Fast reactor core

Abstract

To provide a fast reactor core equipped with a gas expansion module, which can enhance the positive reactivity suppression effect even when assuming ULOF occurrence.SOLUTION: A fast reactor core equipped with a gas expansion module, a hollow tubular structure having one end open and the other end closed, is provided, the fast reactor core having a neutron absorber for absorbing neutrons or a neutron moderator for slowing down neutrons provided at a position adjacent to an outer side of the gas expansion module in a radial direction of the reactor core.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fast reactor core with a gas expansion module for improved safety against loss of liquid metal coolant flow events in a fast reactor. [Background technology]

[0002] Fast reactors, which use high-speed neutrons to sustain nuclear fission reactions, generally consist of a core installed inside a reactor vessel and a coolant (liquid metal coolant) filled inside the reactor vessel. The core of a fast reactor is loaded with multiple fuel assemblies. A fuel assembly has multiple bundled fuel rods and a wrapper tube that contains them. A fuel rod consists of nuclear fuel material and a cladding tube that encloses it.

[0003] The nuclear fuel material enclosed in the fuel rods of the fuel assembly can be in the form of oxide fuel, metal fuel, or nitride fuel. Nuclear fuel material generally includes depleted uranium (U-238) enriched with plutonium (Pu), and enriched uranium fuel, which contains a higher isotope ratio of fissile uranium (U-235) than found in natural sources.

[0004] The core of a fast reactor has a core fuel region containing fuel assemblies, a blanket fuel region surrounding the core fuel region, and a shield region surrounding the blanket fuel region. The blanket fuel region may be omitted. The shield region has a stainless steel reflector to improve the neutron economy of the core.

[0005] Control rods are used to start and shut down fast reactors and to adjust the reactor power. Each control rod has multiple neutron absorbing rods, each made of boron carbide (B4C) pellets sealed in a stainless steel cladding tube, and these neutron absorbing rods are housed in a ring-shaped control rod guide tube.

[0006] When the flow of primary coolant is lost due to a failure of the main circulation pump that circulates the coolant in the reactor vessel, and a failure to shut down the reactor using the control rods occurs (Unprotected Loss of Flow (ULOF)), an inconsistency occurs in the power / flow (P / F) ratio of the core fuel assemblies, and the coolant temperature near the core rises. In fast reactors that use liquid metal as the coolant, positive reactivity is generally inserted when the coolant temperature rises or when the coolant boils, resulting in an increase in power.

[0007] In order to avoid an increase in core power in the unlikely event of a ULOF as described above, a technique described in Patent Document 1 has been proposed. In Patent Document 1, a gas expansion module is arranged adjacent to the outside of the outermost fuel assembly in the core fuel region. During rated operation, the sodium liquid level in the gas expansion module is above the upper end of the core fuel region, and the scattering effect of sodium suppresses radial leakage of neutrons generated in the core fuel. On the other hand, if the coolant pressure at the sodium inlet at the bottom of the gas expansion module drops due to a failure of the main circulation pump or other reasons, the sodium liquid level in the gas expansion module drops below the bottom of the core fuel region, increasing the radial leakage of neutrons. This suppresses the positive reactivity during ULOF and prevents the core power from increasing. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-187361 Summary of the Invention [Problem to be solved by the invention]

[0009] The configuration described in Patent Document 1 is a configuration in which a reflector is disposed behind a gas expansion module in a direction from the center of the core toward the outside in the horizontal direction. Therefore, if the sodium liquid level in the gas expansion module drops due to a malfunction of the main circulation pump, the neutrons that leak in the radial direction of the core are scattered by the reflector, and some of them re-enter the core fuel region. This makes it difficult to reduce the power output of the core, and suppresses the neutron leakage effect of the gas expansion module.

[0010] The present invention has been made to solve such technical problems, and aims to provide a fast reactor core equipped with a gas expansion module that can increase the effect of suppressing positive reactivity even when the occurrence of ULOF is assumed.

[0011] The above and other objects of the present invention and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0012] The core of the fast reactor of the present invention is a core of a fast reactor in which a gas expansion module, which is a hollow tubular structure with one end closed and the other end open, is installed. The core of the fast reactor of the present invention is configured such that a neutron absorber that absorbs neutrons or a neutron moderator that reduces the speed of neutrons is installed at a position adjacent to the outside of the gas expansion module in the radial direction of the core, and the neutron absorber is a neutron absorber other than the control rods. The core of the first fast reactor of the present invention is further configured such that a neutron moderator is arranged adjacent to the outer side of the gas expansion module in the radial direction of the core, and the neutron absorber is arranged adjacent to the gas expansion module and the neutron moderator. The core of the second fast reactor of the present invention further has a radial blanket region between the core fuel region and the shield region, and a gas expansion module between the core fuel region and the radial blanket region, and the neutron absorber is configured to be adjacent to the radial outside of the gas expansion module. The core of the third fast reactor of the present invention is further configured such that the upper end of the neutron absorber is located at a position higher than the liquid level in the gas expansion module when the main circulation pump is started, and the lower end of the neutron absorber is located at a position lower than the liquid level in the gas expansion module when the main circulation pump is stopped. [Effects of the Invention]

[0013] According to the fast reactor core of the present invention described above, the neutron absorber or neutron moderator disposed adjacent to the outside of the gas expansion module can suppress scattering of neutrons leaked during operation of the gas expansion module into the core fuel region, thereby providing a fast reactor core that can increase the positive reactivity suppression effect of the gas expansion module during ULOF.

[0014] Problems, configurations, and effects other than those described above will become clear from the following description of the embodiments. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of a core of a fast reactor according to a first embodiment. [Figure 2] 2 is a longitudinal cross-sectional view of the core of the fast reactor shown in FIG. 1, including a gas expansion module and a neutron absorber. [Figure 3] 1 is a diagram illustrating an overall configuration of an example of a fast reactor nuclear power generation system to which an embodiment of a reactor core is applied. [Figure 4] FIG. 1 is a cross-sectional view of a core of a fast reactor according to a second embodiment. [Figure 5] FIG. 10 is a longitudinal sectional view of the core of a fast reactor according to a third embodiment. [Figure 6] FIG. 10 is a cross-sectional view of the core of a fast reactor according to a fourth embodiment. [Figure 7] FIG. 10 is a cross-sectional view of the core of the fast reactor of the fifth embodiment. [Figure 8] FIG. 10 is a longitudinal sectional view of the core of the fast reactor of the sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the embodiments and examples of the present invention will be described using text and drawings. However, the structures, materials, and other specific configurations shown in the present invention are not limited to the embodiments and examples described here, and can be appropriately combined and improved within the scope of the present invention. Furthermore, elements not directly related to the present invention are omitted from the illustrations.

[0017] The core of the fast reactor of the present invention is a core of a fast reactor in which a gas expansion module, which is a hollow tubular structure with one end closed and the other end open, is installed. The core of the fast reactor of the present invention is configured such that a neutron absorber that absorbs neutrons or a neutron moderator that reduces the speed of neutrons is installed at a position adjacent to the outside of the gas expansion module in the radial direction of the core.

[0018] According to the configuration of the fast reactor core of the present invention, the scattering of neutrons leaked during operation of the gas expansion module into the fuel region of the reactor core can be suppressed by the neutron absorber or neutron moderator disposed adjacent to the outside of the gas expansion module, thereby providing a fast reactor core that can increase the positive reactivity suppression effect of the gas expansion module during ULOF.

[0019] Furthermore, the core of the fast reactor of the present invention can reduce the number of gas expansion modules when compared to a conventional core that does not have a neutron absorber or neutron moderator, even if the reactivity of the required gas expansion modules is the same.

[0020] In the configuration of the fast reactor core, for example, boron carbide (B4C) can be used as the neutron absorber that absorbs neutrons. The neutron absorber can be configured by, for example, storing neutron absorbing rods in which boron carbide pellets are sealed in cladding tubes inside a trumpet tube.

[0021] In the core configuration of the fast reactor described above, neutron moderator materials that reduce the speed of neutrons include, for example, zirconium hydride, yttrium hydride, hafnium hydride, calcium hydride, certain hydrides, silicon carbide, beryllium, etc.

[0022] In the core of the fast reactor described above, the gas expansion modules may be arranged in a continuous line around the radially outer side of the core fuel region. In this configuration, even in a core in which gas expansion modules are installed in a continuous line around the radial outside of the core fuel region, the neutron absorber or neutron moderator can suppress the scattering of neutrons leaking when the gas expansion modules are operating into the core fuel region.

[0023] In the core of the above-mentioned fast reactor, a neutron moderator may be arranged adjacent to the outside of the gas expansion module in the radial direction of the core, and a neutron absorber may be arranged adjacent to the gas expansion module and the neutron moderator. In this configuration, a neutron absorber and a neutron moderator are arranged adjacent to the gas expansion module, which further enhances the effect of suppressing the scattering of neutrons leaking into the core fuel region when the gas expansion module is operating.

[0024] In the core of the above-mentioned fast reactor, a radial blanket region is provided between the core fuel region and the shield region, and a gas expansion module is provided between the core fuel region and the radial blanket region, and the neutron absorber can be configured to be adjacent to the radial outside of the gas expansion module. In this configuration, even in a core having a radial blanket region between the core fuel region and the shield region, the neutron absorber can suppress the scattering of neutrons leaked during operation of the gas expansion module into the core fuel region.

[0025] The core of the fast reactor may be configured such that a sodium plenum is installed above the core fuel region. In this configuration, even in a core in which a sodium plenum is installed above the core fuel region, the neutron absorber or neutron moderator can suppress the scattering of neutrons leaked during operation of the gas expansion module into the core fuel region.

[0026] In this configuration, the fuel core region may further include an inner fuel core region and an outer fuel core region, and the position of the upper end of the outer fuel core region may be higher than the position of the upper end of the inner fuel core region. Since the upper end of the outer core fuel zone is positioned higher than the upper end of the inner core fuel zone, the height of the entire outer core fuel zone is increased, which makes it possible to increase the power output of the outer core fuel zone. This makes it possible to reduce the difference in power output between the outer core fuel zone and the inner core fuel zone, or to make the power output of the outer core fuel zone equal to the power output of the inner core fuel zone.

[0027] In the core of the above-mentioned fast reactor, the upper end of the neutron absorber can be configured to be higher than the liquid level in the gas expansion module when the main circulation pump is started, and the lower end of the neutron absorber can be configured to be lower than the liquid level in the gas expansion module when the main circulation pump is stopped. In this configuration, the neutron absorber can be placed facing the gas space of the gas expansion module whether the main circulation pump is started or stopped, and neutrons that pass through the gas space can be absorbed by the neutron absorber.

[0028] In this configuration, the upper end of the neutron absorber may be positioned higher than the upper end of the gas space in the gas expansion module, so that the neutron absorber covers the entire gas space and can reliably absorb neutrons that pass through the gas space.

[0029] In the core of the fast reactor described above, a neutron absorber that absorbs neutrons may be installed above the gas space of the gas expansion module. In this configuration, a neutron absorber is also installed above the gas space of the gas expansion module, further enhancing the effect of suppressing the scattering of neutrons leaking into the core fuel region when the gas expansion module is operating. [Example]

[0030] Next, a specific example of a fast reactor core will be described.

[0031] (Configuration of fast reactor nuclear power generation system) First, prior to describing the embodiment of the reactor core, an example of a fast reactor nuclear power generation system to which the embodiment of the reactor core is applied will be described. FIG. 3 shows an overall configuration diagram of an example of a fast reactor nuclear power generation system to which the embodiment of the reactor core is applied.

[0032] The fast reactor nuclear power generation system 1 shown in FIG. 3 includes a reactor vessel 2, a reactor core 3, an intermediate heat exchanger 5, a primary main circulation pump 7a, a secondary main circulation pump 7b, and a steam generator 8. The fast reactor nuclear power generation system 1 also includes a main steam system piping 9 a, a high-pressure turbine 11 a, a low-pressure turbine 11 b, a generator 12, a condenser 13, a feedwater / condensate system piping 9 b, a feedwater pump 14, and a feedwater heater 15.

[0033] The reactor core 3 contains fissile material and is contained within the reactor vessel 2 . The intermediate heat exchanger 5 and the primary main circulation pump 7a are connected in sequence to the reactor vessel 2 via the primary cooling system piping 4a. The secondary main circulation pump 7b and the steam generator 8 are connected in turn to the intermediate heat exchanger 5 via the secondary cooling system piping 4b.

[0034] The main steam system piping 9a sends the steam generated in the steam generator 8 to the high-pressure turbine 11a and the low-pressure turbine 11b. The high-pressure turbine 11a and the low-pressure turbine 11b rotate the turbines by the steam sent thereto. The generator 12 is connected to the shaft of the low-pressure turbine 11b and also to the shaft of the high-pressure turbine 11a, although this is not shown. The condenser 13 condenses the steam that has passed through the high-pressure turbine 11a and the low-pressure turbine 11b back into water. The water supply / condensate system piping 9 b returns the water condensed in the condenser 13 to the steam generator 8 . The feedwater pump 14 and the feedwater heater 15 are connected to the feedwater / condensate system piping 9b downstream of the condenser 13.

[0035] The fast reactor nuclear power generation system 1 passes the primary coolant (for example, liquid sodium) heated in the reactor core 3 through the intermediate heat exchanger 5 to heat the secondary coolant (for example, liquid sodium). Furthermore, the fast reactor nuclear power generation system 1 passes secondary coolant through a steam generator 8 to generate steam in the main steam system piping 9a, and then directs this steam to a high-pressure turbine 11a and a low-pressure turbine 11b to generate electricity using a generator 12. The steam used for power generation is condensed into water in a condenser 13, similar to a boiling water reactor (BWR) or pressurized water reactor (PWR) light water reactor nuclear power generation system, and then passes through a feedwater pump 14 and a feedwater heater 15 to be heated and pressurized, respectively, and then supplied to the steam generator 8.

[0036] The core 3 is loaded with a plurality of core fuel assemblies, control rods, and a gas expansion module (GEM), which will be described later. The reactor vessel 2 containing the reactor core 3 is filled with primary coolant. The primary coolant enters the reactor core 3 from the bottom, rises along the core fuel assemblies, and flows into the intermediate heat exchanger 5 located outside the reactor vessel 2 via the primary cooling system piping 4a by the primary main circulation pump 7a. This forms a loop-type fast reactor.

[0037] Although this specification will be described using a loop-type fast reactor as an example, the present invention is not limited to this and can also be applied to a tank-type fast reactor in which the reactor vessel 2, the primary main circulation pump 7a, and the intermediate heat exchanger 5 are housed in a single tank.

[0038] (Example) Next, an example of a core of a fast reactor will be described.

[0039] Example 1 FIG. 1 is a cross-sectional view of a core of a fast reactor according to a first embodiment.

[0040] As shown in FIG. 1, the core 10 of the fast reactor of this embodiment is disposed within the reactor vessel 2 of the fast reactor shown in FIG. 3, and a core fuel region 21 and a reflector region 22 are disposed radially so as to surround the core fuel region 21. Furthermore, gas expansion modules (GEMs) 23 are installed at positions adjacent to the core fuel region 21 and the reflector region 22. Specifically, six gas expansion modules 23 are arranged, one near each of the six corners of the hexagonal core 10.

[0041] Control rods 25 are arranged in the core fuel region 21 and are used for starting up, shutting down, and adjusting the power output of the reactor. Each control rod 25 has multiple neutron absorbing rods, each made of boron carbide (B4C) pellets sealed in a stainless steel cladding tube, and these neutron absorbing rods are housed in a ring-shaped protective tube. The control rods 25 are configured as two independent systems: a main reactor shutdown system and a backup reactor shutdown system, but these are not distinguished in Figure 1.

[0042] Note that the cross-sectional view of the fast reactor core 10 in Figure 1 shows the arrangement relationship between multiple fuel assemblies loaded in the core fuel region 21 of the core 10 and multiple gas expansion modules 23, and for ease of explanation, the number of fuel assemblies loaded in the core fuel region 21 of the core 10 and the number of gas expansion modules 23 are shown in a simplified manner without any particular restrictions.

[0043] The gas expansion module (GEM) 23 is a hollow tubular structure with one end closed and the other end open, and its appearance is similar to the wrapper of the fuel assembly loaded in the core fuel region 21.

[0044] Furthermore, the core 10 of the fast reactor of this embodiment has a neutron absorber 24 that has the function of absorbing neutrons, located adjacent to the radially outer side of the gas expansion module 23, extending radially outward from the center of the core. The neutron absorber 24 has a plurality of neutron absorbing rods each made of boron carbide (B4C) pellets sealed in a stainless steel cladding tube, and these neutron absorbing rods are housed in a wrapper tube similar to the fuel assemblies loaded in the core fuel region 21.

[0045] FIG. 2 is a longitudinal cross-sectional view of the core 10 of the fast reactor shown in FIG. 1, including the gas expansion module 23 and the neutron absorber 24. An area 101 on the left side of FIG. 2 shows a state in which the flow rate of the primary main circulation pump 7a shown in FIG. 3 is at rated operation. Moreover, the area 102 on the right side of Figure 2 shows the state when an accident occurs in which a loss of coolant flow due to the stoppage of the primary main circulation pump 7a due to a loss of power, etc., and a scram failure occur at the same time (the aforementioned ULOF).

[0046] 2, the gas expansion module 23 is configured by vertically arranging a hollow tubular structure with one closed end and the other open, with the upper end closed and the lower end open. The hollow space of the tubular structure contains a coolant sodium (Na) 26 and an inert gas argon (Ar) 27. The coolant sodium (Na) 26 is liquid and is accessible to the tubular structure of the gas expansion module 23 at its open lower end. The inert gas argon (Ar) 27 is contained between the liquid surface of the coolant sodium (Na) 26 and the closed upper end of the tubular structure of the gas expansion module 23 .

[0047] As shown in FIG. 2, a stainless steel neutron shield 28 is disposed on the top of the gas expansion module 23, that is, on the upper end of the tubular structure of the gas expansion module 23. The neutron shield 28 has the property of blocking neutrons and reducing leakage to the outside.

[0048] 2, when the flow rate of the primary main circulation pump 7a is in rated operation, the pressure of the coolant sodium (Na) 26 at the inlet (lower end) of the gas expansion module 23 increases. Therefore, the liquid level of the coolant sodium 26 in the gas expansion module 23 is higher than the upper end of the core fuel of the core fuel assemblies loaded in the core fuel region 21. At this time, the coolant sodium 26 in the gas expansion module 23 acts as a reflector due to the neutron scattering effect, and the amount of neutron leakage from the reactor core 10 is kept small.

[0049] On the other hand, during ULOF, the power / flow rate (P / F) ratio of the fuel assemblies becomes inconsistent, resulting in an increase in the temperature of the sodium coolant 26 and a decrease in its density, which in turn reduces the pressure of the sodium coolant 26 at the inlet of the gas expansion module 23. Therefore, as shown in region 102 on the right side of FIG. 2, the liquid level of the sodium coolant 26 in the gas expansion module 23 becomes lower than the lower end of the core fuel of the core fuel assemblies loaded in the core fuel region 21. At this time, the gas expansion module 23 is filled by the expansion of the inert gas argon (Ar) 27, but the density of the inert gas argon 27 is low, so the neutron scattering effect is reduced. Therefore, the amount of neutron leakage from the reactor core 10 increases.

[0050] From the above, during ULOF, negative applied reactivity is brought about in the reactor core 10 by the gas expansion module 23 . Therefore, even if a positive applied reactivity is brought about in the core 10 due to a decrease in the flow rate of the coolant sodium 26 in the core fuel assemblies in the core fuel region 21 during ULOF, an increase in the power of the core 10 is suppressed by the negative applied reactivity caused by the gas expansion module 23. In other words, the safety of the core 10 during ULOF is improved.

[0051] Furthermore, in the core 10 of this embodiment, neutron absorbers 24 that absorb neutrons are disposed radially outside the gas expansion modules 23, thereby increasing the number of neutrons captured by the gas expansion modules 23 that leak from the core fuel region 21 during ULOF. Therefore, compared to a conventional core that has the gas expansion modules 23 but does not have neutron absorbers disposed radially outside thereof, scattering of neutrons into the core fuel region 21 is suppressed when the liquid level of the sodium coolant 26 in the gas expansion modules 23 drops, and the net amount of neutron leakage increases.

[0052] Also, as shown in Figure 2, the upper end of the neutron absorber 24 is located at a position higher than the liquid level in the gas expansion module 23 when the main circulation pump is started 101, and the lower end of the neutron absorber 24 is located at a position lower than the liquid level in the gas expansion module 23 when the main circulation pump is stopped 102. This allows the neutron absorber 24 to face the gas space of the inert gas argon 27, whether the main circulation pump is started 101 or stopped 102, and neutrons that pass through the gas space can be absorbed by the neutron absorber 24.

[0053] Furthermore, as shown in FIG. 2, the upper end of the neutron absorber 24 is located higher than the upper end of the gas space of the inert gas argon 27 in the gas expansion module 23 . This allows the neutron absorber 24 to cover the entire gas space, ensuring that neutrons that have passed through the gas space are absorbed.

[0054] As described above, according to this embodiment, by arranging the neutron absorber 24 at a position adjacent to the radially outer side of the gas expansion module 23, a fast reactor can be realized that can increase the absolute value of the negative applied reactivity by the gas expansion module 23, even in the event of ULOF.

[0055] 1, one neutron absorber 24 is disposed radially outside the gas expansion module 23, but it is also possible to replace the two neutron reflectors 22 adjacent to the gas expansion module 23 with neutron absorbers 24. In this case, the absolute value of the negative applied reactivity by the gas expansion module 23 is further improved. In addition, when the coolant in the core boils or the coolant density decreases, the net amount of neutron leakage increases.

[0056] Furthermore, if a neutron moderator that reduces the velocity of neutrons is used instead of the neutron absorber 24, the absolute value of the negative applied reactivity by the gas expansion module 23 is further improved. As the material for this neutron moderator, the above-mentioned zirconium hydride, yttrium hydride, hafnium hydride, calcium hydride, certain hydrides, silicon carbide, beryllium, etc. can be used.

[0057] Example 2 Next, a core of a fast reactor according to a second embodiment will be described. FIG. 4 shows a cross-sectional view of a core 20 of a fast reactor according to a second embodiment.

[0058] In the fast reactor core 10 of Example 1, gas expansion modules 23 are discretely loaded outside the core fuel region 21, and neutron absorbers 24 are arranged radially outside the gas expansion modules 23. In contrast, the core 20 of this embodiment differs from the core 10 of Example 1 in that gas expansion modules 23 are loaded circumferentially to surround the core fuel region 21, and neutron absorbers 24 are arranged circumferentially to surround the gas expansion modules 23. In FIG. 4, the same components as those in the core 10 of the first embodiment are denoted by the same reference numerals.

[0059] The core 20 of this embodiment is disposed in the reactor vessel 2 of the fast reactor shown in Fig. 3. The core 20 of this embodiment has, in the radial direction, a core fuel region 21, a gas expansion module (GEM) 23 surrounding the core fuel region 21, and a neutron absorber 24 surrounding the gas expansion module (GEM) 23, as shown in Fig. 4.

[0060] In the core 20 of this embodiment, the gas expansion modules 23 are arranged to the maximum extent possible so as to surround the core fuel region 21. This maximizes the number of neutrons leaking from the gas expansion modules 23 during ULOF, and the leaked neutrons can be absorbed by the neutron absorbers 24 arranged without gaps, thereby further enhancing the same effects as in embodiment 1. In addition, the net amount of neutron leakage increases when the coolant in the core boils or when the coolant density decreases.

[0061] From the viewpoint of neutron shielding, a neutron shield made of stainless steel or boron carbide (B4C) may be further disposed radially outside the neutron absorber 24, although this is not shown.

[0062] Furthermore, a neutron moderator may be disposed in place of the neutron absorber 24 in Fig. 4. In this case, the absolute value of the negative applied reactivity by the gas expansion module 23 is further improved.

[0063] Example 3 Next, a core of a fast reactor according to a third embodiment will be described. FIG. 5 shows a longitudinal cross-sectional view of a core 30 (including gas expansion modules and neutron absorbers) of a fast reactor according to a third embodiment.

[0064] The core 10 of Example 1 had a stainless steel neutron shield 28 at the top above the gas space of the gas expansion module 23 . In contrast, the core 30 of this embodiment differs from the core 10 of the first embodiment in that it has a neutron absorber 29 for absorbing neutrons at the top above the gas space of the gas expansion module 23 . In FIG. 5, the same components as those in the core 10 of the first embodiment are denoted by the same reference numerals.

[0065] The neutron absorber 29 shown in Figure 5 can be made of the same material as the neutron absorber 24 arranged radially outside the gas expansion module 23, or other materials having neutron absorbing properties.

[0066] According to this embodiment, a neutron absorber 29 is provided above the gas space of the gas expansion module 23. As a result, the neutron absorber 29 absorbs scattered neutrons, thereby reducing the number of neutrons scattered in the core fuel region 21, and thus it is possible to further enhance the same effect as the core 10 of the first embodiment.

[0067] It should be noted that a neutron moderator may be disposed in place of the neutron absorber 29 in FIG. 5, in which case the absolute value of the negative applied reactivity by the gas expansion module is further improved.

[0068] Example 4 Next, a core of a fast reactor according to a fourth embodiment will be described. FIG. 6 shows a cross-sectional view of a core 40 of a fast reactor according to a fourth embodiment.

[0069] In the core 10 of Example 1, a reflector region 22 is arranged in contact with the outer side of the core fuel region 21 . In contrast, the core 40 of this embodiment has a blanket region 31 arranged between the core fuel region 21 and the reflector region 22, the reflector region 22 arranged in contact with the outside of the neutron absorber 24, and the blanket region 31 arranged next to the neutron absorber 24. In FIG. 6, the same components as those in the core 10 of the first embodiment are denoted by the same reference numerals.

[0070] As shown in FIG. 6, the core 40 of this embodiment has a blanket region 31 disposed between the core fuel region 21 and the reflector region 22. The blanket region 31 may be configured to be loaded with blanket fuel assemblies having a plurality of fuel rods filled with a plurality of uranium dioxide pellets made from depleted uranium, as described in, for example,

[0005] of the aforementioned Patent Document 1.

[0071] In the core 40 of this embodiment, a blanket region 31 is disposed between the core fuel region 21 and the reflector region 22. This allows depleted uranium or the like to be used as fuel in the blanket region 31. Due to the configuration of the core 40 of this embodiment, even in a core 40 in which a blanket region 31 is provided outside the core fuel region 21, a neutron absorber 24 is arranged radially outside the gas expansion module 23, thereby achieving the same effect as the core 10 of embodiment 1.

[0072] Moreover, a neutron moderator may be disposed in place of the neutron absorber 24 in Fig. 6. In this case, the absolute value of the negative applied reactivity by the gas expansion module 23 is further improved.

[0073] Example 5 Next, a core of a fast reactor according to a fifth embodiment will be described. FIG. 7 shows a cross-sectional view of a core 50 of a fast reactor according to a fifth embodiment.

[0074] In the core 10 of Example 1, one neutron absorber 24 was arranged radially outside the gas expansion module 23 . In contrast to this, the reactor core 50 of this embodiment has two neutron absorbers 24 and one neutron moderator 32 arranged outside the gas expansion module 23 . In FIG. 7, the same components as those in the core 10 of the first embodiment are denoted by the same reference numerals.

[0075] 7, the core 50 of this embodiment has one neutron moderator 32 disposed radially outside the gas expansion module 23, and a neutron absorber 24 disposed outside the gas expansion module 23 and in contact with the gas expansion module 23 and the neutron moderator 32. That is, the core 50 of this embodiment uses both the neutron absorber 24 and the neutron moderator 32.

[0076] The neutron moderator 32 may be made of zirconium hydride, yttrium hydride, hafnium hydride, calcium hydride, certain hydrides, silicon carbide, beryllium, or other materials.

[0077] In the core 50 of this embodiment, the neutron absorber 24 and the neutron moderator 32 are arranged outside the core fuel region 21, and the neutron absorber 24 and the neutron moderator 32 are used in combination. This makes it possible to further improve the absolute value of the negative applied reactivity by the gas expansion module 23 compared to the case where the neutron absorber 24 is used alone.

[0078] Example 6 Next, a core of a fast reactor according to a sixth embodiment will be described. FIG. 8 shows a longitudinal cross-sectional view of a core 60 (including gas expansion modules and neutron absorbers) of a fast reactor according to a sixth embodiment.

[0079] The core 10 of Example 1 had a core fuel region 21 of a fixed height. In contrast to this, in the core 60 of this embodiment, the core fuel region 21 is divided into an inner core fuel region 21A and an outer core fuel region 21B which are at different heights, and further, a sodium plenum 33 is arranged above the core fuel region 21. In FIG. 8, the same components as those in the core 10 of the first embodiment are denoted by the same reference numerals.

[0080] As shown in Figure 8, the core 60 of this embodiment divides the core fuel region 21 into an inner core fuel region 21A and an outer core fuel region 21B, and further, the outer core fuel region 21B has an upper end positioned higher than that of the inner core fuel region 21A.

[0081] In the core 10 of the first embodiment, as shown in FIG. 2, the core fuel region 21 has a constant height, so that the power is smaller outside the core fuel region 21 than inside. In contrast, in the core 60 of this embodiment, the outer core fuel zone 21B has an upper end positioned higher than the inner core fuel zone 21A, and the lower ends are at the same height, so the overall height of the outer core fuel zone 21B is increased, and the output of the outer core fuel zone 21B can be increased. This makes it possible to reduce the difference in output between the outer core fuel zone 21B and the inner core fuel zone 21A, or to make the output of the outer core fuel zone 21B equivalent to the output of the inner core fuel zone 21A.

[0082] The sodium plenum 33 may be configured, for example, as described in the aforementioned Patent Document 1, in an upper portion of the fuel assembly where there are no fuel rod bundles, to be compartmentalized by a duct pipe and to contain the coolant sodium.

[0083] The core 60 of this embodiment, like the core 10 of the first embodiment, has the neutron absorbers 24 arranged radially outside the gas expansion modules 23, and therefore has the same effects as the core 10 of the first embodiment. Furthermore, in the core 60 of this embodiment, the outer core fuel region 21b has an upper end positioned higher than the inner core fuel region 21a, which increases the overall height of the outer core fuel region 21B and enables the power output of the outer core fuel region 21B to be increased. Furthermore, the core 60 of this embodiment is provided with the sodium plenum 33 above the core fuel region 21 (21A, 21B), thereby making it possible to reduce the void reactivity of sodium.

[0084] It should be noted that the present invention is not limited to the above-described embodiments and examples, and includes various modifications. For example, the above-described embodiments and examples have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the described configurations. [Explanation of symbols]

[0085] 1...fast reactor nuclear power generation system, 2...reactor vessel, 3, 10, 20, 30, 40, 50, 60...core, 4a...primary cooling system piping, 4b...secondary cooling system piping, 5...intermediate heat exchanger, 7a...primary main circulation pump, 7b...secondary main circulation pump, 8...steam generator, 9a...main steam system piping, 9b...water supply / condensate system piping, 11a...high-pressure turbine, 11b...low-pressure turbine, 12...generator, 13...condenser, 14...feedwater pump, 15...feedwater heater, 21...core fuel area, 21A...inner core fuel area, 21B...outer core fuel area, 22...reflector area, 23...gas expansion module, 24, 29...neutron absorber, 25...control rod, 26...coolant sodium, 27...inert gas argon, 28...neutron shield, 31...blanket area, 32...neutron moderator, 33...sodium plenum

Claims

1. A core of a fast reactor having a gas expansion module installed, the gas expansion module being a hollow tubular structure having one closed end and the other open end, a neutron absorber that absorbs neutrons or a neutron moderator that reduces the velocity of neutrons is installed at a position adjacent to an outer side of the gas expansion module in the radial direction of the reactor core; The neutron absorber is a neutron absorber other than a control rod, The neutron moderator is disposed adjacent to the outer side of the gas expansion module in the radial direction of the core, and the neutron absorber is disposed adjacent to the gas expansion module and the neutron moderator. Fast reactor core.

2. A core of a fast reactor having a gas expansion module installed, the gas expansion module being a hollow tubular structure having one closed end and the other open end, a neutron absorber that absorbs neutrons or a neutron moderator that reduces the velocity of neutrons is installed at a position adjacent to an outer side of the gas expansion module in the radial direction of the reactor core; a radial blanket region between a core fuel region and a shield region, the gas expansion module between the core fuel region and the radial blanket region, the neutron absorber being adjacent to the radial outer side of the gas expansion module; The neutron absorber is a neutron absorber other than a control rod. Fast reactor core.

3. A core of a fast reactor having a gas expansion module installed, the gas expansion module being a hollow tubular structure having one closed end and the other open end, a neutron absorber that absorbs neutrons or a neutron moderator that reduces the velocity of neutrons is installed at a position adjacent to an outer side of the gas expansion module in the radial direction of the reactor core; The neutron absorber is a neutron absorber other than a control rod, The upper end of the neutron absorber is located at a position higher than the liquid level in the gas expansion module when the main circulation pump is started, and the lower end of the neutron absorber is located at a position lower than the liquid level in the gas expansion module when the main circulation pump is stopped. Fast reactor core.

4. A core of a fast reactor as described in claim 3, wherein the upper end of the neutron absorber is located higher than the upper end of the gas space within the gas expansion module.

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