 1 longer than a certain length and short fuel assembly formed by bundling short fuel rods core fuel 1 loading a shorter than the core fuel 1 of the normal fuel assembly and a blanket 2 including nuclear parent material absorbing neutrons and converting them into fissile material. By this, non-uniformity is attained in core radial direction and axial direction and core fuel length in the short length fuel assembly is made 50% or less of the core fuel length of normal fuel assembly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control technique for a light water-cooled reactor such as a boiling water reactor, and more particularly, to a method for converting uranium to plutonium by devising the selection and arrangement of core components. The present invention relates to a light water reactor core and a method of operating the reactor, which can improve the conversion efficiency to minor actinides and enable effective recycling of minor actinides.

[0002]

2. Description of the Related Art In general, the core of a light water-cooled reactor is composed of a large number of fuel assemblies loaded with fissile materials, and water is used as a coolant for removing heat from fuel. Since the neutron moderating ability of hydrogen atoms contained in water is large, in a conventional light-water-cooled reactor with a large proportion of water, high-energy neutrons generated by fission are greatly reduced, and low-energy thermal neutrons are large neutrons. Occupy part. When a fissile material absorbs neutrons having low energy, the rate of a capture reaction in which nuclear fission takes place in the nucleus without fission, instead of a fission reaction in which about three neutrons are generated. That is, in fission with low energy neutrons, the number of neutrons generated per neutron absorption is small.

On the other hand, in the case of high-energy neutrons, the rate of the capture reaction is small, so that it is possible to increase the average number of neutrons generated per neutron absorption to two or more even if the effect of capture is included, and to use one for the fission chain. For the purpose of maintaining the reaction, the remaining one can be absorbed into a blanket containing a parent material such as U-238 to efficiently generate fissile material. The ratio of fissile material generation and extinction is about 0.5 in a conventional light water reactor, but the ratio of high-energy neutrons increases in a densely packed core with a short fuel-separation distance. It is also possible to set it to about 0.8 to 1.0. By recovering and reusing fissionable substances such as plutonium from spent fuel, it is possible to greatly save nuclear fuel.

[0004] Minor actinides such as neptunium and americium which accumulate in spent fuel and are treated and disposed of as high-level waste are toxic because they last for hundreds to millions of years. It is considered that the minor actinide may be burned as fuel for a nuclear reactor. For this reason, a reactor core in which a minor actinide is uniformly added to a blanket or a special fuel assembly containing a minor actinide is loaded has been considered.

[0005]

As described above, in order to increase the utilization efficiency of nuclear fuel, in a core in which the conversion ratio is improved by increasing the density of the fuel, the amount of coolant for decelerating neutrons is small, and a high energy spectrum is obtained. Therefore, there is a possibility that the reactivity (coolant void coefficient) due to the decrease in the density of the coolant becomes positive as in the conventional large-scale Na-cooled fast reactor.
In light water cooled reactors, it is necessary to set the coolant void coefficient to a negative value from the viewpoint of core safety and stability. One of the countermeasures is to make the core height extremely low and increase the axial neutron leakage.

FIG. 19 is a graph showing a relationship between a core height and a coolant void coefficient in a boiling water cooled dense lattice fuel core. Here, the relationship is shown when the diameter of the fuel is about 12 mm and the distance between the fuels is about 1.5 mm.
According to this, in order to make the coolant void coefficient negative, it is understood that the core height needs to be a flat core of about 60 cm.

FIG. 20A is a vertical sectional view showing the height and diameter of a dense lattice fuel core in a 1,000,000 KWe class boiling water reactor constructed based on the characteristics shown in FIG. In the dense lattice fuel core 101 shown in this figure, the height of the core fuel 1a is 60 cm, and the heights of the outer core blankets 2a, 3a arranged on the upper and lower portions are each 20 cm. FIG. 20 (B) is a vertical sectional view showing the height and diameter of a general lattice fuel core in a 1,000,000 KWe-class boiling water reactor for comparison. In the general lattice fuel core 102 shown in FIG. 20B, the core fuel 1a is arranged in all regions of the core, and the core height is less than about 4 m (370 cm).

Thus, in the dense lattice fuel core 101 shown in FIG. 20A, the height of the core fuel 1 is about 60 cm, and the general lattice fuel core 102 shown in FIG.
The core height becomes smaller as compared with (core fuel height is about 4 m). For this reason, even if the fuel rods are densely arranged, the thermal output of the reactor must be reduced with the same core diameter. Further, in order to ensure the same thermal output in the dense lattice fuel core 101 as in the general lattice fuel core 102, the core diameter must be increased, which results in an increase in the size of the configuration.

Incidentally, as in the case of the dense lattice fuel core 101, in the Na-cooled fast reactor having a fast spectrum, conventionally, in order to reduce the coolant void coefficient and to improve the breeding ratio, depleted uranium and recovered uranium are used. A non-homogeneous core in which a blanket made of a fuel parent material is placed in the core to make the core non-homogeneous has been studied. Among these, there are a radially non-homogeneous core that is non-homogeneous in the radial direction, and an axially non-homogeneous core that is non-homogeneous in the axial direction. On the other hand, a core in which no blanket is arranged inside the core is called a homogeneous core.

FIGS. 21 (A) to 21 (C) show the configurations of these homogeneous cores and each of the non-homogeneous cores as vertical cross sections, and Table 1 shows a comparison of the characteristics of each core. . FIG. 21A shows a homogeneous core 201,
Core blankets 2b, 3b and a radial blanket 4b are respectively disposed on upper and lower portions and side portions of the core fuel 1b. FIG. 21 (B) shows a non-homogeneous core 20 in the radial direction.
2A and 2B, in addition to the configuration of FIG. 21A, a plurality of internal blankets 5b are dispersed and loaded in the radial direction between core fuels 1b. FIG. 21 (C) shows an axially non-homogeneous core 203. In addition to the configuration shown in FIG. 21 (A), the internal blanket 5b is loaded so as to be sandwiched between upper and lower core fuels 1b.

[0011]

[Table 1]

The radially inhomogeneous core 2 shown in FIG.
In 02, the core blank 1b
U23 due to neutron leakage from inside to internal blanket 5b
8 neutron capture increases and the conversion ratio can be increased. Also, when the coolant density in the core is reduced, the neutron spectrum becomes hard and the fast neutrons increase, so that the neutrons leaking to the blanket 5b increase. Thereby, U23
Neutron capture is promoted, and the core reactivity is reduced, that is, the coolant void coefficient can be reduced. From this viewpoint, as can be seen from Table 1, a radially non-homogeneous core capable of increasing the contact area between the core and the blanket is excellent, and the blanket aggregate causes a large increase in power with accumulation of Pu, and a minimum in the early stage of combustion. On the contrary, the core fuel assembly has a large output at the early stage of combustion, and the thermal margin is smaller than that of the homogeneous core. On the other hand, in the axially non-homogeneous core 203 shown in FIG. 21C, there is no drawback of power fluctuation, but it can be seen from Table 1 because the contact area between the core and the blanket is smaller than the radially non-homogeneous core. Thus, a significant reduction in the coolant void coefficient and an improvement in the conversion ratio cannot be expected.

It is also considered that the light water-cooled dense lattice fuel core which aims at a high conversion ratio with respect to such a Na-cooled fast reactor has a thermal margin worse than that of the conventional light water reactor due to a decrease in the coolant area accompanying the densification. In addition, it is necessary not only to significantly reduce the coolant void coefficient until it becomes negative, but also to consider the securing of thermal margin. Cannot be satisfied. In other words, at present, there is a need to create a core concept suitable for a light water cooled dense lattice fuel core.

On the other hand, when minor actinides such as neptunium, americium and curium are recycled as nuclear fuel, many of the minor actinide nuclides have a threshold characteristic that the fission reaction becomes large at a certain energy of neutrons or more. It is known that when added as fuel for a nuclear reactor, the coolant void coefficient shifts in the positive direction, as in the case where the fuel is densified, thereby deteriorating the stability and safety of the core.

Further, in the dense fuel grid, there may be a large difference in power density between the outermost fuel rods in each fuel assembly and other fuel rods due to the difference in the volume of the surrounding coolant. This is because the outermost fuel rods in the fuel assembly have a large coolant volume around them and the contribution of low-energy neutrons having a large fission cross-section is larger than other fuels. In particular, when the fuel cells are arranged in a triangular arrangement in a square channel box, this tendency is caused by a decrease in the fuel filling density at the end. When viewed as a whole core,
In the fuel assembly at the outermost periphery of the core, the coolant around the core also tends to have a higher power density than other assemblies. For this reason, in the dense lattice core, a device for flattening the output is also required.

[0016] The present invention has been made in view of such circumstances, and a denser core for increasing the conversion ratio,
In a reactor loaded with a minor actinide, the core of a light-water-cooled reactor, which can make the coolant void coefficient negative without significantly reducing the core height, increase the conversion ratio, and at the same time achieve a flat power distribution, The purpose is to provide a method of operating the reactor.

[0017]

According to a first aspect of the present invention, there is provided a light water-cooled nuclear reactor in which fuel assemblies having plutonium-enriched core fuel are arranged adjacently in a dense grid. A normal fuel assembly comprising a bundle of normal fuel rods loaded with core fuel having a certain length or more, and a core fuel and a neutron shorter than the core fuel of the normal fuel assembly. A short fuel assembly comprising a bundle of short fuel bundles loaded with a blanket containing a fuel parent material that absorbs and converts it into fissile material, thereby making the core radially and axially non-homogeneous, and A core of a light-water-cooled nuclear reactor is provided, wherein a core fuel length of the short fuel assembly is 50% or less of a core fuel length of the normal fuel assembly.

According to a second aspect of the present invention, in the light water cooled reactor core according to the first aspect, the blanket is disposed above or below the core fuel in the short fuel rods of the short fuel assembly, and the blanket is provided. The short fuel rod loaded with is a part of the fuel rod in the short fuel assembly, and the upper or lower part of the core fuel in the other short fuel rod is a coolant flow path. To provide a light water cooled reactor core.

According to a third aspect of the present invention, in the core of the light water-cooled reactor according to the first or second aspect, a blanket of some short fuel rods in the short fuel assembly has a high neutron moderating ability and a high neutron absorption. Provided is a light water-cooled reactor core, wherein the core is replaced by a compound of an element having a small cross-sectional area.

According to a fourth aspect of the present invention, there is provided a light water-cooled reactor core in which fuel assemblies having plutonium-enriched core fuel are arranged adjacent to each other in a dense lattice pattern, wherein the core fuel core of the fuel assembly is provided. A blanket containing a fuel parent substance is disposed in the upper and lower parts in the direction, wherein a part of the blanket is replaced by a compound of an element having a high neutron moderating ability and a small neutron absorption cross-sectional area, or the fuel assembly The present invention provides a light water-cooled reactor core characterized in that a compound of an element having a high neutron moderating ability and a small neutron absorption cross section is arranged between a core fuel and a blanket.

According to a fifth aspect of the present invention, in the core of the light water-cooled reactor according to the third or fourth aspect, the compound of the element having a high neutron moderating ability and a small neutron absorption cross section is hydrogen, beryllium, lithium-ion. 7 or boron-1
A light water-cooled reactor core, characterized in that the core is a compound of the present invention.

According to a sixth aspect of the present invention, there is provided a light water-cooled reactor core in which fuel assemblies having plutonium-enriched core fuel are arranged adjacent to each other in a dense lattice pattern, wherein the fuel assemblies have a predetermined length or more. A normal fuel assembly formed by bundling normal fuel rods loaded with the core fuel described above, and a short fuel assembly formed by bundling short fuel bundles loaded with a core fuel shorter than the core fuel of the normal fuel assembly Wherein boron carbide or europium oxide is disposed as a neutron absorbing substance on the upper portion of the core fuel dedicated to the short fuel, which is disposed in the central portion of the short fuel assembly, and the short portion of the peripheral portion in the short fuel assembly is provided. The present invention provides a light water-cooled reactor core, wherein the upper part of the fuel dedicated to the fuel is a coolant flow path.

According to a seventh aspect of the present invention, in the light water-cooled reactor core according to any one of the first to sixth aspects,
A light water-cooled reactor core, wherein the blanket is made of a mixture of a minor actinide and depleted uranium or recovered uranium, or the core fuel is a mixture of plutonium and a minor actinide.

According to the invention of claim 8, in the core of the light water-cooled reactor according to claim 7, the minor actinide comprises:
Provided is a light water-cooled nuclear reactor core, which is made of neptunium, americium or curium.

According to a ninth aspect of the present invention, in the core of the light water-cooled nuclear reactor according to any one of the first to eighth aspects,
When the fuel rods are in a triangular arrangement or a square arrangement, and when the fuel rods are in a triangular arrangement, the mantles surrounding the plurality of fuel rods are in a square or hexagonal shape. Provided is a light water-cooled reactor core, wherein a mantle portion surrounding a fuel rod has a square shape.

According to a tenth aspect of the present invention, there is provided a method for operating a light water-cooled reactor having a core according to any one of the first to ninth aspects, wherein a short fuel is used when the control member is inserted from below the core. The blanket in the assembly is placed above the core fuel, and when the control rod is inserted from above the core, the blanket in the short fuel assembly is placed below the core fuel, and the short fuel bundle is placed in the surrounding fuel assemblies. A method for operating a light water-cooled reactor, characterized in that the core is operated with a shallower insertion degree for a control rod containing more bodies.

[0027] According to an eleventh aspect of the present invention, there is provided a method for operating a light water-cooled reactor having a core according to any one of the first to ninth aspects, wherein the short fuel assembly is disposed near the center of the core in the initial stage of combustion. And a method for operating a light water cooled reactor characterized by moving the reactor to the periphery of the reactor core as combustion proceeds.

According to a twelfth aspect of the present invention, in the light water-cooled reactor core according to any one of the first to ninth aspects, the concentration of the fissile material in the outermost fuel in each fuel assembly is the same. Provided is a light water-cooled reactor core characterized by having a concentration of fissile material lower than that of other fuel rods in a fuel assembly.

According to a thirteenth aspect of the present invention, in the core of the light water-cooled reactor according to any one of the first to ninth aspects, the concentration of the fissile material in the fuel assembly disposed at the outermost periphery of the core is reduced. A core of a light water-cooled reactor characterized by having a concentration lower than the concentration of fissile material in a fuel assembly other than the above.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. 1 to 18 for a core of a boiling water reactor.

First Embodiment (FIGS. 1 to 4, Table 2) In this embodiment, a dense lattice fuel core in a 1,000,000 KWe class boiling water reactor will be described as an example. FIG. 1 is a longitudinal sectional view schematically showing a core structure according to the present embodiment,
FIG. 2 is a 1/4 horizontal cross-sectional view of the core shown in FIG.

As shown in FIG. 1, the core 30 of the present embodiment
Numeral 1 is composed of a region of a core fuel 1 made of a mixed oxide enriched with plutonium and a region of a core inner blanket 2 made of depleted uranium as a fuel parent material, and a core diameter D is about 4.5 m. It has become. At the upper and lower portions of the core, regions of core outer blankets 3 and 4 (outer core upper blanket 3 and outer core lower blanket 4) are formed. As shown in FIG. 2, the core fuel 1, the core inner blanket 2, and the core outer blankets 3 and 4 are composed of a fuel assembly (hereinafter, referred to as a normal fuel assembly) including a core fuel 1 having an axial length equal to or more than a certain length. ) 5 and a short fuel assembly (hereinafter, referred to as a short fuel assembly) 6 including the core fuel 1 having a smaller axial length than the core fuel of the normal fuel assembly 5 are loaded adjacently to each other. It is composed of

FIG. 3A is a 1/4 horizontal cross-sectional view showing the structure of the normal fuel assembly 5, and FIG.
FIG. 2 is a vertical sectional view showing a fuel rod (hereinafter, referred to as a normal fuel rod) 7 loaded in a normal fuel assembly 5 shown in FIG. FIG. 4A shows a short fuel assembly 6.
4 is a horizontal sectional view, and FIG. 4B is a vertical sectional view showing a fuel rod (hereinafter, referred to as a short fuel rod) 8 loaded in the short fuel assembly 6 shown in FIG. 4A.

As shown in FIG. 3A, the normal fuel assembly 5 has a large number of normal fuel rods 7 in a channel box 13.
Are bundled in a triangular array, and the outer shape is a square bundle. The main specification of the fuel rod 7 is about 12
mm, the distance between fuel rods is about 1.5 mm, the fuel interval is small, and the volume ratio of water to fuel is small. As shown in FIG. 3 (B), each of the normal fuel rods 7 is filled with a core fuel (normal fuel) 1 in a substantially central portion in a longitudinal direction of the cladding tube 9 and is provided with upper and lower parts of the core fuel 1 outside the core. The upper blanket 3 and the outer core lower blanket 4 are filled. The length h1 (see FIG. 1) of the normal fuel 1 in the normal fuel rod 7 is set to, for example, 110 cm. The length h2 (see FIG. 1) of the outer core blanket 3 and the outer core lower blanket 4 is set to 20 cm. A compression coil spring 10 and an upper end plug 11 are provided at the upper end position of the cladding tube 9.
A lower end plug 12 is provided at a lower end position of the cladding tube 9.
Is provided. A gas plenum for storing the fission gas is secured by the compression coil spring 10, and both ends of the cladding tube 9 are closed by the upper end plug 11 and the lower end plug 12, and are supported by an upper tie plate and a lower tie plate (not shown). Is done. The normal fuel rod 7 having such a configuration is supported in the reactor pressure vessel via an upper grid plate and a core support plate (not shown).

On the other hand, as shown in FIG. 4A, the short fuel assembly 6 is formed by bundling a large number of short fuel rods 8 in a triangular arrangement in a channel box 13 similar to the normal fuel assembly 5. The outer shape is a square bundle. The main specifications of the short fuel rod 8 are that the diameter of the fuel is about 12 mm, the distance between the fuel rods is about 1.5 mm, the interval between the fuels is small, and the volume ratio of water to fuel is small. As shown in FIG. 4B, each short fuel rod 7 is filled with a core fuel (short fuel) 1 at a position lower than a central portion of the cladding tube 9, and a core inner blanket is provided on an upper portion of the core fuel 1. 2 and the lower portion of the core fuel 1 is filled with a lower blanket 4 outside the core. The length h3 (see FIG. 1) of the short fuel 1 in the short fuel rod 7 is, for example, 550.
cm. The length h4 (see FIG. 1) of the blanket 2 in the core is set to 75 cm, and the length h2 (see FIG. 1) of the lower blanket 4 outside the core is set to 20 cm similarly to the fuel rod 7. is there. The cladding tube 9
A compression coil spring 10 and an upper end plug 11 are provided at the upper end of the cover tube 9, and a lower end plug 12 is provided at a lower end of the cladding tube 9, and supported by an upper tie plate and a lower tie plate (not shown). It is supported in the reactor pressure vessel via a grid plate and a core support plate.

As described above, in the present embodiment, the core fuel length of the normal fuel assembly 5 is 110 cm and the short fuel assembly 6
Is 55 cm, and the core fuel length of the short fuel assembly 6 is 50% of the core length of the normal fuel assembly 5. Further, in the present embodiment, the core fuel 1 and the blanket 2, both in the core radial direction and the core axial direction.
The length h4 of the core inner blanket 2 of the short fuel assembly 8 which is in contact with the core fuel 1 of the normal fuel assembly 7 is 75 cm, and the length h4 of the core fuel 1 of the normal fuel assembly 7 It is 50% or more of the height h1 (110 cm). Further, the number ratio of the normal fuel assemblies 7 to the short fuel assemblies 8 is about 3: 2, and the average core height is about 90 cm.
It is.

For the fuel assemblies 5 and 6, components other than the bundle portions of the fuel rods 7 and 8 and the channel box 13, such as the upper handling head and the lower type plate, are not shown. However, these are similar to conventional fuel assemblies.

Next, the operation will be described.

In the core 301 of this embodiment, since the fuel interval is small and the volume ratio of water to fuel is small, the deceleration effect by water is small. Therefore, a fast neutron spectrum is obtained, the number of neutrons generated per fission in the core fuel 1 is large, the useless neutron capture is small, and excess neutrons are absorbed by the depleted uranium blankets 2, 3, and 4. Conversion rate can be improved.

In particular, in the core 301 of the present embodiment, the conventional fuel assembly 5 and the short fuel assembly 6 are arranged, and the in-core blanket 2 of depleted uranium is arranged above the core fuel 1 in the conventional manner. Unlike the non-homogeneous core, the fuel and the depleted uranium blanket are in contact both radially and axially, and the length of the core inner blanket 2 that normally contacts the core fuel 1 of the fuel assembly 5 is defined as the core fuel length. 50% or more, the contact area between the fuel and the depleted uranium blanket is large, the number of neutrons that can jump from the fuel into the depleted uranium blanket can be increased, the conversion rate of fissile material can be improved, and the coolant voids can be improved. When the rate increases, neutrons leaking from the fuel to the depleted uranium blanket increase, and are captured by uranium 238 in the depleted uranium blanket. Since neutrons increases, reactivity decreases, that is, the coolant void coefficient negative.

Therefore, it is possible to achieve a negative coolant void coefficient and a high conversion ratio without having to significantly flatten the core. Further, regarding the power fluctuation, since the core fuel 1 and the core inner blanket 2 are arranged in the axial direction in the short fuel assembly 8, the influence of the large power fluctuation of the depleted uranium blanket on the power of the assembly is large. And a thermal margin can be secured.

Table 2 shows a comparison of specifications and characteristics between a specific example (Example 1 and Example 2) based on this embodiment and a conventional example (conventional flat core).

[0043]

[Table 2]

The conventional core is a 1,000,000 KWe boiling water-cooled dense lattice fuel core. As shown in FIG. 20A, the core height is 60 cm, the core diameter is 340 cm, and the fuel assembly to be loaded is provided. Are all normal fuel assemblies and core fuel 1
The length of a was 60 cm, and the length of the blankets 2a and 2b outside the core was 20 cm.

On the other hand, the core of the first embodiment is a 1,000,000 KWe boiling water-cooled dense lattice fuel core similarly to the conventional example, and the core of the second embodiment is a 1.4 million KWe boiling water cooled dense lattice fuel core. The core. These core diameters are about 480 cm as in the conventional example. In the core of each embodiment, the normal fuel assembly 7 and the short fuel assembly 8 having the configurations shown in FIGS. 3 and 4 were loaded. That is, the length of the core fuel (normal fuel) 1 charged in the normal fuel assembly 7 is 110 cm, and the length of the core fuel (short fuel) 1 charged in the short fuel assembly 8 is 55 cm. The length of the core outer blankets 3 and 4 is 20 cm, and the length of the core inner blanket 2 is 20 cm. The number ratio between the normal fuel assembly 7 and the short fuel assembly 8 is about 3 to 2
And the average core height is about 90 cm. In each of the embodiments and the conventional example, the diameter of the fuel is about 12 mm and the distance between the fuel rods is about 1.5 mm.

As a result of comparing these characteristics, as shown in Table 2, although the core volumes of Examples 1 and 2 are about 1.5 times larger than those of the conventional example, these coolants are used. The void coefficient is almost the same as 0.01Δk / kk ′ /% void. On the other hand, the conversion ratio is 0.96 in the conventional example, 1.02 in Examples 1 and 2, and 0.06 higher in each example. That is, in Examples 1 and 2, it was confirmed that since the core volume could be increased while securing the same coolant void coefficient as in the conventional example, the heat output that could be taken out of the core could be larger than in the conventional example. In particular, in the case of the second embodiment, the heat output can be increased under the same condition of the maximum linear output. As described above, according to the present embodiment, it is possible to increase the conversion ratio and increase the heat output while securing the same coolant void coefficient as that of the conventional example.

In the above embodiment, the core inner blanket 2 is disposed above the core fuel 1 in the short fuel assembly 7.
The same effect can be expected even if is disposed below the core fuel 1.

Second Embodiment (FIGS. 5 and 1 to 3) The core of this embodiment is different from the first embodiment in that the configuration of the short fuel assembly is changed so that two types of short fuel rods are used. It is made to consist of. FIG. 5 (A)
It is a 1/4 horizontal sectional view which shows the structure of a short fuel assembly,
FIGS. 5B and 5C are vertical sectional views showing first and second different short fuel rods, which are constituent elements of the short fuel assembly of FIG. 5A, respectively. Since the configuration other than the short fuel assembly is the same as that of the first embodiment, FIG.
This will be described with reference to FIG.

The short fuel assembly 14 of this embodiment is shown in FIG.
As shown in (A), the second short fuel rods 15
The fuel bundles are arranged in a triangular arrangement in such a manner that the short fuel rods 16 are interspersed with each other, and the periphery thereof is surrounded by a channel box 13.

As shown in FIG. 5 (B), the first short fuel rod 15 fills the core fuel (short fuel) 1 at a position lower than the center of the cladding tube 9, and the upper part of the core fuel 1. Is filled with an inner core blanket 2 and the lower part of the core fuel 1 is filled with an outer core lower blanket 4, which is the same as the configuration shown in FIG. 4B.

As shown in FIG. 5 (C), the second short fuel rod 16 is provided in a cladding tube 9 having a small vertical dimension and a core fuel 1 and an outer core lower blanket 4 having the same length as the first short fuel rod 15. , And there is no blanket of depleted uranium above the core fuel 1.

The core according to the present embodiment includes the first short fuel rod 1 including the core blanket 2 for the depleted uranium.
A short fuel assembly 14 having two types of fuel rods including a fuel rod 5 and a second short fuel rod 16 having no depleted uranium blanket, and a normal fuel assembly 5 shown in FIG.
It is configured by loading in the arrangement shown in FIG. That is, the core blanket 2 of the depleted uranium core
Are arranged in only a part of the short fuel 1, and there is no fuel rod above the other short fuel 1, forming a coolant passage.

According to the core of the second embodiment,
Compared with the core of the first embodiment, the volume ratio of the core blanket 2 of the depleted uranium in the upper part of the core fuel 1 is small, and the coolant ratio is large. Therefore, in the first embodiment, the core fuel 1 becomes closer to the center of the depleted uranium region.
And the average neutron absorption per U238 in the entire region is smaller than that in the depleted uranium surface region. In particular, since the neutron absorption is large in the resonance energy region, the average neutron absorption becomes small unless neutrons are sufficiently supplied in the central portion due to neutron deceleration with higher energy. This is referred to as a self-shielding effect. This tendency becomes stronger when the depleted uranium is densely arranged or as the radial size of the fuel assembly is larger.

Therefore, in the case of dense fuel having a very small fuel rod interval or an aggregate having a large radial size, the amount of depleted uranium is limited, and a coolant is disposed in a portion where no depleted uranium is disposed. Neutrons can reach the center of this region to increase the conversion efficiency per U238. Here, the increase in the coolant ratio acts to increase the resonance region neutrons by reducing the energy of the fast neutrons that have flown in, and also contributes to increasing the conversion efficiency.

As described above, the present embodiment is particularly effective in the case of dense fuel allocation or the case where the size of the fuel assembly is large and the self-shielding effect inside the depleted uranium region becomes large. Become.

In this embodiment, the coolant flow path is provided above the core fuel 1 of the second short fuel rod 16, but the coolant flow path is provided below the core fuel 1 of the second short fuel rod 16. It may be. Further, in the first short fuel assembly 15, the core inner blanket 2 is arranged above the core fuel 1,
Alternatively, core blanket 2 may be arranged below core fuel 1.

Third Embodiment (FIGS. 6, 1 to 3) The core of this embodiment is also a modification of the configuration of the short fuel assembly in the first embodiment. It is made up of fuel rods. FIG.
(A) is a 1/4 horizontal sectional view showing the configuration of a short fuel assembly, and FIGS. 6 (B) and (C) are each FIG. 6 (A).
FIG. 5 is a vertical sectional view showing first and second different short fuel rods which are constituent elements of the short fuel assembly of FIG. Since the configuration other than the short fuel assembly is the same as that of the first embodiment, the configuration will be described with reference to FIGS.

The short fuel assembly 17 of the present embodiment is shown in FIG.
As shown in (A), the second short fuel rods 18
The fuel bundles are arranged in a triangular arrangement in a form in which short fuel rods 19 are interspersed, and the periphery thereof is surrounded by a channel box 13.

As shown in FIG. 6 (B), the first short fuel rod 18 fills the core fuel (short fuel) 1 at a position lower than the center of the cladding tube 9 and, at the top of the core fuel 1. Is filled with depleted uranium core inner blanket 2,
Further, the lower portion of the core fuel 1 is filled with a lower blanket 4 outside the core of depleted uranium, which is the same as the configuration shown in FIG.

As shown in FIG. 6 (C), the second short fuel rod 19 fills the cladding tube 9 with the core fuel 1 and the outer core lower blanket 4 having the same length as the first short fuel rod 15. And a zirconium hydride 2 having an excellent neutron moderating ability and a low neutron absorption cross section
0 is filled.

The core of the present embodiment includes a first short fuel rod 1 including the blanket 2 inside the core of such depleted uranium.
FIG. 2 shows a short fuel assembly 17 having two types of fuel rods, each of which is composed of a fuel rod 8 and a second short fuel rod 19 containing zirconium hydride 20, and the normal fuel assembly 5 shown in FIG. It is configured by loading in the arrangement shown. That is, on the upper part of the core fuel (short fuel) 1, the core blanket 2 of depleted uranium and the zirconium hydride 20 are arranged in a mixed manner.

According to the core of the third embodiment,
Similarly to the first embodiment, in addition to the effect of increasing the heat output while increasing the conversion ratio, it is possible to suppress the hardening of the neutron spectrum accompanying the increase in the coolant void fraction. That is, when the coolant void fraction increases, the neutron spectrum tends to be hardened even in the region of the core blanket 2 due to the decrease in the coolant. Burnup is low in the region of the core inner racket 2 and Pu23 by conversion of U238 is used.
While the accumulation of 9 is small, the coolant void coefficient is negative. However, when the burnup increases and the accumulation of Pu239 increases, the neutrons that have entered cause fission of Ρu239 and exceed the absorption effect of U238. The material void coefficient shifts to the positive side. To avoid this, it is necessary to limit the burnup of the short fuel assembly 17 including the core inner blanket 2. In the present embodiment, hydrogen atoms in zirconium hydride 20 having excellent neutron moderating ability are mixed in the region of the core inner blanket 2, whereby the hardening of the neutron spectrum accompanying the increase in the coolant void fraction is suppressed. Therefore, it is possible to prevent the coolant void coefficient from turning to the positive side.

In the present embodiment, the zirconium hydride 20 is provided on the upper part of the second short fuel rod 19.
9 may be provided below. In addition, zirconium hydride 2
0 is an example of a compound of an element having excellent neutron moderating ability and having a low neutron absorption cross section,
Other similar elements, for example, compounds such as beryllium, lithium-7 and boron-11 can be substituted.

Fourth Embodiment (FIGS. 7 and 8) In the core of this embodiment, all the fuel assemblies to be loaded are normal fuel assemblies, and the normal fuel assemblies are divided into two types of normal fuel rods. It is made to consist of. FIG.
FIG. 7A is a 1/4 horizontal cross-sectional view showing a configuration of a normal fuel assembly, and FIGS. 7B and 7C are respectively FIGS.
FIG. 4 is a vertical sectional view showing first and second different normal fuel rods that are components of the normal fuel assembly of FIG. FIG.
(A) 1/4 of core 302 loaded with normal fuel assembly
It is a horizontal sectional view.

The normal fuel assembly 21 of the present embodiment is shown in FIG.
As shown in (A), the second normal fuel rods 22
The fuel bundles are arranged in a triangular arrangement with the normal fuel rods 23 interspersed, and the periphery thereof is surrounded by the channel box 13.

As shown in FIG. 7 (B), the first normal fuel rod 22 fills a substantially central portion of the cladding tube 9 in the longitudinal direction with the core fuel (normal fuel) 1 and, The portion is filled with a depleted uranium outer blanket 3 and a lower blanket 4 outside the core, and this configuration is the same as the normal fuel rod 7 shown in FIG. 3B.

As shown in FIG. 7 (C), the second normal fuel rod 23 has a substantially central portion in the length direction of the cladding tube 9 filled with the core fuel (normal fuel) 1. This is the same as the normal fuel rod 22 except that the upper and lower portions of the core fuel 1 are filled with zirconium hydride 20 instead of the outer core upper blanket 3 and the outer core lower blanket 4. Is different from the first normal fuel rod 22.

As described above, the core 302 of the present embodiment
A first normal fuel rod 22 including a depleted uranium core outer blanket 3, 4 and a second normal fuel rod 22 including a zirconium hydride 20
The normal fuel assembly 21 including the normal fuel rods 23 is loaded in the arrangement shown in FIG.

According to the core 302 of the fourth embodiment, the neutron absorption amount per unit weight of U238 can be increased, and the conversion efficiency can be increased. That is,
In general, depleted uranium blankets are placed above and below the core fuel to capture neutrons leaking from the core and increase conversion efficiency, but a fuel assembly with densely arranged fuels is used to increase conversion efficiency in the core. In the case of the body, abundant neutrons are present in the core fuel part due to fissioned neutrons, but in the upper and lower blanket parts, only neutrons leaking from the core in one direction are captured, so the fuel is densely arranged. In this case, as described above, self-shielding of resonance energy neutrons by U238 increases, and the neutron absorption amount per unit weight of U238 decreases.

Therefore, in the present embodiment, zirconium hydride containing hydrogen having excellent neutron moderating capability and having a low neutron absorption cross-section is converted into a depleted uranium region in order to decelerate the fast neutrons that have entered and to increase the resonance energy neutrons. , The amount of neutron absorption per unit weight of U238 can be increased, and the conversion efficiency can be increased.

In this embodiment, it is also possible to replace the zirconium hydride 20 with a similar other element, for example, a compound such as beryllium, lithium-7, boron-11, or the like.

Fifth Embodiment (FIGS. 9 and 8) In the core of the present embodiment, all the fuel assemblies to be loaded are normal fuel assemblies, and the normal fuel assemblies include a core fuel, a blanket and In which zirconium hydride is disposed. FIG. 9A is a 水平 horizontal sectional view showing the configuration of a normal fuel assembly, and FIG.
(B) is a vertical sectional view showing a normal fuel rod which is a component of the normal fuel assembly of FIG. 9 (A).

The normal fuel assembly 24 of this embodiment is shown in FIG.
As shown in (A), the same normal fuel rods 25 are bundled in a triangular arrangement to form a fuel bundle, and the periphery thereof is surrounded by a channel box 13. Normal fuel rod 2
As shown in FIG. 9 (B), the core 5 is filled with a core fuel (normal fuel) 1 in a substantially central portion in the length direction of the cladding tube 9 and
The upper and lower portions of the core fuel 1 are filled with an outer core upper blanket 3 and an outer core lower blanket 4 of depleted uranium,
Further, zirconium hydride 20 is arranged between the core fuel 1 and each of the blankets 3 and 4. As described above, the core of the present embodiment is configured by loading the normal fuel assemblies 24 including the normal fuel rods 25 containing the zirconium hydride 20 in the same arrangement as that shown in FIG.

Also in the core of the fifth embodiment, the neutrons are decelerated by hydrogen and the resonance neutrons in the depleted uranium region are increased by disposing the zirconium 20, similarly to the fourth embodiment. And thereby increase the conversion efficiency.

In this embodiment, it is also possible to replace the zirconium hydride 20 with a similar other element, for example, a compound such as beryllium, lithium-7, and boron-11.

Sixth Embodiment (FIGS. 10, 11, and 3)
(B) The core of the present embodiment is obtained by changing the configuration of the short fuel assembly and the arrangement in the core in the first embodiment. FIG. 10A is a １ ／ horizontal cross-sectional view showing the configuration of a short fuel assembly, and FIGS.
It is a vertical sectional view which shows the 1st and 2nd different short fuel rods which are the components of the short fuel assembly of FIG. 10 (A), respectively. FIG. 11 is a 1/4 horizontal cross-sectional view of a core loaded with a normal fuel assembly and the short fuel assembly of FIG. 10 (A).

The short fuel assembly 26 of this embodiment is shown in FIG.
As shown in (A), a triangular array of fuel bundles is formed in such a manner that a second short fuel rod 28 is arranged on the center side of the assembly with respect to a first short fuel rod 27, and the periphery thereof is a channel box. 13.

As shown in FIG. 10B, the first short fuel rod 27 has a configuration in which the cladding tube 9 having a small vertical dimension is filled with the core fuel (short fuel) 1 and the outer core lower blanket 4. And the short fuel rod 16 shown in FIG.
Similarly to the above, a coolant flow path is formed above.

As shown in FIG. 6C, the second short fuel rod 28 is located at a position lower than the center of the cladding tube 9 having a large vertical dimension and has the same length as the first short fuel rod 27. (Short fuel) 1, the upper part of the core fuel 1 is filled with boron carbide 29 which is a neutron absorbing substance, and the lower part of the core fuel 1 is filled with the lower blanket 4 outside the core of depleted uranium. ing.

As shown in FIG. 11, the core of the present embodiment has a first short fuel rod 2 whose upper portion serves as a coolant flow path.
A short fuel assembly 26 having two types of fuel rods, each of which is composed of a fuel rod 7 and a second short fuel rod 28 containing boron carbide 29, is arranged as shown in FIG. , The peripheral portion of the neutron absorbing substance, ie, the boron carbide 29, is a coolant flow path.

According to the core of the present embodiment, as in the first embodiment, it is possible to increase the conversion ratio and the heat output at the same time as in the first embodiment. This is effective when it is desired to secure a negative coolant void coefficient. That is, in the present embodiment, since the boron carbide 29 disposed above the core fuel (short fuel) 1 of the second short fuel rod 28 is surrounded by the coolant, the cooling is performed normally. Due to the reflection effect of the material, relatively few neutrons jump from the core fuel 1 of the adjacent normal fuel assembly 5 into the boron carbide 29 and are absorbed. However, when the coolant void fraction increases, the amount of coolant between the core fuel 1 and the boron carbide 29 decreases, so that neutrons absorbed by the boron carbide 29 relatively increase. Thereby, the reactivity can be reduced, and the coolant void coefficient can be kept negative.

In this embodiment, boron carbide 29 is used as the neutron absorbing material provided above the core fuel 1 of the second short fuel rod 28. However, as the neutron absorbing material, europium oxide or the like is used. It is possible to

Seventh Embodiment (FIG. 12, FIGS. 1 to 3) The core of the present embodiment is a modification of the configuration of the short fuel assembly in the first embodiment, in which a minor actinide is added to a blanket inside the core. Things. FIG.
(A) is a 1/4 horizontal sectional view showing a configuration of a short fuel assembly, and FIG. 12 (B) is a vertical view showing a short fuel rod which is a component of the short fuel assembly of FIG. 12 (A). It is sectional drawing.

The short fuel assembly 30 of this embodiment is shown in FIG.
As shown in FIG. 2A, a fuel bundle is formed by forming short fuel rods 31 having the same configuration in a triangular arrangement, and the fuel bundle is surrounded by a channel box 13.

As shown in FIG. 12 (B), the short fuel rod 31 is filled with the core fuel (short fuel) 1 at a position lower than the center of the cladding tube 9, and at the top of the core fuel 1. A core inner blanket 32 made of a mixture of a minor actinide such as neptunium, americium, curium and the like and depleted uranium is filled. The composition of the core inner blanket 32 is 80% of depleted uranium, 10% of neptunium, 9% of americium, and 1% of curium extracted from spent LWR spent fuel, each in the form of oxide. The lower portion of the core fuel 1 is filled with an outer core lower blanket 4 of depleted uranium.

The core of the present embodiment comprises a short fuel assembly 30 composed of short fuel rods 31 filled with such a core inner blanket 32 and a normal fuel rod 23 shown in FIGS. 3A and 3B. The normal fuel assembly 21 is loaded in the arrangement shown in FIG.

According to the core having the above-described structure, similarly to the first embodiment, the conversion ratio can be increased, and at the same time, the heat output can be increased. Actinide can be recycled effectively. In other words, minor actinides such as neptunium, americium, curium, etc. capture neutrons leaking from the reactor core and partially fission or Ρu2
38. These are also similar to depleted uranium,
The absorption cross section is larger than the fission cross section, and when the coolant void fraction is increased, the number of neutrons jumping from the reactor core is increased, thereby acting to keep the coolant void coefficient negative.
Therefore, it is possible to effectively recycle the minor actinide while keeping the coolant void coefficient negative.

Eighth Embodiment (FIG. 13, FIG. 1, FIG. 2, FIG.
4) The core of the present embodiment is a modification of the normal fuel assembly of the first embodiment, in which a minor actinide is added to the core fuel. FIG. 13A is a 1/4 horizontal cross-sectional view showing the configuration of a normal fuel assembly.
FIG. 13B is a vertical sectional view showing a normal fuel rod which is a component of the normal fuel assembly of FIG. 13A.

The normal fuel assembly 33 of this embodiment is shown in FIG.
As shown in (A), a fuel bundle is formed by forming the normal fuel rods 34 having the same configuration in a triangular arrangement, and the fuel bundle is surrounded by the channel box 13.

As shown in FIG. 13 (B), the normal fuel rod 34 is such that the core fuel 35 filled in the cladding tube 9 is obtained by adding a minor actinide such as neptunium, americium, curium or the like to plutonium. 35
Depleted uranium core blankets 3 and 4 are arranged above and below the core. The composition of the core fuel is 80% depleted uranium, 18% plutonium, 1% neptunium, 0.9% americium, 0.1% curium, each in oxide form.

The normal fuel assembly 33 composed of the normal fuel rods 34 and the short fuel assembly 6 composed of the short fuel rods 8 shown in FIG. 4 are arranged adjacent to each other in the state shown in FIG. The core is configured.

According to the core having such a configuration, as in the first embodiment, in addition to the effect of increasing the conversion ratio and increasing the heat output, the coolant can be efficiently burned while the minor actinide is efficiently burned. The void coefficient can be reduced. That is, since the neutron flux is higher in the core fuel than in the blanket, in the present embodiment in which the minor actinide is added to the core fuel 35, the combustion speed of the minor actinide can be improved as compared with the case where the minor actinide is added to the blanket. it can. However, in the core fuel, when the coolant void ratio increases, the neutron absorption of the minor actinide decreases, so that the reactivity increasing effect is large, and the coolant void coefficient is shifted to the more positive side. Therefore, in the present embodiment, the first
The coolant void coefficient can be reduced by combining the core fuel assembly and the short fuel assembly in which the depleted uranium is disposed on the upper part in the same manner as in the embodiment, so that the coolant void coefficient is reduced while efficiently burning the minor actinide. can do.

Ninth Embodiment (FIG. 14, FIGS. 1 to 3) The core of the present embodiment relates to the deformation of the fuel rod arrangement and the mantle shape of the fuel assembly.

That is, in each of the above-described embodiments, a square bundle is formed by forming the fuel rods in a triangular arrangement for all the fuel assemblies, and the channel box serving as the jacket is formed in a square cross section. It is not limited, and various modifications are possible.

For example, FIGS. 14A and 14B show an example in which the configurations of the normal fuel assembly 36 and the short fuel assembly 37 are respectively modified. In this example, FIG.
As shown in (1), the normal fuel assembly 36 has a configuration in which the normal fuel rods 7 are arranged in a square array to form a square bundle, and are surrounded by the channel box 13 having a square cross section. In addition, as shown in FIG.
Is a configuration in which short fuel rods 8 are arranged in a square array to form a square bundle, and surrounded by a channel box 13 having a square cross section. As the normal fuel rod 7 and the short fuel rod 8, for example, those of the first embodiment (FIGS. 3B and 4B) are applied. Even with such a configuration, it is needless to say that substantially the same effects as in the first embodiment can be obtained.

The configuration shown in FIGS. 14A and 14B can also be applied to the fuel assemblies of the second to eighth embodiments. In this case, for a configuration in which a blanket made of depleted uranium and a minor actinide is provided above the short fuel assembly, the blanket captures neutrons leaking from the reactor core, converts uranium to plutonium, and converts the minor actinide. At the same time, the coolant void coefficient can be made negative.

Although not shown, when the fuel rods are arranged in a triangular arrangement, the channel box serving as the jacket is formed in a hexagonal shape, whereby the densification can be effectively achieved. That is, as a preferable configuration, when the fuel rods are arranged in a triangular arrangement, the outer jacket is formed in a square or hexagonal shape, and when the fuel rods are arranged in a square arrangement, the outer jacket is formed in a square shape.

Tenth Embodiment (FIGS. 3, 4, and 15) This embodiment relates to an operation method for keeping the power distribution of the core flat. The core applied here is substantially the same as that of the first embodiment, and is composed of the normal fuel assembly 5 shown in FIG. 3 and the short fuel assembly 6 shown in FIG. A horizontal cross section (substantially the same as FIG. 2) will be described.

As shown in FIG. 15, in the core loaded with the normal fuel assembly 5 and the short fuel assembly 6, control members 38, 39, 40, and 41 are arranged between the fuel assemblies. These control members 38, 39, 40 and 41 are cruciform control rods inserted from the lower part of the core, and the power distribution of the core is kept flat by controlling the insertion depth.

In the present embodiment, the core is operated with a smaller insertion degree as the short fuel assemblies 6 are more included in the four fuel assemblies 5 and 6 around the control rod. That is,
A control part 38 that does not include the short fuel assembly 6 around it, a control part 39 that contains one short fuel assembly 6 around it, a control part 40 that contains two short fuel assemblies 6 around it, and a short fuel assembly around it The insertion degree is controlled as follows in a control unit 41 including three bodies 6.

Control dedicated 38> Control dedicated 39> Control dedicated 40> Control dedicated 41 Here, the core fuel height of the normal fuel assembly 5 is 1
00cm, core fuel height of short fuel assembly 6 is 50cm
It is. The degree of insertion of each of the control rods 38, 39, 40, 41 is specifically 100 cm, 75 cm, 50 cm, respectively.
cm and 25 cm.

The operation based on the above control method will be described below.

In general, in the short fuel assembly 6, the output of the depleted uranium blanket 2 in the upper part of the core fuel is lower than the output of the core fuel 1. Therefore, the axial output distribution is more distorted in a region where the proportion of the short fuel assemblies 6 is larger, and a large peak tends to appear on the lower side. On the other hand, when all the fuel assemblies around the control rod are the normal fuel assemblies 5, this distortion is minimized. It is desirable to insert the control rods during operation not only to suppress the excess reactivity but also to minimize the distortion of the axial power distribution in order to secure an appropriate thermal margin.

For this reason, the control rod in the region having a large output peak on the lower side is inserted shallowly so that the absorber portion is located only at the peak position, and in the region with little distortion, the control rod is inserted deep in the axial direction. It is effective to make the absorber function uniformly at any axial height. In the present embodiment, by controlling the insertion degree of the control rod as described above, the operation can be performed while keeping the output distribution flat.

In the above example, the degree of control insertion is divided into four stages, but the same effect can be obtained by dividing the degree into two stages as described below according to the degree of distortion of the output distribution.

Control rod 38 = Control rod 39> Control rod 40 = Control rod 41 Here, the degree of insertion of the control rods 38 and 39 is 100c.
m, and the degree of insertion of the control rods 40 and 41 is 50 cm.

The above method can be applied to the cores of the second to ninth embodiments in substantially the same manner.

Eleventh Embodiment (FIGS. 3, 4, and 16) In this embodiment, the fuel arrangement is changed in accordance with the operating state of the reactor, so that a negative coolant void coefficient can be easily secured. It is about the driving method. The core to be applied is the same as that of the first embodiment, and includes the normal fuel assembly 5 shown in FIG. 3 and the short fuel assembly 6 shown in FIG. Shown as a horizontal section.

As shown in FIG. 16, the positions where the short fuel assemblies 6 are loaded are divided into four regions: a region 近 near the center of the core, a region B outside the region 、, and core outer peripheral regions C and D. Can be The short fuel assembly 6 stays in the furnace for four cycles with a cycle length of one year.

In the present embodiment, all the short fuel assemblies 6 are loaded in the area の near the center of the core in the first cycle of the initial combustion, moved to the area B in the second cycle, and finally moved to the area C or After loading in the area D, it is allowed to stay up to the fourth cycle and then unloaded. If the fuel is taken out from the zone C when the combustion of a certain cycle is completed, the fuel to be moved to the core peripheral region next moves to the zone D. In this case, the burnup is the same in the same area,
It is different between the respective regions, and is highest at the periphery C and D around the core and lowest at the center A of the core.

An operation based on the above method will be described below.

As for the coolant void coefficient in the blanket, Pu accumulates as the combustion proceeds, and the negative void coefficient shifts to the positive side. Further, since neutron leakage is small in the center of the core, the absolute value of the negative void coefficient tends to be smaller in the center of the core than in the periphery of the core when the same fuel is used.

Therefore, in the present embodiment, when the burnup of the blanket is low, the blanket is loaded at the center of the core and moved to the periphery of the core as the burnup advances, so that the void coefficient associated with combustion shifts to the positive side. Therefore, a negative coolant void coefficient can be easily secured. Also,
While maintaining the same coolant void coefficient, the burnup of the short fuel assembly can be increased, and the fuel cycle cost can be reduced.

Twelfth Embodiment (FIGS. 2 and 17) In this embodiment, the Pu enrichment of the core fuel in the fuel assembly is set differently at the inner and outer peripheries to achieve a flat output within the fuel assembly. is there. 17A and 17B show the arrangement of fuel rods in the normal fuel assembly 42 and the short fuel assembly 43 applied in the present embodiment, respectively. In addition, the thing of FIG. 2 is applied as a core horizontal cross section.

As shown in FIG. 17A, the normal fuel assembly 42 is divided into an outermost fuel division 44 and other fuel divisions 45, and as shown in FIG. The aggregate 43 is similarly divided into the outermost fuel group 46 and the other fuel group 47.

The setting of the core fuel Pu enrichment of each fuel rod is performed by setting the fuel rods 45 other than the outermost periphery of the normal fuel assembly 42.
And 18% for the fuel rods 47 other than the outermost periphery of the short fuel assembly 43, and 12% for the outermost fuel rods 44 of the normal fuel assembly 42 and the outermost fuel rod 46 of the short fuel assembly 43. And That is, the concentration of fissile Pu in the outermost fuel rod is reduced.

According to such a configuration, the outermost fuel dedicated member 4 arranged at the periphery of the assembly having a low fuel rod filling density, a large coolant volume, and a large proportion of low energy neutrons is provided.
The output peaks generated at the fuel assemblies 4 and 46 are suppressed, and the output within the fuel assemblies 42 and 43 can be flattened. In addition,
The same effect can be obtained by using the blanket containing the parent substance such as depleted uranium for the outermost fuels 44 and 46.

Thirteenth Embodiment (FIGS. 17 and 18) In the thirteenth embodiment , the Pu enrichment of the core fuel in the fuel assembly is set differently at the inner and outer peripheries, and furthermore, the Pu enrichment is arranged at the outermost perimeter of the core. In this case, the Pu enrichment of the core fuel is made different between the different fuel assemblies and the other fuel assemblies, so that the output of the entire core is flattened.

FIG. 18 shows a 水平 horizontal section of the core. This core is divided into a normal fuel assembly 48 arranged at the outermost periphery of the core, and a normal fuel assembly 42 and a short fuel assembly 43 arranged at portions other than the outermost periphery of the core. The normal fuel assemblies 42 arranged in portions other than the outermost periphery of the core are the same as the normal fuel assemblies 42 (FIG. 17A) used in the twelfth embodiment. Similarly, the short fuel assembly 43 is the same as the short fuel assembly 43 (FIG. 17B) used in the twelfth embodiment. Another normal fuel assembly 48 arranged at the outermost periphery of the core has a lower Δu enrichment than the normal fuel assembly 42 described above. The specific Δu enrichment is as follows.

(1) Normal fuel assemblies 4 other than the outermost periphery of the core
2 and the short fuel assembly 43, the core fuel Pu enrichment was 12% at the outermost circumference in the assembly and 18 at the other outer circumferences, respectively.
%. (2) In the normal fuel assembly 48 at the outermost periphery of the core, the core fuel Pu enrichment is 6% at the outermost periphery of the assembly and 12 at the other outer periphery.
%.

The operation of the present embodiment set to such a degree of Pu enrichment will be described. In general, in the fuel assembly at the outermost periphery of the core, the neutron spectrum is softened by the coolant region outside the core, and the power density tends to be higher than that of the fuel assemblies other than the outermost periphery of the core. Therefore, in the present embodiment, Pu of the normal fuel assembly 48 arranged on the outermost periphery of the core is
The enrichment is reduced, the fissile material is reduced, and the power is reduced, so that the power of the entire core can be flattened.

[0122]

As described above, according to the present invention, high conversion and breeding can be achieved in a boiling water reactor, and not only can the utilization rate of uranium resources be greatly increased, but also the core height can be significantly reduced. The coolant void reactivity can be set to a negative value at the same size as the radial size of the conventional core without the necessity of doing so. In addition, the output of the assembly can be flattened at the same time as the fluctuation of the output of the assembly is suppressed, and the thermal margin is not impaired. Furthermore, not only plutonium recycling, but also minor actinides such as neptunium and americium with a long half-life generated from spent fuel can be recycled. The effect is achieved.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view showing a core configuration according to a first embodiment of the present invention.

FIG. 2 is a horizontal sectional view showing a core configuration according to the first embodiment of the present invention.

FIG. 3A is a horizontal sectional view of a normal fuel assembly constituting a core according to the first embodiment of the present invention, and FIG.
FIG. 4 is a vertical sectional view of the normal fuel rod shown in FIG.

FIG. 4A is a horizontal sectional view of a short fuel assembly constituting a core according to the first embodiment of the present invention, and FIG.
FIG. 3 is a vertical sectional view of the short fuel rod shown in FIG.

FIG. 5A is a horizontal sectional view of a short fuel assembly constituting a core according to a second embodiment of the present invention, and FIG.
FIG. 4C is a vertical sectional view of a first short fuel rod shown in FIG. 4C, and FIG. 4C is a vertical sectional view of a second short fuel rod shown in FIG.

FIG. 6A is a horizontal sectional view of a short fuel assembly constituting a core according to a third embodiment of the present invention, and FIG.
FIG. 4C is a vertical sectional view of a first short fuel rod shown in FIG. 4C, and FIG. 4C is a vertical sectional view of a second short fuel rod shown in FIG.

FIG. 7A is a horizontal sectional view of a normal fuel assembly constituting a core according to a fourth embodiment of the present invention, and FIG.
FIG. 4C is a vertical sectional view of a first normal fuel rod shown in FIG. 4C, and FIG. 4C is a vertical sectional view of a second normal fuel rod shown in FIG.

FIG. 8 is a horizontal sectional view of a core according to a fourth embodiment of the present invention.

FIG. 9A is a horizontal sectional view of a short fuel assembly constituting a core according to a fifth embodiment of the present invention, and FIG.
FIG. 3 is a vertical sectional view of the short fuel rod shown in FIG.

10A is a horizontal sectional view of a short fuel assembly constituting a core according to a sixth embodiment of the present invention, and FIG. 10B is a vertical sectional view of a first short fuel rod shown in FIG. 10A. , (C)
FIG. 3 is a vertical sectional view of a second short fuel rod shown in FIG.

FIG. 11 is a horizontal sectional view of a reactor core according to a sixth embodiment of the present invention.

12A is a horizontal sectional view of a short fuel assembly constituting a core according to a seventh embodiment of the present invention, and FIG. 12B is a vertical sectional view of the short fuel rod shown in FIG.

FIG. 13A is a horizontal sectional view of a normal fuel assembly constituting a core according to an eighth embodiment of the present invention, and FIG. 13B is a vertical sectional view of a normal fuel rod shown in FIG.

FIG. 14A is a horizontal sectional view of a normal fuel assembly constituting a core according to a ninth embodiment of the present invention, and FIG. 14B is a horizontal sectional view of a short fuel assembly constituting a core according to the ninth embodiment; .

FIG. 15 is a horizontal cross-sectional view of a core illustrating a control insertion depth of the core according to a tenth embodiment of the present invention.

FIG. 16 is a horizontal cross-sectional view of a core for describing a loading pattern of a short fuel assembly of a core according to an eleventh embodiment of the present invention.

FIG. 17A is a horizontal sectional view of a normal fuel assembly constituting a core according to a twelfth embodiment of the present invention, and FIG. 17B is a horizontal sectional view of a short fuel assembly constituting a core according to the twelfth embodiment; .

FIG. 18 is a horizontal sectional view showing a core according to a thirteenth embodiment of the present invention.

FIG. 19 is a diagram showing a relationship between a core height and a coolant void coefficient in a conventional boiling water type dense lattice fuel core.

20A is a vertical sectional view showing a conventional dense lattice fuel core, and FIG. 20B is a vertical sectional view showing a general lattice fuel core.

21A is a vertical sectional view showing a homogeneous core of a conventional Na-cooled FBR, FIG. 21B is a vertical sectional view showing a radially inhomogeneous core of the Na-cooled FBR, and FIG.
FIG. 3 is a vertical sectional view showing an axially inhomogeneous core of FIG.

[Explanation of symbols]

1, 1a, 1b core fuel 2, 5b core blanket 3, 2a, 2b core blanket (outer core upper blanket) 4, 3a, 3b core core blanket (outer core lower blanket) 4b radial blanket 5 normal fuel Assembly 6 Short fuel assembly 7 Normal fuel rod 8 Short fuel rod 9 Cladding tube 10 Coil spring 11 Upper end plug 12 Lower end plug 13 Channel box 14 Short fuel assembly 15 First short fuel dedicated 16 Second short fuel Dedicated 17 Short fuel assembly 18 First short fuel rod 19 Second short fuel rod 20 Zirconium hydride 21 Fuel assembly 22 First normal fuel dedicated 23 Second normal fuel rod 24 Fuel assembly 25 Fuel rod 26 Short fuel assembly 27 First short fuel rod 28 Second short fuel dedicated 29 Boron carbide 30 Short fuel assembly Body 31 Fuel rod 32 (Minor actinide added) core internal blanket 33 Normal fuel assembly 34 Fuel rod 35 (Minor actinide added) core fuel 36 Square-shaped normal fuel assembly 37 Square-shaped short fuel assembly 38, 39, 40 , 41 control rod 42 normal fuel assembly 43 short fuel assembly 44 outermost fuel allocation 45 outermost fuel allocation 46 outermost circumference fuel allocation 47 other outermost circumference fuel rod 48 outermost core normal fuel assembly 101 , 102, 201, 202, 203, 301, 3
02 core

Claims (13)

[Claims] 1. A light water-cooled reactor core in which fuel assemblies having plutonium-enriched core fuel are arranged adjacent to each other in a dense lattice, wherein a core fuel having a certain length or more is loaded as the fuel assemblies. A normal fuel assembly composed of bundled normal fuel rods and a blanket containing a core fuel shorter than the core fuel of the normal fuel assembly and a fuel parent material that absorbs neutrons and converts it to fissile material are loaded. A short fuel assembly formed by bundling short fuel bundles, thereby making the core radial and axial directions inhomogeneous, and reducing the core fuel length of the short fuel assembly to the core of the normal fuel assembly. A light water-cooled reactor core characterized in that the length is 50% or less of the fuel length. 2. The core of a light water-cooled reactor according to claim 1, wherein the blanket is disposed above or below the core fuel in the short fuel rods of the short fuel assembly.
In addition, the short fuel rod on which the blanket is loaded is a part of the fuel rod in the short fuel assembly, and the upper or lower part of the core fuel in the other short fuel rod is a coolant flow path. A light water cooled nuclear reactor core. 3. The core of a light water-cooled reactor according to claim 1, wherein a blanket of a part of the short fuel rods in the short fuel assembly has an element having a high neutron moderating ability and a small neutron absorption cross section. A light water-cooled reactor core, wherein the core is replaced by the compound of 4. A light water-cooled reactor core in which fuel assemblies having plutonium-enriched core fuel are arranged adjacent to each other in a dense lattice pattern, wherein fuel is disposed on upper and lower portions in the axial direction of the core fuel of the fuel assemblies. A blanket containing a parent substance is arranged, a part of the blanket is replaced by a compound of an element having a high neutron moderating ability and a small neutron absorption cross section, or a blanket with a core fuel of the fuel assembly. A light water-cooled reactor core, wherein a compound of an element having a high neutron moderating ability and a small neutron absorption cross-sectional area is arranged between the two. 5. The light water-cooled reactor core according to claim 3, wherein the compound of the element having a high neutron moderating ability and a small neutron absorption cross section is hydrogen, beryllium, lithium-7 or boron-11. A light water cooled nuclear reactor core, characterized by being a compound of the formula: 6. A light water-cooled reactor core in which fuel assemblies having plutonium-enriched core fuel are arranged adjacent to each other in a dense lattice, wherein a core fuel having a predetermined length or more is loaded as the fuel assemblies. A normal fuel assembly configured by bundling the normal fuel rods, and a short fuel assembly configured by bundling short fuel bundles loaded with a core fuel shorter than the core fuel of the normal fuel assembly, Boron carbide or europium oxide as a neutron-absorbing substance is disposed above the core fuel of the short fuel bundle disposed in the center portion of the short fuel bundle, and the core fuel of the short fuel bundle at a peripheral portion in the short fuel bundle The upper part is a coolant passage, and the reactor core is a light water cooled reactor. 7. The light water cooled reactor core according to claim 1, wherein the blanket is made of a mixture of minor actinide and depleted uranium or recovered uranium, or the core fuel is plutonium. A light water-cooled reactor core, characterized in that a minor actinide is added to the core. 8. The light water-cooled nuclear reactor core according to claim 7, wherein the minor actinide is neptunium, americium or curium. 9. The light water-cooled reactor core according to claim 1, wherein the fuel rods are arranged in a triangular array or a square array, and the fuel rods are arranged in a triangular array. A reactor core for a light water-cooled reactor, characterized in that a mantle portion surrounding a fuel rod is square or hexagonal, and when the fuel rods are arranged in a square, a mantle portion surrounding a plurality of fuel rods is square. 10. A method for operating a light water-cooled reactor having a core according to any one of claims 1 to 9,
When the control rod is inserted from the lower part of the core, the blanket in the short fuel assembly is arranged above the core fuel, and when the control rod is inserted from the upper part of the core, the blanket in the short fuel assembly is arranged below the core fuel, A method for operating a light water-cooled nuclear reactor, wherein the core is operated with a lower insertion degree for a control rod including a larger number of short fuel assemblies in the surrounding fuel assemblies. 11. A method for operating a light water-cooled reactor having a reactor core according to any one of claims 1 to 9,
A method for operating a light water-cooled reactor, comprising loading a short fuel assembly in the vicinity of the center of the core in the early stage of combustion and moving the fuel assembly to the periphery of the core as combustion proceeds. 12. The core of a light water-cooled reactor according to claim 1, wherein the concentration of fissile material in the outermost fuel in each fuel assembly is equal to that in the fuel assembly. A light water-cooled reactor core characterized by having a concentration lower than that of fissile material in other fuel rods. 13. The fuel core of a light water-cooled reactor according to claim 1, wherein the concentration of the fissile material in the fuel assembly disposed at the outermost periphery of the core is other than that of the other fuel assembly. A light water-cooled reactor core characterized by having a concentration lower than the concentration of fissile material.