JPH011997A - Core configuration of fast breeder reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to the core configuration of a fast breeder reactor, and in particular to a fast breeder reactor that uses a control rod assembly using boron carbide as a neutron absorbing material. Regarding the core configuration of the reactor.

(Conventional technology) A fast breeder reactor is a revolutionary nuclear reactor that generates more nuclear fuel than it consumes while generating electricity.In addition to developing high-performance fuel and control systems, it has realized a low-cost nuclear reactor. Research and development is underway to achieve this goal.

As an example of an IO fast breeder reactor, a block diagram of a tank-type fast breeder reactor is shown in FIG. In FIG. 5, a safety vessel 2 is installed on the outer circumferential side of a reactor vessel 1. The reactor vessel 1 is supported by a reactor building 4 via a support member 3.

The upper part of the reactor vessel 1 is closed by a roof slab 5. Additionally, a coolant 6 and a reactor core 7 are housed within the reactor vessel 1 . The reactor core 7 is composed of a plurality of fuel assemblies (not shown), one control rod assembly, etc., and also has 4 volumes of atoms (2!) via a core support mechanism 8. Supported by i1. Furthermore, a partition wall 9 is installed between the core support mechanism 8 and the reactor vessel 1, and this partition wall 9 divides the interior of the reactor vessel 1 into two vertically, with the upper part serving as an upper brenum 10 with zero temperature and low pressure. , the lower part is a low temperature, high pressure lower blennium 11. An intermediate heat exchanger 12 and a main circulation pump 13 are installed on the outer peripheral side of the core support mechanism 8, and an intermediate heat exchanger 12 and a main circulation pump 13 are installed on the outer peripheral side of the core support mechanism 8.
are arranged alternately at equal intervals in the circumferential direction. Further, the space between the liquid level 6A of the cooling member 6 and the lower end surface of the roof slab 5 is a cover gas space 14, and a cover gas 15 such as argon gas is contained in the cover gas space 14.
is filled. Further, a core upper mechanism 16 is installed directly above the reactor core 7 so as to penetrate through the roof slab 5 . This core upper mechanism 16G, tvllill rod drive R
hl (CRD) 171fig9 is located.

FIG. 6 is a cross-sectional view of the core 7 shown in FIG.

The reactor core 7 includes a fuel assembly 18 containing nuclear fuel such as uranium-235 and plutonium-239, and a 1, 11 control rod assembly 19 that controls the nuclear fission reaction of the nuclear fuel in the fuel assembly 18. A large number of υIII rod assemblies 19 are arranged, and the control rod assemblies 19 are designated by the symbol P in FIG.
shows a main reactor shutdown f,+1 I20 rod 19a which is used for the purpose of starting, shutting down, and controlling the output of the nuclear reactor. In addition, the control rods designated by the symbol S are control rods 19b for temporary outage, which are installed to provide redundancy and improve the safety of the reactor core.

FIG. 7 shows the fuel assembly 1 loaded into the reactor core 7 shown in FIG.
FIG. 8 is a sectional view showing an example of FIG. The fuel assembly 18 has a trumpet tube 20, and a large number of fuel bottles 2 are placed inside the trumpet tube 20.
1 is accommodated. This fuel bottle 21 contains uranium 235
, plutonium-239, or other fissile material 71 is provided.

In addition, a handling head 22 is provided at the upper part of the wrapper tube 20, which serves as a gripping part when the fuel assembly 18 is delivered to the reactor core 7 or when it is transferred. An entrance nozzle 23 is provided for fixed support.

FIG. 8 is a sectional view showing an example of the control rod assembly 19 loaded in the reactor core 7 shown in FIG. The control rod assembly has a lower guide tube 27, with a handling head 28 at the upper end of the lower guide tube 27 and a small diameter entrance nozzle 2 at the lower end.
9 are formed respectively.

A ti control rod 30 is provided in the lower guide tube 27 so as to be movable up and down, and the control rod 30 is constructed by housing a number of control elements 32 in a protection tube 31. The control element 32 includes a large number of neutron absorbing materials inside the cladding tube.

A lattice temporary presser 34 is provided on the upper part of the protective tube 31,
This grid temporary presser 34 is connected to the control rod drive mechanism 17 by a connecting rod 35. The control rod assembly 19 configured in this manner has a control rod 30 connected to an 11Jlil rod drive mechanism 17.
By inserting it into the reactor core 7 and using it, the core output,
It is designed to control core reactivity.

The neutron absorbing material provided in the control tII element 32 is made of a material containing an element having a large neutron absorption cross section. Usually, boron-10 (boron with a mass number of 10) is used as an element with a small neutron absorption cross section, and boron-10 (boron with a boron-10 content higher than that of natural boron) is used as a neutron absorbing material. Boron carbide (84C) containing boron (hereinafter referred to as concentrated boron) is used in the form of a pellet.

In the case of natural boron, the content of boron 10 is about 20%, and the other 80% is boron 11 (boron quality is number 11). Incidentally, the effective cross section determined from the core neutron spectrum of a typical fast breeder reactor is approximately 2.5 burns for the neutron absorption cross section of boron-10, and approximately 0.0 burn for the neutron absorption cross section of boron-11. 00004 burn. The above-mentioned concentrated boron has a boron-10 content concentrated to 20% or more, and has enhanced neutron absorption ability.

(Problems to be Solved by the Invention) As mentioned above, in order to produce concentrated boron, boron 1
Since it is necessary to concentrate boron 10 as waste, the content of boron 10 as a waste product is necessarily lower than the boron 10 content in natural boron.
(hereinafter referred to as depleted boron) is produced. The boron 10 content of M-loss boron is lower than the content (20%) of natural boron, and its neutron absorption capacity is low, so conventionally it was often disposed of as waste.
This was not favorable in terms of economy and effective use of boron resources.

On the other hand, although boron 10 has a high neutron absorption ability and is suitable as a neutron absorbing material, it generates a large amount of helium due to the (n, α) reaction, which causes swelling of boron carbide pellets. Swelling is a phenomenon in which helium is generated within a boron carbide pellet, and the boron carbide pellet swells due to the action of this helium. This swelling causes stress to occur due to contact between the boron carbide pellet and the cladding tube, which shortens the mechanical life of the control rod 30. Therefore, from the viewpoint of extending the life of the control rod, it is preferable that the content of boron 10 is low.

Furthermore, if the reduced-boron can be utilized as a neutron absorbing material used in cores with metal fuels, which have been attracting attention in recent years, it is possible to construct an inexpensive core that takes advantage of the characteristics of cores with metal fuels.

The present invention has been made in consideration of the above circumstances, and aims to effectively utilize boron resources, control the swelling of control rods to extend the life of the control rods, and also has the characteristics of a reactor core that uses metal fuel. The purpose of the present invention is to provide a core configuration for a fast breeder reactor that can construct an inexpensive core that takes advantage of the following.

[Structure of the invention]

(Means for solving the problem) The present invention provides a large number of fuel assemblies provided with nuclear fuel such as uranium, and a large number of control rod assemblies provided with a neutron absorbing material made of boron carbide. In the core configuration of a fast breeder reactor, the neutron absorbing material provided in at least some of the control rod assemblies of the large number of control rod assemblies is boron 1.
The content of boron carbide is lower than the content of boron 10 in natural boron.

(Function) In the core configuration of this fast breeder reactor, the control rod assembly is equipped with a neutron absorbing material, and this neutron absorbing material has boron carbide whose boron 10 content is lower than the boron 10 content in natural boron. Therefore, depleted boron, which has conventionally been difficult to use in nuclear reactors, can be used effectively for reactor control, and boron resources can be used effectively.

In addition, since the above-mentioned neutron absorbing material has boron carbide with a lower content of boron 10 than the content of boron 10 in natural boron, helium generation h1 is reduced due to the (n, α) reaction of boron 10, and swelling is reduced. The occurrence is suppressed by -11. Therefore, it is possible to extend the life of the control rod.

Furthermore, when metal fuel is used as the nuclear fuel in at least some of the many fuel assemblies, the surplus reactivity during cycle operation is lower than that in a core composed only of oxide fuel. Less is better, control ■
Even if the aggregate is provided with a neutron absorber made of boron carbide whose boron-10 content is lower than the boron-10 content in natural boron, a sufficient control effect is obtained. Therefore, it is possible to construct an inexpensive core that takes advantage of the useful features of a metal fuel core.

(Example) A first example of a core configuration of a fast breeder reactor according to the present invention will be described with reference to the drawings.

The reactor core 7 shown in FIG.
．． + 1 control rod assembly to the right.

At least some of the fuel assemblies 18 of the large number of fuel assemblies 18 loaded into the reactor core 7 contain metal fuel. Metal fuels include metals such as uranium (U) and plutonium (Pu), or alloys thereof, which are used as nuclear fuel in a metallic state without being oxidized. Metal fuels include uranium metal, uranium-plutonium alloy,
Possible materials include uranium-thorium (Th) alloy, plutonium-thorium alloy, and the like.

Gold i fuel has a very high swelling rate and a burnup of 1 to 2.
It has not been used much in the past due to the fact that only 1% atoI can be obtained, and the eutectic temperature between the fuel and cladding is low, causing problems in terms of fuel integrity.
With the prospect of solving these problems, its useful features are attracting attention.

One of the useful characteristics of metal fuels is that they have high propagation properties. The metal fuel is uranium dioxide (N02
), plutonium dioxide (PuO2), and other oxide fuels have a higher density of fissile atoms and a harder neutron spectrum, making it easier to construct a reactor core with a high breeding rate. In addition, metal fuel has a thermal conductivity more than 6 times that of oxide fuel, and its coexistence with sodium varies, so by filling sodium between the RI tube and the fuel, Heat transfer during this period can be increased.In addition, cores using metal fuel have excellent features such as high inherent safety and ease of reprocessing and molding of metal fuel.

As mentioned above, metal fuel has a high density of fissile atoms,
Since the neutron spectrum is hard, the internal conversion ratio is high (high multiplication property) and the combustion reactivity is low. therefore,
A reactor core containing metal fuel can have a lower surplus reactivity than a core containing only oxide fuel, and the surplus reactivity that must be controlled during power operation becomes smaller. Therefore, a neutron absorbing material used in a core having metal fuel may have a lower neutron absorption capacity than a neutron absorbing material used in a core consisting only of oxide fuel.

On the other hand, the neutron absorbing material provided in the backup shutdown control rods 19b among the large number of control body assemblies 19 loaded in the reactor core 7 in FIG. 1 is made of boron carbide containing natural boron or enriched boron.

This is because the backup shutdown control rod 19b is installed for the purpose of increasing the safety of the reactor core, so it is necessary to ensure a certain level of neutron absorption capacity.

Also, 1111 for main furnace shutdown! The neutron absorbing material provided in the Il rod 19a is constructed as shown in FIG. In FIG. 2, 11 indicates the total length of the neutron absorbing material, and ρ2 is, for example, about half the height of the core. And 1 is the difference between the total length 11 and N2. 12 of the above neutron absorbing materials
In the range of ρ3, boron carbide (B4C) whose content of boron 10 ("B) is lower than the content of boron 10 which is comparable to natural boron is disposed, and in the range of ρ3, boron carbide (B4C) has a lower content of boron 10 ("B) than the boron carbide mentioned above. Boron carbide with a high content of 10 is disposed.However, in FIG. 2, the lower side is the core insertion direction.

Boron carbide arranged in the range of ρ2 is boron 10
boron carbide disposed within the range of g3 includes any of natural boron, enriched boron, and depleted boron. These boron carbides are used, for example, in the form of pellets. Above 1
The reason why the range 2 is set to about half of the core height is because the main reactor shutdown control rod 19a is often inserted only into about half of the core height during operation.

In addition, boron carbide with a relatively high content of boron 10 is placed in the range 13 because boron carbide in this range is inserted into the reactor core 7 when the reactor is shut down, and has the function of shutting down the reactor. Therefore, it is necessary to ensure a certain level of neutron absorption capacity.

Next, the operation of the above embodiment will be explained.

Figure 3 shows the reactor core 7 containing metal fuel (hereinafter referred to as metal fuel core) and the reactor core 7 consisting only of uranium dioxide (UO2)'6 oxide fuel (hereinafter referred to as MOX core). FIG. 3 is a diagram showing a comparison of reactivity values. In this figure, relative values are shown in the case of /j, where the reactivity value is 1 when boron carbide containing natural boron is used in the MOX core. In other words, the vertical axis is the relative value, and the horizontal axis is the boron 10 content (%
).

As is clear from this figure, even if boron carbide with the same boron-10 content is used, the reactivity value is different when used in the MOX core and when used in the metal fuel core, and the metal fuel The reactivity value is slightly higher when used in the reactor core. In particular, the content of boron 10 is 0
%, the difference is large; the relative value for the MOX core is 0°095, while the relative value for the metal fuel core is 0.171. Although not shown, such a tendency exists to some extent even when the content of boron 10 is 20% or more.

In this way, the reactivity value of boron carbide in the metal fuel core is equal to the reactivity 1 of boron carbide in the MOX core.
iIli value (especially when the content of boron 10 is 2
0% or less), even if boron carbide with the same boron-10 content is used, it is more effective in controlling core power and core reactivity when used in a metal fuel core than when used in an MO× core. means high.

The reason why boron carbide has such a high reactivity value in a metal fuel core is due to the following effect.

When the boron-10 content of boron carbide is the same, the reactivity value is the same in the case of a metal fuel reactor core and the case of a MOX reactor core, if only the neutron absorption capacity is compared. The difference in reactivity values shown in FIG. 3 is due to the boron 11 ("B) content rather than the boron 10 content.

In other words, in the case of a MOX core, the neutron spectrum softens (
However, in the case of metal-fueled reactor cores, the neutron spectrum is inherently hard (neutron energy distribution is biased towards the higher side).

On the other hand, boron 11 has a moderating effect, and this moderating effect shifts the neutron spectrum to a softer side (hereinafter referred to as spectrum shift effect). This spectral shift effect occurs even in the case of MOX cores, as well as in metal fuel cores! , i occurs in the same way as b.

Generally, the relationship between neutron energy and the rate at which a fissile material absorbs neutrons and generates neutrons is shown in FIG. In this figure, the horizontal axis shows the energy of neutrons absorbed by fissile material (e.g. plutonium-239, uranium-235), and the vertical axis shows the ratio ν of the number of neutrons absorbed by the fissile material to the number of neutrons generated. (σ
"/σa)".

As shown in this figure, in the region 14 where the neutron energy is high (particularly the region of 1QKcV or more), the dependence of ν on the neutron energy is high. According to this relationship, when neutrons in a region with high energy are slowed down (when the energy of neutrons becomes low), the value of ν decreases, that is, the rate at which fissile material generates neutrons decreases, and the core reactivity increases. decreases.

In other words, the metal fuel core has a harder neutron spectrum than the MOX core (higher energy neutral -r's 7;'1 match), so when the neutron spectrum shifts to the softer side, the neutron energy - In FIa where 1- is high, a3 is strongly influenced by the characteristic that ν is highly dependent on neutron energy, and a current state occurs where the core reactivity is lower than that of the MOX core. Consequently, the reactivity value of boron carbide is slightly higher when used in metal fuel cores than when used in MOX cores.

In addition, in the case of boron carbide in which the J content of boron 10 is O, the neutron absorption capacity is very small, and the core reactivity decreases due to the spectral shift effect. In this case,
A decrease in the core reactivity due to the spectral effect of J3G is caused in the fuel area around the control rods 30.

In this embodiment, boron carbide, which has a boron-10 content lower than that of natural boron, is used as the neutron absorbing material provided in the main reactor shutdown control rod 19a, which is not conventionally used for nuclear reactors. It is now possible to effectively utilize depleted boron, which had a very limited scope, for nuclear reactor control, and boron resources can be used effectively.

In addition, since boron carbide is used as the neutron absorbing material, the content of boron 10 is lower than that of natural boron, so the helium generation h1 due to the (n, α) reaction of boron 10 is reduced, and the occurrence of swelling is reduced. suppressed. Therefore, it is possible to extend the life of the 1J control rod 30.

Furthermore, in this embodiment, all or some of the fuel assemblies 18 out of a large number of fuel assemblies 18 are equipped with metal fuel, so compared to the core 7 composed only of oxide fuel, the The surplus reactivity may be small, and therefore a sufficient control effect can be achieved even when boron carbide, which has a boron-10 content lower than that of natural boron, is used as a neutron absorbing material provided in the main reactor shutdown υ control rod 19a. is obtained. Therefore, it is possible to construct an inexpensive reactor core 7 that takes advantage of the useful features of a reactor core having metal fuel.

In this embodiment, boron carbide, which has a boron 10 content lower than that of natural boron, is disposed behind the neutron absorbing material provided in the main reactor shutdown control rod 19a, in the range of the suppression rod insertion side J2. be done. Therefore, even if the main reactor shutdown control rod 19a is inserted and operated during reactor operation, there is little effect on the power distribution of the reactor core 7, and stable operation of the reactor can be ensured. Furthermore, even if the main reactor shutdown control rod 19a moves up and down due to an earthquake or the like during operation of the reactor, stable operation of the reactor can be similarly ensured.

As described above, in the above embodiment, it is possible to effectively utilize boron resources and extend the life of the control rods 30, while constructing an inexpensive reactor core 7 that takes advantage of the characteristics of the reactor core 7 having metal fuel. This has the effect of ensuring stable operation of the nuclear reactor.

Next, a second embodiment of the present invention will be described.

In this embodiment, at least some a and II control rod assemblies 19 out of a large number of control rod assemblies 19 are alli
Among the many control elements 32 housed in the 2Il rod 30, boron 10 is attached to the control element 32 provided on the outer periphery of the control element 32.
A neutron absorbing material made of boron carbide having a lower content of boron 10 than the boron 10 content of natural boron is provided, while a control element 32 provided in the center thereof has a boron 10 content lower than that of boron carbide. A neutron absorbing material made of boron carbide, which has a high

This embodiment also has the same effects as the first embodiment.

Next, a third embodiment of the present invention will be described.

In general, the main reactor shutdown control rods 19a are one control rod (hereinafter referred to as a "starting rod") that is sequentially withdrawn when the reactor is started up, and the other is a control rod that is completely withdrawn during rated reactor operation (hereinafter referred to as a "starting rod"), and one that is inserted into the reactor core 7 to some extent even during rated reactor operation. , control rods that adjust output and reactivity during rated reactor operation (hereinafter referred to as operating rods)
Tonimin [noreru. In this embodiment, boron carbide, which has a lower boron-10 content than natural boron, is used as the neutron absorbing material provided in the operating rod. Also in this case, the neutron absorbing material is made only of boron carbide, which has a boron 10 content lower than that of natural boron.

In this embodiment, even if operating rods are inserted or withdrawn during rated reactor operation, there is little effect on the core power distribution, and stable rated reactor operation can be ensured. Also,
Even if the operating rod moves up and down due to an earthquake or the like during rated reactor operation, stable rated reactor operation can be maintained. In addition, the first fruit 1 has the same effect as the example.

In the embodiment described above, a large number of 27 control rods
Although we have described the case where boron carbide, which has a boron-10 content lower than that of natural boron, is used as a neutron absorbing material provided in some control rod assemblies 19 among the control rod assemblies 19, In a core system that takes advantage of the characteristics and has a small core surplus reactivity, all control rod assemblies 19 may be equipped with boron carbide in which the content of boron 10 is lower than that of natural boron. moreover,
A neutron absorbing material containing depleted boron is arranged in some of the many control elements 32 containing boron carbide in the control rod assembly 19, and the neutron absorbing material is made of a combination of depleted boron, natural boron, and copper wire boron. A neutron absorbing material can be used.

Although the above embodiment describes a metal fuel core, the present invention is not limited thereto, and even an IVI OX core can be used as a core in which the decrease in combustion reactivity during the operation cycle is relatively small. applicable.

Further, the present invention is not limited to tank-type fast breeder reactors, but can be widely applied to core configurations of fast breeder reactors such as loop-type fast breeder reactors.

(Effects of the Invention) In the core configuration of the fast breeder reactor according to the present invention, the neutron absorbing material provided in at least some of the control rod assemblies has a boron-10 content higher than that of natural boron. Since the boron carbide has a lower content of boron 10, boron carbide with a lower boron 10 content can be effectively used for nuclear reactor control, and boron resources can be effectively used.

Furthermore, by using boron carbide with a low boron-10 content, the present invention can suppress control rod swelling and extend the life of the control rods. This has the effect of making it possible to construct an inexpensive reactor core.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the core configuration of a fast breeder reactor according to the present invention, FIG. 2 is a configuration diagram of a neutron absorbing material provided in the above embodiment, and FIG. 3 is a diagram showing a core with metal fuel and oxidation Figure 4 shows the relationship between neutron energy and the rate at which fissile material absorbs neutrons and generates neutrons. The figure is a configuration diagram of a tank-type fast breeder reactor, Figure 6 is a cross-sectional view of a core not shown in Figure 5 but equipped in the fast breeder reactor, and Figure 7 is a fuel assembly loaded in the core shown in Figure 6. FIG. 8 is a sectional view showing the II fall rod assembly loaded into the core shown in FIG. 6. 7... Core, 18... Fuel assembly, 19... Control rod assembly. 7% 1st grade $22 (Tenda) Isu-containing rod 3 1 kill of the 4th child absorbed in the 1st year of life (e
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Claims (1)

[Claims] 1. In a core configuration of a fast breeder reactor having a large number of fuel assemblies equipped with nuclear fuel such as uranium and a large number of control rod assemblies equipped with a neutron absorbing material made of boron carbide. , the neutron absorbing material provided in at least some of the control rod assemblies of the large number of control rod assemblies includes boron carbide having a boron 10 content lower than that of natural boron. Core configuration of fast breeder reactor. 2. The neutron absorbing material provided in at least some of the control rod assemblies of the large number of control rod assemblies has a boron 10 content on the control rod insertion tip side that is higher than the boron 10 content in natural boron.
Boron carbide, which has a lower content than the boron carbide mentioned above, is disposed on the control rod insertion end side.
A core configuration of a fast breeder reactor according to claim 1, in which boron carbide having a high content of boron carbide is disposed. 3. At least some of the control rod assemblies out of the large number of control rod assemblies have a neutron absorbing material provided on the outer periphery of the control rod assemblies whose boron 10 content is higher than that of natural boron.
The fast breeder reactor according to claim 1, wherein the neutron absorbing material provided in the center thereof is made of boron carbide having a boron-10 content higher than that of the boron carbide. core configuration. 4. A patent claim in which the neutron absorbing material provided in some of the control rod assemblies among the large number of control rod assemblies is made only of boron carbide, the content of boron 10 being lower than the content of boron 10 in natural boron. The core configuration of the fast breeder reactor according to item 1. 5. The core configuration of a fast breeder reactor according to claim 1, wherein the nuclear fuel provided in at least some of the fuel assemblies of the plurality of fuel assemblies is made of a metal fuel such as metallic uranium.