JP6579990B2 - Fast reactor core - Google Patents

Description

  The present invention relates to a core of a fast reactor in which a gas expansion module (GEM: GAS Expansion Module) is loaded on the core.

  Regarding the fuel assembly and core of the fast reactor, as described in Non-Patent Document 1, in the fast breeder reactor, the core is disposed in the reactor vessel, and liquid sodium as a coolant is placed in the reactor vessel. Is filled. The fuel assembly loaded in the core includes a plurality of fuel rods encapsulating plutonium-enriched depleted uranium (U-238), a trumpet tube surrounding the bundled fuel rods, and lower ends of these fuel rods. , And an entrance nozzle for supporting the neutron shield located below the fuel rod, and a coolant outflow portion located above the fuel rod.

The fast breeder reactor core has a core fuel region having an inner core region and an outer core region surrounding the inner core region, a blanket fuel region surrounding the core fuel region, and a shield region surrounding the blanket region. In the case of a standard homogeneous core, the Pu enrichment of the fuel assemblies loaded in the outer core region is higher than the Pu enrichment of the fuel assemblies loaded in the inner core region. As a result, the power distribution in the radial direction of the core is flattened.
Examples of the form of nuclear fuel material stored in each fuel rod of the fuel assembly include metal fuel, nitride fuel, and oxide fuel. Of these, oxide fuels have the greatest track record.

  A mixed oxide fuel obtained by mixing the oxides of Pu and depleted uranium, that is, a pellet of MOX fuel, is filled in a fuel rod at a height of about 80 to 100 cm in the center in the axial direction. Further, in the fuel rod, axial blanket regions filled with a plurality of uranium dioxide pellets made of deteriorated uranium are respectively arranged above and below the MOX fuel filling region. The inner core fuel assembly loaded in the inner core region and the outer core fuel assembly loaded in the outer core region thus have a plurality of fuel rods filled with a plurality of pellets of MOX fuel. The Pu enrichment of the outer core fuel assembly is higher than that of the inner core fuel assembly.

  A blanket fuel assembly having a plurality of fuel rods filled with a plurality of uranium dioxide pellets made of deteriorated uranium is loaded in the blanket fuel region surrounding the core fuel region. Among the neutrons generated by the fission reaction generated in the fuel assembly loaded in the core fuel region, the neutrons leaking from the core fuel region are U-238 in each fuel rod of the blanket fuel assembly loaded in the blanket fuel region. To be absorbed. As a result, Pu-239 which is a fissile nuclide is newly generated in each fuel rod of the blanket fuel assembly.

Control rods are used when the fast breeder reactor is started, stopped, and when the reactor power is adjusted. The control rod has a plurality of neutron absorption rods in which boron carbide (B ₄ C) pellets are enclosed in a stainless steel cladding tube, and these neutron absorption rods are housed in a circular tube-shaped protective tube. . The control rod has two independent systems, the main reactor shutdown system and the after-furnace reactor shutdown system, and the fast breeder reactor can be stopped urgently by either one of the main reactor shutdown system or the after-furnace reactor shutdown system. .

  In general, the void reactivity in the core region of the fast reactor is positive, and assuming an accident (ULOF: Unprotected Loss of Flow Accident) that superimposes the loss of coolant flow rate due to the failure of the main circulation pump and the failure of the scram, When a mismatch occurs in the power / flow rate (P / F) ratio of the fuel assembly and the temperature of sodium (Na) as the coolant rises, positive reactivity is applied and the power of the core increases. In order to avoid such an increase in the output of the core at the time of ULOF, a technique described in Patent Document 1 has been proposed. In Patent Document 1, a gas expansion module (GEM) is disposed adjacent to the outside of the outermost peripheral fuel assembly in the outer core region in a homogeneous core with a Pu enrichment region of 2 in the radial direction. During rated operation, the sodium (Na) liquid level in the gas expansion module (GEM) is above the upper end of the core fuel region, and the scattering effect of sodium (Na) suppresses leakage of neutrons generated in the core fuel in the radial direction. Is done. On the other hand, when the pressure of the coolant at the sodium (Na) inlet at the lower end of the gas expansion module (GEM) is reduced due to a failure of the main circulation pump, the liquid level of sodium (Na) is lower than the lower end of the core fuel region. Lowering, increasing neutron radial leakage. As a result, application of positive reactivity during ULOF is suppressed, and an increase in power output of the core is suppressed.

JP-A-10-153777

Naohiro Hirakawa and Tomohiko Iwasaki, “Introduction to Reactor Physics”, Tohoku University Press, pp. 279-286, October 30, 2003

  However, in the configuration described in Patent Document 1, the gas expansion module (GEM) is arranged adjacent to the outside of the outermost peripheral fuel assembly in the outer core region, and adjacent to the gas expansion module (GEM). The plurality of outermost peripheral fuel assemblies having different Pu enrichment levels. Therefore, in the core configuration of the fast reactor described in Patent Document 1, the gradient of the neutron flux distribution in the radial direction (radial direction) in the vicinity of the gas expansion module (GEM) becomes small, and it is difficult to increase the neutron leakage effect. Become.

  Therefore, the present invention increases the gradient of the neutron flux distribution in the radial direction in the vicinity of the gas expansion module (GEM), so that the negative applied reaction by the gas expansion module (GEM) is assumed even when the generation of ULOF is assumed. A fast reactor core capable of increasing the absolute value of the degree is provided.

In order to solve the above problems, 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 having one end closed and the other end opened, is loaded on the core. The plutonium enrichment of the fuel assembly adjacent to the gas expansion module is higher than the plutonium enrichment of the fuel assembly not adjacent to the gas expansion module.
The core of the fast reactor according to the present invention is a core of a fast reactor in which a gas expansion module, which is a hollow tubular structure having one end closed and the other end opened, is loaded on the core. A plurality of fuel assemblies adjacent to the module have the same plutonium enrichment, and are characterized by being the highest among the plurality of fuel assemblies loaded in the core.

According to the present invention, the negative application by the gas expansion module (GEM) can be achieved even when the occurrence of ULOF is assumed by increasing the gradient of the radial neutron flux distribution in the vicinity of the gas expansion module (GEM). A fast reactor core capable of increasing the absolute value of reactivity can be provided.
Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a cross-sectional view of a core of a fast reactor according to an embodiment 1 of the present invention. It is a longitudinal cross-sectional view of the core of the fast reactor shown in FIG. 1 is an overall configuration diagram of a fast reactor nuclear power generation system having a fast reactor core according to an embodiment of the present invention. It is a figure which shows the relationship between the core radial direction position and neutron flux in the 1/2 area | region of the longitudinal cross-section of the core of a fast reactor. It is a transverse cross section of the core of the fast reactor of Example 2 concerning other examples of the present invention. It is a transverse cross section of the core of the fast reactor of Example 3 concerning other examples of the present invention. It is a longitudinal cross-sectional view of the core of the fast reactor of Example 4 which concerns on the other Example of this invention.

  FIG. 3 is an overall configuration diagram of a fast reactor nuclear power generation system having a fast reactor core according to an embodiment of the present invention. As shown in FIG. 3, a fast reactor nuclear power generation system 1 includes a reactor vessel 2, a core 3 containing a fissile material housed in the reactor vessel 2, and a primary cooling system pipe 4a from the reactor vessel 2. The intermediate heat exchanger 5 and the primary main circulation pump 7a are connected in order, and the steam generator 8 and the secondary main circulation pump 7b are connected in order from the intermediate heat exchanger 5 through the secondary cooling system pipe 4b. Further, a main steam system pipe 9a that sends the steam generated by the steam generator 8 to the high-pressure turbine 11a and the low-pressure turbine 11b, and a condenser that condenses the steam after passing through the high-pressure turbine 11a and the low-pressure turbine 11b and returns it to water. 13. Supply water condensate system pipe 9b for returning the water condensed in the condenser 13 to the steam generator 8, the generator 12 connected to the shafts of the high-pressure turbine 11a and the low-pressure turbine 11b, and the downstream side of the condenser 13 The feed water pump 14 and the feed water heater 15 are connected to the condensate system pipe 9b.

  In the fast reactor nuclear power generation system 1, the primary coolant (for example, liquid sodium) heated in the core 3 is passed through the intermediate heat exchanger 5 to heat the secondary coolant (for example, liquid sodium). Further, the secondary coolant is passed through the steam generator 8 to generate steam in the main steam system pipe 9a. The steam is guided to the high-pressure turbine 11a and the low-pressure turbine 11b, and the generator 12 generates power. The steam used for power generation is condensed in the condenser 13 to become water in the same manner as in the boiling water type (BWR) or pressurized water type (PWR) light water reactor nuclear power generation system, and then the feed water pump 14 and the feed water heater 15 are supplied. The water is heated and pressurized through the steam generator 8 and supplied to the steam generator 8.

The core 3 is loaded with a plurality of core fuel assemblies, control rods, and gas expansion modules (GEM), which will be described later. The reactor vessel 2 that houses the reactor core 3 is filled with a primary coolant, and the primary coolant enters the reactor core 3 from the lower part of the reactor core 3 and rises along the reactor core fuel assembly, and is atomized by the primary main circulation pump 7a. It flows into the intermediate heat exchanger 5 provided outside the furnace vessel 2 through the primary cooling system pipe 4a. This constitutes a loop type fast reactor. In the present specification, a loop type fast reactor will be described as an example. However, the present invention is not limited to this, and a tank type fast reactor in which the reactor vessel 2, the primary main circulation pump 7a and the intermediate heat exchanger 5 are accommodated in one tank. It can also be applied to furnaces.
Hereinafter, the core of a fast reactor according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a transverse sectional view of the core of the fast reactor according to the first embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of the core of the fast reactor shown in FIG. As shown in FIG. 1, the core 10 of the fast reactor of this embodiment is disposed in the reactor vessel 2 (FIG. 3) of the fast reactor, and the inner core region fuel region 21 and the inner core fuel region 21 in the radial direction. The inner core fuel assembly in which the plutonium enrichment of the outer core fuel assembly loaded in the outer core fuel region 22 is loaded in the inner core fuel region 21 is composed of two core fuel regions in the outer core fuel region 22 surrounding the outer core fuel region 22. Homogeneous core higher than the body's plutonium enrichment. Further, a gas expansion module (GEM) 24 is loaded in the fast reactor core 10 so as to surround the outer core fuel region 22, and a reflector region 26 and a shield region 27 are disposed outside the gas expansion module (GEM) 24. Have In the radial direction of the core 10 of the fast reactor, the reflector region 26 surrounds the gas expansion module (GEM) 24 and is adjacent to the gas expansion module (GEM) 24, and the shield region 27 surrounds the reflector region 26. Yes. The fast reactor core 10 is a fuel assembly loaded on the outermost peripheral portion of the outer core fuel region 22 and is adjacent to the gas expansion module (GEM) 24 and has the highest plutonium enrichment. A plutonium enriched fuel assembly 23 is provided. That is, the plutonium enrichment Pu (I) of the inner core fuel assembly loaded in the inner core fuel region 21, the plutonium enrichment Pu (O1) of the outer core fuel assembly loaded in the outer core fuel region 23, And the plutonium enrichment Pu (O2) of the high plutonium enrichment fuel assembly 23 loaded on the outermost peripheral portion of the outer core fuel region 22 is expressed as Pu (O2)> Pu (O1)> Pu (I) It is in.

The inner core fuel region 21 is provided with control rods 25 that are used when the reactor is started, stopped, and output is adjusted. The control rod 25 has a plurality of neutron absorption rods in which boron carbide (B ₄ C) pellets are enclosed in a stainless steel cladding tube, and these neutron absorption rods are housed in a circular tube-shaped protective tube. . The control rod 25 has two independent structures of a main furnace stop system and a post-furnace stop system, but these are shown without distinction in FIG.

Note that the output of the nuclear reactor having the fast reactor core 10 is, for example, about 600,000 kW, and the cross-sectional view of the fast reactor core 10 shown in FIG. 1 shows a plurality of components loaded in the core fuel region of the core 10. The arrangement of the fuel assemblies and the plurality of gas expansion modules (GEM) 24 is shown. For convenience of explanation, the number of fuel assemblies loaded in the core fuel region of the core 10 and the gas expansion modules (GEM) are shown. ) The number of 24 bodies is shown in a simplified manner regardless of the particular number.
The gas expansion module (GEM) 24 is a hollow tubular structure whose one end is closed and the other end is opened, and its appearance is that of a fuel assembly loaded in the inner core fuel region 21 and the outer core fuel region 22. Similar to the trumpet tube.

  As shown on the left side of FIG. 2, when the flow rate of the primary main circulation pump 7a (FIG. 3) is rated, the pressure of the coolant sodium (Na) 28 at the inlet (lower end) of the gas expansion module (GEM) 24 increases. To do. Therefore, the level of the coolant sodium (Na) in the gas expansion module (GEM) 24 depends on the inner core fuel assembly loaded in the inner core fuel region 21 and the outer core fuel assembly loaded in the outer core fuel region 22. And a position higher than the upper end of the core fuel of the high plutonium enriched fuel assembly 23. At this time, the coolant sodium (Na) 28 in the gas expansion module (GEM) 24 plays the role of a reflector due to the neutron scattering effect, so that the amount of neutron leakage from the core 10 can be kept small.

On the other hand, as shown on the right side of FIG. 2, assuming an accident (ULOF) in which the loss of the flow rate of the coolant accompanying the stoppage of the primary main circulation pump 7a due to the loss of the power supply and the scram failure are superimposed, the gas expansion module (GEM) 24 Since the pressure of the coolant sodium (Na) 28 at the inlet portion decreases, the liquid level of the coolant sodium (Na) 28 in the gas expansion module (GEM) 24 is changed to the inner core fuel loaded in the inner core fuel region 21. The position is lower than the lower end of the core fuel of the assembly, the outer core fuel assembly loaded in the outer core fuel region 22, and the high plutonium enriched fuel assembly 23. At this time, the inside of the gas expansion module (GEM) 24 is filled with the expansion of the inert gas argon (Ar) 29, but the density of the inert gas argon (Ar) 29 is reduced, and the neutron scattering effect is small. Become. Therefore, the amount of neutron leakage from the core 10 increases. From the above, the negative expansion reactivity is brought to the core 10 by the gas expansion module (GEM) 24 during ULOF.
Accordingly, during ULOF, the coolant sodium in the inner core fuel assembly loaded in the inner core fuel region 21, the outer core fuel assembly loaded in the outer core fuel region 22, and the high plutonium enriched fuel assembly 23 ( As the flow rate of Na) decreases, the power / flow rate (P / F) ratio of the fuel assembly becomes inconsistent, leading to an increase in coolant sodium (Na) temperature and a decrease in coolant sodium (Na) density, and Even if a positive applied reactivity is provided, an increase in the output of the core 10 is suppressed by the negative applied reactivity by the gas expansion module (GEM) 24. That is, the safety of the core 10 during ULOF is improved.

The absolute value of the negative applied reactivity by the gas expansion module (GEM) 24 of the present embodiment is the core in two regions where the conventional plutonium enrichment is different, that is, the inner core fuel region 21 and the outer core fuel region 22. This is larger than the case where the fuel region is configured and the gas expansion module (GEM) 24 is installed on the outer periphery of the outer core fuel region 22. The reason will be described below with reference to FIG. FIG. 4 is a diagram showing the relationship between the position in the core radial direction and the neutron flux in the ½ region of the longitudinal section of the core of the fast reactor. In FIG. 4, the vertical axis represents the neutron flux (au), the horizontal axis represents the core radial direction position (cm), and a half region 41 of the longitudinal section of the core 10 is shown.
In FIG. 4, the neutron flux distribution of a conventional homogeneous core having an inner core fuel region 21, an outer core fuel region 22, and a gas expansion module (GEM) 24 from the center of the core radially outward is indicated by a solid line 42. Yes. Further, the homogeneous core of the present embodiment having the inner core fuel region 21, the outer core fuel region 22, the high plutonium enriched fuel assembly 23, and the gas expansion module (GEM) 24 from the core center to the radially outer side. The neutron flux distribution is indicated by a dotted line 43.

As shown in FIG. 4, the conventional homogeneous core shows a profile in which the neutron flux distribution relatively gradually decreases from the inside to the outside in the core radial direction position in the gas expansion module (GEM) 24. That is, the gradient of the neutron flux distribution 42 is small with respect to the gas expansion module (GEM) 24, including the outermost peripheral fuel assembly disposed on the outermost periphery of the outer core fuel region 22 adjacent to the inside in the core radial direction position.
On the other hand, in the case of the homogeneous core of the present embodiment, a profile in which the neutron flux distribution sharply decreases from the inside to the outside in the core radial direction position in the gas expansion module (GEM) 24 is shown. That is, including the vicinity of the gas expansion module (GEM) 24, the gradient of the neutron flux distribution 43 is clearly increased with respect to the gradient of the neutron flux distribution 42 of the conventional homogeneous core. Thereby, the amount of neutron leakage to the gas expansion module (GEM) 24 increases, and the reactivity of the gas expansion module (GEM) 24 increases. Here, the neutrons leaking are the neutrons leaking in the radial direction via the gas reflector module (GEM) 24 and the reflector region 26 and the shield region 27 shown in FIG. There are neutrons that leak axially upward in the module (GEM) 24.

As described above, according to the present embodiment, the negative applied reaction by the gas expansion module (GEM) is assumed even if ULOF is assumed by increasing the gradient of the radial neutron flux distribution in the vicinity of the gas expansion module (GEM). A fast reactor core capable of increasing the absolute value of the degree can be realized.
More specifically, the gas expansion module (GEM) 24 is loaded in the circumferential direction so as to surround the outer core fuel region 22, is adjacent to the gas expansion module (GEM) 24, and is the outermost periphery of the outer core fuel region 22. By loading the high plutonium enriched fuel assembly 23 having the highest plutonium enrichment in the part, the gradient of the radial neutron flux distribution in the vicinity of the gas expansion module (GEM) 24 can be increased. This makes it possible to increase the absolute value of the negative applied reactivity by the gas expansion module (GEM) 24 even when an accident (ULOF) in which the loss of the coolant flow rate and the scram failure are superimposed is assumed. Safety can be improved.

  FIG. 5 is a cross-sectional view of the core of the fast reactor according to the second embodiment according to another embodiment of the present invention. In the first embodiment, the gas expansion module (GEM) 24 is loaded in the circumferential direction so as to surround the outer core fuel region 22, is adjacent to the gas expansion module (GEM) 24, and is the outermost peripheral portion of the outer core fuel region 22. In the present embodiment, the gas expansion module (GEM) 24 is discretely disposed outside the outer core fuel region 22, whereas the high plutonium enriched fuel assembly 23 having the highest plutonium enrichment is loaded. And the high plutonium enriched fuel assembly 23 is loaded in the outer core fuel region 22 so as to surround the discretely loaded gas expansion module (GEM) 24. The same components as those in the first embodiment are denoted by the same reference numerals.

  As shown in FIG. 5, the core 20 of the present embodiment is arranged in the reactor vessel 2 (FIG. 3) of the fast reactor, and the inner core region fuel region 21 and the outer side surrounding the inner core fuel region 21 in the radial direction. The plutonium of the inner core fuel assembly loaded in the inner core fuel region 21 is composed of two core fuel regions of the core fuel region 22 and the plutonium enrichment of the outer core fuel assembly loaded in the outer core fuel region 22 is the same. Homogeneous core higher than enrichment. The power of the nuclear reactor having the fast reactor core 20 is, for example, about 300,000 kW, which is a small nuclear reactor core smaller than the power of the nuclear reactor shown in the first embodiment.

Further, as shown in FIG. 5, the core 20 of the small nuclear reactor includes six gas expansion modules (discretely) between the outer core fuel region 22 and the reflector region 26 surrounding the outer core fuel region 22. GEM) 24 is loaded and has a shield region 27 surrounding the reflector region 26. As described above, since the core 20 of the fast reactor of the present embodiment is a core of a small nuclear reactor, since the void reactivity is small, the number of loaded gas expansion modules (GEM) 24 is set to the above-described first embodiment. Less than. The inner core fuel region 21 is provided with control rods 25 that are used when the reactor is started, stopped, and when the output is adjusted. The control rod 25 has a plurality of neutron absorption rods in which boron carbide (B ₄ C) pellets are enclosed in a stainless steel cladding tube, and these neutron absorption rods are housed in a circular tube-shaped protective tube. . The control rod 25 has two independent systems of a main furnace stop system and a post-furnace stop system, but these are shown without distinction in FIG.

Among the six gas expansion modules (GEM) 24 that are discretely loaded in the circumferential direction, between the two gas expansion modules (GEM) 24 that are separated in the circumferential direction, the outermost periphery of the outer core fuel region 22 There are four outermost fuel assemblies loaded in the part, and two of the outermost fuel assemblies are high plutonium enriched fuel assemblies 23 adjacent to each gas expansion module (GEM) 24. . Further, the high plutonium enriched fuel assembly is adjacent to each of the six gas expansion modules (GEM) 24 that are discretely loaded in the circumferential direction and one layer inside the gas expansion module (GEM) 24. A total of six 23 are loaded. That is, in each gas expansion module (GEM) 24, among the six side surfaces having a hexagonal cross section, the three side surfaces closer to the inside of the core 20 are adjacent to the high plutonium enriched fuel assembly 23. Accordingly, the core 20 includes
Eighteen high-plutonium enriched fuel assemblies 23 are loaded adjacent to a gas expansion module (GEM) 24.

  As in the first embodiment, the plutonium enrichment Pu (I) of the inner core fuel assembly loaded in the inner core fuel region 21 and the plutonium enrichment of the outer core fuel assembly loaded in the outer core fuel region 23 are the same. Pu (O1) and the plutonium enrichment Pu (O2) of the high plutonium enrichment fuel assembly 23 loaded on the outermost periphery of the outer core fuel region 22 are Pu (O2)> Pu (O1)> Pu. There is a relationship of (I).

  According to the present embodiment, in addition to the effects of the first embodiment, the number ratio of the high plutonium enriched fuel assemblies loaded adjacent to the gas expansion module (GEM) is smaller than that of the first embodiment. It is possible to relatively reduce the influence on the reduction of the growth ratio due to the loading of the fuel assembly with the plutonium enrichment.

  FIG. 6 is a cross-sectional view of the core of the fast reactor according to the third embodiment according to another embodiment of the present invention. In the first embodiment, the gas expansion module (GEM) 24 is loaded in the circumferential direction so as to surround the outer core fuel region 22, is adjacent to the gas expansion module (GEM) 24, and is the outermost peripheral portion of the outer core fuel region 22. Are loaded with the high plutonium enriched fuel assembly 23 having the highest plutonium enrichment, and the plutonium enrichment of the outer core fuel assembly loaded in the outer core fuel region 22 is loaded in the inner core fuel region 21. The homogenous core is higher than the plutonium enrichment of the inner core fuel assembly. In contrast, in this embodiment, the gas expansion module (GEM) 24 is discretely loaded in the second layer from the outermost layer of the core, and the six surfaces of the discretely loaded gas expansion module (GEM) 24 are loaded. The high plutonium enriched fuel assembly 23 is loaded so as to be adjacent to all sides, and the plutonium enrichment is different in that it is a radial heterogeneous core loaded with one type of core fuel assembly and internal blanket assembly. . The same components as those in the first embodiment are denoted by the same reference numerals.

  As shown in FIG. 6, the core 30 of the fast reactor includes a core fuel assembly 31 having one kind of plutonium enrichment, an internal blanket assembly 32 using depleted uranium, a control rod 25, and a shield disposed on the outermost layer. The gas expansion module (GEM) 24 is loaded in the second layer from the outermost layer of the core 30. One fuel rod 25 is disposed at the center of the core 30 of the fast reactor, and six internal blanket assemblies 32 are disposed in a ring shape so as to be adjacent to all six side surfaces of the fuel rod 25. Twelve core fuel assemblies 31 are arranged so as to surround the outside of the six internal blanket assemblies 32 arranged in the above. Further, 18 internal blanket assemblies 32 are arranged in a ring shape so as to surround the outside of the 12 core fuel assemblies 31, and adjacent to the 18 internal blanket assemblies 32 arranged in the ring shape. In addition, six control rods 25 are arranged apart from each other.

  Further, as shown in FIG. 6, the core 30 of the fast reactor is the second layer from the outermost layer and is spaced apart from each other in the circumferential direction, and six gas expansion modules (GEM) 24 are loaded, and each gas expansion module is loaded. The high plutonium enriched fuel assembly 23 is loaded so as to be adjacent to all six side surfaces of the (GEM) 24. Accordingly, the core 30 is loaded with 36 high-plutonium enriched fuel assemblies 23 adjacent to the gas expansion module (GEM) 24. Of the six high plutonium enriched fuel assemblies 23 disposed adjacent to each gas expansion module (GEM) 24, two high plutonium enriched fuel assemblies 23 disposed radially inward are: Adjacent to the inner blanket assembly 32 arranged in a ring shape. The plutonium enrichment of the high plutonium enrichment fuel assembly 23 is higher than the plutonium enrichment of the core fuel assembly 31.

In this embodiment, the inner blanket assembly 32 is relatively arranged in a ring shape from the center of the core 30 of the fast reactor, the output near the core center is low, and the output from the radially outer side increases as it goes to the outermost periphery. . Accordingly, by arranging the high plutonium enriched fuel assembly 23 so as to surround the gas expansion module (GEM) 24, the neutron flux around the gas expansion module (GEM) 24 is centered on the gas expansion module (GEM) 24. It decreases toward (axis), and its gradient increases. Thereby, the absolute value of the negative reactivity of the gas expansion module (GEM) 24 can be increased.
More specifically, the gas expansion module (GEM) 24 is loaded inward in the radial direction by two layers from the outermost layer, and the high plutonium enriched fuel assembly 23 is loaded around the gas expansion module (GEM) 24. Yes. When considering the relationship between the position in the radial direction of the core in the longitudinal section of the fast reactor core 30 and the neutron flux, the neutron flux distribution is the center of the gas expansion module (GEM) 24 (axial center) in the radial direction. ), And after passing through the center (axial center), the neutron flux distribution shows a profile that rises again due to the influence of the high plutonium enriched fuel assembly 23 loaded on the outermost periphery. This is because neutrons leaking to the gas expansion module (GEM) 24 in the radial direction from the center of the core 30 of the fast reactor and the high plutonium enriched fuel disposed on the outer peripheral side of the gas expansion module (GEM) 24. This is because there are neutrons leaking from the aggregate 23 toward the gas expansion module (GEM) 24 (in the direction toward the core center).

  According to the present embodiment, even if the generation of ULOF is assumed by increasing the gradient of the radial neutron flux distribution in the vicinity of the gas expansion module (GEM), the negative pressure generated by the gas expansion module (GEM) is negative. A radial heterogeneous core that can increase the absolute value of the applied reactivity can be realized.

  FIG. 7 is a longitudinal sectional view of the core of a fast reactor according to embodiment 4 of another embodiment of the present invention. In the present embodiment, the inner core fuel assembly loaded in the inner core fuel region 21, the outer core fuel assembly loaded in the outer core fuel region 22, and the high plutonium enriched fuel assembly 23 are respectively disposed on the upper portions. The difference from the first embodiment is that a sodium plenum region 45 partitioned by a trumpet tube is provided. The same components as those in the first embodiment are denoted by the same reference numerals.

  As shown in FIG. 7, the fast reactor core 40 of the present embodiment includes an inner core fuel assembly and an outer core fuel region 22 loaded in the inner core fuel region 21 in the fast reactor core of the first embodiment described above. The outer core fuel assembly loaded on the fuel cell and the high plutonium enriched fuel assembly 23 loaded adjacent to the gas expansion module (GEM) 24 is partitioned by a trumpet tube and is sodium coolant. A sodium plenum region 45 capable of accommodating (Na) is provided. In FIG. 7, the sodium plenum region of each fuel assembly is simply shown as if it were integrated.

The electric power of the fast reactor in the example is about 750,000 kW. The reactivity of the gas expansion module (GEM) 24 in the case of a conventional homogeneous core without the high plutonium enriched fuel assembly 23 is about -1.9 dollars. On the other hand, in the core 40 of the fast reactor having the high plutonium enriched fuel assembly 23 of this embodiment, the reactivity of the gas expansion module (GEM) 24 is increased by about 50% to about −2.9 $. Become.
On the other hand, the void reactivity when the coolant sodium (Na) boiled in the fuel assembly and the sodium plenum region 45 in the core in which the sodium plenum region 45 is installed is + 2.6 $.

Therefore, when the gas expansion module (GEM) 24 is installed in the conventional homogeneous core, the void reactivity of the entire core including the gas expansion module (GEM) 24 is + 2.6 $ -1.9 $ ≈ + 0.7 $ On the other hand, in the case of the core 40 of the fast reactor according to the present embodiment, the negative value is + 2.6 $ −2.9 $ ≈−0.3 $.
From the above, when the negative reactivity effect of the gas expansion module (GEM) 24 loaded in the core 40 of the fast reactor of this embodiment and the void reactivity reduction effect by the sodium plenum region 45 are combined, the coolant sodium (Na) Even when is boiling, the reactivity applied to the core 40 can be negative. Thereby, the core safety can be further improved.

  According to the present embodiment, in addition to the effects of the first embodiment, the core safety can be further improved as compared with the first embodiment.

  In each of the above-described embodiments, the core fuel is assumed to be a mixed oxide (MOX) fuel in which deteriorated uranium oxide and plutonium oxide are mixed. However, the present invention is not limited to this. For example, metal fuel or nitride fuel may be used. Further, as the coolant, liquid heavy metal such as lead, lead / bismuth, or the like may be used instead of sodium.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace the configurations of other embodiments with respect to a part of the configurations of the embodiments.

DESCRIPTION OF SYMBOLS 1 ... Fast reactor nuclear power generation system 2 ... Reactor vessel 3 ... 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 ... Supply and condensate system piping 10, 20, 30, 40 ... Core 11a ... -High pressure turbine 11b ... Low pressure turbine 12 ... Generator 13 ... Condenser 14 ... Feed water pump 15 ... Feed water heater 21 ... Inner core fuel region 22 ... Outer core fuel Region 23 ... High plutonium enriched fuel assembly 24 ... Gas expansion module (GEM)
25 ... Control rod 26 ... Reflective body region 27 ... Shield body region 28 ... Coolant sodium (Na)
29 ... Inert gas (Ar)
31 ... Core fuel assembly 32 ... Internal blanket assembly 41 ... 1/2 region 42 of the longitudinal section of the core 42 ... Radial neutron flux distribution 43 when GEM is installed on the outer periphery of the homogeneous core ... Radial neutron flux distribution 45 when a high plutonium enriched fuel assembly is installed between the outer core fuel region of the homogeneous core and the GEM ... Sodium plenum region

Claims (14)

A fast reactor core for loading a gas expansion module, which is a hollow tubular structure having one end closed and the other end open, to the core;
A fast reactor core characterized in that a plutonium enrichment of a fuel assembly adjacent to the gas expansion module is higher than a plutonium enrichment of a fuel assembly not adjacent to the gas expansion module. In the core of the fast reactor according to claim 1,
An inner core fuel region, an outer core fuel region surrounding the inner core fuel region, and a reflector region surrounding the outer core fuel region in a radial direction of the core;
A plurality of the gas expansion modules are loaded between the outer core fuel region and the reflector region so as to surround the entire circumference of the outer core fuel region,
The plutonium enrichment of the fuel assembly loaded in the outer core fuel region is higher than the plutonium enrichment of the fuel assembly loaded in the inner core fuel region,
The plutonium enrichment of the fuel assembly loaded on the outermost periphery of the outer core fuel region and adjacent to the gas expansion module is higher than the plutonium enrichment of the fuel assembly loaded in the outer core fuel region. The core of the fast reactor. In the core of the fast reactor according to claim 1,
An inner core fuel region, an outer core fuel region surrounding the inner core fuel region, and a reflector region surrounding the outer core fuel region in a radial direction of the core;
The gas expansion module is loaded between the outer core fuel region and the reflector region in a discrete manner in the circumferential direction.
A fast reactor core characterized in that a plutonium enrichment of a fuel assembly adjacent to the gas expansion module loaded discretely is higher than a plutonium enrichment of a fuel assembly not adjacent to the gas expansion module. . In the core of the fast reactor according to claim 3,
The gas expansion module has a hexagonal shape in cross section,
Of the side surfaces of each gas expansion module, the plutonium enrichment of the three fuel assemblies adjacent to the three side surfaces on the outer core fuel region side is the highest among the plurality of fuel assemblies loaded in the core. A fast reactor core characterized by high height. In the core of the fast reactor according to claim 1,
The core is a radially inhomogeneous core loaded with an internal blanket assembly and core fuel assembly using depleted uranium,
The gas expansion module is radially outer of the core and is loaded in a plurality of discretely in the circumferential direction,
A fast reactor in which a plutonium enrichment of a core fuel assembly adjacent to the gas expansion module loaded in a discrete manner is higher than a plutonium enrichment of a fuel assembly not adjacent to the gas expansion module. Core. In the core of the fast reactor according to claim 5,
The gas expansion module has a hexagonal shape in cross section,
A fast reactor core characterized in that the plutonium enrichment of the six core fuel assemblies adjacent to all sides of each gas expansion module is the highest among the plurality of core fuel assemblies loaded in the core. . In the core of the fast reactor according to claim 2,
Fuel assembly loaded in the outer core fuel region, fuel assembly loaded in the inner core fuel region, and fuel in a fuel assembly loaded on the outermost periphery of the outer core fuel region and adjacent to the gas expansion module A fast reactor core having a sodium plenum region partitioned by a trumpet tube at an upper portion of the region. A fast reactor core for loading a gas expansion module, which is a hollow tubular structure having one end closed and the other end open, to the core;
A fast reactor core characterized in that a plurality of fuel assemblies adjacent to the gas expansion module have the same plutonium enrichment, and the highest among the plurality of fuel assemblies loaded in the core. In the core of the fast reactor according to claim 8,
An inner core fuel region, an outer core fuel region surrounding the inner core fuel region, and a reflector region surrounding the outer core fuel region in a radial direction of the core;
A plurality of the gas expansion modules are loaded between the outer core fuel region and the reflector region so as to surround the entire circumference of the outer core fuel region,
The plutonium enrichment of the fuel assembly loaded in the outer core fuel region is higher than the plutonium enrichment of the fuel assembly loaded in the inner core fuel region,
The plutonium enrichment of the fuel assembly loaded on the outermost periphery of the outer core fuel region and adjacent to the gas expansion module is higher than the plutonium enrichment of the fuel assembly loaded in the outer core fuel region. The core of the fast reactor. In the core of the fast reactor according to claim 8,
An inner core fuel region, an outer core fuel region surrounding the inner core fuel region, and a reflector region surrounding the outer core fuel region in a radial direction of the core;
The gas expansion module is loaded between the outer core fuel region and the reflector region in a discrete manner in the circumferential direction.
A fast reactor core characterized in that a plutonium enrichment of a fuel assembly adjacent to the gas expansion module loaded discretely is higher than a plutonium enrichment of a fuel assembly not adjacent to the gas expansion module. . In the core of the fast reactor according to claim 10,
The gas expansion module has a hexagonal shape in cross section,
Of the side surfaces of each gas expansion module, the plutonium enrichment of the three fuel assemblies adjacent to the three side surfaces on the outer core fuel region side is the highest among the plurality of fuel assemblies loaded in the core. A fast reactor core characterized by high height. In the core of the fast reactor according to claim 8,
The core is a radially inhomogeneous core loaded with an internal blanket assembly and core fuel assembly using depleted uranium,
The gas expansion module is radially outer of the core and is loaded in a plurality of discretely in the circumferential direction,
A fast reactor in which a plutonium enrichment of a core fuel assembly adjacent to the gas expansion module loaded in a discrete manner is higher than a plutonium enrichment of a fuel assembly not adjacent to the gas expansion module. Core. In the core of the fast reactor according to claim 12,
The gas expansion module has a hexagonal shape in cross section,
A fast reactor core characterized in that the plutonium enrichment of the six core fuel assemblies adjacent to all sides of each gas expansion module is the highest among the plurality of core fuel assemblies loaded in the core. . In the core of the fast reactor according to claim 9,
Fuel assembly loaded in the outer core fuel region, fuel assembly loaded in the inner core fuel region, and fuel in a fuel assembly loaded on the outermost periphery of the outer core fuel region and adjacent to the gas expansion module A fast reactor core having a sodium plenum region partitioned by a trumpet tube at an upper portion of the region.

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